zlib库剖析(4)：使用示例example.c
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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;}
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