54 lines
2.8 KiB
C
54 lines
2.8 KiB
C
/* zran.h -- example of deflated stream indexing and random access
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* Copyright (C) 2005, 2012, 2018, 2023, 2024 Mark Adler
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* For conditions of distribution and use, see copyright notice in zlib.h
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* Version 1.5 4 Feb 2024 Mark Adler */
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#include <stdio.h>
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#include "zlib.h"
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// Access point.
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typedef struct point {
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off_t out; // offset in uncompressed data
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off_t in; // offset in compressed file of first full byte
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int bits; // 0, or number of bits (1-7) from byte at in-1
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unsigned dict; // number of bytes in window to use as a dictionary
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unsigned char *window; // preceding 32K (or less) of uncompressed data
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} point_t;
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// Access point list.
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struct deflate_index {
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int have; // number of access points in list
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int mode; // -15 for raw, 15 for zlib, or 31 for gzip
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off_t length; // total length of uncompressed data
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point_t *list; // allocated list of access points
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z_stream strm; // re-usable inflate engine for extraction
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};
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// Make one pass through a zlib, gzip, or raw deflate compressed stream and
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// build an index, with access points about every span bytes of uncompressed
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// output. gzip files with multiple members are fully indexed. span should be
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// chosen to balance the speed of random access against the memory requirements
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// of the list, which is about 32K bytes per access point. The return value is
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// the number of access points on success (>= 1), Z_MEM_ERROR for out of
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// memory, Z_BUF_ERROR for a premature end of input, Z_DATA_ERROR for a format
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// or verification error in the input file, or Z_ERRNO for a file read error.
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// On success, *built points to the resulting index, otherwise it's NULL.
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int deflate_index_build(FILE *in, off_t span, struct deflate_index **built);
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// Use the index to read len bytes from offset into buf. Return the number of
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// bytes read or a negative error code. If data is requested past the end of
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// the uncompressed data, then deflate_index_extract() will return a value less
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// than len, indicating how much was actually read into buf. If given a valid
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// index, this function should not return an error unless the file was modified
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// somehow since the index was generated, given that deflate_index_build() had
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// validated all of the input. If nevertheless there is a failure, Z_BUF_ERROR
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// is returned if the compressed data ends prematurely, Z_DATA_ERROR if the
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// deflate compressed data is not valid, Z_MEM_ERROR if out of memory,
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// Z_STREAM_ERROR if the index is not valid, or Z_ERRNO if there is an error
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// reading or seeking on the input file.
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ptrdiff_t deflate_index_extract(FILE *in, struct deflate_index *index,
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off_t offset, unsigned char *buf, size_t len);
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// Deallocate an index built by deflate_index_build().
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void deflate_index_free(struct deflate_index *index);
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