zlib库剖析(4)：使用示例example.c

    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。

/* 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：

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：

/* ===========================================================================
 * 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）：

/* ===========================================================================
 * 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）：

/* ===========================================================================
 * 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：

/* ===========================================================================
 * 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：

/* ===========================================================================
 * 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）:

/* ===========================================================================
 * 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：

/* ===========================================================================
 * 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;
}