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+/*
+ * Header file for my independent implementation of Deflate
+ * (RFC1951) compression.
+ */
+
+#ifndef DEFLATE_DEFLATE_H
+#define DEFLATE_DEFLATE_H
+
+/*
+ * Types of Deflate data stream.
+ * 
+ * DEFLATE_TYPE_BARE represents the basic Deflate data format, as
+ * defined in RFC 1951. It has no checksum to detect errors and no
+ * magic-number header for ease of recognition, but it does have
+ * internal EOF indication.
+ * 
+ * DEFLATE_TYPE_ZLIB represents the zlib container format, as
+ * defined in RFC 1950. It has a two-byte header, and a four-byte
+ * Adler32 checksum at the end to verify correct decoding, but
+ * apart from those six bytes it's exactly equivalent to
+ * DEFLATE_TYPE_BARE.
+ * 
+ * DEFLATE_TYPE_GZIP represents the gzip compressed file format, as
+ * defined in RFC 1952. This is a more full-featured format, with a
+ * magic number, a CRC checksum of the compressed data, and various
+ * header features including storing the original filename. This
+ * implementation accepts but ignores all of those features on
+ * input except the checksum, and outputs them in the most trivial
+ * fashion. Also, this implementation will not decode multiple
+ * concatenated gzip members (permitted by the RFC).
+ */
+enum {
+    DEFLATE_TYPE_BARE,
+    DEFLATE_TYPE_ZLIB,
+    DEFLATE_TYPE_GZIP
+};
+
+/* ----------------------------------------------------------------------
+ * Compression functions. Create a compression context with
+ * deflate_compress_new(); feed it data with repeated calls to
+ * deflate_compress_data(); destroy it with
+ * deflate_compress_free().
+ */
+
+typedef struct deflate_compress_ctx deflate_compress_ctx;
+
+/*
+ * Create a new compression context. `type' indicates whether it's
+ * bare Deflate (as used in, say, zip files) or Zlib (as used in,
+ * say, PDF).
+ */
+deflate_compress_ctx *deflate_compress_new(int type);
+
+/*
+ * Free a compression context previously allocated by
+ * deflate_compress_new().
+ */
+void deflate_compress_free(deflate_compress_ctx *ctx);
+
+/*
+ * Give the compression context some data to compress. The input
+ * data is passed in `inblock', and has length `inlen'. This
+ * function may or may not produce some output data; if so, it is
+ * written to a dynamically allocated chunk of memory, a pointer to
+ * that memory is stored in `outblock', and the length of output
+ * data is stored in `outlen'. It is common for no data to be
+ * output, if the input data has merely been stored in internal
+ * buffers.
+ * 
+ * `flushtype' indicates whether you want to force buffered data to
+ * be output. It can be one of the following values:
+ * 
+ *  - DEFLATE_NO_FLUSH: nothing is output if the compressor would
+ *    rather not. Use this when the best compression is desired
+ *    (i.e. most of the time).
+ *
+ *  - DEFLATE_SYNC_FLUSH: all the buffered data is output, but the
+ *    compressed data stream remains open and ready to continue
+ *    compressing data. Use this in interactive protocols when a
+ *    single compressed data stream is split across several network
+ *    packets.
+ * 
+ *  - DEFLATE_END_OF_DATA: all the buffered data is output and the
+ *    compressed data stream is cleaned up. Any checksums required
+ *    at the end of the stream are also output.
+ */
+void deflate_compress_data(deflate_compress_ctx *ctx,
+			   const void *inblock, int inlen, int flushtype,
+			   void **outblock, int *outlen);
+
+enum {
+    DEFLATE_NO_FLUSH,
+    DEFLATE_SYNC_FLUSH,
+    DEFLATE_END_OF_DATA
+};
+
+/* ----------------------------------------------------------------------
+ * Decompression functions. Create a decompression context with
+ * deflate_decompress_new(); feed it data with repeated calls to
+ * deflate_decompress_data(); destroy it with
+ * deflate_decompress_free().
+ */
+
+typedef struct deflate_decompress_ctx deflate_decompress_ctx;
+
+/*
+ * Create a new decompression context. `type' means the same as it
+ * does in deflate_compress_new().
+ */
+deflate_decompress_ctx *deflate_decompress_new(int type);
+
+/*
+ * Free a decompression context previously allocated by
+ * deflate_decompress_new().
+ */
+void deflate_decompress_free(deflate_decompress_ctx *ctx);
+
+/*
+ * Give the decompression context some data to decompress. The
+ * input data is passed in `inblock', and has length `inlen'. This
+ * function may or may not produce some output data; if so, it is
+ * written to a dynamically allocated chunk of memory, a pointer to
+ * that memory is stored in `outblock', and the length of output
+ * data is stored in `outlen'.
+ *
+ * Returns 0 on success, or a non-zero error code if there was a
+ * decoding error. In case of an error return, the data decoded
+ * before the error is still returned as well. The possible errors
+ * are listed below.
+ * 
+ * If you want to check that the compressed data stream was
+ * correctly terminated, you can call this function with inlen==0
+ * to signal input EOF and see if an error comes back. If you don't
+ * care, don't bother.
+ */
+int deflate_decompress_data(deflate_decompress_ctx *ctx,
+			    const void *inblock, int inlen,
+			    void **outblock, int *outlen);
+
+/*
+ * Enumeration of error codes. The strange macro is so that I can
+ * define description arrays in the accompanying source.
+ */
+#define DEFLATE_ERRORLIST(A) \
+    A(DEFLATE_NO_ERR, "success"), \
+    A(DEFLATE_ERR_ZLIB_HEADER, "invalid zlib header"), \
+    A(DEFLATE_ERR_ZLIB_WRONGCOMP, "zlib header specifies non-deflate compression"), \
+    A(DEFLATE_ERR_GZIP_HEADER, "invalid gzip header"), \
+    A(DEFLATE_ERR_GZIP_WRONGCOMP, "gzip header specifies non-deflate compression"), \
+    A(DEFLATE_ERR_GZIP_FHCRC, "gzip header specifies disputed FHCRC flag"), \
+    A(DEFLATE_ERR_SMALL_HUFTABLE, "under-committed Huffman code space"), \
+    A(DEFLATE_ERR_LARGE_HUFTABLE, "over-committed Huffman code space"), \
+    A(DEFLATE_ERR_CHECKSUM, "incorrect data checksum"), \
+    A(DEFLATE_ERR_INLEN, "incorrect data length"), \
+    A(DEFLATE_ERR_UNEXPECTED_EOF, "unexpected end of data")
+#define DEFLATE_ENUM_DEF(x,y) x
+enum { DEFLATE_ERRORLIST(DEFLATE_ENUM_DEF), DEFLATE_NUM_ERRORS };
+#undef DEFLATE_ENUM_DEF
+
+/*
+ * Arrays mapping the above error codes to, respectively, a text
+ * error string and a textual representation of the symbolic error
+ * code.
+ */
+extern const char *const deflate_error_msg[DEFLATE_NUM_ERRORS];
+extern const char *const deflate_error_sym[DEFLATE_NUM_ERRORS];
+
+#endif /* DEFLATE_DEFLATE_H */