librtmp 源码分析笔记 RTMP_ReadPacket_librtmp readpacket-优快云博客

本文详细剖析librtmp库中RTMP_ReadPacket函数，讲解如何配合RTMPPacket_IsReady宏读取完整RTMPPacket。内容涉及ReadN、消息头解析、包体读取等关键步骤，以及包元数据的保存与复用，旨在理解RTMP协议的实现细节。

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索性一口气把RTMP_ReadPacket也记录下来，好尽快开始对具体上层协议实现细节进行细读。

与RTMP_SendPacket不同，RTMP_ReadPacket需要多次调用（每次读取一个chunk），并配合RTMPPacket_IsReady这个宏使用才能读取一个完整的RTMPPacket。

大致如下：

while（isPlaying && RTMP_ReadPacket(r,&packet)）{
  if(RTMPPacket_IsReady(&packet)){
    //已成功接收到一个完整包，在此进行处理
  }
}

其中，

#define RTMPPacket_IsReady(a)	((a)->m_nBytesRead == (a)->m_nBodySize)

下面开始看一下 RTMP_ReadPacket

int
RTMP_ReadPacket( RTMP *r, RTMPPacket *packet )
{
	uint8_t hbuf[RTMP_MAX_HEADER_SIZE]	= { 0 };
	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 );

	if ( ReadN( r, (char *) hbuf, 1 ) == 0 )
	{
		RTMP_Log( RTMP_LOGERROR, "%s, failed to read RTMP packet header", __FUNCTION__ );
		return(FALSE);
	}

ReadN也是老朋友了，读取第一个字节，开始对packet流进行解析

	packet->m_headerType	= (hbuf[0] & 0xc0) >> 6;
	packet->m_nChannel	= (hbuf[0] & 0x3f);
	header++;
	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);
		}
		packet->m_nChannel	= hbuf[1];
		packet->m_nChannel	+= 64;
		header++;
	}else if ( packet->m_nChan