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| author | Jörg Frings-Fürst <debian@jff-webhsoting.net> | 2019-07-13 18:04:58 +0200 |
|---|---|---|
| committer | Jörg Frings-Fürst <debian@jff-webhsoting.net> | 2019-07-13 18:04:58 +0200 |
| commit | aa9051108ed042b0acc138d2aea37a0a3e51610a (patch) | |
| tree | d54fff2198af7c562e83f98761c5c3f8a128715f /doc/rfc3986.htm | |
| parent | 033557f8d81c917824bcd2aa7749e05afe6129c6 (diff) | |
Remove rfc files
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| -rw-r--r-- | doc/rfc3986.htm | 3539 |
1 files changed, 0 insertions, 3539 deletions
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-<span class="pre noprint docinfo top">[<a href="http://tools.ietf.org/html/">RFCs/IDs</a>] [<a href="http://tools.ietf.org/rfc/rfc3986.txt">Plain Text</a>] [From <a href="http://tools.ietf.org/html/draft-fielding-uri-rfc2396bis">draft-fielding-uri-rfc2396bis</a>] </span><br>
-<span class="pre noprint docinfo"> </span><br>
-<span class="pre noprint docinfo"> STANDARD</span><br>
-<span class="pre noprint docinfo"> </span><br>
-<pre>Network Working Group T. Berners-Lee
-Request for Comments: 3986 W3C/MIT
-STD: 66 R. Fielding
-Updates: <a href="http://tools.ietf.org/html/rfc1738">1738</a> Day Software
-Obsoletes: <a href="http://tools.ietf.org/html/rfc2732">2732</a>, <a href="http://tools.ietf.org/html/rfc2396">2396</a>, <a href="http://tools.ietf.org/html/rfc1808">1808</a> L. Masinter
-Category: Standards Track Adobe Systems
- January 2005
-
-
- <span class="h1"><h1>Uniform Resource Identifier (URI): Generic Syntax</h1></span>
-
-Status of This Memo
-
- This document specifies an Internet standards track protocol for the
- Internet community, and requests discussion and suggestions for
- improvements. Please refer to the current edition of the "Internet
- Official Protocol Standards" (STD 1) for the standardization state
- and status of this protocol. Distribution of this memo is unlimited.
-
-Copyright Notice
-
- Copyright (C) The Internet Society (2005).
-
-Abstract
-
- A Uniform Resource Identifier (URI) is a compact sequence of
- characters that identifies an abstract or physical resource. This
- specification defines the generic URI syntax and a process for
- resolving URI references that might be in relative form, along with
- guidelines and security considerations for the use of URIs on the
- Internet. The URI syntax defines a grammar that is a superset of all
- valid URIs, allowing an implementation to parse the common components
- of a URI reference without knowing the scheme-specific requirements
- of every possible identifier. This specification does not define a
- generative grammar for URIs; that task is performed by the individual
- specifications of each URI scheme.
-
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-<span class="grey">Berners-Lee, et al. Standards Track [Page 1]</span>
-<a name="page-2" id="page-2" href="#page-2"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
-Table of Contents
-
- <a href="#section-1">1</a>. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-4">4</a>
- <a href="#section-1.1">1.1</a>. Overview of URIs . . . . . . . . . . . . . . . . . . . . <a href="#page-4">4</a>
- <a href="#section-1.1.1">1.1.1</a>. Generic Syntax . . . . . . . . . . . . . . . . . <a href="#page-6">6</a>
- <a href="#section-1.1.2">1.1.2</a>. Examples . . . . . . . . . . . . . . . . . . . . <a href="#page-7">7</a>
- <a href="#section-1.1.3">1.1.3</a>. URI, URL, and URN . . . . . . . . . . . . . . . <a href="#page-7">7</a>
- <a href="#section-1.2">1.2</a>. Design Considerations . . . . . . . . . . . . . . . . . <a href="#page-8">8</a>
- <a href="#section-1.2.1">1.2.1</a>. Transcription . . . . . . . . . . . . . . . . . <a href="#page-8">8</a>
- <a href="#section-1.2.2">1.2.2</a>. Separating Identification from Interaction . . . <a href="#page-9">9</a>
- <a href="#section-1.2.3">1.2.3</a>. Hierarchical Identifiers . . . . . . . . . . . . <a href="#page-10">10</a>
- <a href="#section-1.3">1.3</a>. Syntax Notation . . . . . . . . . . . . . . . . . . . . <a href="#page-11">11</a>
- <a href="#section-2">2</a>. Characters . . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-11">11</a>
- <a href="#section-2.1">2.1</a>. Percent-Encoding . . . . . . . . . . . . . . . . . . . . <a href="#page-12">12</a>
- <a href="#section-2.2">2.2</a>. Reserved Characters . . . . . . . . . . . . . . . . . . <a href="#page-12">12</a>
- <a href="#section-2.3">2.3</a>. Unreserved Characters . . . . . . . . . . . . . . . . . <a href="#page-13">13</a>
- <a href="#section-2.4">2.4</a>. When to Encode or Decode . . . . . . . . . . . . . . . . <a href="#page-14">14</a>
- <a href="#section-2.5">2.5</a>. Identifying Data . . . . . . . . . . . . . . . . . . . . <a href="#page-14">14</a>
- <a href="#section-3">3</a>. Syntax Components . . . . . . . . . . . . . . . . . . . . . . <a href="#page-16">16</a>
- <a href="#section-3.1">3.1</a>. Scheme . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-17">17</a>
- <a href="#section-3.2">3.2</a>. Authority . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-17">17</a>
- <a href="#section-3.2.1">3.2.1</a>. User Information . . . . . . . . . . . . . . . . <a href="#page-18">18</a>
- <a href="#section-3.2.2">3.2.2</a>. Host . . . . . . . . . . . . . . . . . . . . . . <a href="#page-18">18</a>
- <a href="#section-3.2.3">3.2.3</a>. Port . . . . . . . . . . . . . . . . . . . . . . <a href="#page-22">22</a>
- <a href="#section-3.3">3.3</a>. Path . . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-22">22</a>
- <a href="#section-3.4">3.4</a>. Query . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-23">23</a>
- <a href="#section-3.5">3.5</a>. Fragment . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-24">24</a>
- <a href="#section-4">4</a>. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-25">25</a>
- <a href="#section-4.1">4.1</a>. URI Reference . . . . . . . . . . . . . . . . . . . . . <a href="#page-25">25</a>
- <a href="#section-4.2">4.2</a>. Relative Reference . . . . . . . . . . . . . . . . . . . <a href="#page-26">26</a>
- <a href="#section-4.3">4.3</a>. Absolute URI . . . . . . . . . . . . . . . . . . . . . . <a href="#page-27">27</a>
- <a href="#section-4.4">4.4</a>. Same-Document Reference . . . . . . . . . . . . . . . . <a href="#page-27">27</a>
- <a href="#section-4.5">4.5</a>. Suffix Reference . . . . . . . . . . . . . . . . . . . . <a href="#page-27">27</a>
- <a href="#section-5">5</a>. Reference Resolution . . . . . . . . . . . . . . . . . . . . . <a href="#page-28">28</a>
- <a href="#section-5.1">5.1</a>. Establishing a Base URI . . . . . . . . . . . . . . . . <a href="#page-28">28</a>
- <a href="#section-5.1.1">5.1.1</a>. Base URI Embedded in Content . . . . . . . . . . <a href="#page-29">29</a>
- <a href="#section-5.1.2">5.1.2</a>. Base URI from the Encapsulating Entity . . . . . <a href="#page-29">29</a>
- <a href="#section-5.1.3">5.1.3</a>. Base URI from the Retrieval URI . . . . . . . . <a href="#page-30">30</a>
- <a href="#section-5.1.4">5.1.4</a>. Default Base URI . . . . . . . . . . . . . . . . <a href="#page-30">30</a>
- <a href="#section-5.2">5.2</a>. Relative Resolution . . . . . . . . . . . . . . . . . . <a href="#page-30">30</a>
- <a href="#section-5.2.1">5.2.1</a>. Pre-parse the Base URI . . . . . . . . . . . . . <a href="#page-31">31</a>
- <a href="#section-5.2.2">5.2.2</a>. Transform References . . . . . . . . . . . . . . <a href="#page-31">31</a>
- <a href="#section-5.2.3">5.2.3</a>. Merge Paths . . . . . . . . . . . . . . . . . . <a href="#page-32">32</a>
- <a href="#section-5.2.4">5.2.4</a>. Remove Dot Segments . . . . . . . . . . . . . . <a href="#page-33">33</a>
- <a href="#section-5.3">5.3</a>. Component Recomposition . . . . . . . . . . . . . . . . <a href="#page-35">35</a>
- <a href="#section-5.4">5.4</a>. Reference Resolution Examples . . . . . . . . . . . . . <a href="#page-35">35</a>
- <a href="#section-5.4.1">5.4.1</a>. Normal Examples . . . . . . . . . . . . . . . . <a href="#page-36">36</a>
- <a href="#section-5.4.2">5.4.2</a>. Abnormal Examples . . . . . . . . . . . . . . . <a href="#page-36">36</a>
-
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-<span class="grey">Berners-Lee, et al. Standards Track [Page 2]</span>
-<a name="page-3" id="page-3" href="#page-3"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
- <a href="#section-6">6</a>. Normalization and Comparison . . . . . . . . . . . . . . . . . <a href="#page-38">38</a>
- <a href="#section-6.1">6.1</a>. Equivalence . . . . . . . . . . . . . . . . . . . . . . <a href="#page-38">38</a>
- <a href="#section-6.2">6.2</a>. Comparison Ladder . . . . . . . . . . . . . . . . . . . <a href="#page-39">39</a>
- <a href="#section-6.2.1">6.2.1</a>. Simple String Comparison . . . . . . . . . . . . <a href="#page-39">39</a>
- <a href="#section-6.2.2">6.2.2</a>. Syntax-Based Normalization . . . . . . . . . . . <a href="#page-40">40</a>
- <a href="#section-6.2.3">6.2.3</a>. Scheme-Based Normalization . . . . . . . . . . . <a href="#page-41">41</a>
- <a href="#section-6.2.4">6.2.4</a>. Protocol-Based Normalization . . . . . . . . . . <a href="#page-42">42</a>
- <a href="#section-7">7</a>. Security Considerations . . . . . . . . . . . . . . . . . . . <a href="#page-43">43</a>
- <a href="#section-7.1">7.1</a>. Reliability and Consistency . . . . . . . . . . . . . . <a href="#page-43">43</a>
- <a href="#section-7.2">7.2</a>. Malicious Construction . . . . . . . . . . . . . . . . . <a href="#page-43">43</a>
- <a href="#section-7.3">7.3</a>. Back-End Transcoding . . . . . . . . . . . . . . . . . . <a href="#page-44">44</a>
- <a href="#section-7.4">7.4</a>. Rare IP Address Formats . . . . . . . . . . . . . . . . <a href="#page-45">45</a>
- <a href="#section-7.5">7.5</a>. Sensitive Information . . . . . . . . . . . . . . . . . <a href="#page-45">45</a>
- <a href="#section-7.6">7.6</a>. Semantic Attacks . . . . . . . . . . . . . . . . . . . . <a href="#page-45">45</a>
- <a href="#section-8">8</a>. IANA Considerations . . . . . . . . . . . . . . . . . . . . . <a href="#page-46">46</a>
- <a href="#section-9">9</a>. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-46">46</a>
- <a href="#section-10">10</a>. References . . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-46">46</a>
- <a href="#section-10.1">10.1</a>. Normative References . . . . . . . . . . . . . . . . . . <a href="#page-46">46</a>
- <a href="#section-10.2">10.2</a>. Informative References . . . . . . . . . . . . . . . . . <a href="#page-47">47</a>
- A. Collected ABNF for URI . . . . . . . . . . . . . . . . . . . . <a href="#page-49">49</a>
- B. Parsing a URI Reference with a Regular Expression . . . . . . <a href="#page-50">50</a>
- C. Delimiting a URI in Context . . . . . . . . . . . . . . . . . <a href="#page-51">51</a>
- D. Changes from <a href="http://tools.ietf.org/html/rfc2396">RFC 2396</a> . . . . . . . . . . . . . . . . . . . . <a href="#page-53">53</a>
- D.1. Additions . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-53">53</a>
- D.2. Modifications . . . . . . . . . . . . . . . . . . . . . <a href="#page-53">53</a>
- Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-56">56</a>
- Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-60">60</a>
- Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . <a href="#page-61">61</a>
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-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
-<span class="h2"><h2><a name="section-1">1</a>. Introduction</h2></span>
-
- A Uniform Resource Identifier (URI) provides a simple and extensible
- means for identifying a resource. This specification of URI syntax
- and semantics is derived from concepts introduced by the World Wide
- Web global information initiative, whose use of these identifiers
- dates from 1990 and is described in "Universal Resource Identifiers
- in WWW" [<a href="http://tools.ietf.org/html/rfc1630" title=""Universal Resource Identifiers in WWW: A Unifying Syntax for the Expression of Names and Addresses of Objects on the Network as used in the World-Wide Web"">RFC1630</a>]. The syntax is designed to meet the
- recommendations laid out in "Functional Recommendations for Internet
- Resource Locators" [<a href="http://tools.ietf.org/html/rfc1736" title=""Functional Recommendations for Internet Resource Locators"">RFC1736</a>] and "Functional Requirements for Uniform
- Resource Names" [<a href="http://tools.ietf.org/html/rfc1737" title=""Functional Requirements for Uniform Resource Names"">RFC1737</a>].
-
- This document obsoletes [<a href="http://tools.ietf.org/html/rfc2396" title=""Uniform Resource Identifiers (URI): Generic Syntax"">RFC2396</a>], which merged "Uniform Resource
- Locators" [<a href="http://tools.ietf.org/html/rfc1738" title=""Uniform Resource Locators (URL)"">RFC1738</a>] and "Relative Uniform Resource Locators"
- [<a href="http://tools.ietf.org/html/rfc1808" title=""Relative Uniform Resource Locators"">RFC1808</a>] in order to define a single, generic syntax for all URIs.
- It obsoletes [<a href="http://tools.ietf.org/html/rfc2732" title=""Format for Literal IPv6 Addresses in URL&#39;s"">RFC2732</a>], which introduced syntax for an IPv6 address.
- It excludes portions of <a href="http://tools.ietf.org/html/rfc1738">RFC 1738</a> that defined the specific syntax of
- individual URI schemes; those portions will be updated as separate
- documents. The process for registration of new URI schemes is
- defined separately by [<a href="#ref-BCP35" title=""Registration Procedures for URL Scheme Names"">BCP35</a>]. Advice for designers of new URI
- schemes can be found in [<a href="http://tools.ietf.org/html/rfc2718" title=""Guidelines for new URL Schemes"">RFC2718</a>]. All significant changes from <a href="http://tools.ietf.org/html/rfc2396">RFC</a>
- <a href="http://tools.ietf.org/html/rfc2396">2396</a> are noted in Appendix D.
-
- This specification uses the terms "character" and "coded character
- set" in accordance with the definitions provided in [<a href="#ref-BCP19" title=""IANA Charset Registration Procedures"">BCP19</a>], and
- "character encoding" in place of what [<a href="#ref-BCP19" title=""IANA Charset Registration Procedures"">BCP19</a>] refers to as a
- "charset".
-
-<span class="h3"><h3><a name="section-1.1">1.1</a>. Overview of URIs</h3></span>
-
- URIs are characterized as follows:
-
- Uniform
-
- Uniformity provides several benefits. It allows different types
- of resource identifiers to be used in the same context, even when
- the mechanisms used to access those resources may differ. It
- allows uniform semantic interpretation of common syntactic
- conventions across different types of resource identifiers. It
- allows introduction of new types of resource identifiers without
- interfering with the way that existing identifiers are used. It
- allows the identifiers to be reused in many different contexts,
- thus permitting new applications or protocols to leverage a pre-
- existing, large, and widely used set of resource identifiers.
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-<a name="page-5" id="page-5" href="#page-5"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
- Resource
-
- This specification does not limit the scope of what might be a
- resource; rather, the term "resource" is used in a general sense
- for whatever might be identified by a URI. Familiar examples
- include an electronic document, an image, a source of information
- with a consistent purpose (e.g., "today's weather report for Los
- Angeles"), a service (e.g., an HTTP-to-SMS gateway), and a
- collection of other resources. A resource is not necessarily
- accessible via the Internet; e.g., human beings, corporations, and
- bound books in a library can also be resources. Likewise,
- abstract concepts can be resources, such as the operators and
- operands of a mathematical equation, the types of a relationship
- (e.g., "parent" or "employee"), or numeric values (e.g., zero,
- one, and infinity).
-
- Identifier
-
- An identifier embodies the information required to distinguish
- what is being identified from all other things within its scope of
- identification. Our use of the terms "identify" and "identifying"
- refer to this purpose of distinguishing one resource from all
- other resources, regardless of how that purpose is accomplished
- (e.g., by name, address, or context). These terms should not be
- mistaken as an assumption that an identifier defines or embodies
- the identity of what is referenced, though that may be the case
- for some identifiers. Nor should it be assumed that a system
- using URIs will access the resource identified: in many cases,
- URIs are used to denote resources without any intention that they
- be accessed. Likewise, the "one" resource identified might not be
- singular in nature (e.g., a resource might be a named set or a
- mapping that varies over time).
-
- A URI is an identifier consisting of a sequence of characters
- matching the syntax rule named <URI> in <a href="#section-3">Section 3</a>. It enables
- uniform identification of resources via a separately defined
- extensible set of naming schemes (<a href="#section-3.1">Section 3.1</a>). How that
- identification is accomplished, assigned, or enabled is delegated to
- each scheme specification.
-
- This specification does not place any limits on the nature of a
- resource, the reasons why an application might seek to refer to a
- resource, or the kinds of systems that might use URIs for the sake of
- identifying resources. This specification does not require that a
- URI persists in identifying the same resource over time, though that
- is a common goal of all URI schemes. Nevertheless, nothing in this
-
-
-
-
-
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-<a name="page-6" id="page-6" href="#page-6"><span class="break"> </span></a>
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-
-
- specification prevents an application from limiting itself to
- particular types of resources, or to a subset of URIs that maintains
- characteristics desired by that application.
-
- URIs have a global scope and are interpreted consistently regardless
- of context, though the result of that interpretation may be in
- relation to the end-user's context. For example, "<a href="http://localhost/">http://localhost/</a>"
- has the same interpretation for every user of that reference, even
- though the network interface corresponding to "localhost" may be
- different for each end-user: interpretation is independent of access.
- However, an action made on the basis of that reference will take
- place in relation to the end-user's context, which implies that an
- action intended to refer to a globally unique thing must use a URI
- that distinguishes that resource from all other things. URIs that
- identify in relation to the end-user's local context should only be
- used when the context itself is a defining aspect of the resource,
- such as when an on-line help manual refers to a file on the end-
- user's file system (e.g., "file:///etc/hosts").
-
-<span class="h4"><h4><a name="section-1.1.1">1.1.1</a>. Generic Syntax</h4></span>
-
- Each URI begins with a scheme name, as defined in <a href="#section-3.1">Section 3.1</a>, that
- refers to a specification for assigning identifiers within that
- scheme. As such, the URI syntax is a federated and extensible naming
- system wherein each scheme's specification may further restrict the
- syntax and semantics of identifiers using that scheme.
-
- This specification defines those elements of the URI syntax that are
- required of all URI schemes or are common to many URI schemes. It
- thus defines the syntax and semantics needed to implement a scheme-
- independent parsing mechanism for URI references, by which the
- scheme-dependent handling of a URI can be postponed until the
- scheme-dependent semantics are needed. Likewise, protocols and data
- formats that make use of URI references can refer to this
- specification as a definition for the range of syntax allowed for all
- URIs, including those schemes that have yet to be defined. This
- decouples the evolution of identification schemes from the evolution
- of protocols, data formats, and implementations that make use of
- URIs.
-
- A parser of the generic URI syntax can parse any URI reference into
- its major components. Once the scheme is determined, further
- scheme-specific parsing can be performed on the components. In other
- words, the URI generic syntax is a superset of the syntax of all URI
- schemes.
-
-
-
-
-
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-<a name="page-7" id="page-7" href="#page-7"><span class="break"> </span></a>
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-
-
-<span class="h4"><h4><a name="section-1.1.2">1.1.2</a>. Examples</h4></span>
-
- The following example URIs illustrate several URI schemes and
- variations in their common syntax components:
-
- <a href="ftp://ftp.is.co.za/rfc/rfc1808.txt">ftp://ftp.is.co.za/rfc/rfc1808.txt</a>
-
- <a href="http://www.ietf.org/rfc/rfc2396.txt">http://www.ietf.org/rfc/rfc2396.txt</a>
-
- ldap://[2001:db8::7]/c=GB?objectClass?one
-
- mailto:John.Doe@example.com
-
- news:comp.infosystems.www.servers.unix
-
- tel:+1-816-555-1212
-
- telnet://192.0.2.16:80/
-
- urn:oasis:names:specification:docbook:dtd:xml:4.1.2
-
-
-<span class="h4"><h4><a name="section-1.1.3">1.1.3</a>. URI, URL, and URN</h4></span>
-
- A URI can be further classified as a locator, a name, or both. The
- term "Uniform Resource Locator" (URL) refers to the subset of URIs
- that, in addition to identifying a resource, provide a means of
- locating the resource by describing its primary access mechanism
- (e.g., its network "location"). The term "Uniform Resource Name"
- (URN) has been used historically to refer to both URIs under the
- "urn" scheme [<a href="http://tools.ietf.org/html/rfc2141" title=""URN Syntax"">RFC2141</a>], which are required to remain globally unique
- and persistent even when the resource ceases to exist or becomes
- unavailable, and to any other URI with the properties of a name.
-
- An individual scheme does not have to be classified as being just one
- of "name" or "locator". Instances of URIs from any given scheme may
- have the characteristics of names or locators or both, often
- depending on the persistence and care in the assignment of
- identifiers by the naming authority, rather than on any quality of
- the scheme. Future specifications and related documentation should
- use the general term "URI" rather than the more restrictive terms
- "URL" and "URN" [<a href="http://tools.ietf.org/html/rfc3305" title=""Report from the Joint W3C/IETF URI Planning Interest Group: Uniform Resource Identifiers (URIs), URLs, and Uniform Resource Names (URNs): Clarifications and Recommendations"">RFC3305</a>].
-
-
-
-
-
-
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 7]</span>
-<a name="page-8" id="page-8" href="#page-8"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
-<span class="h3"><h3><a name="section-1.2">1.2</a>. Design Considerations</h3></span>
-
-<span class="h4"><h4><a name="section-1.2.1">1.2.1</a>. Transcription</h4></span>
-
- The URI syntax has been designed with global transcription as one of
- its main considerations. A URI is a sequence of characters from a
- very limited set: the letters of the basic Latin alphabet, digits,
- and a few special characters. A URI may be represented in a variety
- of ways; e.g., ink on paper, pixels on a screen, or a sequence of
- character encoding octets. The interpretation of a URI depends only
- on the characters used and not on how those characters are
- represented in a network protocol.
-
- The goal of transcription can be described by a simple scenario.
- Imagine two colleagues, Sam and Kim, sitting in a pub at an
- international conference and exchanging research ideas. Sam asks Kim
- for a location to get more information, so Kim writes the URI for the
- research site on a napkin. Upon returning home, Sam takes out the
- napkin and types the URI into a computer, which then retrieves the
- information to which Kim referred.
-
- There are several design considerations revealed by the scenario:
-
- o A URI is a sequence of characters that is not always represented
- as a sequence of octets.
-
- o A URI might be transcribed from a non-network source and thus
- should consist of characters that are most likely able to be
- entered into a computer, within the constraints imposed by
- keyboards (and related input devices) across languages and
- locales.
-
- o A URI often has to be remembered by people, and it is easier for
- people to remember a URI when it consists of meaningful or
- familiar components.
-
- These design considerations are not always in alignment. For
- example, it is often the case that the most meaningful name for a URI
- component would require characters that cannot be typed into some
- systems. The ability to transcribe a resource identifier from one
- medium to another has been considered more important than having a
- URI consist of the most meaningful of components.
-
- In local or regional contexts and with improving technology, users
- might benefit from being able to use a wider range of characters;
- such use is not defined by this specification. Percent-encoded
- octets (<a href="#section-2.1">Section 2.1</a>) may be used within a URI to represent characters
- outside the range of the US-ASCII coded character set if this
-
-
-
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-<a name="page-9" id="page-9" href="#page-9"><span class="break"> </span></a>
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-
-
- representation is allowed by the scheme or by the protocol element in
- which the URI is referenced. Such a definition should specify the
- character encoding used to map those characters to octets prior to
- being percent-encoded for the URI.
-
-<span class="h4"><h4><a name="section-1.2.2">1.2.2</a>. Separating Identification from Interaction</h4></span>
-
- A common misunderstanding of URIs is that they are only used to refer
- to accessible resources. The URI itself only provides
- identification; access to the resource is neither guaranteed nor
- implied by the presence of a URI. Instead, any operation associated
- with a URI reference is defined by the protocol element, data format
- attribute, or natural language text in which it appears.
-
- Given a URI, a system may attempt to perform a variety of operations
- on the resource, as might be characterized by words such as "access",
- "update", "replace", or "find attributes". Such operations are
- defined by the protocols that make use of URIs, not by this
- specification. However, we do use a few general terms for describing
- common operations on URIs. URI "resolution" is the process of
- determining an access mechanism and the appropriate parameters
- necessary to dereference a URI; this resolution may require several
- iterations. To use that access mechanism to perform an action on the
- URI's resource is to "dereference" the URI.
-
- When URIs are used within information retrieval systems to identify
- sources of information, the most common form of URI dereference is
- "retrieval": making use of a URI in order to retrieve a
- representation of its associated resource. A "representation" is a
- sequence of octets, along with representation metadata describing
- those octets, that constitutes a record of the state of the resource
- at the time when the representation is generated. Retrieval is
- achieved by a process that might include using the URI as a cache key
- to check for a locally cached representation, resolution of the URI
- to determine an appropriate access mechanism (if any), and
- dereference of the URI for the sake of applying a retrieval
- operation. Depending on the protocols used to perform the retrieval,
- additional information might be supplied about the resource (resource
- metadata) and its relation to other resources.
-
- URI references in information retrieval systems are designed to be
- late-binding: the result of an access is generally determined when it
- is accessed and may vary over time or due to other aspects of the
- interaction. These references are created in order to be used in the
- future: what is being identified is not some specific result that was
- obtained in the past, but rather some characteristic that is expected
- to be true for future results. In such cases, the resource referred
- to by the URI is actually a sameness of characteristics as observed
-
-
-
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-
-
- over time, perhaps elucidated by additional comments or assertions
- made by the resource provider.
-
- Although many URI schemes are named after protocols, this does not
- imply that use of these URIs will result in access to the resource
- via the named protocol. URIs are often used simply for the sake of
- identification. Even when a URI is used to retrieve a representation
- of a resource, that access might be through gateways, proxies,
- caches, and name resolution services that are independent of the
- protocol associated with the scheme name. The resolution of some
- URIs may require the use of more than one protocol (e.g., both DNS
- and HTTP are typically used to access an "http" URI's origin server
- when a representation isn't found in a local cache).
-
-<span class="h4"><h4><a name="section-1.2.3">1.2.3</a>. Hierarchical Identifiers</h4></span>
-
- The URI syntax is organized hierarchically, with components listed in
- order of decreasing significance from left to right. For some URI
- schemes, the visible hierarchy is limited to the scheme itself:
- everything after the scheme component delimiter (":") is considered
- opaque to URI processing. Other URI schemes make the hierarchy
- explicit and visible to generic parsing algorithms.
-
- The generic syntax uses the slash ("/"), question mark ("?"), and
- number sign ("#") characters to delimit components that are
- significant to the generic parser's hierarchical interpretation of an
- identifier. In addition to aiding the readability of such
- identifiers through the consistent use of familiar syntax, this
- uniform representation of hierarchy across naming schemes allows
- scheme-independent references to be made relative to that hierarchy.
-
- It is often the case that a group or "tree" of documents has been
- constructed to serve a common purpose, wherein the vast majority of
- URI references in these documents point to resources within the tree
- rather than outside it. Similarly, documents located at a particular
- site are much more likely to refer to other resources at that site
- than to resources at remote sites. Relative referencing of URIs
- allows document trees to be partially independent of their location
- and access scheme. For instance, it is possible for a single set of
- hypertext documents to be simultaneously accessible and traversable
- via each of the "file", "http", and "ftp" schemes if the documents
- refer to each other with relative references. Furthermore, such
- document trees can be moved, as a whole, without changing any of the
- relative references.
-
- A relative reference (<a href="#section-4.2">Section 4.2</a>) refers to a resource by describing
- the difference within a hierarchical name space between the reference
- context and the target URI. The reference resolution algorithm,
-
-
-
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-<a name="page-11" id="page-11" href="#page-11"><span class="break"> </span></a>
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-
-
- presented in <a href="#section-5">Section 5</a>, defines how such a reference is transformed
- to the target URI. As relative references can only be used within
- the context of a hierarchical URI, designers of new URI schemes
- should use a syntax consistent with the generic syntax's hierarchical
- components unless there are compelling reasons to forbid relative
- referencing within that scheme.
-
- NOTE: Previous specifications used the terms "partial URI" and
- "relative URI" to denote a relative reference to a URI. As some
- readers misunderstood those terms to mean that relative URIs are a
- subset of URIs rather than a method of referencing URIs, this
- specification simply refers to them as relative references.
-
- All URI references are parsed by generic syntax parsers when used.
- However, because hierarchical processing has no effect on an absolute
- URI used in a reference unless it contains one or more dot-segments
- (complete path segments of "." or "..", as described in <a href="#section-3.3">Section 3.3</a>),
- URI scheme specifications can define opaque identifiers by
- disallowing use of slash characters, question mark characters, and
- the URIs "scheme:." and "scheme:..".
-
-<span class="h3"><h3><a name="section-1.3">1.3</a>. Syntax Notation</h3></span>
-
- This specification uses the Augmented Backus-Naur Form (ABNF)
- notation of [<a href="http://tools.ietf.org/html/rfc2234" title=""Augmented BNF for Syntax Specifications: ABNF"">RFC2234</a>], including the following core ABNF syntax rules
- defined by that specification: ALPHA (letters), CR (carriage return),
- DIGIT (decimal digits), DQUOTE (double quote), HEXDIG (hexadecimal
- digits), LF (line feed), and SP (space). The complete URI syntax is
- collected in Appendix A.
-
-<span class="h2"><h2><a name="section-2">2</a>. Characters</h2></span>
-
- The URI syntax provides a method of encoding data, presumably for the
- sake of identifying a resource, as a sequence of characters. The URI
- characters are, in turn, frequently encoded as octets for transport
- or presentation. This specification does not mandate any particular
- character encoding for mapping between URI characters and the octets
- used to store or transmit those characters. When a URI appears in a
- protocol element, the character encoding is defined by that protocol;
- without such a definition, a URI is assumed to be in the same
- character encoding as the surrounding text.
-
- The ABNF notation defines its terminal values to be non-negative
- integers (codepoints) based on the US-ASCII coded character set
- [<a href="#ref-ASCII" title=""Coded Character Set -- 7-bit American Standard Code for Information Interchange"">ASCII</a>]. Because a URI is a sequence of characters, we must invert
- that relation in order to understand the URI syntax. Therefore, the
-
-
-
-
-
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-
-
- integer values used by the ABNF must be mapped back to their
- corresponding characters via US-ASCII in order to complete the syntax
- rules.
-
- A URI is composed from a limited set of characters consisting of
- digits, letters, and a few graphic symbols. A reserved subset of
- those characters may be used to delimit syntax components within a
- URI while the remaining characters, including both the unreserved set
- and those reserved characters not acting as delimiters, define each
- component's identifying data.
-
-<span class="h3"><h3><a name="section-2.1">2.1</a>. Percent-Encoding</h3></span>
-
- A percent-encoding mechanism is used to represent a data octet in a
- component when that octet's corresponding character is outside the
- allowed set or is being used as a delimiter of, or within, the
- component. A percent-encoded octet is encoded as a character
- triplet, consisting of the percent character "%" followed by the two
- hexadecimal digits representing that octet's numeric value. For
- example, "%20" is the percent-encoding for the binary octet
- "00100000" (ABNF: %x20), which in US-ASCII corresponds to the space
- character (SP). <a href="#section-2.4">Section 2.4</a> describes when percent-encoding and
- decoding is applied.
-
- pct-encoded = "%" HEXDIG HEXDIG
-
- The uppercase hexadecimal digits 'A' through 'F' are equivalent to
- the lowercase digits 'a' through 'f', respectively. If two URIs
- differ only in the case of hexadecimal digits used in percent-encoded
- octets, they are equivalent. For consistency, URI producers and
- normalizers should use uppercase hexadecimal digits for all percent-
- encodings.
-
-<span class="h3"><h3><a name="section-2.2">2.2</a>. Reserved Characters</h3></span>
-
- URIs include components and subcomponents that are delimited by
- characters in the "reserved" set. These characters are called
- "reserved" because they may (or may not) be defined as delimiters by
- the generic syntax, by each scheme-specific syntax, or by the
- implementation-specific syntax of a URI's dereferencing algorithm.
- If data for a URI component would conflict with a reserved
- character's purpose as a delimiter, then the conflicting data must be
- percent-encoded before the URI is formed.
-
-
-
-
-
-
-
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-
-
- reserved = gen-delims / sub-delims
-
- gen-delims = ":" / "/" / "?" / "#" / "[" / "]" / "@"
-
- sub-delims = "!" / "$" / "&" / "'" / "(" / ")"
- / "*" / "+" / "," / ";" / "="
-
- The purpose of reserved characters is to provide a set of delimiting
- characters that are distinguishable from other data within a URI.
- URIs that differ in the replacement of a reserved character with its
- corresponding percent-encoded octet are not equivalent. Percent-
- encoding a reserved character, or decoding a percent-encoded octet
- that corresponds to a reserved character, will change how the URI is
- interpreted by most applications. Thus, characters in the reserved
- set are protected from normalization and are therefore safe to be
- used by scheme-specific and producer-specific algorithms for
- delimiting data subcomponents within a URI.
-
- A subset of the reserved characters (gen-delims) is used as
- delimiters of the generic URI components described in <a href="#section-3">Section 3</a>. A
- component's ABNF syntax rule will not use the reserved or gen-delims
- rule names directly; instead, each syntax rule lists the characters
- allowed within that component (i.e., not delimiting it), and any of
- those characters that are also in the reserved set are "reserved" for
- use as subcomponent delimiters within the component. Only the most
- common subcomponents are defined by this specification; other
- subcomponents may be defined by a URI scheme's specification, or by
- the implementation-specific syntax of a URI's dereferencing
- algorithm, provided that such subcomponents are delimited by
- characters in the reserved set allowed within that component.
-
- URI producing applications should percent-encode data octets that
- correspond to characters in the reserved set unless these characters
- are specifically allowed by the URI scheme to represent data in that
- component. If a reserved character is found in a URI component and
- no delimiting role is known for that character, then it must be
- interpreted as representing the data octet corresponding to that
- character's encoding in US-ASCII.
-
-<span class="h3"><h3><a name="section-2.3">2.3</a>. Unreserved Characters</h3></span>
-
- Characters that are allowed in a URI but do not have a reserved
- purpose are called unreserved. These include uppercase and lowercase
- letters, decimal digits, hyphen, period, underscore, and tilde.
-
- unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
-
-
-
-
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-
-
- URIs that differ in the replacement of an unreserved character with
- its corresponding percent-encoded US-ASCII octet are equivalent: they
- identify the same resource. However, URI comparison implementations
- do not always perform normalization prior to comparison (see Section
- 6). For consistency, percent-encoded octets in the ranges of ALPHA
- (%41-%5A and %61-%7A), DIGIT (%30-%39), hyphen (%2D), period (%2E),
- underscore (%5F), or tilde (%7E) should not be created by URI
- producers and, when found in a URI, should be decoded to their
- corresponding unreserved characters by URI normalizers.
-
-<span class="h3"><h3><a name="section-2.4">2.4</a>. When to Encode or Decode</h3></span>
-
- Under normal circumstances, the only time when octets within a URI
- are percent-encoded is during the process of producing the URI from
- its component parts. This is when an implementation determines which
- of the reserved characters are to be used as subcomponent delimiters
- and which can be safely used as data. Once produced, a URI is always
- in its percent-encoded form.
-
- When a URI is dereferenced, the components and subcomponents
- significant to the scheme-specific dereferencing process (if any)
- must be parsed and separated before the percent-encoded octets within
- those components can be safely decoded, as otherwise the data may be
- mistaken for component delimiters. The only exception is for
- percent-encoded octets corresponding to characters in the unreserved
- set, which can be decoded at any time. For example, the octet
- corresponding to the tilde ("~") character is often encoded as "%7E"
- by older URI processing implementations; the "%7E" can be replaced by
- "~" without changing its interpretation.
-
- Because the percent ("%") character serves as the indicator for
- percent-encoded octets, it must be percent-encoded as "%25" for that
- octet to be used as data within a URI. Implementations must not
- percent-encode or decode the same string more than once, as decoding
- an already decoded string might lead to misinterpreting a percent
- data octet as the beginning of a percent-encoding, or vice versa in
- the case of percent-encoding an already percent-encoded string.
-
-<span class="h3"><h3><a name="section-2.5">2.5</a>. Identifying Data</h3></span>
-
- URI characters provide identifying data for each of the URI
- components, serving as an external interface for identification
- between systems. Although the presence and nature of the URI
- production interface is hidden from clients that use its URIs (and is
- thus beyond the scope of the interoperability requirements defined by
- this specification), it is a frequent source of confusion and errors
- in the interpretation of URI character issues. Implementers have to
- be aware that there are multiple character encodings involved in the
-
-
-
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-
-
- production and transmission of URIs: local name and data encoding,
- public interface encoding, URI character encoding, data format
- encoding, and protocol encoding.
-
- Local names, such as file system names, are stored with a local
- character encoding. URI producing applications (e.g., origin
- servers) will typically use the local encoding as the basis for
- producing meaningful names. The URI producer will transform the
- local encoding to one that is suitable for a public interface and
- then transform the public interface encoding into the restricted set
- of URI characters (reserved, unreserved, and percent-encodings).
- Those characters are, in turn, encoded as octets to be used as a
- reference within a data format (e.g., a document charset), and such
- data formats are often subsequently encoded for transmission over
- Internet protocols.
-
- For most systems, an unreserved character appearing within a URI
- component is interpreted as representing the data octet corresponding
- to that character's encoding in US-ASCII. Consumers of URIs assume
- that the letter "X" corresponds to the octet "01011000", and even
- when that assumption is incorrect, there is no harm in making it. A
- system that internally provides identifiers in the form of a
- different character encoding, such as EBCDIC, will generally perform
- character translation of textual identifiers to UTF-8 [<a href="#ref-STD63" title=""UTF-8, a transformation format of ISO 10646"">STD63</a>] (or
- some other superset of the US-ASCII character encoding) at an
- internal interface, thereby providing more meaningful identifiers
- than those resulting from simply percent-encoding the original
- octets.
-
- For example, consider an information service that provides data,
- stored locally using an EBCDIC-based file system, to clients on the
- Internet through an HTTP server. When an author creates a file with
- the name "Laguna Beach" on that file system, the "http" URI
- corresponding to that resource is expected to contain the meaningful
- string "Laguna%20Beach". If, however, that server produces URIs by
- using an overly simplistic raw octet mapping, then the result would
- be a URI containing "%D3%81%87%A4%95%81@%C2%85%81%83%88". An
- internal transcoding interface fixes this problem by transcoding the
- local name to a superset of US-ASCII prior to producing the URI.
- Naturally, proper interpretation of an incoming URI on such an
- interface requires that percent-encoded octets be decoded (e.g.,
- "%20" to SP) before the reverse transcoding is applied to obtain the
- local name.
-
- In some cases, the internal interface between a URI component and the
- identifying data that it has been crafted to represent is much less
- direct than a character encoding translation. For example, portions
- of a URI might reflect a query on non-ASCII data, or numeric
-
-
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-
-
- coordinates on a map. Likewise, a URI scheme may define components
- with additional encoding requirements that are applied prior to
- forming the component and producing the URI.
-
- When a new URI scheme defines a component that represents textual
- data consisting of characters from the Universal Character Set [<a href="#ref-UCS" title=""Information Technology - Universal Multiple-Octet Coded Character Set (UCS)"">UCS</a>],
- the data should first be encoded as octets according to the UTF-8
- character encoding [<a href="#ref-STD63" title=""UTF-8, a transformation format of ISO 10646"">STD63</a>]; then only those octets that do not
- correspond to characters in the unreserved set should be percent-
- encoded. For example, the character A would be represented as "A",
- the character LATIN CAPITAL LETTER A WITH GRAVE would be represented
- as "%C3%80", and the character KATAKANA LETTER A would be represented
- as "%E3%82%A2".
-
-<span class="h2"><h2><a name="section-3">3</a>. Syntax Components</h2></span>
-
- The generic URI syntax consists of a hierarchical sequence of
- components referred to as the scheme, authority, path, query, and
- fragment.
-
- URI = scheme ":" hier-part [ "?" query ] [ "#" fragment ]
-
- hier-part = "//" authority path-abempty
- / path-absolute
- / path-rootless
- / path-empty
-
- The scheme and path components are required, though the path may be
- empty (no characters). When authority is present, the path must
- either be empty or begin with a slash ("/") character. When
- authority is not present, the path cannot begin with two slash
- characters ("//"). These restrictions result in five different ABNF
- rules for a path (<a href="#section-3.3">Section 3.3</a>), only one of which will match any
- given URI reference.
-
- The following are two example URIs and their component parts:
-
- foo://example.com:8042/over/there?name=ferret#nose
- \_/ \______________/\_________/ \_________/ \__/
- | | | | |
- scheme authority path query fragment
- | _____________________|__
- / \ / \
- urn:example:animal:ferret:nose
-
-
-
-
-
-
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-
-
-<span class="h3"><h3><a name="section-3.1">3.1</a>. Scheme</h3></span>
-
- Each URI begins with a scheme name that refers to a specification for
- assigning identifiers within that scheme. As such, the URI syntax is
- a federated and extensible naming system wherein each scheme's
- specification may further restrict the syntax and semantics of
- identifiers using that scheme.
-
- Scheme names consist of a sequence of characters beginning with a
- letter and followed by any combination of letters, digits, plus
- ("+"), period ("."), or hyphen ("-"). Although schemes are case-
- insensitive, the canonical form is lowercase and documents that
- specify schemes must do so with lowercase letters. An implementation
- should accept uppercase letters as equivalent to lowercase in scheme
- names (e.g., allow "HTTP" as well as "http") for the sake of
- robustness but should only produce lowercase scheme names for
- consistency.
-
- scheme = ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )
-
- Individual schemes are not specified by this document. The process
- for registration of new URI schemes is defined separately by [<a href="#ref-BCP35" title=""Registration Procedures for URL Scheme Names"">BCP35</a>].
- The scheme registry maintains the mapping between scheme names and
- their specifications. Advice for designers of new URI schemes can be
- found in [<a href="http://tools.ietf.org/html/rfc2718" title=""Guidelines for new URL Schemes"">RFC2718</a>]. URI scheme specifications must define their own
- syntax so that all strings matching their scheme-specific syntax will
- also match the <absolute-URI> grammar, as described in <a href="#section-4.3">Section 4.3</a>.
-
- When presented with a URI that violates one or more scheme-specific
- restrictions, the scheme-specific resolution process should flag the
- reference as an error rather than ignore the unused parts; doing so
- reduces the number of equivalent URIs and helps detect abuses of the
- generic syntax, which might indicate that the URI has been
- constructed to mislead the user (<a href="#section-7.6">Section 7.6</a>).
-
-<span class="h3"><h3><a name="section-3.2">3.2</a>. Authority</h3></span>
-
- Many URI schemes include a hierarchical element for a naming
- authority so that governance of the name space defined by the
- remainder of the URI is delegated to that authority (which may, in
- turn, delegate it further). The generic syntax provides a common
- means for distinguishing an authority based on a registered name or
- server address, along with optional port and user information.
-
- The authority component is preceded by a double slash ("//") and is
- terminated by the next slash ("/"), question mark ("?"), or number
- sign ("#") character, or by the end of the URI.
-
-
-
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-
-
- authority = [ userinfo "@" ] host [ ":" port ]
-
- URI producers and normalizers should omit the ":" delimiter that
- separates host from port if the port component is empty. Some
- schemes do not allow the userinfo and/or port subcomponents.
-
- If a URI contains an authority component, then the path component
- must either be empty or begin with a slash ("/") character. Non-
- validating parsers (those that merely separate a URI reference into
- its major components) will often ignore the subcomponent structure of
- authority, treating it as an opaque string from the double-slash to
- the first terminating delimiter, until such time as the URI is
- dereferenced.
-
-<span class="h4"><h4><a name="section-3.2.1">3.2.1</a>. User Information</h4></span>
-
- The userinfo subcomponent may consist of a user name and, optionally,
- scheme-specific information about how to gain authorization to access
- the resource. The user information, if present, is followed by a
- commercial at-sign ("@") that delimits it from the host.
-
- userinfo = *( unreserved / pct-encoded / sub-delims / ":" )
-
- Use of the format "user:password" in the userinfo field is
- deprecated. Applications should not render as clear text any data
- after the first colon (":") character found within a userinfo
- subcomponent unless the data after the colon is the empty string
- (indicating no password). Applications may choose to ignore or
- reject such data when it is received as part of a reference and
- should reject the storage of such data in unencrypted form. The
- passing of authentication information in clear text has proven to be
- a security risk in almost every case where it has been used.
-
- Applications that render a URI for the sake of user feedback, such as
- in graphical hypertext browsing, should render userinfo in a way that
- is distinguished from the rest of a URI, when feasible. Such
- rendering will assist the user in cases where the userinfo has been
- misleadingly crafted to look like a trusted domain name
- (<a href="#section-7.6">Section 7.6</a>).
-
-<span class="h4"><h4><a name="section-3.2.2">3.2.2</a>. Host</h4></span>
-
- The host subcomponent of authority is identified by an IP literal
- encapsulated within square brackets, an IPv4 address in dotted-
- decimal form, or a registered name. The host subcomponent is case-
- insensitive. The presence of a host subcomponent within a URI does
- not imply that the scheme requires access to the given host on the
- Internet. In many cases, the host syntax is used only for the sake
-
-
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-
-
- of reusing the existing registration process created and deployed for
- DNS, thus obtaining a globally unique name without the cost of
- deploying another registry. However, such use comes with its own
- costs: domain name ownership may change over time for reasons not
- anticipated by the URI producer. In other cases, the data within the
- host component identifies a registered name that has nothing to do
- with an Internet host. We use the name "host" for the ABNF rule
- because that is its most common purpose, not its only purpose.
-
- host = IP-literal / IPv4address / reg-name
-
- The syntax rule for host is ambiguous because it does not completely
- distinguish between an IPv4address and a reg-name. In order to
- disambiguate the syntax, we apply the "first-match-wins" algorithm:
- If host matches the rule for IPv4address, then it should be
- considered an IPv4 address literal and not a reg-name. Although host
- is case-insensitive, producers and normalizers should use lowercase
- for registered names and hexadecimal addresses for the sake of
- uniformity, while only using uppercase letters for percent-encodings.
-
- A host identified by an Internet Protocol literal address, version 6
- [<a href="http://tools.ietf.org/html/rfc3513" title=""Internet Protocol Version 6 (IPv6) Addressing Architecture"">RFC3513</a>] or later, is distinguished by enclosing the IP literal
- within square brackets ("[" and "]"). This is the only place where
- square bracket characters are allowed in the URI syntax. In
- anticipation of future, as-yet-undefined IP literal address formats,
- an implementation may use an optional version flag to indicate such a
- format explicitly rather than rely on heuristic determination.
-
- IP-literal = "[" ( IPv6address / IPvFuture ) "]"
-
- IPvFuture = "v" 1*HEXDIG "." 1*( unreserved / sub-delims / ":" )
-
- The version flag does not indicate the IP version; rather, it
- indicates future versions of the literal format. As such,
- implementations must not provide the version flag for the existing
- IPv4 and IPv6 literal address forms described below. If a URI
- containing an IP-literal that starts with "v" (case-insensitive),
- indicating that the version flag is present, is dereferenced by an
- application that does not know the meaning of that version flag, then
- the application should return an appropriate error for "address
- mechanism not supported".
-
- A host identified by an IPv6 literal address is represented inside
- the square brackets without a preceding version flag. The ABNF
- provided here is a translation of the text definition of an IPv6
- literal address provided in [<a href="http://tools.ietf.org/html/rfc3513" title=""Internet Protocol Version 6 (IPv6) Addressing Architecture"">RFC3513</a>]. This syntax does not support
- IPv6 scoped addressing zone identifiers.
-
-
-
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-
-
- A 128-bit IPv6 address is divided into eight 16-bit pieces. Each
- piece is represented numerically in case-insensitive hexadecimal,
- using one to four hexadecimal digits (leading zeroes are permitted).
- The eight encoded pieces are given most-significant first, separated
- by colon characters. Optionally, the least-significant two pieces
- may instead be represented in IPv4 address textual format. A
- sequence of one or more consecutive zero-valued 16-bit pieces within
- the address may be elided, omitting all their digits and leaving
- exactly two consecutive colons in their place to mark the elision.
-
- IPv6address = 6( h16 ":" ) ls32
- / "::" 5( h16 ":" ) ls32
- / [ h16 ] "::" 4( h16 ":" ) ls32
- / [ *1( h16 ":" ) h16 ] "::" 3( h16 ":" ) ls32
- / [ *2( h16 ":" ) h16 ] "::" 2( h16 ":" ) ls32
- / [ *3( h16 ":" ) h16 ] "::" h16 ":" ls32
- / [ *4( h16 ":" ) h16 ] "::" ls32
- / [ *5( h16 ":" ) h16 ] "::" h16
- / [ *6( h16 ":" ) h16 ] "::"
-
- ls32 = ( h16 ":" h16 ) / IPv4address
- ; least-significant 32 bits of address
-
- h16 = 1*4HEXDIG
- ; 16 bits of address represented in hexadecimal
-
- A host identified by an IPv4 literal address is represented in
- dotted-decimal notation (a sequence of four decimal numbers in the
- range 0 to 255, separated by "."), as described in [<a href="http://tools.ietf.org/html/rfc1123" title=""Requirements for Internet Hosts - Application and Support"">RFC1123</a>] by
- reference to [<a href="http://tools.ietf.org/html/rfc0952" title=""DoD Internet host table specification"">RFC0952</a>]. Note that other forms of dotted notation may
- be interpreted on some platforms, as described in <a href="#section-7.4">Section 7.4</a>, but
- only the dotted-decimal form of four octets is allowed by this
- grammar.
-
- IPv4address = dec-octet "." dec-octet "." dec-octet "." dec-octet
-
- dec-octet = DIGIT ; 0-9
- / %x31-39 DIGIT ; 10-99
- / "1" 2DIGIT ; 100-199
- / "2" %x30-34 DIGIT ; 200-249
- / "25" %x30-35 ; 250-255
-
- A host identified by a registered name is a sequence of characters
- usually intended for lookup within a locally defined host or service
- name registry, though the URI's scheme-specific semantics may require
- that a specific registry (or fixed name table) be used instead. The
- most common name registry mechanism is the Domain Name System (DNS).
- A registered name intended for lookup in the DNS uses the syntax
-
-
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-
-
- defined in <a href="#section-3.5">Section 3.5</a> of [<a href="http://tools.ietf.org/html/rfc1034" title=""Domain names - concepts and facilities"">RFC1034</a>] and <a href="#section-2.1">Section 2.1</a> of [<a href="http://tools.ietf.org/html/rfc1123" title=""Requirements for Internet Hosts - Application and Support"">RFC1123</a>].
- Such a name consists of a sequence of domain labels separated by ".",
- each domain label starting and ending with an alphanumeric character
- and possibly also containing "-" characters. The rightmost domain
- label of a fully qualified domain name in DNS may be followed by a
- single "." and should be if it is necessary to distinguish between
- the complete domain name and some local domain.
-
- reg-name = *( unreserved / pct-encoded / sub-delims )
-
- If the URI scheme defines a default for host, then that default
- applies when the host subcomponent is undefined or when the
- registered name is empty (zero length). For example, the "file" URI
- scheme is defined so that no authority, an empty host, and
- "localhost" all mean the end-user's machine, whereas the "http"
- scheme considers a missing authority or empty host invalid.
-
- This specification does not mandate a particular registered name
- lookup technology and therefore does not restrict the syntax of reg-
- name beyond what is necessary for interoperability. Instead, it
- delegates the issue of registered name syntax conformance to the
- operating system of each application performing URI resolution, and
- that operating system decides what it will allow for the purpose of
- host identification. A URI resolution implementation might use DNS,
- host tables, yellow pages, NetInfo, WINS, or any other system for
- lookup of registered names. However, a globally scoped naming
- system, such as DNS fully qualified domain names, is necessary for
- URIs intended to have global scope. URI producers should use names
- that conform to the DNS syntax, even when use of DNS is not
- immediately apparent, and should limit these names to no more than
- 255 characters in length.
-
- The reg-name syntax allows percent-encoded octets in order to
- represent non-ASCII registered names in a uniform way that is
- independent of the underlying name resolution technology. Non-ASCII
- characters must first be encoded according to UTF-8 [<a href="#ref-STD63" title=""UTF-8, a transformation format of ISO 10646"">STD63</a>], and then
- each octet of the corresponding UTF-8 sequence must be percent-
- encoded to be represented as URI characters. URI producing
- applications must not use percent-encoding in host unless it is used
- to represent a UTF-8 character sequence. When a non-ASCII registered
- name represents an internationalized domain name intended for
- resolution via the DNS, the name must be transformed to the IDNA
- encoding [<a href="http://tools.ietf.org/html/rfc3490" title=""Internationalizing Domain Names in Applications (IDNA)"">RFC3490</a>] prior to name lookup. URI producers should
- provide these registered names in the IDNA encoding, rather than a
- percent-encoding, if they wish to maximize interoperability with
- legacy URI resolvers.
-
-
-
-
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-
-
-<span class="h4"><h4><a name="section-3.2.3">3.2.3</a>. Port</h4></span>
-
- The port subcomponent of authority is designated by an optional port
- number in decimal following the host and delimited from it by a
- single colon (":") character.
-
- port = *DIGIT
-
- A scheme may define a default port. For example, the "http" scheme
- defines a default port of "80", corresponding to its reserved TCP
- port number. The type of port designated by the port number (e.g.,
- TCP, UDP, SCTP) is defined by the URI scheme. URI producers and
- normalizers should omit the port component and its ":" delimiter if
- port is empty or if its value would be the same as that of the
- scheme's default.
-
-<span class="h3"><h3><a name="section-3.3">3.3</a>. Path</h3></span>
-
- The path component contains data, usually organized in hierarchical
- form, that, along with data in the non-hierarchical query component
- (<a href="#section-3.4">Section 3.4</a>), serves to identify a resource within the scope of the
- URI's scheme and naming authority (if any). The path is terminated
- by the first question mark ("?") or number sign ("#") character, or
- by the end of the URI.
-
- If a URI contains an authority component, then the path component
- must either be empty or begin with a slash ("/") character. If a URI
- does not contain an authority component, then the path cannot begin
- with two slash characters ("//"). In addition, a URI reference
- (<a href="#section-4.1">Section 4.1</a>) may be a relative-path reference, in which case the
- first path segment cannot contain a colon (":") character. The ABNF
- requires five separate rules to disambiguate these cases, only one of
- which will match the path substring within a given URI reference. We
- use the generic term "path component" to describe the URI substring
- matched by the parser to one of these rules.
-
- path = path-abempty ; begins with "/" or is empty
- / path-absolute ; begins with "/" but not "//"
- / path-noscheme ; begins with a non-colon segment
- / path-rootless ; begins with a segment
- / path-empty ; zero characters
-
- path-abempty = *( "/" segment )
- path-absolute = "/" [ segment-nz *( "/" segment ) ]
- path-noscheme = segment-nz-nc *( "/" segment )
- path-rootless = segment-nz *( "/" segment )
- path-empty = 0<pchar>
-
-
-
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-
-
- segment = *pchar
- segment-nz = 1*pchar
- segment-nz-nc = 1*( unreserved / pct-encoded / sub-delims / "@" )
- ; non-zero-length segment without any colon ":"
-
- pchar = unreserved / pct-encoded / sub-delims / ":" / "@"
-
- A path consists of a sequence of path segments separated by a slash
- ("/") character. A path is always defined for a URI, though the
- defined path may be empty (zero length). Use of the slash character
- to indicate hierarchy is only required when a URI will be used as the
- context for relative references. For example, the URI
- <mailto:fred@example.com> has a path of "fred@example.com", whereas
- the URI <foo://info.example.com?fred> has an empty path.
-
- The path segments "." and "..", also known as dot-segments, are
- defined for relative reference within the path name hierarchy. They
- are intended for use at the beginning of a relative-path reference
- (<a href="#section-4.2">Section 4.2</a>) to indicate relative position within the hierarchical
- tree of names. This is similar to their role within some operating
- systems' file directory structures to indicate the current directory
- and parent directory, respectively. However, unlike in a file
- system, these dot-segments are only interpreted within the URI path
- hierarchy and are removed as part of the resolution process (Section
- 5.2).
-
- Aside from dot-segments in hierarchical paths, a path segment is
- considered opaque by the generic syntax. URI producing applications
- often use the reserved characters allowed in a segment to delimit
- scheme-specific or dereference-handler-specific subcomponents. For
- example, the semicolon (";") and equals ("=") reserved characters are
- often used to delimit parameters and parameter values applicable to
- that segment. The comma (",") reserved character is often used for
- similar purposes. For example, one URI producer might use a segment
- such as "name;v=1.1" to indicate a reference to version 1.1 of
- "name", whereas another might use a segment such as "name,1.1" to
- indicate the same. Parameter types may be defined by scheme-specific
- semantics, but in most cases the syntax of a parameter is specific to
- the implementation of the URI's dereferencing algorithm.
-
-<span class="h3"><h3><a name="section-3.4">3.4</a>. Query</h3></span>
-
- The query component contains non-hierarchical data that, along with
- data in the path component (<a href="#section-3.3">Section 3.3</a>), serves to identify a
- resource within the scope of the URI's scheme and naming authority
- (if any). The query component is indicated by the first question
- mark ("?") character and terminated by a number sign ("#") character
- or by the end of the URI.
-
-
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-
-
- query = *( pchar / "/" / "?" )
-
- The characters slash ("/") and question mark ("?") may represent data
- within the query component. Beware that some older, erroneous
- implementations may not handle such data correctly when it is used as
- the base URI for relative references (<a href="#section-5.1">Section 5.1</a>), apparently
- because they fail to distinguish query data from path data when
- looking for hierarchical separators. However, as query components
- are often used to carry identifying information in the form of
- "key=value" pairs and one frequently used value is a reference to
- another URI, it is sometimes better for usability to avoid percent-
- encoding those characters.
-
-<span class="h3"><h3><a name="section-3.5">3.5</a>. Fragment</h3></span>
-
- The fragment identifier component of a URI allows indirect
- identification of a secondary resource by reference to a primary
- resource and additional identifying information. The identified
- secondary resource may be some portion or subset of the primary
- resource, some view on representations of the primary resource, or
- some other resource defined or described by those representations. A
- fragment identifier component is indicated by the presence of a
- number sign ("#") character and terminated by the end of the URI.
-
- fragment = *( pchar / "/" / "?" )
-
- The semantics of a fragment identifier are defined by the set of
- representations that might result from a retrieval action on the
- primary resource. The fragment's format and resolution is therefore
- dependent on the media type [<a href="http://tools.ietf.org/html/rfc2046" title=""Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types"">RFC2046</a>] of a potentially retrieved
- representation, even though such a retrieval is only performed if the
- URI is dereferenced. If no such representation exists, then the
- semantics of the fragment are considered unknown and are effectively
- unconstrained. Fragment identifier semantics are independent of the
- URI scheme and thus cannot be redefined by scheme specifications.
-
- Individual media types may define their own restrictions on or
- structures within the fragment identifier syntax for specifying
- different types of subsets, views, or external references that are
- identifiable as secondary resources by that media type. If the
- primary resource has multiple representations, as is often the case
- for resources whose representation is selected based on attributes of
- the retrieval request (a.k.a., content negotiation), then whatever is
- identified by the fragment should be consistent across all of those
- representations. Each representation should either define the
- fragment so that it corresponds to the same secondary resource,
- regardless of how it is represented, or should leave the fragment
- undefined (i.e., not found).
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 24]</span>
-<a name="page-25" id="page-25" href="#page-25"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
- As with any URI, use of a fragment identifier component does not
- imply that a retrieval action will take place. A URI with a fragment
- identifier may be used to refer to the secondary resource without any
- implication that the primary resource is accessible or will ever be
- accessed.
-
- Fragment identifiers have a special role in information retrieval
- systems as the primary form of client-side indirect referencing,
- allowing an author to specifically identify aspects of an existing
- resource that are only indirectly provided by the resource owner. As
- such, the fragment identifier is not used in the scheme-specific
- processing of a URI; instead, the fragment identifier is separated
- from the rest of the URI prior to a dereference, and thus the
- identifying information within the fragment itself is dereferenced
- solely by the user agent, regardless of the URI scheme. Although
- this separate handling is often perceived to be a loss of
- information, particularly for accurate redirection of references as
- resources move over time, it also serves to prevent information
- providers from denying reference authors the right to refer to
- information within a resource selectively. Indirect referencing also
- provides additional flexibility and extensibility to systems that use
- URIs, as new media types are easier to define and deploy than new
- schemes of identification.
-
- The characters slash ("/") and question mark ("?") are allowed to
- represent data within the fragment identifier. Beware that some
- older, erroneous implementations may not handle this data correctly
- when it is used as the base URI for relative references (Section
- 5.1).
-
-<span class="h2"><h2><a name="section-4">4</a>. Usage</h2></span>
-
- When applications make reference to a URI, they do not always use the
- full form of reference defined by the "URI" syntax rule. To save
- space and take advantage of hierarchical locality, many Internet
- protocol elements and media type formats allow an abbreviation of a
- URI, whereas others restrict the syntax to a particular form of URI.
- We define the most common forms of reference syntax in this
- specification because they impact and depend upon the design of the
- generic syntax, requiring a uniform parsing algorithm in order to be
- interpreted consistently.
-
-<span class="h3"><h3><a name="section-4.1">4.1</a>. URI Reference</h3></span>
-
- URI-reference is used to denote the most common usage of a resource
- identifier.
-
- URI-reference = URI / relative-ref
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 25]</span>
-<a name="page-26" id="page-26" href="#page-26"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
- A URI-reference is either a URI or a relative reference. If the
- URI-reference's prefix does not match the syntax of a scheme followed
- by its colon separator, then the URI-reference is a relative
- reference.
-
- A URI-reference is typically parsed first into the five URI
- components, in order to determine what components are present and
- whether the reference is relative. Then, each component is parsed
- for its subparts and their validation. The ABNF of URI-reference,
- along with the "first-match-wins" disambiguation rule, is sufficient
- to define a validating parser for the generic syntax. Readers
- familiar with regular expressions should see Appendix B for an
- example of a non-validating URI-reference parser that will take any
- given string and extract the URI components.
-
-<span class="h3"><h3><a name="section-4.2">4.2</a>. Relative Reference</h3></span>
-
- A relative reference takes advantage of the hierarchical syntax
- (<a href="#section-1.2.3">Section 1.2.3</a>) to express a URI reference relative to the name space
- of another hierarchical URI.
-
- relative-ref = relative-part [ "?" query ] [ "#" fragment ]
-
- relative-part = "//" authority path-abempty
- / path-absolute
- / path-noscheme
- / path-empty
-
- The URI referred to by a relative reference, also known as the target
- URI, is obtained by applying the reference resolution algorithm of
- <a href="#section-5">Section 5</a>.
-
- A relative reference that begins with two slash characters is termed
- a network-path reference; such references are rarely used. A
- relative reference that begins with a single slash character is
- termed an absolute-path reference. A relative reference that does
- not begin with a slash character is termed a relative-path reference.
-
- A path segment that contains a colon character (e.g., "this:that")
- cannot be used as the first segment of a relative-path reference, as
- it would be mistaken for a scheme name. Such a segment must be
- preceded by a dot-segment (e.g., "./this:that") to make a relative-
- path reference.
-
-
-
-
-
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 26]</span>
-<a name="page-27" id="page-27" href="#page-27"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
-<span class="h3"><h3><a name="section-4.3">4.3</a>. Absolute URI</h3></span>
-
- Some protocol elements allow only the absolute form of a URI without
- a fragment identifier. For example, defining a base URI for later
- use by relative references calls for an absolute-URI syntax rule that
- does not allow a fragment.
-
- absolute-URI = scheme ":" hier-part [ "?" query ]
-
- URI scheme specifications must define their own syntax so that all
- strings matching their scheme-specific syntax will also match the
- <absolute-URI> grammar. Scheme specifications will not define
- fragment identifier syntax or usage, regardless of its applicability
- to resources identifiable via that scheme, as fragment identification
- is orthogonal to scheme definition. However, scheme specifications
- are encouraged to include a wide range of examples, including
- examples that show use of the scheme's URIs with fragment identifiers
- when such usage is appropriate.
-
-<span class="h3"><h3><a name="section-4.4">4.4</a>. Same-Document Reference</h3></span>
-
- When a URI reference refers to a URI that is, aside from its fragment
- component (if any), identical to the base URI (<a href="#section-5.1">Section 5.1</a>), that
- reference is called a "same-document" reference. The most frequent
- examples of same-document references are relative references that are
- empty or include only the number sign ("#") separator followed by a
- fragment identifier.
-
- When a same-document reference is dereferenced for a retrieval
- action, the target of that reference is defined to be within the same
- entity (representation, document, or message) as the reference;
- therefore, a dereference should not result in a new retrieval action.
-
- Normalization of the base and target URIs prior to their comparison,
- as described in Sections 6.2.2 and 6.2.3, is allowed but rarely
- performed in practice. Normalization may increase the set of same-
- document references, which may be of benefit to some caching
- applications. As such, reference authors should not assume that a
- slightly different, though equivalent, reference URI will (or will
- not) be interpreted as a same-document reference by any given
- application.
-
-<span class="h3"><h3><a name="section-4.5">4.5</a>. Suffix Reference</h3></span>
-
- The URI syntax is designed for unambiguous reference to resources and
- extensibility via the URI scheme. However, as URI identification and
- usage have become commonplace, traditional media (television, radio,
- newspapers, billboards, etc.) have increasingly used a suffix of the
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 27]</span>
-<a name="page-28" id="page-28" href="#page-28"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
- URI as a reference, consisting of only the authority and path
- portions of the URI, such as
-
- www.w3.org/Addressing/
-
- or simply a DNS registered name on its own. Such references are
- primarily intended for human interpretation rather than for machines,
- with the assumption that context-based heuristics are sufficient to
- complete the URI (e.g., most registered names beginning with "www"
- are likely to have a URI prefix of "http://"). Although there is no
- standard set of heuristics for disambiguating a URI suffix, many
- client implementations allow them to be entered by the user and
- heuristically resolved.
-
- Although this practice of using suffix references is common, it
- should be avoided whenever possible and should never be used in
- situations where long-term references are expected. The heuristics
- noted above will change over time, particularly when a new URI scheme
- becomes popular, and are often incorrect when used out of context.
- Furthermore, they can lead to security issues along the lines of
- those described in [<a href="http://tools.ietf.org/html/rfc1535" title=""A Security Problem and Proposed Correction With Widely Deployed DNS Software"">RFC1535</a>].
-
- As a URI suffix has the same syntax as a relative-path reference, a
- suffix reference cannot be used in contexts where a relative
- reference is expected. As a result, suffix references are limited to
- places where there is no defined base URI, such as dialog boxes and
- off-line advertisements.
-
-<span class="h2"><h2><a name="section-5">5</a>. Reference Resolution</h2></span>
-
- This section defines the process of resolving a URI reference within
- a context that allows relative references so that the result is a
- string matching the <URI> syntax rule of <a href="#section-3">Section 3</a>.
-
-<span class="h3"><h3><a name="section-5.1">5.1</a>. Establishing a Base URI</h3></span>
-
- The term "relative" implies that a "base URI" exists against which
- the relative reference is applied. Aside from fragment-only
- references (<a href="#section-4.4">Section 4.4</a>), relative references are only usable when a
- base URI is known. A base URI must be established by the parser
- prior to parsing URI references that might be relative. A base URI
- must conform to the <absolute-URI> syntax rule (<a href="#section-4.3">Section 4.3</a>). If the
- base URI is obtained from a URI reference, then that reference must
- be converted to absolute form and stripped of any fragment component
- prior to its use as a base URI.
-
-
-
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 28]</span>
-<a name="page-29" id="page-29" href="#page-29"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
- The base URI of a reference can be established in one of four ways,
- discussed below in order of precedence. The order of precedence can
- be thought of in terms of layers, where the innermost defined base
- URI has the highest precedence. This can be visualized graphically
- as follows:
-
- .----------------------------------------------------------.
- | .----------------------------------------------------. |
- | | .----------------------------------------------. | |
- | | | .----------------------------------------. | | |
- | | | | .----------------------------------. | | | |
- | | | | | <relative-reference> | | | | |
- | | | | `----------------------------------' | | | |
- | | | | (5.1.1) Base URI embedded in content | | | |
- | | | `----------------------------------------' | | |
- | | | (5.1.2) Base URI of the encapsulating entity | | |
- | | | (message, representation, or none) | | |
- | | `----------------------------------------------' | |
- | | (5.1.3) URI used to retrieve the entity | |
- | `----------------------------------------------------' |
- | (5.1.4) Default Base URI (application-dependent) |
- `----------------------------------------------------------'
-
-<span class="h4"><h4><a name="section-5.1.1">5.1.1</a>. Base URI Embedded in Content</h4></span>
-
- Within certain media types, a base URI for relative references can be
- embedded within the content itself so that it can be readily obtained
- by a parser. This can be useful for descriptive documents, such as
- tables of contents, which may be transmitted to others through
- protocols other than their usual retrieval context (e.g., email or
- USENET news).
-
- It is beyond the scope of this specification to specify how, for each
- media type, a base URI can be embedded. The appropriate syntax, when
- available, is described by the data format specification associated
- with each media type.
-
-<span class="h4"><h4><a name="section-5.1.2">5.1.2</a>. Base URI from the Encapsulating Entity</h4></span>
-
- If no base URI is embedded, the base URI is defined by the
- representation's retrieval context. For a document that is enclosed
- within another entity, such as a message or archive, the retrieval
- context is that entity. Thus, the default base URI of a
- representation is the base URI of the entity in which the
- representation is encapsulated.
-
-
-
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 29]</span>
-<a name="page-30" id="page-30" href="#page-30"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
- A mechanism for embedding a base URI within MIME container types
- (e.g., the message and multipart types) is defined by MHTML
- [<a href="http://tools.ietf.org/html/rfc2557" title=""MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)"">RFC2557</a>]. Protocols that do not use the MIME message header syntax,
- but that do allow some form of tagged metadata to be included within
- messages, may define their own syntax for defining a base URI as part
- of a message.
-
-<span class="h4"><h4><a name="section-5.1.3">5.1.3</a>. Base URI from the Retrieval URI</h4></span>
-
- If no base URI is embedded and the representation is not encapsulated
- within some other entity, then, if a URI was used to retrieve the
- representation, that URI shall be considered the base URI. Note that
- if the retrieval was the result of a redirected request, the last URI
- used (i.e., the URI that resulted in the actual retrieval of the
- representation) is the base URI.
-
-<span class="h4"><h4><a name="section-5.1.4">5.1.4</a>. Default Base URI</h4></span>
-
- If none of the conditions described above apply, then the base URI is
- defined by the context of the application. As this definition is
- necessarily application-dependent, failing to define a base URI by
- using one of the other methods may result in the same content being
- interpreted differently by different types of applications.
-
- A sender of a representation containing relative references is
- responsible for ensuring that a base URI for those references can be
- established. Aside from fragment-only references, relative
- references can only be used reliably in situations where the base URI
- is well defined.
-
-<span class="h3"><h3><a name="section-5.2">5.2</a>. Relative Resolution</h3></span>
-
- This section describes an algorithm for converting a URI reference
- that might be relative to a given base URI into the parsed components
- of the reference's target. The components can then be recomposed, as
- described in <a href="#section-5.3">Section 5.3</a>, to form the target URI. This algorithm
- provides definitive results that can be used to test the output of
- other implementations. Applications may implement relative reference
- resolution by using some other algorithm, provided that the results
- match what would be given by this one.
-
-
-
-
-
-
-
-
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 30]</span>
-<a name="page-31" id="page-31" href="#page-31"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
-<span class="h4"><h4><a name="section-5.2.1">5.2.1</a>. Pre-parse the Base URI</h4></span>
-
- The base URI (Base) is established according to the procedure of
- <a href="#section-5.1">Section 5.1</a> and parsed into the five main components described in
- <a href="#section-3">Section 3</a>. Note that only the scheme component is required to be
- present in a base URI; the other components may be empty or
- undefined. A component is undefined if its associated delimiter does
- not appear in the URI reference; the path component is never
- undefined, though it may be empty.
-
- Normalization of the base URI, as described in Sections 6.2.2 and
- 6.2.3, is optional. A URI reference must be transformed to its
- target URI before it can be normalized.
-
-<span class="h4"><h4><a name="section-5.2.2">5.2.2</a>. Transform References</h4></span>
-
- For each URI reference (R), the following pseudocode describes an
- algorithm for transforming R into its target URI (T):
-
- -- The URI reference is parsed into the five URI components
- --
- (R.scheme, R.authority, R.path, R.query, R.fragment) = parse(R);
-
- -- A non-strict parser may ignore a scheme in the reference
- -- if it is identical to the base URI's scheme.
- --
- if ((not strict) and (R.scheme == Base.scheme)) then
- undefine(R.scheme);
- endif;
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 31]</span>
-<a name="page-32" id="page-32" href="#page-32"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
- if defined(R.scheme) then
- T.scheme = R.scheme;
- T.authority = R.authority;
- T.path = remove_dot_segments(R.path);
- T.query = R.query;
- else
- if defined(R.authority) then
- T.authority = R.authority;
- T.path = remove_dot_segments(R.path);
- T.query = R.query;
- else
- if (R.path == "") then
- T.path = Base.path;
- if defined(R.query) then
- T.query = R.query;
- else
- T.query = Base.query;
- endif;
- else
- if (R.path starts-with "/") then
- T.path = remove_dot_segments(R.path);
- else
- T.path = merge(Base.path, R.path);
- T.path = remove_dot_segments(T.path);
- endif;
- T.query = R.query;
- endif;
- T.authority = Base.authority;
- endif;
- T.scheme = Base.scheme;
- endif;
-
- T.fragment = R.fragment;
-
-<span class="h4"><h4><a name="section-5.2.3">5.2.3</a>. Merge Paths</h4></span>
-
- The pseudocode above refers to a "merge" routine for merging a
- relative-path reference with the path of the base URI. This is
- accomplished as follows:
-
- o If the base URI has a defined authority component and an empty
- path, then return a string consisting of "/" concatenated with the
- reference's path; otherwise,
-
-
-
-
-
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 32]</span>
-<a name="page-33" id="page-33" href="#page-33"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
- o return a string consisting of the reference's path component
- appended to all but the last segment of the base URI's path (i.e.,
- excluding any characters after the right-most "/" in the base URI
- path, or excluding the entire base URI path if it does not contain
- any "/" characters).
-
-<span class="h4"><h4><a name="section-5.2.4">5.2.4</a>. Remove Dot Segments</h4></span>
-
- The pseudocode also refers to a "remove_dot_segments" routine for
- interpreting and removing the special "." and ".." complete path
- segments from a referenced path. This is done after the path is
- extracted from a reference, whether or not the path was relative, in
- order to remove any invalid or extraneous dot-segments prior to
- forming the target URI. Although there are many ways to accomplish
- this removal process, we describe a simple method using two string
- buffers.
-
- 1. The input buffer is initialized with the now-appended path
- components and the output buffer is initialized to the empty
- string.
-
- 2. While the input buffer is not empty, loop as follows:
-
- A. If the input buffer begins with a prefix of "../" or "./",
- then remove that prefix from the input buffer; otherwise,
-
- B. if the input buffer begins with a prefix of "/./" or "/.",
- where "." is a complete path segment, then replace that
- prefix with "/" in the input buffer; otherwise,
-
- C. if the input buffer begins with a prefix of "/../" or "/..",
- where ".." is a complete path segment, then replace that
- prefix with "/" in the input buffer and remove the last
- segment and its preceding "/" (if any) from the output
- buffer; otherwise,
-
- D. if the input buffer consists only of "." or "..", then remove
- that from the input buffer; otherwise,
-
- E. move the first path segment in the input buffer to the end of
- the output buffer, including the initial "/" character (if
- any) and any subsequent characters up to, but not including,
- the next "/" character or the end of the input buffer.
-
- 3. Finally, the output buffer is returned as the result of
- remove_dot_segments.
-
-
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 33]</span>
-<a name="page-34" id="page-34" href="#page-34"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
- Note that dot-segments are intended for use in URI references to
- express an identifier relative to the hierarchy of names in the base
- URI. The remove_dot_segments algorithm respects that hierarchy by
- removing extra dot-segments rather than treat them as an error or
- leaving them to be misinterpreted by dereference implementations.
-
- The following illustrates how the above steps are applied for two
- examples of merged paths, showing the state of the two buffers after
- each step.
-
- STEP OUTPUT BUFFER INPUT BUFFER
-
- 1 : /a/b/c/./../../g
- 2E: /a /b/c/./../../g
- 2E: /a/b /c/./../../g
- 2E: /a/b/c /./../../g
- 2B: /a/b/c /../../g
- 2C: /a/b /../g
- 2C: /a /g
- 2E: /a/g
-
- STEP OUTPUT BUFFER INPUT BUFFER
-
- <a href="#section-1">1</a> : mid/content=5/../6
- 2E: mid /content=5/../6
- 2E: mid/content=5 /../6
- 2C: mid /6
- 2E: mid/6
-
- Some applications may find it more efficient to implement the
- remove_dot_segments algorithm by using two segment stacks rather than
- strings.
-
- Note: Beware that some older, erroneous implementations will fail
- to separate a reference's query component from its path component
- prior to merging the base and reference paths, resulting in an
- interoperability failure if the query component contains the
- strings "/../" or "/./".
-
-
-
-
-
-
-
-
-
-
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 34]</span>
-<a name="page-35" id="page-35" href="#page-35"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
-<span class="h3"><h3><a name="section-5.3">5.3</a>. Component Recomposition</h3></span>
-
- Parsed URI components can be recomposed to obtain the corresponding
- URI reference string. Using pseudocode, this would be:
-
- result = ""
-
- if defined(scheme) then
- append scheme to result;
- append ":" to result;
- endif;
-
- if defined(authority) then
- append "//" to result;
- append authority to result;
- endif;
-
- append path to result;
-
- if defined(query) then
- append "?" to result;
- append query to result;
- endif;
-
- if defined(fragment) then
- append "#" to result;
- append fragment to result;
- endif;
-
- return result;
-
- Note that we are careful to preserve the distinction between a
- component that is undefined, meaning that its separator was not
- present in the reference, and a component that is empty, meaning that
- the separator was present and was immediately followed by the next
- component separator or the end of the reference.
-
-<span class="h3"><h3><a name="section-5.4">5.4</a>. Reference Resolution Examples</h3></span>
-
- Within a representation with a well defined base URI of
-
- http://a/b/c/d;p?q
-
- a relative reference is transformed to its target URI as follows.
-
-
-
-
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 35]</span>
-<a name="page-36" id="page-36" href="#page-36"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
-<span class="h4"><h4><a name="section-5.4.1">5.4.1</a>. Normal Examples</h4></span>
-
- "g:h" = "g:h"
- "g" = "<a href="http://a/b/c/g">http://a/b/c/g</a>"
- "./g" = "<a href="http://a/b/c/g">http://a/b/c/g</a>"
- "g/" = "<a href="http://a/b/c/g/">http://a/b/c/g/</a>"
- "/g" = "<a href="http://a/g">http://a/g</a>"
- "//g" = "http://g"
- "?y" = "http://a/b/c/d;p?y"
- "g?y" = "<a href="http://a/b/c/g?y">http://a/b/c/g?y</a>"
- "#s" = "http://a/b/c/d;p?q#s"
- "g#s" = "<a href="http://a/b/c/g#s">http://a/b/c/g#s</a>"
- "g?y#s" = "<a href="http://a/b/c/g?y#s">http://a/b/c/g?y#s</a>"
- ";x" = "http://a/b/c/;x"
- "g;x" = "http://a/b/c/g;x"
- "g;x?y#s" = "http://a/b/c/g;x?y#s"
- "" = "http://a/b/c/d;p?q"
- "." = "<a href="http://a/b/c/">http://a/b/c/</a>"
- "./" = "<a href="http://a/b/c/">http://a/b/c/</a>"
- ".." = "<a href="http://a/b/">http://a/b/</a>"
- "../" = "<a href="http://a/b/">http://a/b/</a>"
- "../g" = "<a href="http://a/b/g">http://a/b/g</a>"
- "../.." = "<a href="http://a/">http://a/</a>"
- "../../" = "<a href="http://a/">http://a/</a>"
- "../../g" = "<a href="http://a/g">http://a/g</a>"
-
-<span class="h4"><h4><a name="section-5.4.2">5.4.2</a>. Abnormal Examples</h4></span>
-
- Although the following abnormal examples are unlikely to occur in
- normal practice, all URI parsers should be capable of resolving them
- consistently. Each example uses the same base as that above.
-
- Parsers must be careful in handling cases where there are more ".."
- segments in a relative-path reference than there are hierarchical
- levels in the base URI's path. Note that the ".." syntax cannot be
- used to change the authority component of a URI.
-
- "../../../g" = "<a href="http://a/g">http://a/g</a>"
- "../../../../g" = "<a href="http://a/g">http://a/g</a>"
-
-
-
-
-
-
-
-
-
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 36]</span>
-<a name="page-37" id="page-37" href="#page-37"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
- Similarly, parsers must remove the dot-segments "." and ".." when
- they are complete components of a path, but not when they are only
- part of a segment.
-
- "/./g" = "<a href="http://a/g">http://a/g</a>"
- "/../g" = "<a href="http://a/g">http://a/g</a>"
- "g." = "<a href="http://a/b/c/g">http://a/b/c/g</a>."
- ".g" = "<a href="http://a/b/c/.g">http://a/b/c/.g</a>"
- "g.." = "<a href="http://a/b/c/g">http://a/b/c/g</a>.."
- "..g" = "<a href="http://a/b/c/..g">http://a/b/c/..g</a>"
-
- Less likely are cases where the relative reference uses unnecessary
- or nonsensical forms of the "." and ".." complete path segments.
-
- "./../g" = "<a href="http://a/b/g">http://a/b/g</a>"
- "./g/." = "<a href="http://a/b/c/g/">http://a/b/c/g/</a>"
- "g/./h" = "<a href="http://a/b/c/g/h">http://a/b/c/g/h</a>"
- "g/../h" = "<a href="http://a/b/c/h">http://a/b/c/h</a>"
- "g;x=1/./y" = "http://a/b/c/g;x=1/y"
- "g;x=1/../y" = "<a href="http://a/b/c/y">http://a/b/c/y</a>"
-
- Some applications fail to separate the reference's query and/or
- fragment components from the path component before merging it with
- the base path and removing dot-segments. This error is rarely
- noticed, as typical usage of a fragment never includes the hierarchy
- ("/") character and the query component is not normally used within
- relative references.
-
- "g?y/./x" = "<a href="http://a/b/c/g?y/./x">http://a/b/c/g?y/./x</a>"
- "g?y/../x" = "<a href="http://a/b/c/g?y/../x">http://a/b/c/g?y/../x</a>"
- "g#s/./x" = "<a href="http://a/b/c/g#s/./x">http://a/b/c/g#s/./x</a>"
- "g#s/../x" = "<a href="http://a/b/c/g#s/../x">http://a/b/c/g#s/../x</a>"
-
- Some parsers allow the scheme name to be present in a relative
- reference if it is the same as the base URI scheme. This is
- considered to be a loophole in prior specifications of partial URI
- [<a href="http://tools.ietf.org/html/rfc1630" title=""Universal Resource Identifiers in WWW: A Unifying Syntax for the Expression of Names and Addresses of Objects on the Network as used in the World-Wide Web"">RFC1630</a>]. Its use should be avoided but is allowed for backward
- compatibility.
-
- "http:g" = "http:g" ; for strict parsers
- / "<a href="http://a/b/c/g">http://a/b/c/g</a>" ; for backward compatibility
-
-
-
-
-
-
-
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 37]</span>
-<a name="page-38" id="page-38" href="#page-38"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
-<span class="h2"><h2><a name="section-6">6</a>. Normalization and Comparison</h2></span>
-
- One of the most common operations on URIs is simple comparison:
- determining whether two URIs are equivalent without using the URIs to
- access their respective resource(s). A comparison is performed every
- time a response cache is accessed, a browser checks its history to
- color a link, or an XML parser processes tags within a namespace.
- Extensive normalization prior to comparison of URIs is often used by
- spiders and indexing engines to prune a search space or to reduce
- duplication of request actions and response storage.
-
- URI comparison is performed for some particular purpose. Protocols
- or implementations that compare URIs for different purposes will
- often be subject to differing design trade-offs in regards to how
- much effort should be spent in reducing aliased identifiers. This
- section describes various methods that may be used to compare URIs,
- the trade-offs between them, and the types of applications that might
- use them.
-
-<span class="h3"><h3><a name="section-6.1">6.1</a>. Equivalence</h3></span>
-
- Because URIs exist to identify resources, presumably they should be
- considered equivalent when they identify the same resource. However,
- this definition of equivalence is not of much practical use, as there
- is no way for an implementation to compare two resources unless it
- has full knowledge or control of them. For this reason,
- determination of equivalence or difference of URIs is based on string
- comparison, perhaps augmented by reference to additional rules
- provided by URI scheme definitions. We use the terms "different" and
- "equivalent" to describe the possible outcomes of such comparisons,
- but there are many application-dependent versions of equivalence.
-
- Even though it is possible to determine that two URIs are equivalent,
- URI comparison is not sufficient to determine whether two URIs
- identify different resources. For example, an owner of two different
- domain names could decide to serve the same resource from both,
- resulting in two different URIs. Therefore, comparison methods are
- designed to minimize false negatives while strictly avoiding false
- positives.
-
- In testing for equivalence, applications should not directly compare
- relative references; the references should be converted to their
- respective target URIs before comparison. When URIs are compared to
- select (or avoid) a network action, such as retrieval of a
- representation, fragment components (if any) should be excluded from
- the comparison.
-
-
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 38]</span>
-<a name="page-39" id="page-39" href="#page-39"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
-<span class="h3"><h3><a name="section-6.2">6.2</a>. Comparison Ladder</h3></span>
-
- A variety of methods are used in practice to test URI equivalence.
- These methods fall into a range, distinguished by the amount of
- processing required and the degree to which the probability of false
- negatives is reduced. As noted above, false negatives cannot be
- eliminated. In practice, their probability can be reduced, but this
- reduction requires more processing and is not cost-effective for all
- applications.
-
- If this range of comparison practices is considered as a ladder, the
- following discussion will climb the ladder, starting with practices
- that are cheap but have a relatively higher chance of producing false
- negatives, and proceeding to those that have higher computational
- cost and lower risk of false negatives.
-
-<span class="h4"><h4><a name="section-6.2.1">6.2.1</a>. Simple String Comparison</h4></span>
-
- If two URIs, when considered as character strings, are identical,
- then it is safe to conclude that they are equivalent. This type of
- equivalence test has very low computational cost and is in wide use
- in a variety of applications, particularly in the domain of parsing.
-
- Testing strings for equivalence requires some basic precautions.
- This procedure is often referred to as "bit-for-bit" or
- "byte-for-byte" comparison, which is potentially misleading. Testing
- strings for equality is normally based on pair comparison of the
- characters that make up the strings, starting from the first and
- proceeding until both strings are exhausted and all characters are
- found to be equal, until a pair of characters compares unequal, or
- until one of the strings is exhausted before the other.
-
- This character comparison requires that each pair of characters be
- put in comparable form. For example, should one URI be stored in a
- byte array in EBCDIC encoding and the second in a Java String object
- (UTF-16), bit-for-bit comparisons applied naively will produce
- errors. It is better to speak of equality on a character-for-
- character basis rather than on a byte-for-byte or bit-for-bit basis.
- In practical terms, character-by-character comparisons should be done
- codepoint-by-codepoint after conversion to a common character
- encoding.
-
- False negatives are caused by the production and use of URI aliases.
- Unnecessary aliases can be reduced, regardless of the comparison
- method, by consistently providing URI references in an already-
- normalized form (i.e., a form identical to what would be produced
- after normalization is applied, as described below).
-
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 39]</span>
-<a name="page-40" id="page-40" href="#page-40"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
- Protocols and data formats often limit some URI comparisons to simple
- string comparison, based on the theory that people and
- implementations will, in their own best interest, be consistent in
- providing URI references, or at least consistent enough to negate any
- efficiency that might be obtained from further normalization.
-
-<span class="h4"><h4><a name="section-6.2.2">6.2.2</a>. Syntax-Based Normalization</h4></span>
-
- Implementations may use logic based on the definitions provided by
- this specification to reduce the probability of false negatives.
- This processing is moderately higher in cost than character-for-
- character string comparison. For example, an application using this
- approach could reasonably consider the following two URIs equivalent:
-
- example://a/b/c/%7Bfoo%7D
- eXAMPLE://a/./b/../b/%63/%7bfoo%7d
-
- Web user agents, such as browsers, typically apply this type of URI
- normalization when determining whether a cached response is
- available. Syntax-based normalization includes such techniques as
- case normalization, percent-encoding normalization, and removal of
- dot-segments.
-
-<span class="h5"><h5><a name="section-6.2.2.1">6.2.2.1</a>. Case Normalization</h5></span>
-
- For all URIs, the hexadecimal digits within a percent-encoding
- triplet (e.g., "%3a" versus "%3A") are case-insensitive and therefore
- should be normalized to use uppercase letters for the digits A-F.
-
- When a URI uses components of the generic syntax, the component
- syntax equivalence rules always apply; namely, that the scheme and
- host are case-insensitive and therefore should be normalized to
- lowercase. For example, the URI <HTTP://www.EXAMPLE.com/> is
- equivalent to <http://www.example.com/>. The other generic syntax
- components are assumed to be case-sensitive unless specifically
- defined otherwise by the scheme (see <a href="#section-6.2.3">Section 6.2.3</a>).
-
-<span class="h5"><h5><a name="section-6.2.2.2">6.2.2.2</a>. Percent-Encoding Normalization</h5></span>
-
- The percent-encoding mechanism (<a href="#section-2.1">Section 2.1</a>) is a frequent source of
- variance among otherwise identical URIs. In addition to the case
- normalization issue noted above, some URI producers percent-encode
- octets that do not require percent-encoding, resulting in URIs that
- are equivalent to their non-encoded counterparts. These URIs should
- be normalized by decoding any percent-encoded octet that corresponds
- to an unreserved character, as described in <a href="#section-2.3">Section 2.3</a>.
-
-
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 40]</span>
-<a name="page-41" id="page-41" href="#page-41"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
-<span class="h5"><h5><a name="section-6.2.2.3">6.2.2.3</a>. Path Segment Normalization</h5></span>
-
- The complete path segments "." and ".." are intended only for use
- within relative references (<a href="#section-4.1">Section 4.1</a>) and are removed as part of
- the reference resolution process (<a href="#section-5.2">Section 5.2</a>). However, some
- deployed implementations incorrectly assume that reference resolution
- is not necessary when the reference is already a URI and thus fail to
- remove dot-segments when they occur in non-relative paths. URI
- normalizers should remove dot-segments by applying the
- remove_dot_segments algorithm to the path, as described in
- <a href="#section-5.2.4">Section 5.2.4</a>.
-
-<span class="h4"><h4><a name="section-6.2.3">6.2.3</a>. Scheme-Based Normalization</h4></span>
-
- The syntax and semantics of URIs vary from scheme to scheme, as
- described by the defining specification for each scheme.
- Implementations may use scheme-specific rules, at further processing
- cost, to reduce the probability of false negatives. For example,
- because the "http" scheme makes use of an authority component, has a
- default port of "80", and defines an empty path to be equivalent to
- "/", the following four URIs are equivalent:
-
- http://example.com
- http://example.com/
- <a href="http://example.com/">http://example.com:/</a>
- <a href="http://example.com/">http://example.com:80/</a>
-
- In general, a URI that uses the generic syntax for authority with an
- empty path should be normalized to a path of "/". Likewise, an
- explicit ":port", for which the port is empty or the default for the
- scheme, is equivalent to one where the port and its ":" delimiter are
- elided and thus should be removed by scheme-based normalization. For
- example, the second URI above is the normal form for the "http"
- scheme.
-
- Another case where normalization varies by scheme is in the handling
- of an empty authority component or empty host subcomponent. For many
- scheme specifications, an empty authority or host is considered an
- error; for others, it is considered equivalent to "localhost" or the
- end-user's host. When a scheme defines a default for authority and a
- URI reference to that default is desired, the reference should be
- normalized to an empty authority for the sake of uniformity, brevity,
- and internationalization. If, however, either the userinfo or port
- subcomponents are non-empty, then the host should be given explicitly
- even if it matches the default.
-
- Normalization should not remove delimiters when their associated
- component is empty unless licensed to do so by the scheme
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 41]</span>
-<a name="page-42" id="page-42" href="#page-42"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
- specification. For example, the URI "http://example.com/?" cannot be
- assumed to be equivalent to any of the examples above. Likewise, the
- presence or absence of delimiters within a userinfo subcomponent is
- usually significant to its interpretation. The fragment component is
- not subject to any scheme-based normalization; thus, two URIs that
- differ only by the suffix "#" are considered different regardless of
- the scheme.
-
- Some schemes define additional subcomponents that consist of case-
- insensitive data, giving an implicit license to normalizers to
- convert this data to a common case (e.g., all lowercase). For
- example, URI schemes that define a subcomponent of path to contain an
- Internet hostname, such as the "mailto" URI scheme, cause that
- subcomponent to be case-insensitive and thus subject to case
- normalization (e.g., "mailto:Joe@Example.COM" is equivalent to
- "mailto:Joe@example.com", even though the generic syntax considers
- the path component to be case-sensitive).
-
- Other scheme-specific normalizations are possible.
-
-<span class="h4"><h4><a name="section-6.2.4">6.2.4</a>. Protocol-Based Normalization</h4></span>
-
- Substantial effort to reduce the incidence of false negatives is
- often cost-effective for web spiders. Therefore, they implement even
- more aggressive techniques in URI comparison. For example, if they
- observe that a URI such as
-
- http://example.com/data
-
- redirects to a URI differing only in the trailing slash
-
- http://example.com/data/
-
- they will likely regard the two as equivalent in the future. This
- kind of technique is only appropriate when equivalence is clearly
- indicated by both the result of accessing the resources and the
- common conventions of their scheme's dereference algorithm (in this
- case, use of redirection by HTTP origin servers to avoid problems
- with relative references).
-
-
-
-
-
-
-
-
-
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 42]</span>
-<a name="page-43" id="page-43" href="#page-43"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
-<span class="h2"><h2><a name="section-7">7</a>. Security Considerations</h2></span>
-
- A URI does not in itself pose a security threat. However, as URIs
- are often used to provide a compact set of instructions for access to
- network resources, care must be taken to properly interpret the data
- within a URI, to prevent that data from causing unintended access,
- and to avoid including data that should not be revealed in plain
- text.
-
-<span class="h3"><h3><a name="section-7.1">7.1</a>. Reliability and Consistency</h3></span>
-
- There is no guarantee that once a URI has been used to retrieve
- information, the same information will be retrievable by that URI in
- the future. Nor is there any guarantee that the information
- retrievable via that URI in the future will be observably similar to
- that retrieved in the past. The URI syntax does not constrain how a
- given scheme or authority apportions its namespace or maintains it
- over time. Such guarantees can only be obtained from the person(s)
- controlling that namespace and the resource in question. A specific
- URI scheme may define additional semantics, such as name persistence,
- if those semantics are required of all naming authorities for that
- scheme.
-
-<span class="h3"><h3><a name="section-7.2">7.2</a>. Malicious Construction</h3></span>
-
- It is sometimes possible to construct a URI so that an attempt to
- perform a seemingly harmless, idempotent operation, such as the
- retrieval of a representation, will in fact cause a possibly damaging
- remote operation. The unsafe URI is typically constructed by
- specifying a port number other than that reserved for the network
- protocol in question. The client unwittingly contacts a site running
- a different protocol service, and data within the URI contains
- instructions that, when interpreted according to this other protocol,
- cause an unexpected operation. A frequent example of such abuse has
- been the use of a protocol-based scheme with a port component of
- "25", thereby fooling user agent software into sending an unintended
- or impersonating message via an SMTP server.
-
- Applications should prevent dereference of a URI that specifies a TCP
- port number within the "well-known port" range (0 - 1023) unless the
- protocol being used to dereference that URI is compatible with the
- protocol expected on that well-known port. Although IANA maintains a
- registry of well-known ports, applications should make such
- restrictions user-configurable to avoid preventing the deployment of
- new services.
-
-
-
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 43]</span>
-<a name="page-44" id="page-44" href="#page-44"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
- When a URI contains percent-encoded octets that match the delimiters
- for a given resolution or dereference protocol (for example, CR and
- LF characters for the TELNET protocol), these percent-encodings must
- not be decoded before transmission across that protocol. Transfer of
- the percent-encoding, which might violate the protocol, is less
- harmful than allowing decoded octets to be interpreted as additional
- operations or parameters, perhaps triggering an unexpected and
- possibly harmful remote operation.
-
-<span class="h3"><h3><a name="section-7.3">7.3</a>. Back-End Transcoding</h3></span>
-
- When a URI is dereferenced, the data within it is often parsed by
- both the user agent and one or more servers. In HTTP, for example, a
- typical user agent will parse a URI into its five major components,
- access the authority's server, and send it the data within the
- authority, path, and query components. A typical server will take
- that information, parse the path into segments and the query into
- key/value pairs, and then invoke implementation-specific handlers to
- respond to the request. As a result, a common security concern for
- server implementations that handle a URI, either as a whole or split
- into separate components, is proper interpretation of the octet data
- represented by the characters and percent-encodings within that URI.
-
- Percent-encoded octets must be decoded at some point during the
- dereference process. Applications must split the URI into its
- components and subcomponents prior to decoding the octets, as
- otherwise the decoded octets might be mistaken for delimiters.
- Security checks of the data within a URI should be applied after
- decoding the octets. Note, however, that the "%00" percent-encoding
- (NUL) may require special handling and should be rejected if the
- application is not expecting to receive raw data within a component.
-
- Special care should be taken when the URI path interpretation process
- involves the use of a back-end file system or related system
- functions. File systems typically assign an operational meaning to
- special characters, such as the "/", "\", ":", "[", and "]"
- characters, and to special device names like ".", "..", "...", "aux",
- "lpt", etc. In some cases, merely testing for the existence of such
- a name will cause the operating system to pause or invoke unrelated
- system calls, leading to significant security concerns regarding
- denial of service and unintended data transfer. It would be
- impossible for this specification to list all such significant
- characters and device names. Implementers should research the
- reserved names and characters for the types of storage device that
- may be attached to their applications and restrict the use of data
- obtained from URI components accordingly.
-
-
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 44]</span>
-<a name="page-45" id="page-45" href="#page-45"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
-<span class="h3"><h3><a name="section-7.4">7.4</a>. Rare IP Address Formats</h3></span>
-
- Although the URI syntax for IPv4address only allows the common
- dotted-decimal form of IPv4 address literal, many implementations
- that process URIs make use of platform-dependent system routines,
- such as gethostbyname() and inet_aton(), to translate the string
- literal to an actual IP address. Unfortunately, such system routines
- often allow and process a much larger set of formats than those
- described in <a href="#section-3.2.2">Section 3.2.2</a>.
-
- For example, many implementations allow dotted forms of three
- numbers, wherein the last part is interpreted as a 16-bit quantity
- and placed in the right-most two bytes of the network address (e.g.,
- a Class B network). Likewise, a dotted form of two numbers means
- that the last part is interpreted as a 24-bit quantity and placed in
- the right-most three bytes of the network address (Class A), and a
- single number (without dots) is interpreted as a 32-bit quantity and
- stored directly in the network address. Adding further to the
- confusion, some implementations allow each dotted part to be
- interpreted as decimal, octal, or hexadecimal, as specified in the C
- language (i.e., a leading 0x or 0X implies hexadecimal; a leading 0
- implies octal; otherwise, the number is interpreted as decimal).
-
- These additional IP address formats are not allowed in the URI syntax
- due to differences between platform implementations. However, they
- can become a security concern if an application attempts to filter
- access to resources based on the IP address in string literal format.
- If this filtering is performed, literals should be converted to
- numeric form and filtered based on the numeric value, and not on a
- prefix or suffix of the string form.
-
-<span class="h3"><h3><a name="section-7.5">7.5</a>. Sensitive Information</h3></span>
-
- URI producers should not provide a URI that contains a username or
- password that is intended to be secret. URIs are frequently
- displayed by browsers, stored in clear text bookmarks, and logged by
- user agent history and intermediary applications (proxies). A
- password appearing within the userinfo component is deprecated and
- should be considered an error (or simply ignored) except in those
- rare cases where the 'password' parameter is intended to be public.
-
-<span class="h3"><h3><a name="section-7.6">7.6</a>. Semantic Attacks</h3></span>
-
- Because the userinfo subcomponent is rarely used and appears before
- the host in the authority component, it can be used to construct a
- URI intended to mislead a human user by appearing to identify one
- (trusted) naming authority while actually identifying a different
- authority hidden behind the noise. For example
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 45]</span>
-<a name="page-46" id="page-46" href="#page-46"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
- ftp://cnn.example.com&story=breaking_news@10.0.0.1/top_story.htm
-
- might lead a human user to assume that the host is 'cnn.example.com',
- whereas it is actually '10.0.0.1'. Note that a misleading userinfo
- subcomponent could be much longer than the example above.
-
- A misleading URI, such as that above, is an attack on the user's
- preconceived notions about the meaning of a URI rather than an attack
- on the software itself. User agents may be able to reduce the impact
- of such attacks by distinguishing the various components of the URI
- when they are rendered, such as by using a different color or tone to
- render userinfo if any is present, though there is no panacea. More
- information on URI-based semantic attacks can be found in [<a href="#ref-Siedzik" title=""Semantic Attacks: What&#39;s in a URL?"">Siedzik</a>].
-
-<span class="h2"><h2><a name="section-8">8</a>. IANA Considerations</h2></span>
-
- URI scheme names, as defined by <scheme> in <a href="#section-3.1">Section 3.1</a>, form a
- registered namespace that is managed by IANA according to the
- procedures defined in [<a href="#ref-BCP35" title=""Registration Procedures for URL Scheme Names"">BCP35</a>]. No IANA actions are required by this
- document.
-
-<span class="h2"><h2><a name="section-9">9</a>. Acknowledgements</h2></span>
-
- This specification is derived from <a href="http://tools.ietf.org/html/rfc2396">RFC 2396</a> [<a href="http://tools.ietf.org/html/rfc2396" title=""Uniform Resource Identifiers (URI): Generic Syntax"">RFC2396</a>], <a href="http://tools.ietf.org/html/rfc1808">RFC 1808</a>
- [<a href="http://tools.ietf.org/html/rfc1808" title=""Relative Uniform Resource Locators"">RFC1808</a>], and <a href="http://tools.ietf.org/html/rfc1738">RFC 1738</a> [<a href="http://tools.ietf.org/html/rfc1738" title=""Uniform Resource Locators (URL)"">RFC1738</a>]; the acknowledgements in those
- documents still apply. It also incorporates the update (with
- corrections) for IPv6 literals in the host syntax, as defined by
- Robert M. Hinden, Brian E. Carpenter, and Larry Masinter in
- [<a href="http://tools.ietf.org/html/rfc2732" title=""Format for Literal IPv6 Addresses in URL&#39;s"">RFC2732</a>]. In addition, contributions by Gisle Aas, Reese Anschultz,
- Daniel Barclay, Tim Bray, Mike Brown, Rob Cameron, Jeremy Carroll,
- Dan Connolly, Adam M. Costello, John Cowan, Jason Diamond, Martin
- Duerst, Stefan Eissing, Clive D.W. Feather, Al Gilman, Tony Hammond,
- Elliotte Harold, Pat Hayes, Henry Holtzman, Ian B. Jacobs, Michael
- Kay, John C. Klensin, Graham Klyne, Dan Kohn, Bruce Lilly, Andrew
- Main, Dave McAlpin, Ira McDonald, Michael Mealling, Ray Merkert,
- Stephen Pollei, Julian Reschke, Tomas Rokicki, Miles Sabin, Kai
- Schaetzl, Mark Thomson, Ronald Tschalaer, Norm Walsh, Marc Warne,
- Stuart Williams, and Henry Zongaro are gratefully acknowledged.
-
-<span class="h2"><h2><a name="section-10">10</a>. References</h2></span>
-
-<span class="h3"><h3><a name="section-10.1">10.1</a>. Normative References</h3></span>
-
- [<a name="ref-ASCII" id="ref-ASCII">ASCII</a>] American National Standards Institute, "Coded Character
- Set -- 7-bit American Standard Code for Information
- Interchange", ANSI X3.4, 1986.
-
-
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 46]</span>
-<a name="page-47" id="page-47" href="#page-47"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
- [<a name="ref-RFC2234" id="ref-RFC2234">RFC2234</a>] Crocker, D. and P. Overell, "Augmented BNF for Syntax
- Specifications: ABNF", <a href="http://tools.ietf.org/html/rfc2234">RFC 2234</a>, November 1997.
-
- [<a name="ref-STD63" id="ref-STD63">STD63</a>] Yergeau, F., "UTF-8, a transformation format of
- ISO 10646", STD 63, <a href="http://tools.ietf.org/html/rfc3629">RFC 3629</a>, November 2003.
-
- [<a name="ref-UCS" id="ref-UCS">UCS</a>] International Organization for Standardization,
- "Information Technology - Universal Multiple-Octet Coded
- Character Set (UCS)", ISO/IEC 10646:2003, December 2003.
-
-<span class="h3"><h3><a name="section-10.2">10.2</a>. Informative References</h3></span>
-
- [<a name="ref-BCP19" id="ref-BCP19">BCP19</a>] Freed, N. and J. Postel, "IANA Charset Registration
- Procedures", <a href="http://tools.ietf.org/html/bcp19">BCP 19</a>, <a href="http://tools.ietf.org/html/rfc2978">RFC 2978</a>, October 2000.
-
- [<a name="ref-BCP35" id="ref-BCP35">BCP35</a>] Petke, R. and I. King, "Registration Procedures for URL
- Scheme Names", <a href="http://tools.ietf.org/html/bcp35">BCP 35</a>, <a href="http://tools.ietf.org/html/rfc2717">RFC 2717</a>, November 1999.
-
- [<a name="ref-RFC0952" id="ref-RFC0952">RFC0952</a>] Harrenstien, K., Stahl, M., and E. Feinler, "DoD Internet
- host table specification", <a href="http://tools.ietf.org/html/rfc952">RFC 952</a>, October 1985.
-
- [<a name="ref-RFC1034" id="ref-RFC1034">RFC1034</a>] Mockapetris, P., "Domain names - concepts and facilities",
- STD 13, <a href="http://tools.ietf.org/html/rfc1034">RFC 1034</a>, November 1987.
-
- [<a name="ref-RFC1123" id="ref-RFC1123">RFC1123</a>] Braden, R., "Requirements for Internet Hosts - Application
- and Support", STD 3, <a href="http://tools.ietf.org/html/rfc1123">RFC 1123</a>, October 1989.
-
- [<a name="ref-RFC1535" id="ref-RFC1535">RFC1535</a>] Gavron, E., "A Security Problem and Proposed Correction
- With Widely Deployed DNS Software", <a href="http://tools.ietf.org/html/rfc1535">RFC 1535</a>,
- October 1993.
-
- [<a name="ref-RFC1630" id="ref-RFC1630">RFC1630</a>] Berners-Lee, T., "Universal Resource Identifiers in WWW: A
- Unifying Syntax for the Expression of Names and Addresses
- of Objects on the Network as used in the World-Wide Web",
- <a href="http://tools.ietf.org/html/rfc1630">RFC 1630</a>, June 1994.
-
- [<a name="ref-RFC1736" id="ref-RFC1736">RFC1736</a>] Kunze, J., "Functional Recommendations for Internet
- Resource Locators", <a href="http://tools.ietf.org/html/rfc1736">RFC 1736</a>, February 1995.
-
- [<a name="ref-RFC1737" id="ref-RFC1737">RFC1737</a>] Sollins, K. and L. Masinter, "Functional Requirements for
- Uniform Resource Names", <a href="http://tools.ietf.org/html/rfc1737">RFC 1737</a>, December 1994.
-
- [<a name="ref-RFC1738" id="ref-RFC1738">RFC1738</a>] Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform
- Resource Locators (URL)", <a href="http://tools.ietf.org/html/rfc1738">RFC 1738</a>, December 1994.
-
- [<a name="ref-RFC1808" id="ref-RFC1808">RFC1808</a>] Fielding, R., "Relative Uniform Resource Locators",
- <a href="http://tools.ietf.org/html/rfc1808">RFC 1808</a>, June 1995.
-
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 47]</span>
-<a name="page-48" id="page-48" href="#page-48"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
- [<a name="ref-RFC2046" id="ref-RFC2046">RFC2046</a>] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
- Extensions (MIME) Part Two: Media Types", <a href="http://tools.ietf.org/html/rfc2046">RFC 2046</a>,
- November 1996.
-
- [<a name="ref-RFC2141" id="ref-RFC2141">RFC2141</a>] Moats, R., "URN Syntax", <a href="http://tools.ietf.org/html/rfc2141">RFC 2141</a>, May 1997.
-
- [<a name="ref-RFC2396" id="ref-RFC2396">RFC2396</a>] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
- Resource Identifiers (URI): Generic Syntax", <a href="http://tools.ietf.org/html/rfc2396">RFC 2396</a>,
- August 1998.
-
- [<a name="ref-RFC2518" id="ref-RFC2518">RFC2518</a>] Goland, Y., Whitehead, E., Faizi, A., Carter, S., and D.
- Jensen, "HTTP Extensions for Distributed Authoring --
- WEBDAV", <a href="http://tools.ietf.org/html/rfc2518">RFC 2518</a>, February 1999.
-
- [<a name="ref-RFC2557" id="ref-RFC2557">RFC2557</a>] Palme, J., Hopmann, A., and N. Shelness, "MIME
- Encapsulation of Aggregate Documents, such as HTML
- (MHTML)", <a href="http://tools.ietf.org/html/rfc2557">RFC 2557</a>, March 1999.
-
- [<a name="ref-RFC2718" id="ref-RFC2718">RFC2718</a>] Masinter, L., Alvestrand, H., Zigmond, D., and R. Petke,
- "Guidelines for new URL Schemes", <a href="http://tools.ietf.org/html/rfc2718">RFC 2718</a>, November 1999.
-
- [<a name="ref-RFC2732" id="ref-RFC2732">RFC2732</a>] Hinden, R., Carpenter, B., and L. Masinter, "Format for
- Literal IPv6 Addresses in URL's", <a href="http://tools.ietf.org/html/rfc2732">RFC 2732</a>, December 1999.
-
- [<a name="ref-RFC3305" id="ref-RFC3305">RFC3305</a>] Mealling, M. and R. Denenberg, "Report from the Joint
- W3C/IETF URI Planning Interest Group: Uniform Resource
- Identifiers (URIs), URLs, and Uniform Resource Names
- (URNs): Clarifications and Recommendations", <a href="http://tools.ietf.org/html/rfc3305">RFC 3305</a>,
- August 2002.
-
- [<a name="ref-RFC3490" id="ref-RFC3490">RFC3490</a>] Faltstrom, P., Hoffman, P., and A. Costello,
- "Internationalizing Domain Names in Applications (IDNA)",
- <a href="http://tools.ietf.org/html/rfc3490">RFC 3490</a>, March 2003.
-
- [<a name="ref-RFC3513" id="ref-RFC3513">RFC3513</a>] Hinden, R. and S. Deering, "Internet Protocol Version 6
- (IPv6) Addressing Architecture", <a href="http://tools.ietf.org/html/rfc3513">RFC 3513</a>, April 2003.
-
- [<a name="ref-Siedzik" id="ref-Siedzik">Siedzik</a>] Siedzik, R., "Semantic Attacks: What's in a URL?",
- April 2001, <<a href="http://www.giac.org/practical/gsec/Richard_Siedzik_GSEC.pdf">http://www.giac.org/practical/gsec/</a>
- <a href="http://www.giac.org/practical/gsec/Richard_Siedzik_GSEC.pdf">Richard_Siedzik_GSEC.pdf</a>>.
-
-
-
-
-
-
-
-
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 48]</span>
-<a name="page-49" id="page-49" href="#page-49"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
-Appendix A. Collected ABNF for URI
-
- URI = scheme ":" hier-part [ "?" query ] [ "#" fragment ]
-
- hier-part = "//" authority path-abempty
- / path-absolute
- / path-rootless
- / path-empty
-
- URI-reference = URI / relative-ref
-
- absolute-URI = scheme ":" hier-part [ "?" query ]
-
- relative-ref = relative-part [ "?" query ] [ "#" fragment ]
-
- relative-part = "//" authority path-abempty
- / path-absolute
- / path-noscheme
- / path-empty
-
- scheme = ALPHA *( ALPHA / DIGIT / "+" / "-" / "." )
-
- authority = [ userinfo "@" ] host [ ":" port ]
- userinfo = *( unreserved / pct-encoded / sub-delims / ":" )
- host = IP-literal / IPv4address / reg-name
- port = *DIGIT
-
- IP-literal = "[" ( IPv6address / IPvFuture ) "]"
-
- IPvFuture = "v" 1*HEXDIG "." 1*( unreserved / sub-delims / ":" )
-
- IPv6address = 6( h16 ":" ) ls32
- / "::" 5( h16 ":" ) ls32
- / [ h16 ] "::" 4( h16 ":" ) ls32
- / [ *1( h16 ":" ) h16 ] "::" 3( h16 ":" ) ls32
- / [ *2( h16 ":" ) h16 ] "::" 2( h16 ":" ) ls32
- / [ *3( h16 ":" ) h16 ] "::" h16 ":" ls32
- / [ *4( h16 ":" ) h16 ] "::" ls32
- / [ *5( h16 ":" ) h16 ] "::" h16
- / [ *6( h16 ":" ) h16 ] "::"
-
- h16 = 1*4HEXDIG
- ls32 = ( h16 ":" h16 ) / IPv4address
- IPv4address = dec-octet "." dec-octet "." dec-octet "." dec-octet
-
-
-
-
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 49]</span>
-<a name="page-50" id="page-50" href="#page-50"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
- dec-octet = DIGIT ; 0-9
- / %x31-39 DIGIT ; 10-99
- / "1" 2DIGIT ; 100-199
- / "2" %x30-34 DIGIT ; 200-249
- / "25" %x30-35 ; 250-255
-
- reg-name = *( unreserved / pct-encoded / sub-delims )
-
- path = path-abempty ; begins with "/" or is empty
- / path-absolute ; begins with "/" but not "//"
- / path-noscheme ; begins with a non-colon segment
- / path-rootless ; begins with a segment
- / path-empty ; zero characters
-
- path-abempty = *( "/" segment )
- path-absolute = "/" [ segment-nz *( "/" segment ) ]
- path-noscheme = segment-nz-nc *( "/" segment )
- path-rootless = segment-nz *( "/" segment )
- path-empty = 0<pchar>
-
- segment = *pchar
- segment-nz = 1*pchar
- segment-nz-nc = 1*( unreserved / pct-encoded / sub-delims / "@" )
- ; non-zero-length segment without any colon ":"
-
- pchar = unreserved / pct-encoded / sub-delims / ":" / "@"
-
- query = *( pchar / "/" / "?" )
-
- fragment = *( pchar / "/" / "?" )
-
- pct-encoded = "%" HEXDIG HEXDIG
-
- unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"
- reserved = gen-delims / sub-delims
- gen-delims = ":" / "/" / "?" / "#" / "[" / "]" / "@"
- sub-delims = "!" / "$" / "&" / "'" / "(" / ")"
- / "*" / "+" / "," / ";" / "="
-
-Appendix B. Parsing a URI Reference with a Regular Expression
-
- As the "first-match-wins" algorithm is identical to the "greedy"
- disambiguation method used by POSIX regular expressions, it is
- natural and commonplace to use a regular expression for parsing the
- potential five components of a URI reference.
-
- The following line is the regular expression for breaking-down a
- well-formed URI reference into its components.
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 50]</span>
-<a name="page-51" id="page-51" href="#page-51"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
- ^(([^:/?#]+):)?(//([^/?#]*))?([^?#]*)(\?([^#]*))?(#(.*))?
- 12 3 4 5 6 7 8 9
-
- The numbers in the second line above are only to assist readability;
- they indicate the reference points for each subexpression (i.e., each
- paired parenthesis). We refer to the value matched for subexpression
- <n> as $<n>. For example, matching the above expression to
-
- <a href="http://www.ics.uci.edu/pub/ietf/uri/#Related">http://www.ics.uci.edu/pub/ietf/uri/#Related</a>
-
- results in the following subexpression matches:
-
- $1 = http:
- $2 = http
- $3 = //www.ics.uci.edu
- $4 = www.ics.uci.edu
- $5 = /pub/ietf/uri/
- $6 = <undefined>
- $7 = <undefined>
- $8 = #Related
- $9 = Related
-
- where <undefined> indicates that the component is not present, as is
- the case for the query component in the above example. Therefore, we
- can determine the value of the five components as
-
- scheme = $2
- authority = $4
- path = $5
- query = $7
- fragment = $9
-
- Going in the opposite direction, we can recreate a URI reference from
- its components by using the algorithm of <a href="#section-5.3">Section 5.3</a>.
-
-Appendix C. Delimiting a URI in Context
-
- URIs are often transmitted through formats that do not provide a
- clear context for their interpretation. For example, there are many
- occasions when a URI is included in plain text; examples include text
- sent in email, USENET news, and on printed paper. In such cases, it
- is important to be able to delimit the URI from the rest of the text,
- and in particular from punctuation marks that might be mistaken for
- part of the URI.
-
- In practice, URIs are delimited in a variety of ways, but usually
- within double-quotes "http://example.com/", angle brackets
- <http://example.com/>, or just by using whitespace:
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 51]</span>
-<a name="page-52" id="page-52" href="#page-52"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
- http://example.com/
-
- These wrappers do not form part of the URI.
-
- In some cases, extra whitespace (spaces, line-breaks, tabs, etc.) may
- have to be added to break a long URI across lines. The whitespace
- should be ignored when the URI is extracted.
-
- No whitespace should be introduced after a hyphen ("-") character.
- Because some typesetters and printers may (erroneously) introduce a
- hyphen at the end of line when breaking it, the interpreter of a URI
- containing a line break immediately after a hyphen should ignore all
- whitespace around the line break and should be aware that the hyphen
- may or may not actually be part of the URI.
-
- Using <> angle brackets around each URI is especially recommended as
- a delimiting style for a reference that contains embedded whitespace.
-
- The prefix "URL:" (with or without a trailing space) was formerly
- recommended as a way to help distinguish a URI from other bracketed
- designators, though it is not commonly used in practice and is no
- longer recommended.
-
- For robustness, software that accepts user-typed URI should attempt
- to recognize and strip both delimiters and embedded whitespace.
-
- For example, the text
-
- Yes, Jim, I found it under "<a href="http://www.w3.org/Addressing/">http://www.w3.org/Addressing/</a>",
- but you can probably pick it up from <ftp://foo.example.
- http://www.ics.uci.edu/pub/
- <a href="http://www.ics.uci.edu/pub/ietf/uri/historical.html#WARNING">ietf/uri/historical.html#WARNING</a>>.
-
- contains the URI references
-
- <a href="http://www.w3.org/Addressing/">http://www.w3.org/Addressing/</a>
- ftp://foo.example.com/rfc/
- <a href="http://www.ics.uci.edu/pub/ietf/uri/historical.html#WARNING">http://www.ics.uci.edu/pub/ietf/uri/historical.html#WARNING</a>
-
-
-
-
-
-
-
-
-
-
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 52]</span>
-<a name="page-53" id="page-53" href="#page-53"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
-Appendix D. Changes from <a href="http://tools.ietf.org/html/rfc2396">RFC 2396</a>
-
-D.1. Additions
-
- An ABNF rule for URI has been introduced to correspond to one common
- usage of the term: an absolute URI with optional fragment.
-
- IPv6 (and later) literals have been added to the list of possible
- identifiers for the host portion of an authority component, as
- described by [<a href="http://tools.ietf.org/html/rfc2732" title=""Format for Literal IPv6 Addresses in URL&#39;s"">RFC2732</a>], with the addition of "[" and "]" to the
- reserved set and a version flag to anticipate future versions of IP
- literals. Square brackets are now specified as reserved within the
- authority component and are not allowed outside their use as
- delimiters for an IP literal within host. In order to make this
- change without changing the technical definition of the path, query,
- and fragment components, those rules were redefined to directly
- specify the characters allowed.
-
- As [<a href="http://tools.ietf.org/html/rfc2732" title=""Format for Literal IPv6 Addresses in URL&#39;s"">RFC2732</a>] defers to [<a href="http://tools.ietf.org/html/rfc3513" title=""Internet Protocol Version 6 (IPv6) Addressing Architecture"">RFC3513</a>] for definition of an IPv6 literal
- address, which, unfortunately, lacks an ABNF description of
- IPv6address, we created a new ABNF rule for IPv6address that matches
- the text representations defined by <a href="#section-2.2">Section 2.2</a> of [<a href="http://tools.ietf.org/html/rfc3513" title=""Internet Protocol Version 6 (IPv6) Addressing Architecture"">RFC3513</a>].
- Likewise, the definition of IPv4address has been improved in order to
- limit each decimal octet to the range 0-255.
-
- <a href="#section-6">Section 6</a>, on URI normalization and comparison, has been completely
- rewritten and extended by using input from Tim Bray and discussion
- within the W3C Technical Architecture Group.
-
-D.2. Modifications
-
- The ad-hoc BNF syntax of <a href="http://tools.ietf.org/html/rfc2396">RFC 2396</a> has been replaced with the ABNF of
- [<a href="http://tools.ietf.org/html/rfc2234" title=""Augmented BNF for Syntax Specifications: ABNF"">RFC2234</a>]. This change required all rule names that formerly
- included underscore characters to be renamed with a dash instead. In
- addition, a number of syntax rules have been eliminated or simplified
- to make the overall grammar more comprehensible. Specifications that
- refer to the obsolete grammar rules may be understood by replacing
- those rules according to the following table:
-
-
-
-
-
-
-
-
-
-
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 53]</span>
-<a name="page-54" id="page-54" href="#page-54"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
- +----------------+--------------------------------------------------+
- | obsolete rule | translation |
- +----------------+--------------------------------------------------+
- | absoluteURI | absolute-URI |
- | relativeURI | relative-part [ "?" query ] |
- | hier_part | ( "//" authority path-abempty / |
- | | path-absolute ) [ "?" query ] |
- | | |
- | opaque_part | path-rootless [ "?" query ] |
- | net_path | "//" authority path-abempty |
- | abs_path | path-absolute |
- | rel_path | path-rootless |
- | rel_segment | segment-nz-nc |
- | reg_name | reg-name |
- | server | authority |
- | hostport | host [ ":" port ] |
- | hostname | reg-name |
- | path_segments | path-abempty |
- | param | *<pchar excluding ";"> |
- | | |
- | uric | unreserved / pct-encoded / ";" / "?" / ":" |
- | | / "@" / "&" / "=" / "+" / "$" / "," / "/" |
- | | |
- | uric_no_slash | unreserved / pct-encoded / ";" / "?" / ":" |
- | | / "@" / "&" / "=" / "+" / "$" / "," |
- | | |
- | mark | "-" / "_" / "." / "!" / "~" / "*" / "'" |
- | | / "(" / ")" |
- | | |
- | escaped | pct-encoded |
- | hex | HEXDIG |
- | alphanum | ALPHA / DIGIT |
- +----------------+--------------------------------------------------+
-
- Use of the above obsolete rules for the definition of scheme-specific
- syntax is deprecated.
-
- <a href="#section-2">Section 2</a>, on characters, has been rewritten to explain what
- characters are reserved, when they are reserved, and why they are
- reserved, even when they are not used as delimiters by the generic
- syntax. The mark characters that are typically unsafe to decode,
- including the exclamation mark ("!"), asterisk ("*"), single-quote
- ("'"), and open and close parentheses ("(" and ")"), have been moved
- to the reserved set in order to clarify the distinction between
- reserved and unreserved and, hopefully, to answer the most common
- question of scheme designers. Likewise, the section on
- percent-encoded characters has been rewritten, and URI normalizers
- are now given license to decode any percent-encoded octets
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 54]</span>
-<a name="page-55" id="page-55" href="#page-55"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
- corresponding to unreserved characters. In general, the terms
- "escaped" and "unescaped" have been replaced with "percent-encoded"
- and "decoded", respectively, to reduce confusion with other forms of
- escape mechanisms.
-
- The ABNF for URI and URI-reference has been redesigned to make them
- more friendly to LALR parsers and to reduce complexity. As a result,
- the layout form of syntax description has been removed, along with
- the uric, uric_no_slash, opaque_part, net_path, abs_path, rel_path,
- path_segments, rel_segment, and mark rules. All references to
- "opaque" URIs have been replaced with a better description of how the
- path component may be opaque to hierarchy. The relativeURI rule has
- been replaced with relative-ref to avoid unnecessary confusion over
- whether they are a subset of URI. The ambiguity regarding the
- parsing of URI-reference as a URI or a relative-ref with a colon in
- the first segment has been eliminated through the use of five
- separate path matching rules.
-
- The fragment identifier has been moved back into the section on
- generic syntax components and within the URI and relative-ref rules,
- though it remains excluded from absolute-URI. The number sign ("#")
- character has been moved back to the reserved set as a result of
- reintegrating the fragment syntax.
-
- The ABNF has been corrected to allow the path component to be empty.
- This also allows an absolute-URI to consist of nothing after the
- "scheme:", as is present in practice with the "dav:" namespace
- [<a href="http://tools.ietf.org/html/rfc2518" title=""HTTP Extensions for Distributed Authoring -- WEBDAV"">RFC2518</a>] and with the "about:" scheme used internally by many WWW
- browser implementations. The ambiguity regarding the boundary
- between authority and path has been eliminated through the use of
- five separate path matching rules.
-
- Registry-based naming authorities that use the generic syntax are now
- defined within the host rule. This change allows current
- implementations, where whatever name provided is simply fed to the
- local name resolution mechanism, to be consistent with the
- specification. It also removes the need to re-specify DNS name
- formats here. Furthermore, it allows the host component to contain
- percent-encoded octets, which is necessary to enable
- internationalized domain names to be provided in URIs, processed in
- their native character encodings at the application layers above URI
- processing, and passed to an IDNA library as a registered name in the
- UTF-8 character encoding. The server, hostport, hostname,
- domainlabel, toplabel, and alphanum rules have been removed.
-
- The resolving relative references algorithm of [<a href="http://tools.ietf.org/html/rfc2396" title=""Uniform Resource Identifiers (URI): Generic Syntax"">RFC2396</a>] has been
- rewritten with pseudocode for this revision to improve clarity and
- fix the following issues:
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 55]</span>
-<a name="page-56" id="page-56" href="#page-56"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
- o [<a href="http://tools.ietf.org/html/rfc2396" title=""Uniform Resource Identifiers (URI): Generic Syntax"">RFC2396</a>] <a href="#section-5.2">section 5.2</a>, step 6a, failed to account for a base URI
- with no path.
-
- o Restored the behavior of [<a href="http://tools.ietf.org/html/rfc1808" title=""Relative Uniform Resource Locators"">RFC1808</a>] where, if the reference
- contains an empty path and a defined query component, the target
- URI inherits the base URI's path component.
-
- o The determination of whether a URI reference is a same-document
- reference has been decoupled from the URI parser, simplifying the
- URI processing interface within applications in a way consistent
- with the internal architecture of deployed URI processing
- implementations. The determination is now based on comparison to
- the base URI after transforming a reference to absolute form,
- rather than on the format of the reference itself. This change
- may result in more references being considered "same-document"
- under this specification than there would be under the rules given
- in <a href="http://tools.ietf.org/html/rfc2396">RFC 2396</a>, especially when normalization is used to reduce
- aliases. However, it does not change the status of existing
- same-document references.
-
- o Separated the path merge routine into two routines: merge, for
- describing combination of the base URI path with a relative-path
- reference, and remove_dot_segments, for describing how to remove
- the special "." and ".." segments from a composed path. The
- remove_dot_segments algorithm is now applied to all URI reference
- paths in order to match common implementations and to improve the
- normalization of URIs in practice. This change only impacts the
- parsing of abnormal references and same-scheme references wherein
- the base URI has a non-hierarchical path.
-
-Index
-
- A
- ABNF 11
- absolute 27
- absolute-path 26
- absolute-URI 27
- access 9
- authority 17, 18
-
- B
- base URI 28
-
- C
- character encoding 4
- character 4
- characters 8, 11
- coded character set 4
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 56]</span>
-<a name="page-57" id="page-57" href="#page-57"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
- D
- dec-octet 20
- dereference 9
- dot-segments 23
-
- F
- fragment 16, 24
-
- G
- gen-delims 13
- generic syntax 6
-
- H
- h16 20
- hier-part 16
- hierarchical 10
- host 18
-
- I
- identifier 5
- IP-literal 19
- IPv4 20
- IPv4address 19, 20
- IPv6 19
- IPv6address 19, 20
- IPvFuture 19
-
- L
- locator 7
- ls32 20
-
- M
- merge 32
-
- N
- name 7
- network-path 26
-
- P
- path 16, 22, 26
- path-abempty 22
- path-absolute 22
- path-empty 22
- path-noscheme 22
- path-rootless 22
- path-abempty 16, 22, 26
- path-absolute 16, 22, 26
- path-empty 16, 22, 26
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 57]</span>
-<a name="page-58" id="page-58" href="#page-58"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
- path-rootless 16, 22
- pchar 23
- pct-encoded 12
- percent-encoding 12
- port 22
-
- Q
- query 16, 23
-
- R
- reg-name 21
- registered name 20
- relative 10, 28
- relative-path 26
- relative-ref 26
- remove_dot_segments 33
- representation 9
- reserved 12
- resolution 9, 28
- resource 5
- retrieval 9
-
- S
- same-document 27
- sameness 9
- scheme 16, 17
- segment 22, 23
- segment-nz 23
- segment-nz-nc 23
- sub-delims 13
- suffix 27
-
- T
- transcription 8
-
- U
- uniform 4
- unreserved 13
- URI grammar
- absolute-URI 27
- ALPHA 11
- authority 18
- CR 11
- dec-octet 20
- DIGIT 11
- DQUOTE 11
- fragment 24
- gen-delims 13
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 58]</span>
-<a name="page-59" id="page-59" href="#page-59"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
- h16 20
- HEXDIG 11
- hier-part 16
- host 19
- IP-literal 19
- IPv4address 20
- IPv6address 20
- IPvFuture 19
- LF 11
- ls32 20
- OCTET 11
- path 22
- path-abempty 22
- path-absolute 22
- path-empty 22
- path-noscheme 22
- path-rootless 22
- pchar 23
- pct-encoded 12
- port 22
- query 24
- reg-name 21
- relative-ref 26
- reserved 13
- scheme 17
- segment 23
- segment-nz 23
- segment-nz-nc 23
- SP 11
- sub-delims 13
- unreserved 13
- URI 16
- URI-reference 25
- userinfo 18
- URI 16
- URI-reference 25
- URL 7
- URN 7
- userinfo 18
-
-
-
-
-
-
-
-
-
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 59]</span>
-<a name="page-60" id="page-60" href="#page-60"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
-Authors' Addresses
-
- Tim Berners-Lee
- World Wide Web Consortium
- Massachusetts Institute of Technology
- 77 Massachusetts Avenue
- Cambridge, MA 02139
- USA
-
- Phone: +1-617-253-5702
- Fax: +1-617-258-5999
- EMail: timbl@w3.org
- URI: <a href="http://www.w3.org/People/Berners-Lee/">http://www.w3.org/People/Berners-Lee/</a>
-
-
- Roy T. Fielding
- Day Software
- 5251 California Ave., Suite 110
- Irvine, CA 92617
- USA
-
- Phone: +1-949-679-2960
- Fax: +1-949-679-2972
- EMail: fielding@gbiv.com
- URI: <a href="http://roy.gbiv.com/">http://roy.gbiv.com/</a>
-
-
- Larry Masinter
- Adobe Systems Incorporated
- 345 Park Ave
- San Jose, CA 95110
- USA
-
- Phone: +1-408-536-3024
- EMail: LMM@acm.org
- URI: <a href="http://larry.masinter.net/">http://larry.masinter.net/</a>
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-<span class="grey">Berners-Lee, et al. Standards Track [Page 60]</span>
-<a name="page-61" id="page-61" href="#page-61"><span class="break"> </span></a>
-<span class="grey"><a href="http://tools.ietf.org/html/rfc3986">RFC 3986</a> URI Generic Syntax January 2005</span>
-
-
-Full Copyright Statement
-
- Copyright (C) The Internet Society (2005).
-
- This document is subject to the rights, licenses and restrictions
- contained in <a href="http://tools.ietf.org/html/bcp78">BCP 78</a>, and except as set forth therein, the authors
- retain all their rights.
-
- This document and the information contained herein are provided on an
- "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
- OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
- ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
- INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
- INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
- WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
-
-Intellectual Property
-
- The IETF takes no position regarding the validity or scope of any
- Intellectual Property Rights or other rights that might be claimed to
- pertain to the implementation or use of the technology described in
- this document or the extent to which any license under such rights
- might or might not be available; nor does it represent that it has
- made any independent effort to identify any such rights. Information
- on the IETF's procedures with respect to rights in IETF Documents can
- be found in <a href="http://tools.ietf.org/html/bcp78">BCP 78</a> and <a href="http://tools.ietf.org/html/bcp79">BCP 79</a>.
-
- Copies of IPR disclosures made to the IETF Secretariat and any
- assurances of licenses to be made available, or the result of an
- attempt made to obtain a general license or permission for the use of
- such proprietary rights by implementers or users of this
- specification can be obtained from the IETF on-line IPR repository at
- <a href="http://www.ietf.org/ipr">http://www.ietf.org/ipr</a>.
-
- The IETF invites any interested party to bring to its attention any
- copyrights, patents or patent applications, or other proprietary
- rights that may cover technology that may be required to implement
- this standard. Please address the information to the IETF at ietf-
- ipr@ietf.org.
-
-
-Acknowledgement
-
- Funding for the RFC Editor function is currently provided by the
- Internet Society.
-
-
-
-
-
-
-Berners-Lee, et al. Standards Track [Page 61]
-<span class="break"> </span>
-
-</pre><br>
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