C++实现tar包解析

tar(tape archive)是Unix和类Unix系统上文件打包工具，可以将多个文件合并为一个文件，使用tar工具打出来的包称为tar包。一般打包后的文件名后缀为”.tar”，也可以为其它。tar代表未被压缩的tar文件，已被压缩的tar文件则追加压缩文件的扩展名，如经过gzip压缩后的tar文件，扩展名为”.tar.gz”。在windows系统中用WinRAR也可以解压缩打开tar包。tar文件格式已经成为POSIX标准，最初是POSIX.1-1998，目前是POSIX.1-2001.

tar中的数据都是以512字节为单位。tar由两部分组成即头部+内容，其中头部是512字节的头部结构，内容是存放一个文件内容的地方。

tar文件格式的详细介绍可以参考：https://en.wikipedia.org/wiki/Tar_(computing)#File_header

通过执行以下命令生成测试tar包：

tar -cvf test.tar *

test.tar中包含两个文件blog_info.txt和github_info.txt.

其中blog_info.txt文件内容如下：

name: fengbingchun
address: http://blog.csdn.net/fengbingchun?viewmode=contents

github_info.txt文件内容如下：

name: fengbingchun
address: https://github.com/fengbingchun

实现代码tar.hpp:

#ifndef FBC_MESSY_TEST_TAR_HPP_
#define FBC_MESSY_TEST_TAR_HPP_#include <vector>
#include <string>/* reference:http://www.gnu.org/software/tar/manual/html_node/Standard.htmlhttp://stackoverflow.com/questions/2505042/how-to-parse-a-tar-file-in-chttp://directory.fsf.org/wiki/Libtarhttp://work.freenet59.ru/svn/pkgsrc_haiku/trunk/archivers/libarchive/files/contrib/untar.chttps://codeistry.wordpress.com/2014/08/14/how-to-parse-a-tar-file/http://stackoverflow.com/questions/17862383/how-to-know-the-files-inside-the-tar-parserhttps://en.wikipedia.org/wiki/Tar_(computing)
*//* tar Header Block, from POSIX 1003.1-1990.  *//* POSIX header.  */typedef struct posix_header
{                                     /* byte offset */char name[100];               /*   0 */char mode[8];                 /* 100 */char uid[8];                  /* 108 */char gid[8];                  /* 116 */char size[12];                /* 124 */char mtime[12];               /* 136 */char chksum[8];               /* 148 */char typeflag;                /* 156 */char linkname[100];           /* 157 */char magic[6];                /* 257 */char version[2];              /* 263 */char uname[32];               /* 265 */char gname[32];               /* 297 */char devmajor[8];             /* 329 */char devminor[8];             /* 337 */char prefix[155];             /* 345 *//* 500 */
} tar_posix_header;/*location  size  field0         100   File name100       8     File mode108       8     Owner's numeric user ID116       8     Group's numeric user ID124       12    File size in bytes136       12    Last modification time in numeric Unix time format148       8     Checksum for header block156       1     Link indicator (file type)157       100   Name of linked file
*/#define TMAGIC   "ustar"        /* ustar and a null */
#define TMAGLEN  6
#define TVERSION "00"           /* 00 and no null */
#define TVERSLEN 2/* Values used in typeflag field.  */
#define REGTYPE  '0'            /* regular file */
#define AREGTYPE '\0'           /* regular file */
#define LNKTYPE  '1'            /* link */
#define SYMTYPE  '2'            /* reserved */
#define CHRTYPE  '3'            /* character special */
#define BLKTYPE  '4'            /* block special */
#define DIRTYPE  '5'            /* directory */
#define FIFOTYPE '6'            /* FIFO special */
#define CONTTYPE '7'            /* reserved */class TarFile {
public:TarFile(const char* tar_name);bool IsValidTarFile();std::vector<std::string> GetFileNames();bool GetFileContents(const char* file_name, char* contents);size_t GetFileSize(const char* file_name);size_t GetTarSize();~TarFile();
private:FILE* file;size_t size;std::vector<std::string> file_names;std::vector<size_t> file_sizes;std::vector<size_t> file_data_start_addrs;
};int test_tar();#endif // FBC_MESSY_TEST_TAR_HPP_

tar.cpp：

#include "tar.hpp"TarFile::TarFile(const char* tar_name): file(nullptr), size(0)
{file_names.clear();file_sizes.clear();file_data_start_addrs.clear();file = fopen(tar_name, "rb");
}TarFile::~TarFile()
{if (file) {fclose(file);file = nullptr;}file_names.clear();file_sizes.clear();file_data_start_addrs.clear();
}bool TarFile::IsValidTarFile()
{if (!file) return false;const int block_size{ 512 };unsigned char buf[block_size];tar_posix_header* header = (tar_posix_header*)buf;memset(buf, 0, block_size);fseek(file, 0, SEEK_END);size = ftell(file);fseek(file, 0, SEEK_SET);if (size % block_size != 0) {fprintf(stderr, "tar file size should be a multiple of 512 bytes: %d\n", size);return false;}size_t pos{ 0 };while (1) {size_t read_size = fread(buf, block_size, 1, file);if (read_size != 1) break;if (strncmp(header->magic, TMAGIC, 5)) break;pos += block_size;size_t file_size{0};sscanf(header->size, "%lo", &file_size);size_t file_block_count = (file_size + block_size - 1) / block_size;switch (header->typeflag) {case '0': // intentionally dropping throughcase '\0':// normal filefile_sizes.push_back(file_size);file_names.push_back(std::string(header->name));file_data_start_addrs.push_back(pos);break;case '1':// hard linkbreak;case '2':// symbolic linkbreak;case '3':// device file/special filebreak;case '4':// block devicebreak;case '5':// directorybreak;case '6':// named pipebreak;default:break;}pos += file_block_count * block_size;fseek(file, pos, SEEK_SET);}fseek(file, 0, SEEK_SET);return true;
}std::vector<std::string> TarFile::GetFileNames()
{return file_names;
}bool TarFile::GetFileContents(const char* file_name, char* contents)
{bool flag = false;for (int i = 0; i < file_names.size(); i++) {std::string name_(file_name);if (file_names[i].compare(name_) == 0) {int file_size = file_sizes[i];flag = true;fseek(file, file_data_start_addrs[i], SEEK_SET);fread(contents, file_size, 1, file);fseek(file, 0, SEEK_SET);break;}}return flag;
}size_t TarFile::GetFileSize(const char* file_name)
{size_t file_size{0};for (int i = 0; i < file_names.size(); i++) {std::string name_(file_name);if (file_names[i].compare(name_) == 0) {file_size = file_sizes[i];break;}}return file_size;
}size_t TarFile::GetTarSize()
{return size;
}//
int test_tar()
{const std::string tar_file_path{ "E:/GitCode/Messy_Test/testdata/test.tar" };TarFile tarfile(tar_file_path.c_str());bool is_valid_tar_file = tarfile.IsValidTarFile();if (!is_valid_tar_file) {fprintf(stderr, "it is not a valid tar file: %s\n", tar_file_path.c_str());return -1;}fprintf(stderr, "tar file size: %d byte\n", tarfile.GetTarSize());std::vector<std::string> file_names = tarfile.GetFileNames();fprintf(stderr, "tar file count: %d\n", file_names.size());for (auto name : file_names) {fprintf(stderr, "=====================================\n");size_t file_size = tarfile.GetFileSize(name.c_str());fprintf(stderr, "file name: %s,  size: %d byte\n", name.c_str(), file_size);char* contents = new char[file_size + 1];tarfile.GetFileContents(name.c_str(), contents);contents[file_size] = '\0';fprintf(stderr, "contents:\n%s\n", contents);delete[] contents;}return 0;
}

测试结果如下：

GitHub：https://github.com/fengbingchun/Messy_Test