[搜片神器]直接从DHT网络下载BT种子的方法

        /* 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;
        }

dht_periodic(const void *buf, size_t buflen,const struct sockaddr *fromAddr, int fromlen,time_t *tosleep,dht_callback *callback, void *closure)
函数里面的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,
            }

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:

1 request 
2 data 
3 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.

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);
}

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).

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);
}

// 处理一个完整的包数据
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) 
                    {
                        //保存数据
                        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;
}