BitTorrent种子文件的解析+（1）

原文：http://hi.baidu.com/i_miss_you_all/blog/item/c87a5e8a3125e5dafd1f10a3.html

LINUX C 编程实战 童永清 （著）

chapter 13 BT 下载软件的开发

//parse_metafile.c

#include <stdio.h>

#include <stdlib.h>

#include <ctype.h>

#include <malloc.h>

#include <string.h>

#include <time.h>

#include "parse_metafile.h"

#include "sha1.h"

char metafile[] = "/home/dtdlut/linux_c_language/chapter13/bittorrent/test.torrent";

char *metafile_content = NULL; //保存种子文件的内容

int filesize; //种子文件的长度

int piece_length =0; //每个piece的长度，通常为256KB 即262144字节

char *pieces = NULL; //保存每个pieces的哈希值，每个哈希值为20字节

int pieces_length =0; //缓冲区pieces的长度

int multi_file =0; //指明是单文件还是多文件

char *file_name =NULL; //对于单文件，存放文件名；对于多文件，存放目录名

long long file_length =0; //存放待下载文件的总长度

Files *files_head = NULL; //只对多文件种子有效，存放各个文件的路径和长度

unsigned char info_hash[20]; //保存info_hash值，连接tracker和peer时使用

unsigned char peer_id[20] ; //保存peer_id的值，连接peer时使用

Announce_list *announce_list_head = NULL;

#define DEBUG

//功能：解析种子文件

//参数：metafile_name是种子文件名

//返回：处理成功返回0，否则返回－1

//附注：将种子文件的内容读到全局变量metafile_content所指向的缓冲区中以方便处理。实现代码为：

int read_metafile(char *metafile_name)

{

long i;

//以2进制、只读的方式打开文件

FILE *fp = fopen(metafile_name, "rb");

if(fp == NULL)

{

printf("%s:%d can not open file\n", __FILE__, __LINE__);

return -1;

}

//获取种子文件的长度，filesize为全局变量，在parse_metafile.c头部定义

fseek(fp, 0, SEEK_END);

filesize = ftell(fp);

if(filesize == -1)

{

printf("%s:%d fseek failed \n", __FILE__, __LINE__);

return -1;

}

metafile_content = (char *)malloc(filesize+1);

if(metafile_content == NULL)

{

printf("%s:%d malloc failed\n", __FILE__, __LINE__);

return -1;

}

fseek(fp, 0, SEEK_SET);

for(i=0; i<filesize; i++)

metafile_content[i] = fgetc(fp);

fclose(fp);

#ifdef DEBUG

printf("metafile size is: %d\n", filesize);

#endif

return 0;

}

//功能：从种子文件中查找某个关键字

//参数：keyword为要查找的关键字，position用于返回关键字第一个字符所在的下标

//返回：成功执行并找到关键字返回1， 未找到返回0， 执行失败返回－1

int find_keyword(char *keyword, long *position)

{

long i;

*position = -1;

if(keyword == NULL)

{

return 0;

}

for(i=0; i<filesize-strlen(keyword); i++)

{

if(memcmp(&metafile_content[i], keyword, strlen(keyword)) == 0)

{

*position = i;

return 1;

}

}

return 0;

}

//功能:获取Tracker地址，并将获取的地址保存到全局变量announce_list_head指向的链表中

int read_announce_list()

{

Announce_list *node = NULL;

Announce_list *p = NULL;

int len = 0;

long i;

if( find_keyword("13:announce-list", &i) == 0)

{

if( find_keyword("8:announce", &i) == 1)

{

i = i+ strlen("8:announce");

while( isdigit(metafile_content[i]) )

{

len = len *10 +(metafile_content[i] - '0');

i++;

}

i++; //跳过 ';'

node = (Announce_list *) malloc(sizeof(Announce_list));

strncpy(node->announce, &metafile_content[i], len);

node->announce[len] = '\0';

node->next = NULL;

announce_list_head = node;

}

}

else

{

//如果有13:announce-list关键词就不用处理8:announce关键词

i = i+ strlen("13:announce-list");

i++; //跳过'l'

while(metafile_content[i] != 'e')

{

i++; //跳过'l'

while( isdigit(metafile_content[i]))

{

len = len * 10 +(metafile_content[i] - '0');

i++;

}

if(metafile_content[i] == ':')

i++;

else

return -1;

//只处理以http开头的tracker地址，不处理以udp开头的地址

if(memcmp(&metafile_content[i], "http", 4) == 0)

{

node = (Announce_list*)malloc(sizeof(Announce_list));

strncpy(node->announce, &metafile_content[i], len);

node->announce[len] = '\0';

node->next = NULL;

if(announce_list_head == NULL)

announce_list_head = node;

else

{

p = announce_list_head;

while(p->next != NULL)

p = p->next; //使p指针指向最后那个结点

p->next = node; //node成为tracker列表的最后一个结点

}

}

i = i +len;

len = 0;

i++; //跳过'e'

if( i >= filesize)

return -1;

}//while循环结束

}

#ifdef DEBUG

p = announce_list_head;

// printf("ANNOUNCEANNOUNCEANNOUNCEANNOUNCEANNOUNCEANNOUNCEANNOUNCE\n");

while(p != NULL)

{

printf("%s\n", p->announce);

p = p->next;

}

//printf("ANNOUNCEANNOUNCEANNOUNCEANNOUNCEANNOUNCEANNOUNCEANNOUNCE\n");

#endif

return 0;

}

//功能:连接某些tracker时会返回一个重定向的URL, 需要连接该URL才能获取Peer

int add_an_annouce(char *url)

{

Announce_list *p = announce_list_head, *q;

//若参数指定的URL在Tracker列表中已经存在，则无需添加

while(p != NULL)

{

if(strcmp(p->announce, url) == 0)

break;

p = p->next;

}

if( p != NULL)

return 0;

q = (Announce_list*)malloc(sizeof(Announce_list));

strcpy(q->announce, url);

q->next = NULL;

p = announce_list_head;

if(p = NULL)

{

announce_list_head = q;

return 1;

}

while( p->next != NULL)

p = p->next;

p->next = q;

return 1;

}

//功能:判断是下载多个文件还是单文件，若含有关键字"5:files"则说明下载的是

//多个文件

int is_multi_files()

{

long i;

if((find_keyword("5:files", &i) )== 1)

{

multi_file = 1;

return 1;

}

#ifdef DEBUG

// printf("IS_MULTI_FILESIS_MULTI_FILESIS_MULTI_FILESIS_MULTI_FILESIS_MULTI_FILES\n");

printf("is_multi_files: %d\n", multi_file);

// printf("IS_MULTI_FILESIS_MULTI_FILESIS_MULTI_FILESIS_MULTI_FILESIS_MULTI_FILES\n");

#endif

return 0;

}

//功能:获取piece的长度

int get_piece_length()

{

long i;

if(find_keyword("12:piece length", &i) == 1)

{

i = i+ strlen("12:piece length"); //跳过"12:piece length"

i++; //跳过'i'

while(metafile_content[i] != 'e')

{

piece_length = piece_length * 10 +(metafile_content[i]-'0');

i++;

}

}

else

return -1;

#ifdef DEBUG

//printf("PIECE_LENGTHPIECE_LENGTHPIECE_LENGTHPIECE_LENGTHPIECE_LENGTHPIECE_LENGTH\n");

printf("piece length: %d\n", piece_length);

//printf("PIECE_LENGTHPIECE_LENGTHPIECE_LENGTHPIECE_LENGTHPIECE_LENGTHPIECE_LENGTH\n");

#endif

return 0;

}

//功能:获取每个piece的hash值， 并保存到pieces所指向的缓冲区中

int get_pieces()

{

long i;

if( find_keyword("6:pieces", &i) == 1)

{

i = i + strlen("6:pieces"); //跳过"6:pieces"

while(metafile_content[i] != ':')

{

pieces_length = pieces_length * 10 + (metafile_content[i] - '0');

i++;

}

i++; //跳过':'

pieces = (char*) malloc(pieces_length + 1);

memcpy(pieces, &metafile_content[i], pieces_length);

pieces[piece_length] = '\0';

}

else

return -1;

#ifdef DEBUG

//printf("GET_PIECESGET_PIECESGET_PIECESGET_PIECESGET_PIECESGET_PIECESGET_PIECESGET_PIECES\n");

printf("get_pieces ok\n");

//printf("GET_PIECESGET_PIECESGET_PIECESGET_PIECESGET_PIECESGET_PIECESGET_PIECESGET_PIECES\n");

#endif

return 0;

}

int get_file_name()

{

long i;

int count = 0;

if(find_keyword("4:name", &i) == 1)

{

i = i+6;

while(metafile_content[i] != ':')

{

count = count * 10 + (metafile_content[i] - '0');

i++;

}

i++;

file_name = (char *) malloc( count +1);

memcpy(file_name, &metafile_content[i], count);

file_name[count] = '\0';

}

else

{

return -1;

}

#ifdef DEBUG

// printf("\n COUNT is %ld\n", count);

// printf("FILE_NAMEFILE_NAMEFILE_NAMEFILE_NAMEFILE_NAMEFILE_NAMEFILE_NAME\n");

printf("file_name:%s\n", file_name);

// printf("FILE_NAMEFILE_NAMEFILE_NAMEFILE_NAMEFILE_NAMEFILE_NAMEFILE_NAME\n");

#endif

return 0;

}

//功能: 获取待下载文件的长度

int get_file_length()

{

long i;

if(is_multi_files() ==1 )

{

if(files_head == NULL)

{

// printf("files_head is null\n");

get_files_length_path();

}

Files *p = files_head;

while(p != NULL)

{

file_length += p->length;

p = p->next;

}

}

else

{

// printf("is not multi files\n");

if( find_keyword("6:length", &i) == 1)

{

i = i+ strlen("6:length"); //跳过"6:length"

i++; //跳过'i'

while(metafile_content[i] != 'e')

{

file_length = file_length* 10 + (metafile_content[i] - '0');

i++;

}

}

}

#ifdef DEBUG

// printf("FILE_LENGTHFILE_LENGTHFILE_LENGTHFILE_LENGTHFILE_LENGTHFILE_LENGTHFILE_LENGTH\n");

printf("file_length: %lld\n", file_length);

// printf("FILE_LENGTHFILE_LENGTHFILE_LENGTHFILE_LENGTHFILE_LENGTHFILE_LENGTHFILE_LENGTH\n");

#endif

return 0;

}

//功能：对于多个文件，获取各个文件的路径以及长度

int get_files_length_path()

{

long i;

unsigned long length;

int count;

Files *node = NULL;

Files *p = NULL;

if(is_multi_files() != 1)

{

// printf("NOT FILES\n");

return 0;

}

int num = 0;

for(i=0; i<filesize - 8 ; i++)

{

if(memcmp(&metafile_content[i], "6:length", 8) == 0)

{

i= i+8; //跳过"6:length"

i++; //跳过'i'

length = 0;

num++;

while(metafile_content[i] != 'e')

{

length = length * 10 +(metafile_content[i]-'0');

i++;

}

// printf("length is %ld and num is %d\n", length, num);

node = (Files*) malloc(sizeof(Files));

node->length = length;

node->next = NULL;

if(files_head == NULL)

files_head =node;

else

{

p = files_head;

while(p->next)

p = p->next;

p->next = node;

}

}

if(memcmp(&metafile_content[i], "4:path",6) == 0)

{

i = i+6; //跳过"4:path"

i++; //跳过'l',由于是多文件肯定有多个文件路径

count = 0;

while(metafile_content[i] != ':')

{

count = count * 10 + (metafile_content[i] - '0');

i++;

}

i++; //跳过':'

p = files_head;

while( p ->next != NULL)

p = p->next;

memcpy(p->path, &metafile_content[i], count);

*(p->path + count) = '\0';

// printf("path is %s\n ", p->path);

}

}

//printf("get file length path\n");

return 0;

}

//功能:计算info_hash的值

int get_info_hash()

{

int push_pop = 0;

long i, begin, end;

if(metafile_content == NULL)

return -1;

//begin的值表示的是关键字"4:info"对应值的起始下标

if( find_keyword("4:info", &i) == 1)

begin = i+6;

else

return -1;

i = i+6; //跳过"4:info"

for(; i < filesize;)

{

if(metafile_content[i] == 'd')

{

push_pop++;

i++;

}

else if(metafile_content[i] == 'l')

{

push_pop++;

i++;

}

else if(metafile_content[i] == 'i')

{

i++; //跳过'i'

if( i==filesize)

return -1;

while(metafile_content[i] != 'e')

{

if( (i+1) == filesize )

{

printf("here 2\n");

return -1;

}

else

i++; //继续判断下一个字符是否为'e'

}

i++; //跳过'e'

}

else if((metafile_content[i] >= '0') && ( metafile_content[i] <= '9'))

{

int number = 0;

while((metafile_content[i] >= '0') && (metafile_content[i] <= '9'))

{

number = number * 10 + (metafile_content[i] - '0');

i++;

}

i++; //跳过 ':'

i = i+ number; //跳过number个字符

}

else if( metafile_content[i] == 'e')

{

push_pop--;

if(push_pop == 0)

{

end = i;

break;

}

else

i++;

}

else return -1;

}

if( i == filesize)

return -1;

SHA1_CTX context;

SHA1Init(&context);

SHA1Update(&context, &metafile_content[begin], end-begin+1);

SHA1Final(info_hash, &context);

#ifdef DEBUG

printf("info_hash:");

for(i=0; i<20;i++)

printf("%.2x ", info_hash[i]);

printf("\n");

#endif

return 0;

}

//功能:生成一个唯一的peer id

//

int get_peer_id()

{

//设置产生随机数的种子

srand(time(NULL));

//使用rand函数生成一个随机数，并使用该随机数来构造peer_id

//peer_id前8位固定为-TT1000-

sprintf(peer_id, "-TT1000-%12d", rand());

#ifdef DEBUG

printf("peer_id %s\n", peer_id);

#endif

return 0;

}

//功能:释放动态申请的内存

void release_memory_in_parse_metafile()

{

Announce_list *p;

Files *q;

if(metafile_content != NULL)

free(metafile_content);

if(file_name != NULL)

free(file_name);

if(pieces != NULL)

free(pieces);

while(announce_list_head != NULL)

{

p = announce_list_head;

announce_list_head = announce_list_head->next;

free(p);

}

while( files_head != NULL)

{

q = files_head;

files_head = files_head->next;

free(q);

}

}

//功能:调用parse_metafile.c 中定义的函数，完成解析种子文件。该函数由main调用

//返回:解析成功返回0，否则返回－1

int main()

{

int ret;

//读取种子文件

ret = read_metafile(metafile);

if(ret < 0)

{

printf("%s:%d wrong", __FILE__, __LINE__);

return -1;

}

//从种子文件中读取tracker服务器的地址

ret = read_announce_list();

if(ret < 0)

{

printf("%s:%d wrong", __FILE__, __LINE__);

return -1;

}

//判断是否为多文件

ret = is_multi_files();

if(ret < 0)

{

printf("%s:%d wrong", __FILE__, __LINE__);

return -1;

}

//获取每个piece的长度，一般为256KB

ret = get_piece_length();

if(ret < 0)

{

printf("%s:%d wrong", __FILE__, __LINE__);

return -1;

}

//读取每个piece的哈希值

ret = get_pieces();

if(ret < 0)

{

printf("%s:%d wrong", __FILE__, __LINE__);

return -1;

}

//获取要下载的文件名，对于多文件的种子，获取的是目录名

ret = get_file_name();

if(ret < 0)

{

printf("%s:%d wrong", __FILE__, __LINE__);

return -1;

}

//对于多文件的种子，获取各个待下载的文件路径和文件长度

ret = get_files_length_path();

if(ret < 0)

{

printf("%s:%d wrong", __FILE__, __LINE__);

return -1;

}

//获取待下载文件的总长度

ret = get_file_length();

if(ret < 0)

{

printf("%s:%d wrong\n", __FILE__, __LINE__);

return -1;

}

//获得info_hash，生成peer_id

ret = get_info_hash();

if(ret < 0)

{

printf("%s:%d wrong", __FILE__, __LINE__);

return -1;

}

ret = get_peer_id();

if(ret < 0)

{

printf("%s:%d wrong", __FILE__, __LINE__);

return -1;

}

return 0;

}

//parse_metafile.h

//parse_metafile.h

#ifndef PARSE_METAFILE

#define PARSE_METAFILE

//保存从种子文件中获得的tracker的URL

typedef struct _Announce_list

{

char announce[128];

struct _Announce_list *next;

}Announce_list;

//保存各个待下载文件的路径和长度

typedef struct _Files

{

char path[256];

long length;

struct _Files *next;

}Files;

int read_metafile(char *metafile_name); //读取种子文件

int find_keyword (char *keyword, long *position); //在种子文件中查找某个关键词

int read_announce_list(); //获取各个tracker服务器的地址

int add_an_announce(char *url); //向tracker列表添加一个URL

int get_piece_length(); //获取每个piece的长度，一般为256KB

int get_pieces(); //获取各个piece的哈希值

int is_multi_files(); //判断下载的是单个文件还是多个文件

int get_file_name(); //获取文件名，对于多文件，获取的是目录名

int get_file_length(); //获取下载文件的总长度

int get_files_length_path(); //获取文件的路径和长度，对多文件种子有效

int get_info_hash(); //由info关键词对应的值计算info_hash

int get_peer_id(); //生成peer_id,每个peer都有一个20字节的peer_id

void release_memory_in_parse_metafile(); //释放parse_metafile.c中动态分配的内存

int parse_metafile(char *metafile); //调用本文件中定义的函数，完成解析种子文件

#endif