RTMPdump（libRTMP） 源代码分析 10： 处理各种消息（Message）

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RTMPdump(libRTMP) 源代码分析系列文章：

RTMPdump 源代码分析 1： main()函数

RTMPDump (libRTMP) 源代码分析2：解析RTMP地址——RTMP_ParseURL()

RTMPdump (libRTMP) 源代码分析3： AMF编码

RTMPdump (libRTMP) 源代码分析4： 连接第一步——握手 (HandShake)

RTMPdump (libRTMP) 源代码分析5： 建立一个流媒体连接  (NetConnection部分)

RTMPdump (libRTMP) 源代码分析6： 建立一个流媒体连接  (NetStream部分 1)

RTMPdump (libRTMP) 源代码分析7： 建立一个流媒体连接  (NetStream部分 2)

RTMPdump (libRTMP) 源代码分析8： 发送消息 (Message)

RTMPdump (libRTMP) 源代码分析9： 接收消息 (Message)  (接收视音频数据)

RTMPdump (libRTMP) 源代码分析10： 处理各种消息 (Message)

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函数调用结构图

RTMPDump (libRTMP)的整体的函数调用结构图如下图所示。

单击查看大图

详细分析

已经连续写了一系列的博客了，其实大部分内容都是去年搞RTMP研究的时候积累的经验，回顾一下过去的知识，其实RTMPdump（libRTMP）主要的功能也都分析的差不多了，现在感觉还需要一些查漏补缺。主要就是它是如何处理各种消息（Message）的这方面还没有研究的特明白，在此需要详细研究一下。

再来看一下RTMPdump（libRTMP）的“灵魂”函数RTMP_ClientPacket()，主要完成了各种消息的处理。

//处理接收到的数据
int
RTMP_ClientPacket(RTMP *r, RTMPPacket *packet)
{
  int bHasMediaPacket = 0;
  switch (packet->m_packetType)
    {
	//RTMP消息类型ID=1,设置块大小
    case 0x01:
      /* chunk size */
		//----------------
		r->dlg->AppendCInfo("处理收到的数据。消息 Set Chunk Size (typeID=1)。");
		//-----------------------------
		RTMP_LogPrintf("处理消息 Set Chunk Size (typeID=1)\n");
      HandleChangeChunkSize(r, packet);
      break;
	//RTMP消息类型ID=3，致谢
    case 0x03:
      /* bytes read report */
      RTMP_Log(RTMP_LOGDEBUG, "%s, received: bytes read report", __FUNCTION__);
      break;
	//RTMP消息类型ID=4，用户控制
    case 0x04:
      /* ctrl */
		//----------------
		r->dlg->AppendCInfo("处理收到的数据。消息 User Control (typeID=4)。");
		//-----------------------------
		RTMP_LogPrintf("处理消息 User Control (typeID=4)\n");
      HandleCtrl(r, packet);
      break;
	//RTMP消息类型ID=5
    case 0x05:
      /* server bw */
		//----------------
		r->dlg->AppendCInfo("处理收到的数据。消息 Window Acknowledgement Size (typeID=5)。");
		//-----------------------------
		RTMP_LogPrintf("处理消息 Window Acknowledgement Size (typeID=5)\n");
      HandleServerBW(r, packet);
      break;
	//RTMP消息类型ID=6
    case 0x06:
      /* client bw */
		//----------------
		r->dlg->AppendCInfo("处理收到的数据。消息 Set Peer Bandwidth (typeID=6)。");
		//-----------------------------
		RTMP_LogPrintf("处理消息 Set Peer Bandwidth (typeID=6)\n");
      HandleClientBW(r, packet);
      break;
	//RTMP消息类型ID=8，音频数据
    case 0x08:
      /* audio data */
      /*RTMP_Log(RTMP_LOGDEBUG, "%s, received: audio %lu bytes", __FUNCTION__, packet.m_nBodySize); */
      HandleAudio(r, packet);
      bHasMediaPacket = 1;
      if (!r->m_mediaChannel)
	r->m_mediaChannel = packet->m_nChannel;
      if (!r->m_pausing)
	r->m_mediaStamp = packet->m_nTimeStamp;
      break;
	//RTMP消息类型ID=9，视频数据
    case 0x09:
      /* video data */
      /*RTMP_Log(RTMP_LOGDEBUG, "%s, received: video %lu bytes", __FUNCTION__, packet.m_nBodySize); */
      HandleVideo(r, packet);
      bHasMediaPacket = 1;
      if (!r->m_mediaChannel)
	r->m_mediaChannel = packet->m_nChannel;
      if (!r->m_pausing)
	r->m_mediaStamp = packet->m_nTimeStamp;
      break;
	//RTMP消息类型ID=15，AMF3编码，忽略
    case 0x0F:			/* flex stream send */
      RTMP_Log(RTMP_LOGDEBUG,
	  "%s, flex stream send, size %lu bytes, not supported, ignoring",
	  __FUNCTION__, packet->m_nBodySize);
      break;
	//RTMP消息类型ID=16，AMF3编码，忽略
    case 0x10:			/* flex shared object */
      RTMP_Log(RTMP_LOGDEBUG,
	  "%s, flex shared object, size %lu bytes, not supported, ignoring",
	  __FUNCTION__, packet->m_nBodySize);
      break;
	//RTMP消息类型ID=17，AMF3编码，忽略
    case 0x11:			/* flex message */
      {
	RTMP_Log(RTMP_LOGDEBUG,
	    "%s, flex message, size %lu bytes, not fully supported",
	    __FUNCTION__, packet->m_nBodySize);
	/*RTMP_LogHex(packet.m_body, packet.m_nBodySize); */

	/* some DEBUG code */
#if 0
	   RTMP_LIB_AMFObject obj;
	   int nRes = obj.Decode(packet.m_body+1, packet.m_nBodySize-1);
	   if(nRes < 0) {
	   RTMP_Log(RTMP_LOGERROR, "%s, error decoding AMF3 packet", __FUNCTION__);
	   /*return; */
	   }

	   obj.Dump();
#endif

	if (HandleInvoke(r, packet->m_body + 1, packet->m_nBodySize - 1) == 1)
	  bHasMediaPacket = 2;
	break;
      }
	//RTMP消息类型ID=18，AMF0编码，数据消息
    case 0x12:
      /* metadata (notify) */

      RTMP_Log(RTMP_LOGDEBUG, "%s, received: notify %lu bytes", __FUNCTION__,
	  packet->m_nBodySize);
	  //处理元数据,暂时注释
	  /*
      if (HandleMetadata(r, packet->m_body, packet->m_nBodySize))
	bHasMediaPacket = 1;
      break;
	  */
	//RTMP消息类型ID=19，AMF0编码，忽略
    case 0x13:
      RTMP_Log(RTMP_LOGDEBUG, "%s, shared object, not supported, ignoring",
	  __FUNCTION__);
      break;
	//RTMP消息类型ID=20，AMF0编码，命令消息
	//处理命令消息！
    case 0x14:
		//----------------
		r->dlg->AppendCInfo("处理收到的数据。消息 命令 (AMF0编码) (typeID=20)。");
		//-----------------------------
      /* invoke */
      RTMP_Log(RTMP_LOGDEBUG, "%s, received: invoke %lu bytes", __FUNCTION__,
	  packet->m_nBodySize);
	  RTMP_LogPrintf("处理命令消息 (typeID=20，AMF0编码)\n");
      /*RTMP_LogHex(packet.m_body, packet.m_nBodySize); */

      if (HandleInvoke(r, packet->m_body, packet->m_nBodySize) == 1)
	bHasMediaPacket = 2;
      break;
	//RTMP消息类型ID=22
    case 0x16:
      {
	/* go through FLV packets and handle metadata packets */
	unsigned int pos = 0;
	uint32_t nTimeStamp = packet->m_nTimeStamp;

	while (pos + 11 < packet->m_nBodySize)
	  {
	    uint32_t dataSize = AMF_DecodeInt24(packet->m_body + pos + 1);	/* size without header (11) and prevTagSize (4) */

	    if (pos + 11 + dataSize + 4 > packet->m_nBodySize)
	      {
		RTMP_Log(RTMP_LOGWARNING, "Stream corrupt?!");
		break;
	      }
	    if (packet->m_body[pos] == 0x12)
	      {
		HandleMetadata(r, packet->m_body + pos + 11, dataSize);
	      }
	    else if (packet->m_body[pos] == 8 || packet->m_body[pos] == 9)
	      {
		nTimeStamp = AMF_DecodeInt24(packet->m_body + pos + 4);
		nTimeStamp |= (packet->m_body[pos + 7] << 24);
	      }
	    pos += (11 + dataSize + 4);
	  }
	if (!r->m_pausing)
	  r->m_mediaStamp = nTimeStamp;

	/* FLV tag(s) */
	/*RTMP_Log(RTMP_LOGDEBUG, "%s, received: FLV tag(s) %lu bytes", __FUNCTION__, packet.m_nBodySize); */
	bHasMediaPacket = 1;
	break;
      }
    default:
      RTMP_Log(RTMP_LOGDEBUG, "%s, unknown packet type received: 0x%02x", __FUNCTION__,
	  packet->m_packetType);
#ifdef _DEBUG
      RTMP_LogHex(RTMP_LOGDEBUG, (const uint8_t *)packet->m_body, packet->m_nBodySize);
#endif
    }

  return bHasMediaPacket;
}

前文已经分析过当消息类型ID为0x14（20）的时候，即AMF0编码的命令消息的时候，会调用HandleInvoke()进行处理。

参考：RTMPdump（libRTMP） 源代码分析 7： 建立一个流媒体连接 （NetStream部分 2）

这里就不再对这种类型ID的消息进行分析了，分析一下其他类型的消息，毕竟从发起一个RTMP连接到接收视音频数据这个过程中是要处理很多消息的。

参考：RTMP流媒体播放过程

下面我们按照消息ID从小到大的顺序，看看接收到的各种消息都是如何处理的。

消息类型ID是0x01的消息功能是“设置块（Chunk）大小”，处理函数是HandleChangeChunkSize()，可见函数内容很简单。

static void
HandleChangeChunkSize(RTMP *r, const RTMPPacket *packet)
{
  if (packet->m_nBodySize >= 4)
    {
      r->m_inChunkSize = AMF_DecodeInt32(packet->m_body);
      RTMP_Log(RTMP_LOGDEBUG, "%s, received: chunk size change to %d", __FUNCTION__,
	  r->m_inChunkSize);
    }
}

消息类型ID是0x03的消息功能是“致谢”，没有处理函数。

消息类型ID是0x04的消息功能是“用户控制（UserControl）”，处理函数是HandleCtrl()，这类的消息出现的频率非常高，函数体如下所示。具体用户控制消息的作用这里就不多说了，有相应的文档可以参考。

注：该函数中间有一段很长的英文注释，英语好的大神可以看一看

//处理用户控制(UserControl)消息。用户控制消息是服务器端发出的。
static void
HandleCtrl(RTMP *r, const RTMPPacket *packet)
{
  short nType = -1;
  unsigned int tmp;
  if (packet->m_body && packet->m_nBodySize >= 2)
	//事件类型(2B)
    nType = AMF_DecodeInt16(packet->m_body);
  RTMP_Log(RTMP_LOGDEBUG, "%s, received ctrl. type: %d, len: %d", __FUNCTION__, nType,
      packet->m_nBodySize);
  /*RTMP_LogHex(packet.m_body, packet.m_nBodySize); */

  if (packet->m_nBodySize >= 6)
    {
	//不同事件类型做不同处理
      switch (nType)
	{
	//流开始
	case 0:
	//流ID
	  tmp = AMF_DecodeInt32(packet->m_body + 2);
	  RTMP_Log(RTMP_LOGDEBUG, "%s, Stream Begin %d", __FUNCTION__, tmp);
	  break;
	//流结束
	case 1:
	//流ID
	  tmp = AMF_DecodeInt32(packet->m_body + 2);
	  RTMP_Log(RTMP_LOGDEBUG, "%s, Stream EOF %d", __FUNCTION__, tmp);
	  if (r->m_pausing == 1)
	    r->m_pausing = 2;
	  break;
	//流枯竭
	case 2:
	//流ID
	  tmp = AMF_DecodeInt32(packet->m_body + 2);
	  RTMP_Log(RTMP_LOGDEBUG, "%s, Stream Dry %d", __FUNCTION__, tmp);
	  break;
	//是录制流
	case 4:
	  tmp = AMF_DecodeInt32(packet->m_body + 2);
	  RTMP_Log(RTMP_LOGDEBUG, "%s, Stream IsRecorded %d", __FUNCTION__, tmp);
	  break;
	//Ping客户端
	case 6:		/* server ping. reply with pong. */
	  tmp = AMF_DecodeInt32(packet->m_body + 2);
	  RTMP_Log(RTMP_LOGDEBUG, "%s, Ping %d", __FUNCTION__, tmp);
	  RTMP_SendCtrl(r, 0x07, tmp, 0);
	  break;

	/* FMS 3.5 servers send the following two controls to let the client
	 * know when the server has sent a complete buffer. I.e., when the
	 * server has sent an amount of data equal to m_nBufferMS in duration.
	 * The server meters its output so that data arrives at the client
	 * in realtime and no faster.
	 *
	 * The rtmpdump program tries to set m_nBufferMS as large as
	 * possible, to force the server to send data as fast as possible.
	 * In practice, the server appears to cap this at about 1 hour's
	 * worth of data. After the server has sent a complete buffer, and
	 * sends this BufferEmpty message, it will wait until the play
	 * duration of that buffer has passed before sending a new buffer.
	 * The BufferReady message will be sent when the new buffer starts.
	 * (There is no BufferReady message for the very first buffer;
	 * presumably the Stream Begin message is sufficient for that
	 * purpose.)
	 *
	 * If the network speed is much faster than the data bitrate, then
	 * there may be long delays between the end of one buffer and the
	 * start of the next.
	 *
	 * Since usually the network allows data to be sent at
	 * faster than realtime, and rtmpdump wants to download the data
	 * as fast as possible, we use this RTMP_LF_BUFX hack: when we
	 * get the BufferEmpty message, we send a Pause followed by an
	 * Unpause. This causes the server to send the next buffer immediately
	 * instead of waiting for the full duration to elapse. (That's
	 * also the purpose of the ToggleStream function, which rtmpdump
	 * calls if we get a read timeout.)
	 *
	 * Media player apps don't need this hack since they are just
	 * going to play the data in realtime anyway. It also doesn't work
	 * for live streams since they obviously can only be sent in
	 * realtime. And it's all moot if the network speed is actually
	 * slower than the media bitrate.
	 */
	case 31:
	  tmp = AMF_DecodeInt32(packet->m_body + 2);
	  RTMP_Log(RTMP_LOGDEBUG, "%s, Stream BufferEmpty %d", __FUNCTION__, tmp);
	  if (!(r->Link.lFlags & RTMP_LF_BUFX))
	    break;
	  if (!r->m_pausing)
	    {
	      r->m_pauseStamp = r->m_channelTimestamp[r->m_mediaChannel];
	      RTMP_SendPause(r, TRUE, r->m_pauseStamp);
	      r->m_pausing = 1;
	    }
	  else if (r->m_pausing == 2)
	    {
	      RTMP_SendPause(r, FALSE, r->m_pauseStamp);
	      r->m_pausing = 3;
	    }
	  break;

	case 32:
	  tmp = AMF_DecodeInt32(packet->m_body + 2);
	  RTMP_Log(RTMP_LOGDEBUG, "%s, Stream BufferReady %d", __FUNCTION__, tmp);
	  break;

	default:
	  tmp = AMF_DecodeInt32(packet->m_body + 2);
	  RTMP_Log(RTMP_LOGDEBUG, "%s, Stream xx %d", __FUNCTION__, tmp);
	  break;
	}

    }

  if (nType == 0x1A)
    {
      RTMP_Log(RTMP_LOGDEBUG, "%s, SWFVerification ping received: ", __FUNCTION__);
      if (packet->m_nBodySize > 2 && packet->m_body[2] > 0x01)
	{
	  RTMP_Log(RTMP_LOGERROR,
            "%s: SWFVerification Type %d request not supported! Patches welcome...",
	    __FUNCTION__, packet->m_body[2]);
	}
#ifdef CRYPTO
      /*RTMP_LogHex(packet.m_body, packet.m_nBodySize); */

      /* respond with HMAC SHA256 of decompressed SWF, key is the 30byte player key, also the last 30 bytes of the server handshake are applied */
      else if (r->Link.SWFSize)
	{
	  RTMP_SendCtrl(r, 0x1B, 0, 0);
	}
      else
	{
	  RTMP_Log(RTMP_LOGERROR,
	      "%s: Ignoring SWFVerification request, use --swfVfy!",
	      __FUNCTION__);
	}
#else
      RTMP_Log(RTMP_LOGERROR,
	  "%s: Ignoring SWFVerification request, no CRYPTO support!",
	  __FUNCTION__);
#endif
    }
}

消息类型ID是0x05的消息功能是“窗口致谢大小（Window Acknowledgement Size，翻译的真是挺别扭）”，处理函数是HandleServerBW()。在这里注意一下，该消息在Adobe官方公开的文档中叫“Window Acknowledgement Size”，但是在Adobe公开协议规范之前，破解RTMP协议的组织一直管该协议叫“ServerBW”，只是个称呼，倒是也无所谓~处理代码很简单：

static void
HandleServerBW(RTMP *r, const RTMPPacket *packet)
{
  r->m_nServerBW = AMF_DecodeInt32(packet->m_body);
  RTMP_Log(RTMP_LOGDEBUG, "%s: server BW = %d", __FUNCTION__, r->m_nServerBW);
}

消息类型ID是0x06的消息功能是“设置对等端带宽（Set Peer Bandwidth）”，处理函数是HandleClientBW()。与上一种消息一样，该消息在Adobe官方公开的文档中叫“Set Peer Bandwidth”，但是在Adobe公开协议规范之前，破解RTMP协议的组织一直管该协议叫“ClientBW”。处理函数也不复杂：

static void
HandleClientBW(RTMP *r, const RTMPPacket *packet)
{
  r->m_nClientBW = AMF_DecodeInt32(packet->m_body);
  if (packet->m_nBodySize > 4)
    r->m_nClientBW2 = packet->m_body[4];
  else
    r->m_nClientBW2 = -1;
  RTMP_Log(RTMP_LOGDEBUG, "%s: client BW = %d %d", __FUNCTION__, r->m_nClientBW,
      r->m_nClientBW2);
}

消息类型ID是0x08的消息用于传输音频数据，在这里不处理。

消息类型ID是0x09的消息用于传输音频数据，在这里不处理。

消息类型ID是0x0F-11的消息用于传输AMF3编码的命令。

消息类型ID是0x12-14的消息用于传输AMF0编码的命令。

注：消息类型ID是0x14的消息很重要，用于传输AMF0编码的命令，已经做过分析。

rtmpdump源代码（Linux）：http://download.csdn.net/detail/leixiaohua1020/6376561

rtmpdump源代码（VC 2005 工程）：http://download.csdn.net/detail/leixiaohua1020/6563163