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1 | /* zran.c -- example of zlib/gzip stream indexing and random access |
2 | * Copyright (C) 2005 Mark Adler | |
3 | * For conditions of distribution and use, see copyright notice in zlib.h | |
4 | Version 1.0 29 May 2005 Mark Adler */ | |
5 | ||
6 | /* Illustrate the use of Z_BLOCK, inflatePrime(), and inflateSetDictionary() | |
7 | for random access of a compressed file. A file containing a zlib or gzip | |
8 | stream is provided on the command line. The compressed stream is decoded in | |
9 | its entirety, and an index built with access points about every SPAN bytes | |
10 | in the uncompressed output. The compressed file is left open, and can then | |
11 | be read randomly, having to decompress on the average SPAN/2 uncompressed | |
12 | bytes before getting to the desired block of data. | |
13 | ||
14 | An access point can be created at the start of any deflate block, by saving | |
15 | the starting file offset and bit of that block, and the 32K bytes of | |
16 | uncompressed data that precede that block. Also the uncompressed offset of | |
17 | that block is saved to provide a referece for locating a desired starting | |
18 | point in the uncompressed stream. build_index() works by decompressing the | |
19 | input zlib or gzip stream a block at a time, and at the end of each block | |
20 | deciding if enough uncompressed data has gone by to justify the creation of | |
21 | a new access point. If so, that point is saved in a data structure that | |
22 | grows as needed to accommodate the points. | |
23 | ||
24 | To use the index, an offset in the uncompressed data is provided, for which | |
25 | the latest accees point at or preceding that offset is located in the index. | |
26 | The input file is positioned to the specified location in the index, and if | |
27 | necessary the first few bits of the compressed data is read from the file. | |
28 | inflate is initialized with those bits and the 32K of uncompressed data, and | |
29 | the decompression then proceeds until the desired offset in the file is | |
30 | reached. Then the decompression continues to read the desired uncompressed | |
31 | data from the file. | |
32 | ||
33 | Another approach would be to generate the index on demand. In that case, | |
34 | requests for random access reads from the compressed data would try to use | |
35 | the index, but if a read far enough past the end of the index is required, | |
36 | then further index entries would be generated and added. | |
37 | ||
38 | There is some fair bit of overhead to starting inflation for the random | |
39 | access, mainly copying the 32K byte dictionary. So if small pieces of the | |
40 | file are being accessed, it would make sense to implement a cache to hold | |
41 | some lookahead and avoid many calls to extract() for small lengths. | |
42 | ||
43 | Another way to build an index would be to use inflateCopy(). That would | |
44 | not be constrained to have access points at block boundaries, but requires | |
45 | more memory per access point, and also cannot be saved to file due to the | |
46 | use of pointers in the state. The approach here allows for storage of the | |
47 | index in a file. | |
48 | */ | |
49 | ||
50 | #include <stdio.h> | |
51 | #include <stdlib.h> | |
52 | #include <string.h> | |
53 | #include "zlib.h" | |
54 | ||
55 | #define local static | |
56 | ||
57 | #define SPAN 1048576L /* desired distance between access points */ | |
58 | #define WINSIZE 32768U /* sliding window size */ | |
59 | #define CHUNK 16384 /* file input buffer size */ | |
60 | ||
61 | /* access point entry */ | |
62 | struct point { | |
63 | off_t out; /* corresponding offset in uncompressed data */ | |
64 | off_t in; /* offset in input file of first full byte */ | |
65 | int bits; /* number of bits (1-7) from byte at in - 1, or 0 */ | |
66 | unsigned char window[WINSIZE]; /* preceding 32K of uncompressed data */ | |
67 | }; | |
68 | ||
69 | /* access point list */ | |
70 | struct access { | |
71 | int have; /* number of list entries filled in */ | |
72 | int size; /* number of list entries allocated */ | |
73 | struct point *list; /* allocated list */ | |
74 | }; | |
75 | ||
76 | /* Deallocate an index built by build_index() */ | |
77 | local void free_index(struct access *index) | |
78 | { | |
79 | if (index != NULL) { | |
80 | free(index->list); | |
81 | free(index); | |
82 | } | |
83 | } | |
84 | ||
85 | /* Add an entry to the access point list. If out of memory, deallocate the | |
86 | existing list and return NULL. */ | |
87 | local struct access *addpoint(struct access *index, int bits, | |
88 | off_t in, off_t out, unsigned left, unsigned char *window) | |
89 | { | |
90 | struct point *next; | |
91 | ||
92 | /* if list is empty, create it (start with eight points) */ | |
93 | if (index == NULL) { | |
94 | index = malloc(sizeof(struct access)); | |
95 | if (index == NULL) return NULL; | |
96 | index->list = malloc(sizeof(struct point) << 3); | |
97 | if (index->list == NULL) { | |
98 | free(index); | |
99 | return NULL; | |
100 | } | |
101 | index->size = 8; | |
102 | index->have = 0; | |
103 | } | |
104 | ||
105 | /* if list is full, make it bigger */ | |
106 | else if (index->have == index->size) { | |
107 | index->size <<= 1; | |
108 | next = realloc(index->list, sizeof(struct point) * index->size); | |
109 | if (next == NULL) { | |
110 | free_index(index); | |
111 | return NULL; | |
112 | } | |
113 | index->list = next; | |
114 | } | |
115 | ||
116 | /* fill in entry and increment how many we have */ | |
117 | next = index->list + index->have; | |
118 | next->bits = bits; | |
119 | next->in = in; | |
120 | next->out = out; | |
121 | if (left) | |
122 | memcpy(next->window, window + WINSIZE - left, left); | |
123 | if (left < WINSIZE) | |
124 | memcpy(next->window + left, window, WINSIZE - left); | |
125 | index->have++; | |
126 | ||
127 | /* return list, possibly reallocated */ | |
128 | return index; | |
129 | } | |
130 | ||
131 | /* Make one entire pass through the compressed stream and build an index, with | |
132 | access points about every span bytes of uncompressed output -- span is | |
133 | chosen to balance the speed of random access against the memory requirements | |
134 | of the list, about 32K bytes per access point. Note that data after the end | |
135 | of the first zlib or gzip stream in the file is ignored. build_index() | |
136 | returns the number of access points on success (>= 1), Z_MEM_ERROR for out | |
137 | of memory, Z_DATA_ERROR for an error in the input file, or Z_ERRNO for a | |
138 | file read error. On success, *built points to the resulting index. */ | |
139 | local int build_index(FILE *in, off_t span, struct access **built) | |
140 | { | |
141 | int ret; | |
142 | off_t totin, totout; /* our own total counters to avoid 4GB limit */ | |
143 | off_t last; /* totout value of last access point */ | |
144 | struct access *index; /* access points being generated */ | |
145 | z_stream strm; | |
146 | unsigned char input[CHUNK]; | |
147 | unsigned char window[WINSIZE]; | |
148 | ||
149 | /* initialize inflate */ | |
150 | strm.zalloc = Z_NULL; | |
151 | strm.zfree = Z_NULL; | |
152 | strm.opaque = Z_NULL; | |
153 | strm.avail_in = 0; | |
154 | strm.next_in = Z_NULL; | |
155 | ret = inflateInit2(&strm, 47); /* automatic zlib or gzip decoding */ | |
156 | if (ret != Z_OK) | |
157 | return ret; | |
158 | ||
159 | /* inflate the input, maintain a sliding window, and build an index -- this | |
160 | also validates the integrity of the compressed data using the check | |
161 | information at the end of the gzip or zlib stream */ | |
162 | totin = totout = last = 0; | |
163 | index = NULL; /* will be allocated by first addpoint() */ | |
164 | strm.avail_out = 0; | |
165 | do { | |
166 | /* get some compressed data from input file */ | |
167 | strm.avail_in = fread(input, 1, CHUNK, in); | |
168 | if (ferror(in)) { | |
169 | ret = Z_ERRNO; | |
170 | goto build_index_error; | |
171 | } | |
172 | if (strm.avail_in == 0) { | |
173 | ret = Z_DATA_ERROR; | |
174 | goto build_index_error; | |
175 | } | |
176 | strm.next_in = input; | |
177 | ||
178 | /* process all of that, or until end of stream */ | |
179 | do { | |
180 | /* reset sliding window if necessary */ | |
181 | if (strm.avail_out == 0) { | |
182 | strm.avail_out = WINSIZE; | |
183 | strm.next_out = window; | |
184 | } | |
185 | ||
186 | /* inflate until out of input, output, or at end of block -- | |
187 | update the total input and output counters */ | |
188 | totin += strm.avail_in; | |
189 | totout += strm.avail_out; | |
190 | ret = inflate(&strm, Z_BLOCK); /* return at end of block */ | |
191 | totin -= strm.avail_in; | |
192 | totout -= strm.avail_out; | |
193 | if (ret == Z_NEED_DICT) | |
194 | ret = Z_DATA_ERROR; | |
195 | if (ret == Z_MEM_ERROR || ret == Z_DATA_ERROR) | |
196 | goto build_index_error; | |
197 | if (ret == Z_STREAM_END) | |
198 | break; | |
199 | ||
200 | /* if at end of block, consider adding an index entry (note that if | |
201 | data_type indicates an end-of-block, then all of the | |
202 | uncompressed data from that block has been delivered, and none | |
203 | of the compressed data after that block has been consumed, | |
204 | except for up to seven bits) -- the totout == 0 provides an | |
205 | entry point after the zlib or gzip header, and assures that the | |
206 | index always has at least one access point; we avoid creating an | |
207 | access point after the last block by checking bit 6 of data_type | |
208 | */ | |
209 | if ((strm.data_type & 128) && !(strm.data_type & 64) && | |
210 | (totout == 0 || totout - last > span)) { | |
211 | index = addpoint(index, strm.data_type & 7, totin, | |
212 | totout, strm.avail_out, window); | |
213 | if (index == NULL) { | |
214 | ret = Z_MEM_ERROR; | |
215 | goto build_index_error; | |
216 | } | |
217 | last = totout; | |
218 | } | |
219 | } while (strm.avail_in != 0); | |
220 | } while (ret != Z_STREAM_END); | |
221 | ||
222 | /* clean up and return index (release unused entries in list) */ | |
223 | (void)inflateEnd(&strm); | |
224 | index = realloc(index, sizeof(struct point) * index->have); | |
225 | index->size = index->have; | |
226 | *built = index; | |
227 | return index->size; | |
228 | ||
229 | /* return error */ | |
230 | build_index_error: | |
231 | (void)inflateEnd(&strm); | |
232 | if (index != NULL) | |
233 | free_index(index); | |
234 | return ret; | |
235 | } | |
236 | ||
237 | /* Use the index to read len bytes from offset into buf, return bytes read or | |
238 | negative for error (Z_DATA_ERROR or Z_MEM_ERROR). If data is requested past | |
239 | the end of the uncompressed data, then extract() will return a value less | |
240 | than len, indicating how much as actually read into buf. This function | |
241 | should not return a data error unless the file was modified since the index | |
242 | was generated. extract() may also return Z_ERRNO if there is an error on | |
243 | reading or seeking the input file. */ | |
244 | local int extract(FILE *in, struct access *index, off_t offset, | |
245 | unsigned char *buf, int len) | |
246 | { | |
247 | int ret, skip; | |
248 | z_stream strm; | |
249 | struct point *here; | |
250 | unsigned char input[CHUNK]; | |
251 | unsigned char discard[WINSIZE]; | |
252 | ||
253 | /* proceed only if something reasonable to do */ | |
254 | if (len < 0) | |
255 | return 0; | |
256 | ||
257 | /* find where in stream to start */ | |
258 | here = index->list; | |
259 | ret = index->have; | |
260 | while (--ret && here[1].out <= offset) | |
261 | here++; | |
262 | ||
263 | /* initialize file and inflate state to start there */ | |
264 | strm.zalloc = Z_NULL; | |
265 | strm.zfree = Z_NULL; | |
266 | strm.opaque = Z_NULL; | |
267 | strm.avail_in = 0; | |
268 | strm.next_in = Z_NULL; | |
269 | ret = inflateInit2(&strm, -15); /* raw inflate */ | |
270 | if (ret != Z_OK) | |
271 | return ret; | |
272 | ret = fseeko(in, here->in - (here->bits ? 1 : 0), SEEK_SET); | |
273 | if (ret == -1) | |
274 | goto extract_ret; | |
275 | if (here->bits) { | |
276 | ret = getc(in); | |
277 | if (ret == -1) { | |
278 | ret = ferror(in) ? Z_ERRNO : Z_DATA_ERROR; | |
279 | goto extract_ret; | |
280 | } | |
281 | (void)inflatePrime(&strm, here->bits, ret >> (8 - here->bits)); | |
282 | } | |
283 | (void)inflateSetDictionary(&strm, here->window, WINSIZE); | |
284 | ||
285 | /* skip uncompressed bytes until offset reached, then satisfy request */ | |
286 | offset -= here->out; | |
287 | strm.avail_in = 0; | |
288 | skip = 1; /* while skipping to offset */ | |
289 | do { | |
290 | /* define where to put uncompressed data, and how much */ | |
291 | if (offset == 0 && skip) { /* at offset now */ | |
292 | strm.avail_out = len; | |
293 | strm.next_out = buf; | |
294 | skip = 0; /* only do this once */ | |
295 | } | |
296 | if (offset > WINSIZE) { /* skip WINSIZE bytes */ | |
297 | strm.avail_out = WINSIZE; | |
298 | strm.next_out = discard; | |
299 | offset -= WINSIZE; | |
300 | } | |
301 | else if (offset != 0) { /* last skip */ | |
302 | strm.avail_out = (unsigned)offset; | |
303 | strm.next_out = discard; | |
304 | offset = 0; | |
305 | } | |
306 | ||
307 | /* uncompress until avail_out filled, or end of stream */ | |
308 | do { | |
309 | if (strm.avail_in == 0) { | |
310 | strm.avail_in = fread(input, 1, CHUNK, in); | |
311 | if (ferror(in)) { | |
312 | ret = Z_ERRNO; | |
313 | goto extract_ret; | |
314 | } | |
315 | if (strm.avail_in == 0) { | |
316 | ret = Z_DATA_ERROR; | |
317 | goto extract_ret; | |
318 | } | |
319 | strm.next_in = input; | |
320 | } | |
321 | ret = inflate(&strm, Z_NO_FLUSH); /* normal inflate */ | |
322 | if (ret == Z_NEED_DICT) | |
323 | ret = Z_DATA_ERROR; | |
324 | if (ret == Z_MEM_ERROR || ret == Z_DATA_ERROR) | |
325 | goto extract_ret; | |
326 | if (ret == Z_STREAM_END) | |
327 | break; | |
328 | } while (strm.avail_out != 0); | |
329 | ||
330 | /* if reach end of stream, then don't keep trying to get more */ | |
331 | if (ret == Z_STREAM_END) | |
332 | break; | |
333 | ||
334 | /* do until offset reached and requested data read, or stream ends */ | |
335 | } while (skip); | |
336 | ||
337 | /* compute number of uncompressed bytes read after offset */ | |
338 | ret = skip ? 0 : len - strm.avail_out; | |
339 | ||
340 | /* clean up and return bytes read or error */ | |
341 | extract_ret: | |
342 | (void)inflateEnd(&strm); | |
343 | return ret; | |
344 | } | |
345 | ||
346 | /* Demonstrate the use of build_index() and extract() by processing the file | |
347 | provided on the command line, and the extracting 16K from about 2/3rds of | |
348 | the way through the uncompressed output, and writing that to stdout. */ | |
349 | int main(int argc, char **argv) | |
350 | { | |
351 | int len; | |
352 | off_t offset; | |
353 | FILE *in; | |
354 | struct access *index = NULL; | |
355 | unsigned char buf[CHUNK]; | |
356 | ||
357 | /* open input file */ | |
358 | if (argc != 2) { | |
359 | fprintf(stderr, "usage: zran file.gz\n"); | |
360 | return 1; | |
361 | } | |
362 | in = fopen(argv[1], "rb"); | |
363 | if (in == NULL) { | |
364 | fprintf(stderr, "zran: could not open %s for reading\n", argv[1]); | |
365 | return 1; | |
366 | } | |
367 | ||
368 | /* build index */ | |
369 | len = build_index(in, SPAN, &index); | |
370 | if (len < 0) { | |
371 | fclose(in); | |
372 | switch (len) { | |
373 | case Z_MEM_ERROR: | |
374 | fprintf(stderr, "zran: out of memory\n"); | |
375 | break; | |
376 | case Z_DATA_ERROR: | |
377 | fprintf(stderr, "zran: compressed data error in %s\n", argv[1]); | |
378 | break; | |
379 | case Z_ERRNO: | |
380 | fprintf(stderr, "zran: read error on %s\n", argv[1]); | |
381 | break; | |
382 | default: | |
383 | fprintf(stderr, "zran: error %d while building index\n", len); | |
384 | } | |
385 | return 1; | |
386 | } | |
387 | fprintf(stderr, "zran: built index with %d access points\n", len); | |
388 | ||
389 | /* use index by reading some bytes from an arbitrary offset */ | |
390 | offset = (index->list[index->have - 1].out << 1) / 3; | |
391 | len = extract(in, index, offset, buf, CHUNK); | |
392 | if (len < 0) | |
393 | fprintf(stderr, "zran: extraction failed: %s error\n", | |
394 | len == Z_MEM_ERROR ? "out of memory" : "input corrupted"); | |
395 | else { | |
396 | fwrite(buf, 1, len, stdout); | |
397 | fprintf(stderr, "zran: extracted %d bytes at %llu\n", len, offset); | |
398 | } | |
399 | ||
400 | /* clean up and exit */ | |
401 | free_index(index); | |
402 | fclose(in); | |
403 | return 0; | |
404 | } |