1 /* zran.h -- example of deflated stream indexing and random access 2 * Copyright (C) 2005, 2012, 2018, 2023 Mark Adler 3 * For conditions of distribution and use, see copyright notice in zlib.h 4 * Version 1.3 18 Feb 2023 Mark Adler */ 5 6 #include <stdio.h> 7 #include "zlib.h" 8 9 // Access point. 10 typedef struct point { 11 off_t out; // offset in uncompressed data 12 off_t in; // offset in compressed file of first full byte 13 int bits; // 0, or number of bits (1-7) from byte at in-1 14 unsigned char window[32768]; // preceding 32K of uncompressed data 15 } point_t; 16 17 // Access point list. 18 struct deflate_index { 19 int have; // number of access points in list 20 int mode; // -15 for raw, 15 for zlib, or 31 for gzip 21 off_t length; // total length of uncompressed data 22 point_t *list; // allocated list of access points 23 }; 24 25 // Make one pass through a zlib, gzip, or raw deflate compressed stream and 26 // build an index, with access points about every span bytes of uncompressed 27 // output. gzip files with multiple members are fully indexed. span should be 28 // chosen to balance the speed of random access against the memory requirements 29 // of the list, which is about 32K bytes per access point. The return value is 30 // the number of access points on success (>= 1), Z_MEM_ERROR for out of 31 // memory, Z_BUF_ERROR for a premature end of input, Z_DATA_ERROR for a format 32 // or verification error in the input file, or Z_ERRNO for a file read error. 33 // On success, *built points to the resulting index. 34 int deflate_index_build(FILE *in, off_t span, struct deflate_index **built); 35 36 // Use the index to read len bytes from offset into buf. Return the number of 37 // bytes read or a negative error code. If data is requested past the end of 38 // the uncompressed data, then deflate_index_extract() will return a value less 39 // than len, indicating how much was actually read into buf. If given a valid 40 // index, this function should not return an error unless the file was modified 41 // somehow since the index was generated, given that deflate_index_build() had 42 // validated all of the input. If nevertheless there is a failure, Z_BUF_ERROR 43 // is returned if the compressed data ends prematurely, Z_DATA_ERROR if the 44 // deflate compressed data is not valid, Z_MEM_ERROR if out of memory, 45 // Z_STREAM_ERROR if the index is not valid, or Z_ERRNO if there is an error 46 // reading or seeking on the input file. 47 ptrdiff_t deflate_index_extract(FILE *in, struct deflate_index *index, 48 off_t offset, unsigned char *buf, size_t len); 49 50 // Deallocate an index built by deflate_index_build(). 51 void deflate_index_free(struct deflate_index *index); 52