summaryrefslogtreecommitdiffstats
path: root/compat/zlib/examples/gzlog.c
blob: f71f817c8b6e129de06d61c4851fa99a00d8f690 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
/*
 * gzlog.c
 * Copyright (C) 2004 Mark Adler
 * For conditions of distribution and use, see copyright notice in gzlog.h
 * version 1.0, 26 Nov 2004
 *
 */

#include <string.h>             /* memcmp() */
#include <stdlib.h>             /* malloc(), free(), NULL */
#include <sys/types.h>          /* size_t, off_t */
#include <unistd.h>             /* read(), close(), sleep(), ftruncate(), */
                                /* lseek() */
#include <fcntl.h>              /* open() */
#include <sys/file.h>           /* flock() */
#include "zlib.h"               /* deflateInit2(), deflate(), deflateEnd() */

#include "gzlog.h"              /* interface */
#define local static

/* log object structure */
typedef struct {
    int id;                 /* object identifier */
    int fd;                 /* log file descriptor */
    off_t extra;            /* offset of extra "ap" subfield */
    off_t mark_off;         /* offset of marked data */
    off_t last_off;         /* offset of last block */
    unsigned long crc;      /* uncompressed crc */
    unsigned long len;      /* uncompressed length (modulo 2^32) */
    unsigned stored;        /* length of current stored block */
} gz_log;

#define GZLOGID 19334       /* gz_log object identifier */

#define LOCK_RETRY 1            /* retry lock once a second */
#define LOCK_PATIENCE 1200      /* try about twenty minutes before forcing */

/* acquire a lock on a file */
local int lock(int fd)
{
    int patience;

    /* try to lock every LOCK_RETRY seconds for LOCK_PATIENCE seconds */
    patience = LOCK_PATIENCE;
    do {
        if (flock(fd, LOCK_EX + LOCK_NB) == 0)
            return 0;
        (void)sleep(LOCK_RETRY);
        patience -= LOCK_RETRY;
    } while (patience > 0);

    /* we've run out of patience -- give up */
    return -1;
}

/* release lock */
local void unlock(int fd)
{
    (void)flock(fd, LOCK_UN);
}

/* release a log object */
local void log_clean(gz_log *log)
{
    unlock(log->fd);
    (void)close(log->fd);
    free(log);
}

/* read an unsigned long from a byte buffer little-endian */
local unsigned long make_ulg(unsigned char *buf)
{
    int n;
    unsigned long val;

    val = (unsigned long)(*buf++);
    for (n = 8; n < 32; n += 8)
        val += (unsigned long)(*buf++) << n;
    return val;
}

/* read an off_t from a byte buffer little-endian */
local off_t make_off(unsigned char *buf)
{
    int n;
    off_t val;

    val = (off_t)(*buf++);
    for (n = 8; n < 64; n += 8)
        val += (off_t)(*buf++) << n;
    return val;
}

/* write an unsigned long little-endian to byte buffer */
local void dice_ulg(unsigned long val, unsigned char *buf)
{
    int n;

    for (n = 0; n < 4; n++) {
        *buf++ = val & 0xff;
        val >>= 8;
    }
}

/* write an off_t little-endian to byte buffer */
local void dice_off(off_t val, unsigned char *buf)
{
    int n;

    for (n = 0; n < 8; n++) {
        *buf++ = val & 0xff;
        val >>= 8;
    }
}

/* initial, empty gzip file for appending */
local char empty_gz[] = {
    0x1f, 0x8b,                 /* magic gzip id */
    8,                          /* compression method is deflate */
    4,                          /* there is an extra field */
    0, 0, 0, 0,                 /* no modification time provided */
    0, 0xff,                    /* no extra flags, no OS */
    20, 0, 'a', 'p', 16, 0,     /* extra field with "ap" subfield */
    32, 0, 0, 0, 0, 0, 0, 0,    /* offset of uncompressed data */
    32, 0, 0, 0, 0, 0, 0, 0,    /* offset of last block */
    1, 0, 0, 0xff, 0xff,        /* empty stored block (last) */
    0, 0, 0, 0,                 /* crc */
    0, 0, 0, 0                  /* uncompressed length */
};

/* initialize a log object with locking */
void *gzlog_open(char *path)
{
    unsigned xlen;
    unsigned char temp[20];
    unsigned sub_len;
    int good;
    gz_log *log;

    /* allocate log structure */
    log = malloc(sizeof(gz_log));
    if (log == NULL)
        return NULL;
    log->id = GZLOGID;

    /* open file, creating it if necessary, and locking it */
    log->fd = open(path, O_RDWR | O_CREAT, 0600);
    if (log->fd < 0) {
        free(log);
        return NULL;
    }
    if (lock(log->fd)) {
        close(log->fd);
        free(log);
        return NULL;
    }

    /* if file is empty, write new gzip stream */
    if (lseek(log->fd, 0, SEEK_END) == 0) {
        if (write(log->fd, empty_gz, sizeof(empty_gz)) != sizeof(empty_gz)) {
            log_clean(log);
            return NULL;
        }
    }

    /* check gzip header */
    (void)lseek(log->fd, 0, SEEK_SET);
    if (read(log->fd, temp, 12) != 12 || temp[0] != 0x1f ||
        temp[1] != 0x8b || temp[2] != 8 || (temp[3] & 4) == 0) {
        log_clean(log);
        return NULL;
    }

    /* process extra field to find "ap" sub-field */
    xlen = temp[10] + (temp[11] << 8);
    good = 0;
    while (xlen) {
        if (xlen < 4 || read(log->fd, temp, 4) != 4)
            break;
        sub_len = temp[2];
        sub_len += temp[3] << 8;
        xlen -= 4;
        if (memcmp(temp, "ap", 2) == 0 && sub_len == 16) {
            good = 1;
            break;
        }
        if (xlen < sub_len)
            break;
        (void)lseek(log->fd, sub_len, SEEK_CUR);
        xlen -= sub_len;
    }
    if (!good) {
        log_clean(log);
        return NULL;
    }

    /* read in "ap" sub-field */
    log->extra = lseek(log->fd, 0, SEEK_CUR);
    if (read(log->fd, temp, 16) != 16) {
        log_clean(log);
        return NULL;
    }
    log->mark_off = make_off(temp);
    log->last_off = make_off(temp + 8);

    /* get crc, length of gzip file */
    (void)lseek(log->fd, log->last_off, SEEK_SET);
    if (read(log->fd, temp, 13) != 13 ||
        memcmp(temp, "\001\000\000\377\377", 5) != 0) {
        log_clean(log);
        return NULL;
    }
    log->crc = make_ulg(temp + 5);
    log->len = make_ulg(temp + 9);

    /* set up to write over empty last block */
    (void)lseek(log->fd, log->last_off + 5, SEEK_SET);
    log->stored = 0;
    return (void *)log;
}

/* maximum amount to put in a stored block before starting a new one */
#define MAX_BLOCK 16384

/* write a block to a log object */
int gzlog_write(void *obj, char *data, size_t len)
{
    size_t some;
    unsigned char temp[5];
    gz_log *log;

    /* check object */
    log = (gz_log *)obj;
    if (log == NULL || log->id != GZLOGID)
        return 1;

    /* write stored blocks until all of the input is written */
    do {
        some = MAX_BLOCK - log->stored;
        if (some > len)
            some = len;
        if (write(log->fd, data, some) != some)
            return 1;
        log->crc = crc32(log->crc, data, some);
        log->len += some;
        len -= some;
        data += some;
        log->stored += some;

        /* if the stored block is full, end it and start another */
        if (log->stored == MAX_BLOCK) {
            (void)lseek(log->fd, log->last_off, SEEK_SET);
            temp[0] = 0;
            dice_ulg(log->stored + ((unsigned long)(~log->stored) << 16),
                     temp + 1);
            if (write(log->fd, temp, 5) != 5)
                return 1;
            log->last_off = lseek(log->fd, log->stored, SEEK_CUR);
            (void)lseek(log->fd, 5, SEEK_CUR);
            log->stored = 0;
        }
    } while (len);
    return 0;
}

/* recompress the remaining stored deflate data in place */
local int recomp(gz_log *log)
{
    z_stream strm;
    size_t len, max;
    unsigned char *in;
    unsigned char *out;
    unsigned char temp[16];

    /* allocate space and read it all in (it's around 1 MB) */
    len = log->last_off - log->mark_off;
    max = len + (len >> 12) + (len >> 14) + 11;
    out = malloc(max);
    if (out == NULL)
        return 1;
    in = malloc(len);
    if (in == NULL) {
        free(out);
        return 1;
    }
    (void)lseek(log->fd, log->mark_off, SEEK_SET);
    if (read(log->fd, in, len) != len) {
        free(in);
        free(out);
        return 1;
    }

    /* recompress in memory, decoding stored data as we go */
    /* note: this assumes that unsigned is four bytes or more */
    /*       consider not making that assumption */
    strm.zalloc = Z_NULL;
    strm.zfree = Z_NULL;
    strm.opaque = Z_NULL;
    if (deflateInit2(&strm, Z_BEST_COMPRESSION, Z_DEFLATED, -15, 8,
        Z_DEFAULT_STRATEGY) != Z_OK) {
        free(in);
        free(out);
        return 1;
    }
    strm.next_in = in;
    strm.avail_out = max;
    strm.next_out = out;
    while (len >= 5) {
        if (strm.next_in[0] != 0)
            break;
        strm.avail_in = strm.next_in[1] + (strm.next_in[2] << 8);
        strm.next_in += 5;
        len -= 5;
        if (strm.avail_in != 0) {
            if (len < strm.avail_in)
                break;
            len -= strm.avail_in;
            (void)deflate(&strm, Z_NO_FLUSH);
            if (strm.avail_in != 0 || strm.avail_out == 0)
                break;
        }
    }
    (void)deflate(&strm, Z_SYNC_FLUSH);
    (void)deflateEnd(&strm);
    free(in);
    if (len != 0 || strm.avail_out == 0) {
        free(out);
        return 1;
    }

    /* overwrite stored data with compressed data */
    (void)lseek(log->fd, log->mark_off, SEEK_SET);
    len = max - strm.avail_out;
    if (write(log->fd, out, len) != len) {
        free(out);
        return 1;
    }
    free(out);

    /* write last empty block, crc, and length */
    log->mark_off = log->last_off = lseek(log->fd, 0, SEEK_CUR);
    temp[0] = 1;
    dice_ulg(0xffffL << 16, temp + 1);
    dice_ulg(log->crc, temp + 5);
    dice_ulg(log->len, temp + 9);
    if (write(log->fd, temp, 13) != 13)
        return 1;

    /* truncate file to discard remaining stored data and old trailer */
    ftruncate(log->fd, lseek(log->fd, 0, SEEK_CUR));

    /* update extra field to point to new last empty block */
    (void)lseek(log->fd, log->extra, SEEK_SET);
    dice_off(log->mark_off, temp);
    dice_off(log->last_off, temp + 8);
    if (write(log->fd, temp, 16) != 16)
        return 1;
    return 0;
}

/* maximum accumulation of stored blocks before compressing */
#define MAX_STORED 1048576

/* close log object */
int gzlog_close(void *obj)
{
    unsigned char temp[8];
    gz_log *log;

    /* check object */
    log = (gz_log *)obj;
    if (log == NULL || log->id != GZLOGID)
        return 1;

    /* go to start of most recent block being written */
    (void)lseek(log->fd, log->last_off, SEEK_SET);

    /* if some stuff was put there, update block */
    if (log->stored) {
        temp[0] = 0;
        dice_ulg(log->stored + ((unsigned long)(~log->stored) << 16),
                 temp + 1);
        if (write(log->fd, temp, 5) != 5)
            return 1;
        log->last_off = lseek(log->fd, log->stored, SEEK_CUR);
    }

    /* write last block (empty) */
    if (write(log->fd, "\001\000\000\377\377", 5) != 5)
        return 1;

    /* write updated crc and uncompressed length */
    dice_ulg(log->crc, temp);
    dice_ulg(log->len, temp + 4);
    if (write(log->fd, temp, 8) != 8)
        return 1;

    /* put offset of that last block in gzip extra block */
    (void)lseek(log->fd, log->extra + 8, SEEK_SET);
    dice_off(log->last_off, temp);
    if (write(log->fd, temp, 8) != 8)
        return 1;

    /* if more than 1 MB stored, then time to compress it */
    if (log->last_off - log->mark_off > MAX_STORED) {
        if (recomp(log))
            return 1;
    }

    /* unlock and close file */
    log_clean(log);
    return 0;
}