linux C 解析.torrent

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