zlib剖析（四）

下面分析test/example.c，它示范了zlib库的各个函数的使用。

下面代码定义要压缩的字符串、压缩时使用的字典、压缩/解压缩的内存分配策略等。

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/* example.c -- usage example of the zlib compression library

* Copyright (C) 1995-2006, 2011 Jean-loup Gailly.

* For conditions of distribution and use, see copyright notice in zlib.h

*/

/* @(#) $Id$ */

#include "zlib.h"

#include <stdio.h>

#ifdef STDC

# include <string.h>

# include <stdlib.h>

#endif

#if defined(VMS) || defined(RISCOS)

# define TESTFILE "foo-gz"

#else

# define TESTFILE "foo.gz"

#endif

#define CHECK_ERR(err, msg) { \

if (err != Z_OK) { \

fprintf(stderr, "%s error: %d\n", msg, err); \

exit(1); \

} \

}

const char hello[] = "hello, hello!"; /* 字符长度为14（末尾还有一个null字符） */

/* "hello world" would be more standard, but the repeated "hello"

* stresses the compression code better, sorry...

*/

const char dictionary[] = "hello";

uLong dictId; /* 字典的Adler32校验值 */

void test_deflate OF((Byte *compr, uLong comprLen));

void test_inflate OF((Byte *compr, uLong comprLen,

Byte *uncompr, uLong uncomprLen));

void test_large_deflate OF((Byte *compr, uLong comprLen,

Byte *uncompr, uLong uncomprLen));

void test_large_inflate OF((Byte *compr, uLong comprLen,

Byte *uncompr, uLong uncomprLen));

void test_flush OF((Byte *compr, uLong *comprLen));

void test_sync OF((Byte *compr, uLong comprLen,

Byte *uncompr, uLong uncomprLen));

void test_dict_deflate OF((Byte *compr, uLong comprLen));

void test_dict_inflate OF((Byte *compr, uLong comprLen,

Byte *uncompr, uLong uncomprLen));

int main OF((int argc, char *argv[]));

/* Z_SOLO表示把zlib库编译成单独的不依赖第三方的库 */

#ifdef Z_SOLO

/* 使用自定义的内存分配策略 */

void *myalloc OF((void *, unsigned, unsigned));

void myfree OF((void *, void *));

void *myalloc(q, n, m)

void *q;

unsigned n, m;

{

q = Z_NULL;

return calloc(n, m);

}

void myfree(void *q, void *p)

{

q = Z_NULL;

free(p);

}

static alloc_func zalloc = myalloc;

static free_func zfree = myfree;

#else /* !Z_SOLO */

/* 使用zlib默认的内存分配策略 */

static alloc_func zalloc = (alloc_func)0;

static free_func zfree = (free_func)0;

下面测试compress和uncompress的用法：

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void test_compress OF((Byte *compr, uLong comprLen,

Byte *uncompr, uLong uncomprLen));

void test_gzio OF((const char *fname,

Byte *uncompr, uLong uncomprLen));

/* ===========================================================================

* 测试compress()和uncompress()

*/

void test_compress(compr, comprLen, uncompr, uncomprLen)

Byte *compr, *uncompr;

uLong comprLen, uncomprLen;

{

int err;

uLong len = (uLong)strlen(hello)+1; /* 获取字符串长度 */

/* 压缩字符串 */

err = compress(compr, &comprLen, (const Bytef*)hello, len);

CHECK_ERR(err, "compress");

strcpy((char*)uncompr, "garbage");

/* 解压字符串 */

err = uncompress(uncompr, &uncomprLen, compr, comprLen);

CHECK_ERR(err, "uncompress");

/* 比较解压后的结果 */

if (strcmp((char*)uncompr, hello)) {

fprintf(stderr, "bad uncompress\n");

exit(1);

} else {

printf("uncompress(): %s\n", (char *)uncompr);

}

}

下面测试gzip文件的读写操作：

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/* ===========================================================================

* 测试.gz文件的读写操作

*/

void test_gzio(fname, uncompr, uncomprLen)

const char *fname; /* gz文件名 */

Byte *uncompr;

uLong uncomprLen;

{

#ifdef NO_GZCOMPRESS

fprintf(stderr, "NO_GZCOMPRESS -- gz* functions cannot compress\n");

#else

int err;

int len = (int)strlen(hello)+1;

gzFile file;

z_off_t pos;

file = gzopen(fname, "wb"); /* 打开要写入的gz文件 */

if (file == NULL) {

fprintf(stderr, "gzopen error\n");

exit(1);

}

gzputc(file, 'h'); /* 写入一个字符'h' */

if (gzputs(file, "ello") != 4) { /* 写入字符串"ello" */

fprintf(stderr, "gzputs err: %s\n", gzerror(file, &err));

exit(1);

}

if (gzprintf(file, ", %s!", "hello") != 8) { /* 按格式写入字符串", hello!" */

fprintf(stderr, "gzprintf err: %s\n", gzerror(file, &err));

exit(1);

}

gzseek(file, 1L, SEEK_CUR); /* 读写头向前移动1字节（即添加一个0字节） */

gzclose(file); /* 关闭gz文件 */

file = gzopen(fname, "rb"); /* 打开要读取的gz文件 */

if (file == NULL) {

fprintf(stderr, "gzopen error\n");

exit(1);

}

strcpy((char*)uncompr, "garbage");

/* 从压缩文件中读取给定大小的解压字节数 */

if (gzread(file, uncompr, (unsigned)uncomprLen) != len) {

fprintf(stderr, "gzread err: %s\n", gzerror(file, &err));

exit(1);

}

if (strcmp((char*)uncompr, hello)) { /* 比较解压后的结果 */

fprintf(stderr, "bad gzread: %s\n", (char*)uncompr);

exit(1);

} else {

printf("gzread(): %s\n", (char*)uncompr);

}

pos = gzseek(file, -8L, SEEK_CUR); /* 读写头向后移动8字节，应该停留在第6个字符处 */

if (pos != 6 || gztell(file) != pos) { /* 判断是否停留在第6个字符处 */

fprintf(stderr, "gzseek error, pos=%ld, gztell=%ld\n",

(long)pos, (long)gztell(file));

exit(1);

}

if (gzgetc(file) != ' ') { /* 从当前位置读取1个字符，应该为字符' ' */

fprintf(stderr, "gzgetc error\n");

exit(1);

}

if (gzungetc(' ', file) != ' ') { /* 推回这个字符到流中 */

fprintf(stderr, "gzungetc error\n");

exit(1);

}

/* 从压缩文件当前位置读取指定长度的解压字节数，直到len-1个字符被读取 */

gzgets(file, (char*)uncompr, (int)uncomprLen);

if (strlen((char*)uncompr) != 7) { /* " hello!" */

fprintf(stderr, "gzgets err after gzseek: %s\n", gzerror(file, &err));

exit(1);

}

if (strcmp((char*)uncompr, hello + 6)) {

fprintf(stderr, "bad gzgets after gzseek\n");

exit(1);

} else {

printf("gzgets() after gzseek: %s\n", (char*)uncompr);

}

gzclose(file); /* 关闭gz文件 */

#endif

}

#endif /* Z_SOLO */

下面用小缓冲区测试压缩、解压操作（deflate/deflate）：

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/* ===========================================================================

* 测试deflate()：使用小缓冲区

*/

void test_deflate(compr, comprLen)

Byte *compr;

uLong comprLen;

{

z_stream c_stream; /* 压缩流 */

int err;

uLong len = (uLong)strlen(hello)+1;

/* 这三个字段要在defalteInit之前初始化 */

c_stream.zalloc = zalloc;

c_stream.zfree = zfree;

c_stream.opaque = (voidpf)0;

/* 初始化压缩流的状态，使用默认压缩级别 */

err = deflateInit(&c_stream, Z_DEFAULT_COMPRESSION);

CHECK_ERR(err, "deflateInit");

/* 设置压缩操作的输入数据和输出缓冲区 */

c_stream.next_in = (Bytef*)hello; /* 输入缓冲区指向输入字符串 */

c_stream.next_out = compr;

/* 第一个循环：将flush设为Z_NO_FLUSH（表示还有输入数据未读完），将所有输入都读进去并进行压缩

根据avail_in和avail_out，不停地调用deflate将输入缓冲区的数据压缩

并写到输出缓冲区，直到输入字符串读完或输出缓冲区用完

*/

while (c_stream.total_in != len && c_stream.total_out < comprLen) {

c_stream.avail_in = c_stream.avail_out = 1; /* 强制小缓冲区 */

err = deflate(&c_stream, Z_NO_FLUSH);

CHECK_ERR(err, "deflate");

}

/* 第二个循环：将flush设置为Z_FINISH，不再输入，让deflate()完成全部的压缩输出

注意因为deflate压缩时可能是异步的（为了加速压缩，读取一次输入后不一定立刻就会产生压缩输出，

可能读完K字节后才会产生输出），所以上一个循环可能还没产生全部输出，需要这个循环，让flush保持Z_FINISH

（表示输入数据已读完），多次调用deflate()，直到返回Z_STREAM_END，表示处理完全部输入并产生了全部的压缩输出

*/

for (;;) { /* 完成压缩流的刷新，仍然强制小缓冲区 */

c_stream.avail_out = 1;

err = deflate(&c_stream, Z_FINISH);

if (err == Z_STREAM_END) break;

CHECK_ERR(err, "deflate");

}

err = deflateEnd(&c_stream); /* 释放压缩流的资源 */

CHECK_ERR(err, "deflateEnd");

}

/* ===========================================================================

* 测试inflate()：使用小缓冲区

*/

void test_inflate(compr, comprLen, uncompr, uncomprLen)

Byte *compr, *uncompr;

uLong comprLen, uncomprLen;

{

int err;

z_stream d_stream; /* 解压流 */

strcpy((char*)uncompr, "garbage");

/* 这些个字段要在infalteInit之前初始化 */

d_stream.zalloc = zalloc;

d_stream.zfree = zfree;

d_stream.opaque = (voidpf)0;

d_stream.next_in = compr; /* 设置输入缓冲区 */

d_stream.avail_in = 0;

d_stream.next_out = uncompr; /* 设置输出缓冲区 */

/* 初始化解压流的状态 */

err = inflateInit(&d_stream);

CHECK_ERR(err, "inflateInit");

/* 只需一个循环：根据avail_in和avail_out，不停地调用inflate将输入缓冲区的数据

解压，直到返回Z_STREAM_END，表示处理完全部输入并产生了全部的解压输出

这里与flush参数是否为Z_FINISH无关

*/

while (d_stream.total_out < uncomprLen && d_stream.total_in < comprLen) {

d_stream.avail_in = d_stream.avail_out = 1; /* 强制小缓冲区 */

err = inflate(&d_stream, Z_NO_FLUSH);

if (err == Z_STREAM_END) break;

CHECK_ERR(err, "inflate");

}

err = inflateEnd(&d_stream); /* 释放解压流的资源 */

CHECK_ERR(err, "inflateEnd");

if (strcmp((char*)uncompr, hello)) { /* 比较解压后的数据 */

fprintf(stderr, "bad inflate\n");

exit(1);

} else {

printf("inflate(): %s\n", (char *)uncompr);

}

}

下面使用大缓冲区测试压缩、解压操作（deflate/deflate）：

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/* ===========================================================================

* 测试deflate()：使用大缓冲区和动态改变的压缩级别

*/

void test_large_deflate(compr, comprLen, uncompr, uncomprLen)

Byte *compr, *uncompr;

uLong comprLen, uncomprLen;

{

z_stream c_stream; /* 压缩流 */

int err;

/* 这三个字段要在defalteInit之前初始化 */

c_stream.zalloc = zalloc;

c_stream.zfree = zfree;

c_stream.opaque = (voidpf)0;

/* 初始化压缩流的状态，使用最快速度压缩 */

err = deflateInit(&c_stream, Z_BEST_SPEED);

CHECK_ERR(err, "deflateInit");

c_stream.next_out = compr;

c_stream.avail_out = (uInt)comprLen;

/* 这里，uncompr几乎都为0，因此可以很好地被压缩 */

c_stream.next_in = uncompr;

c_stream.avail_in = (uInt)uncomprLen;

err = deflate(&c_stream, Z_NO_FLUSH); /* 压缩输入数据 */

CHECK_ERR(err, "deflate");

if (c_stream.avail_in != 0) {

fprintf(stderr, "deflate not greedy\n");

exit(1);

}

/* 把已压缩的数据转换成未压缩: */

/* 设置流的压缩级别（为未压缩）和压缩策略 */

deflateParams(&c_stream, Z_NO_COMPRESSION, Z_DEFAULT_STRATEGY);

c_stream.next_in = compr;

c_stream.avail_in = (uInt)comprLen/2;

err = deflate(&c_stream, Z_NO_FLUSH);

CHECK_ERR(err, "deflate");

/* 转换回压缩模式（最高压缩率）: */

deflateParams(&c_stream, Z_BEST_COMPRESSION, Z_FILTERED);

c_stream.next_in = uncompr;

c_stream.avail_in = (uInt)uncomprLen;

err = deflate(&c_stream, Z_NO_FLUSH);

CHECK_ERR(err, "deflate");

/* 流刷新，产生全部压缩输出 */

err = deflate(&c_stream, Z_FINISH);

if (err != Z_STREAM_END) {

fprintf(stderr, "deflate should report Z_STREAM_END\n");

exit(1);

}

err = deflateEnd(&c_stream); /* 释放流的资源 */

CHECK_ERR(err, "deflateEnd");

}

/* ===========================================================================

* 测试inflate()：使用大缓冲区

*/

void test_large_inflate(compr, comprLen, uncompr, uncomprLen)

Byte *compr, *uncompr;

uLong comprLen, uncomprLen;

{

int err;

z_stream d_stream; /* 解压流 */

strcpy((char*)uncompr, "garbage");

/* 这些个字段要在infalteInit之前初始化 */

d_stream.zalloc = zalloc;

d_stream.zfree = zfree;

d_stream.opaque = (voidpf)0;

d_stream.next_in = compr;

d_stream.avail_in = (uInt)comprLen;

/* 初始化解压流 */

err = inflateInit(&d_stream);

CHECK_ERR(err, "inflateInit");

/* 解压 */

for (;;) {

d_stream.next_out = uncompr; /* 抛弃输出 */

d_stream.avail_out = (uInt)uncomprLen;

err = inflate(&d_stream, Z_NO_FLUSH); /* 解压输入数据 */

if (err == Z_STREAM_END) break;

CHECK_ERR(err, "large inflate");

}

err = inflateEnd(&d_stream);

CHECK_ERR(err, "inflateEnd");

if (d_stream.total_out != 2*uncomprLen + comprLen/2) {

fprintf(stderr, "bad large inflate: %ld\n", d_stream.total_out);

exit(1);

} else {

printf("large_inflate(): OK\n");

}

}

下面使用完全刷新模式测试压缩操作deflate：

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/* ===========================================================================

* 测试deflate()：使用完全刷新

*/

void test_flush(compr, comprLen)

Byte *compr;

uLong *comprLen;

{

z_stream c_stream; /* 压缩流 */

int err;

uInt len = (uInt)strlen(hello)+1;

c_stream.zalloc = zalloc;

c_stream.zfree = zfree;

c_stream.opaque = (voidpf)0;

err = deflateInit(&c_stream, Z_DEFAULT_COMPRESSION);

CHECK_ERR(err, "deflateInit");

c_stream.next_in = (Bytef*)hello;

c_stream.next_out = compr;

c_stream.avail_in = 3;

c_stream.avail_out = (uInt)*comprLen;

/* 使用完全刷新来压缩字符串 */

err = deflate(&c_stream, Z_FULL_FLUSH);

CHECK_ERR(err, "deflate");

compr[3]++; /* 在第一个压缩块中强制产生一个错误 */

c_stream.avail_in = len - 3;

err = deflate(&c_stream, Z_FINISH);

if (err != Z_STREAM_END) {

CHECK_ERR(err, "deflate");

}

err = deflateEnd(&c_stream);

CHECK_ERR(err, "deflateEnd");

*comprLen = c_stream.total_out;

}

下面测试同步方式的解压操作inflateSync：

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/* ===========================================================================

* Test inflateSync()

*/

void test_sync(compr, comprLen, uncompr, uncomprLen)

Byte *compr, *uncompr;

uLong comprLen, uncomprLen;

{

int err;

z_stream d_stream; /* 解压流 */

strcpy((char*)uncompr, "garbage");

d_stream.zalloc = zalloc;

d_stream.zfree = zfree;

d_stream.opaque = (voidpf)0;

d_stream.next_in = compr; /* 设置输入缓冲区 */

d_stream.avail_in = 2; /* 只读取zlib头部信息 */

err = inflateInit(&d_stream);

CHECK_ERR(err, "inflateInit");

d_stream.next_out = uncompr; /* 设置输出缓冲区 */

d_stream.avail_out = (uInt)uncomprLen;

inflate(&d_stream, Z_NO_FLUSH);

CHECK_ERR(err, "inflate");

d_stream.avail_in = (uInt)comprLen-2; /* 读取所有压缩数据 */

err = inflateSync(&d_stream); /* 但忽略损坏的部分 */

CHECK_ERR(err, "inflateSync");

err = inflate(&d_stream, Z_FINISH); /* 完成解压 */

if (err != Z_DATA_ERROR) {

fprintf(stderr, "inflate should report DATA_ERROR\n");

/* 因为不正确的adler32 */

exit(1);

}

err = inflateEnd(&d_stream);

CHECK_ERR(err, "inflateEnd");

printf("after inflateSync(): hel%s\n", (char *)uncompr);

}

下面用预设的字典测试压缩、解压操作（deflate/inflate）:

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/* ===========================================================================

* 测试：deflate()：使用预设的字典

*/

void test_dict_deflate(compr, comprLen)

Byte *compr;

uLong comprLen;

{

z_stream c_stream; /* 压缩流 */

int err;

c_stream.zalloc = zalloc;

c_stream.zfree = zfree;

c_stream.opaque = (voidpf)0;

err = deflateInit(&c_stream, Z_BEST_COMPRESSION);

CHECK_ERR(err, "deflateInit");

/* 设置压缩流要使用的字典 */

err = deflateSetDictionary(&c_stream,

(const Bytef*)dictionary, (int)sizeof(dictionary));

CHECK_ERR(err, "deflateSetDictionary");

dictId = c_stream.adler; /* 得到字典的Alder32校验值 */

c_stream.next_out = compr;

c_stream.avail_out = (uInt)comprLen;

c_stream.next_in = (Bytef*)hello; /* 输入要压缩的字符串 */

c_stream.avail_in = (uInt)strlen(hello)+1;

/* 直接进行压缩 */

err = deflate(&c_stream, Z_FINISH);

if (err != Z_STREAM_END) {

fprintf(stderr, "deflate should report Z_STREAM_END\n");

exit(1);

}

err = deflateEnd(&c_stream);

CHECK_ERR(err, "deflateEnd");

}

/* ===========================================================================

* 测试inflate()：使用预设的字典

*/

void test_dict_inflate(compr, comprLen, uncompr, uncomprLen)

Byte *compr, *uncompr;

uLong comprLen, uncomprLen;

{

int err;

z_stream d_stream; /* 解压流 */

strcpy((char*)uncompr, "garbage");

d_stream.zalloc = zalloc;

d_stream.zfree = zfree;

d_stream.opaque = (voidpf)0;

d_stream.next_in = compr;

d_stream.avail_in = (uInt)comprLen;

err = inflateInit(&d_stream);

CHECK_ERR(err, "inflateInit");

d_stream.next_out = uncompr;

d_stream.avail_out = (uInt)uncomprLen;

for (;;) { /* 解压 */

err = inflate(&d_stream, Z_NO_FLUSH);

if (err == Z_STREAM_END) break;

if (err == Z_NEED_DICT) { /* 如果需要字典 */

if (d_stream.adler != dictId) { /* 校验是否与压缩时的字典值一致 */

fprintf(stderr, "unexpected dictionary");

exit(1);

}

/* 设置解压需要的字典 */

err = inflateSetDictionary(&d_stream, (const Bytef*)dictionary,

(int)sizeof(dictionary));

}

CHECK_ERR(err, "inflate with dict");

}

err = inflateEnd(&d_stream);

CHECK_ERR(err, "inflateEnd");

if (strcmp((char*)uncompr, hello)) { /* 比较解压后的字符串 */

fprintf(stderr, "bad inflate with dict\n");

exit(1);

} else {

printf("inflate with dictionary: %s\n", (char *)uncompr);

}

}

下面是命令行程序：

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/* ===========================================================================

* Usage: example [output.gz [input.gz]]

*/

int main(argc, argv)

int argc;

char *argv[];

{

Byte *compr, *uncompr;

uLong comprLen = 10000*sizeof(int); /* 在MSDOS上不会溢出 */

uLong uncomprLen = comprLen;

static const char* myVersion = ZLIB_VERSION;

/* 检查zlib版本是否一致 */

if (zlibVersion()[0] != myVersion[0]) {

fprintf(stderr, "incompatible zlib version\n");

exit(1);

} else if (strcmp(zlibVersion(), ZLIB_VERSION) != 0) {

fprintf(stderr, "warning: different zlib version\n");

}

/* 打印版本和zlib编译信息 */

printf("zlib version %s = 0x%04x, compile flags = 0x%lx\n",

ZLIB_VERSION, ZLIB_VERNUM, zlibCompileFlags());

/* 分配输入、输出缓冲区的内存 */

compr = (Byte*)calloc((uInt)comprLen, 1);

uncompr = (Byte*)calloc((uInt)uncomprLen, 1);

/* 清空compr和uncompr，以避免读到未初始化的数据，并且确保uncompr能很好

* 地被压缩

*/

if (compr == Z_NULL || uncompr == Z_NULL) {

printf("out of memory\n");

exit(1);

}

/* 下面运行各个测试函数 */

#ifdef Z_SOLO

argc = strlen(argv[0]);

#else

test_compress(compr, comprLen, uncompr, uncomprLen);

test_gzio((argc > 1 ? argv[1] : TESTFILE),

uncompr, uncomprLen);

#endif

test_deflate(compr, comprLen);

test_inflate(compr, comprLen, uncompr, uncomprLen);

test_large_deflate(compr, comprLen, uncompr, uncomprLen);

test_large_inflate(compr, comprLen, uncompr, uncomprLen);

test_flush(compr, &comprLen);

test_sync(compr, comprLen, uncompr, uncomprLen);

comprLen = uncomprLen;

test_dict_deflate(compr, comprLen);

test_dict_inflate(compr, comprLen, uncompr, uncomprLen);

/* 释放缓冲区资源 */

free(compr);

free(uncompr);

return 0;

}