/* zran.h -- example of deflated stream indexing and random access * Copyright (C) 2005, 2012, 2018, 2023 Mark Adler * For conditions of distribution and use, see copyright notice in zlib.h * Version 1.3 18 Feb 2023 Mark Adler */ #include <stdio.h> #include "zlib.h" // Access point. typedef struct point { off_t out; // offset in uncompressed data off_t in; // offset in compressed file of first full byte int bits; // 0, or number of bits (1-7) from byte at in-1 unsigned char window[32768]; // preceding 32K of uncompressed data } point_t; // Access point list. struct deflate_index { int have; // number of access points in list int mode; // -15 for raw, 15 for zlib, or 31 for gzip off_t length; // total length of uncompressed data point_t *list; // allocated list of access points }; // Make one pass through a zlib, gzip, or raw deflate compressed stream and // build an index, with access points about every span bytes of uncompressed // output. gzip files with multiple members are fully indexed. span should be // chosen to balance the speed of random access against the memory requirements // of the list, which is about 32K bytes per access point. The return value is // the number of access points on success (>= 1), Z_MEM_ERROR for out of // memory, Z_BUF_ERROR for a premature end of input, Z_DATA_ERROR for a format // or verification error in the input file, or Z_ERRNO for a file read error. // On success, *built points to the resulting index. int deflate_index_build(FILE *in, off_t span, struct deflate_index **built); // Use the index to read len bytes from offset into buf. Return the number of // bytes read or a negative error code. If data is requested past the end of // the uncompressed data, then deflate_index_extract() will return a value less // than len, indicating how much was actually read into buf. If given a valid // index, this function should not return an error unless the file was modified // somehow since the index was generated, given that deflate_index_build() had // validated all of the input. If nevertheless there is a failure, Z_BUF_ERROR // is returned if the compressed data ends prematurely, Z_DATA_ERROR if the // deflate compressed data is not valid, Z_MEM_ERROR if out of memory, // Z_STREAM_ERROR if the index is not valid, or Z_ERRNO if there is an error // reading or seeking on the input file. ptrdiff_t deflate_index_extract(FILE *in, struct deflate_index *index, off_t offset, unsigned char *buf, size_t len); // Deallocate an index built by deflate_index_build(). void deflate_index_free(struct deflate_index *index);