gcc/zlib/examples/gzlog.c

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2005-09-12 19:03:48 +02:00
/*
* 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;
}