RTMPdump 源代码分析 6： 建立一个流媒体连接 （NetStream部分 1）
前文已经分析了 RTMPdump中建立一个NetConnection的过程：RTMPdump 源代码分析 5： 建立一个流媒体连接 （NetConnection部分）
多余的话不多说，下面先来看看RTMP_ConnectStream()，该函数主要用于在NetConnection基础上建立一个NetStream。
RTMP_ConnectStream()
//读取收下来的ChunkintRTMP_ReadPacket(RTMP *r, RTMPPacket *packet){//packet 存读取完后的的数据//Chunk Header最大值18 uint8_t hbuf[RTMP_MAX_HEADER_SIZE] = { 0 };//header 指向的是从Socket中收下来的数据 char *header = (char *)hbuf; int nSize, hSize, nToRead, nChunk; int didAlloc = FALSE; RTMP_Log(RTMP_LOGDEBUG2, "%s: fd=%d", __FUNCTION__, r->m_sb.sb_socket); //收下来的数据存入hbuf if (ReadN(r, (char *)hbuf, 1) == 0) { RTMP_Log(RTMP_LOGERROR, "%s, failed to read RTMP packet header", __FUNCTION__); return FALSE; } //块类型fmt packet->m_headerType = (hbuf[0] & 0xc0) >> 6; //块流ID（2-63） packet->m_nChannel = (hbuf[0] & 0x3f); header++; //块流ID第1字节为0时，块流ID占2个字节 if (packet->m_nChannel == 0) { if (ReadN(r, (char *)&hbuf[1], 1) != 1){ RTMP_Log(RTMP_LOGERROR, "%s, failed to read RTMP packet header 2nd byte", __FUNCTION__); return FALSE;} //计算块流ID（64-319） packet->m_nChannel = hbuf[1]; packet->m_nChannel += 64; header++; } //块流ID第1字节为0时，块流ID占3个字节 else if (packet->m_nChannel == 1) { int tmp; if (ReadN(r, (char *)&hbuf[1], 2) != 2){ RTMP_Log(RTMP_LOGERROR, "%s, failed to read RTMP packet header 3nd byte", __FUNCTION__); return FALSE;} tmp = (hbuf[2] << 8) + hbuf[1]; //计算块流ID（64-65599） packet->m_nChannel = tmp + 64; RTMP_Log(RTMP_LOGDEBUG, "%s, m_nChannel: %0x", __FUNCTION__, packet->m_nChannel); header += 2; } //ChunkHeader的大小（4种） nSize = packetSize[packet->m_headerType]; if (nSize == RTMP_LARGE_HEADER_SIZE)/* if we get a full header the timestamp is absolute */ packet->m_hasAbsTimestamp = TRUE;//11字节的完整ChunkMsgHeader的TimeStamp是绝对值 else if (nSize < RTMP_LARGE_HEADER_SIZE) {/* using values from the last message of this channel */ if (r->m_vecChannelsIn[packet->m_nChannel])memcpy(packet, r->m_vecChannelsIn[packet->m_nChannel], sizeof(RTMPPacket)); } nSize--; if (nSize > 0 && ReadN(r, header, nSize) != nSize) { RTMP_Log(RTMP_LOGERROR, "%s, failed to read RTMP packet header. type: %x", __FUNCTION__, (unsigned int)hbuf[0]); return FALSE; } hSize = nSize + (header - (char *)hbuf); if (nSize >= 3) {//TimeStamp(注意 BigEndian to SmallEndian)(11，7，3字节首部都有) packet->m_nTimeStamp = AMF_DecodeInt24(header); /*RTMP_Log(RTMP_LOGDEBUG, "%s, reading RTMP packet chunk on channel %x, headersz %i, timestamp %i, abs timestamp %i", __FUNCTION__, packet.m_nChannel, nSize, packet.m_nTimeStamp, packet.m_hasAbsTimestamp); *///消息长度(11，7字节首部都有) if (nSize >= 6){ packet->m_nBodySize = AMF_DecodeInt24(header + 3); packet->m_nBytesRead = 0; RTMPPacket_Free(packet);//(11，7字节首部都有) if (nSize > 6) { //Msg type ID packet->m_packetType = header[6]; //Msg Stream ID if (nSize == 11)packet->m_nInfoField2 = DecodeInt32LE(header + 7); }} //Extend TimeStamp if (packet->m_nTimeStamp == 0xffffff){ if (ReadN(r, header + nSize, 4) != 4) { RTMP_Log(RTMP_LOGERROR, "%s, failed to read extended timestamp", __FUNCTION__); return FALSE; } packet->m_nTimeStamp = AMF_DecodeInt32(header + nSize); hSize += 4;} } RTMP_LogHexString(RTMP_LOGDEBUG2, (uint8_t *)hbuf, hSize); if (packet->m_nBodySize > 0 && packet->m_body == NULL) { if (!RTMPPacket_Alloc(packet, packet->m_nBodySize)){ RTMP_Log(RTMP_LOGDEBUG, "%s, failed to allocate packet", __FUNCTION__); return FALSE;} didAlloc = TRUE; packet->m_headerType = (hbuf[0] & 0xc0) >> 6; } nToRead = packet->m_nBodySize - packet->m_nBytesRead; nChunk = r->m_inChunkSize; if (nToRead < nChunk) nChunk = nToRead; /* Does the caller want the raw chunk? */ if (packet->m_chunk) { packet->m_chunk->c_headerSize = hSize; memcpy(packet->m_chunk->c_header, hbuf, hSize); packet->m_chunk->c_chunk = packet->m_body + packet->m_nBytesRead; packet->m_chunk->c_chunkSize = nChunk; } if (ReadN(r, packet->m_body + packet->m_nBytesRead, nChunk) != nChunk) { RTMP_Log(RTMP_LOGERROR, "%s, failed to read RTMP packet body. len: %lu", __FUNCTION__, packet->m_nBodySize); return FALSE; } RTMP_LogHexString(RTMP_LOGDEBUG2, (uint8_t *)packet->m_body + packet->m_nBytesRead, nChunk); packet->m_nBytesRead += nChunk; /* keep the packet as ref for other packets on this channel */ if (!r->m_vecChannelsIn[packet->m_nChannel]) r->m_vecChannelsIn[packet->m_nChannel] = (RTMPPacket *) malloc(sizeof(RTMPPacket)); memcpy(r->m_vecChannelsIn[packet->m_nChannel], packet, sizeof(RTMPPacket)); //读取完毕 if (RTMPPacket_IsReady(packet)) { /* make packet's timestamp absolute */ if (!packet->m_hasAbsTimestamp)packet->m_nTimeStamp += r->m_channelTimestamp[packet->m_nChannel];/* timestamps seem to be always relative!! */ r->m_channelTimestamp[packet->m_nChannel] = packet->m_nTimeStamp; /* reset the data from the stored packet. we keep the header since we may use it later if a new packet for this channel */ /* arrives and requests to re-use some info (small packet header) */ r->m_vecChannelsIn[packet->m_nChannel]->m_body = NULL; r->m_vecChannelsIn[packet->m_nChannel]->m_nBytesRead = 0; r->m_vecChannelsIn[packet->m_nChannel]->m_hasAbsTimestamp = FALSE;/* can only be false if we reuse header */ } else { packet->m_body = NULL;/* so it won't be erased on free */ } return TRUE;}这里解析的就是块（Chunk）
可参考：RTMP规范简单分析
具体的解析代码我就不多说了，直接参考RTMP协议规范就可以了，一个字节一个字节的解析就OK了。