[搜片神器]直接從DHT網絡下載BT種子的方法

        /* This is how you trigger a search for a torrent hash.  If port (the second argument) is non-zero, it also performs an announce.
           Since peers expire announced data after 30 minutes, it's a good idea to reannounce every 28 minutes or so. */
        if(searching) {
            //m_dht.dht_random_bytes((void*)hashList[2],20);
            if(m_soListen >= 0)
                m_dht.dht_search(hashList[2], 0, AF_INET, DHT_callback, this);
            if(s6 >= 0)
                m_dht.dht_search(hashList[2], 0, AF_INET6, DHT_callback, this);
            searching = 0;
        }

搜索到對方返回的IP信息和端口號後,你們能夠分析dht.c裏面的函數代碼dht_periodic(const void *buf, size_t buflen,const struct sockaddr *fromAddr, int fromlen,time_t *tosleep,dht_callback *callback, void *closure)函數裏面的ANNOUNCE_PEER返回請求裏面帶有對方代表本身此BT種子對應的認證碼peerid.

dht_periodic(const void *buf, size_t buflen,const struct sockaddr *fromAddr, int fromlen,time_t *tosleep,dht_callback *callback, void *closure)
函數裏面的ANNOUNCE_PEER

        case ANNOUNCE_PEER:
            _dout("Announce peer!From IP:%s:%d\n",inet_ntoa(tempip->sin_addr),tempip->sin_port);
            new_node(id, fromAddr, fromlen, 1);

            if(id_cmp(info_hash, zeroes) == 0) 
            {
                _dout("Announce_peer with no info_hash.\n");
                send_error(fromAddr, fromlen, tid, tid_len,203, "Announce_peer with no info_hash");
                break;
            }
            if(!token_match(token, token_len, fromAddr)) {
                _dout("Incorrect token for announce_peer.\n");
                send_error(fromAddr, fromlen, tid, tid_len,203, "Announce_peer with wrong token");
                break;
            }
            if(port == 0) {
                _dout("Announce_peer with forbidden port %d.\n", port);
                send_error(fromAddr, fromlen, tid, tid_len,203, "Announce_peer with forbidden port number");
                break;
            }
            if(callback) 
            {
                (*callback)(closure, DHT_EVENT_ANNOUNCE_PEER_VALUES, info_hash,(void *)fromAddr, port,id);//此ID就是peerid,
            }

知道了對應的IP,端口號,還有種子ID號,就能夠向對方發送請求了.

獲取HASH是經過UDP網絡,但下載BT種子是經過TCP來處理,至關於別人是TCP服務器,咱們鏈接過去,直接下載對應PEERID的種子就好了.

BT種子在DHT網絡下載流程

先看http://www.bittorrent.org/beps/bep_0010.html協議介紹,咱們必須先握手

handshake message

此包構造比較簡單,按照格式進行組裝就好了,而後發送出去,對方就會迴應本身是什麼客戶端的軟件提供種子下載.

void CH31BTMgr::Encode_handshake()
{
	//a byte with value 19 (the length of the string that follows);
	//the UTF-8 string "BitTorrent protocol" (which is the same as in ASCII);
	//eight reserved bytes used to mark extensions;
	//the 20 bytes of the torrent info hash;
	//the 20 bytes of the peer ID.
	char btname[256];
	memset(btname,0,sizeof(btname));
	sprintf(btname,"BitTorrent protocol");
	char msg[1280];
	memset(msg,0,sizeof(msg));
	msg[0]=19;
	memcpy(&msg[1],btname,19);
	char ext[8];
	memset(ext,0,sizeof(ext));
	ext[5]=0x10;

	memcpy(&msg[20],ext,8);
	memcpy(&msg[28],m_hash,20);
	memcpy(&msg[48],m_peer_id,20);
	int res1=Write(msg, 68);//TCP發送消息
}

在發送握手後,咱們能夠接着發送種子數據請求包,須要學習http://www.bittorrent.org/beps/bep_0009.html 裏面的內容:　　

extension header
The metadata extension uses the extension protocol (specified in BEP 0010 ) to advertize its existence. It adds the "ut_metadata" entry to the "m" dictionary in the extension header hand-shake message. This identifies the message code used for this message. It also adds "metadata_size" to the handshake message (not the "m" dictionary) specifying an integer value of the number of bytes of the metadata.

Example extension handshake message:

{'m': {'ut_metadata', 3}, 'metadata_size': 31235}
extension message
The extension messages are bencoded. There are 3 different kinds of messages:

0 request 
1 data 
2 reject 
The bencoded messages have a key "msg_type" which value is an integer corresponding to the type of message. They also have a key "piece", which indicates which part of the metadata this message refers to.

In order to support future extensability, an unrecognized message ID MUST be ignored.

這就須要會bencode的相關代碼,這個你們能夠網上搜索進行編譯,若是實現搞不定,能夠留下郵箱我將此類代碼發送給你,其實也是網上收集整理的.

void CH31BTMgr::Encode_Ext_handshake()
{
    entry m;
    m["ut_metadata"] = 0;
    entry e;
    e["m"]=m;

    char msg[200];
    char* header = msg;
    char* p = &msg[6];
    int len = bencode(p, e);
    int total_size = 2 + len;
    namespace io = detail;
    io::write_uint32(total_size, header);
    io::write_uint8(20, header);
    io::write_uint8(0, header);

    int res1=Write(msg, len + 6);
}

若是別人迴應的是2,那就直接退出吧,說明別人拒絕了你.

若是迴應是1,則返回的是數據區,每塊是16K大小,最後一包不是.

data
The data message adds another entry to the dictionary, "total_size". This key has the same semantics as the "metadata_size" in the extension header. This is an integer.

The metadata piece is appended to the bencoded dictionary, it is not a part of the dictionary, but it is a part of the message (the length prefix MUST include it).

If the piece is the last piece of the metadata, it may be less than 16kiB. If it is not the last piece of the metadata, it MUST be 16kiB.

Example:

{'msg_type': 1, 'piece': 0, 'total_size': 3425}
d8:msg_typei1e5:piecei0e10:total_sizei34256eexxxxxxxx...
The x represents binary data (the metadata).

下面給出如何進行提交我須要第幾包的數據代碼:

void CH31BTMgr::write_metadata_packet(int type, int piece)
{
    ASSERT(type >= 0 && type <= 2);
    ASSERT(piece >= 0);

    entry e;
    e["msg_type"] = type;
    e["piece"] = piece;

    char const* metadata = 0;
    int metadata_piece_size = 0;

    if (type == 1)
    {
        e["total_size"] = 14132;
        int offset = piece * 16 * 1024;
        //metadata = m_tp.metadata().begin + offset;
        metadata_piece_size = (std::min)(int(14132 - offset), 16 * 1024);
    }

    char msg[200];
    char* header = msg;
    char* p = &msg[6];
    int len = bencode(p, e);
    int total_size = 2 + len + metadata_piece_size;
    namespace io = detail;
    io::write_uint32(total_size, header);
    io::write_uint8(20, header);
    io::write_uint8(m_message_index, header);

    int res1=Write(msg, len + 6);
}

在接收到一包請求後咱們才能夠繼續下一包的請求,下面給了咱們如何解析這一包的問題代碼:

// 處理一個完整的包數據
bool CH31BTMgr::DeCodeFrameData(char * buffer,int buflen)
{
    char * p = (char *)mhFindstr(buffer, buflen, "ut_metadatai", 12);
    if(p) 
    {
        m_message_index=atoi(&p[12]);
        if(m_message_index==2)
        {
            return false;
        }
        write_metadata_packet(0,0);
        char filename[256];
        memset(filename,0,sizeof(filename));
        sprintf(filename,"%s\\torrent.txt",m_workPath);
        DelFile(filename);
    } 

    p = (char *)mhFindstr(buffer, buflen, "metadata_sizei", 14);
    if(p) 
    {
        m_metadata_size=atoi(&p[14]);
        m_fileCnt=(int)(m_metadata_size/16384)+1;
    } 

    p = (char *)mhFindstr(buffer, buflen, "msg_typei", 9);
    if(p) 
    {
        int type1=atoi(&p[9]);
        if(type1==1)
        {
            p = (char *)mhFindstr(buffer, buflen, "piecei", 6);
            if(p) 
            {
                int piece=atoi(&p[6]);
                p = (char *)mhFindstr(buffer, buflen, "total_sizei", 11);
                if(p) 
                {
                    int total_size=atoi(&p[11]);
                    p = (char *)mhFindstr(buffer, buflen, "ee", 2);
                    if(p) 
                    {
                        //保存數據
                        FILE* pfile=NULL;
                        char filename[256];

                        memset(filename,0,sizeof(filename));
                        sprintf(filename,"%s\\torrent.txt",m_workPath);
                        char openmethod[5]="a";
                        if(piece==0)
                            sprintf(openmethod,"w");
                        if((pfile=fopen(filename,openmethod))!=NULL)
                        {
                            if((piece+1)*16*1024<total_size)
                            {
                                fseek(pfile,(piece)*16*1024,SEEK_SET);
                                fwrite(&p[2],1,16*1024,pfile);
                                write_metadata_packet(0,piece+1);
                                fclose(pfile);
                            }
                            else
                            {
                                fwrite(&p[2],1,total_size-(piece)*16*1024,pfile);
                                fclose(pfile);
                                ManageTorrentFileToRealFile(filename);
                            }
                        }
                    }
                }
            }
        }
        else if(type1==2)
        {
            return false;
        }
    } 
    
    return true;
}

void * mhFindstr(const void *haystack, size_t haystacklen,const void *needle, size_t needlelen)
{
const char *h =(const char *) haystack;
const char *n =(const char *) needle;
size_t i;

/* size_t is unsigned */
if(needlelen > haystacklen)
return NULL;

for(i = 0; i <= haystacklen - needlelen; i++) {
if(memcmp(h + i, n, needlelen) == 0)
return (void*)(h + i);
}
return NULL;
}