RTMPdump（libRTMP） 源代码分析 9： 接收消息（Message）（接收视音频数据）(九)
{
/* 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;
}
函数代码看似很多，但是并不是很复杂，可以理解为在从事“简单重复性劳动”（和搬砖差不多）。基本上是一个字节一个字节的读取，然后按照RTMP协议规范进行解析。具体如何解析可以参考RTMP协议规范。
在RTMP_ReadPacket()函数里完成从Socket中读取数据的函数是ReadN()，继续看看它的源代码：
[cpp]
//从HTTP或SOCKET中读取数据
static int
ReadN(RTMP *r, char *buffer, int n)
{
int nOriginalSize = n;
int avail;
char *ptr;
r->m_sb.sb_timedout = FALSE;
#ifdef _DEBUG
memset(buffer, 0, n);
#endif
ptr = buffer;
while (n > 0)
{
int nBytes = 0, nRead;
if (r->Link.protocol & RTMP_FEATURE_HTTP)
{
while (!r->m_resplen)
{
if (r->m_sb.sb_size < 144)
{
if (!r->m_unackd)
HTTP_Post(r, RTMPT_IDLE, "", 1);
if (RTMPSockBuf_Fill(&r->m_sb) < 1)
{
if (!r->m_sb.sb_timedout)
RTMP_Close(r);
return 0;
}
HTTP_read(r, 0);
}
if (r->m_resplen && !r->m_sb.sb_size)
RTMPSockBuf_Fill(&r->m_sb);
avail = r->m_sb.sb_size;
if (avail > r->m_resplen)
avail = r->m_resplen;
}
else
{
avail = r->m_sb.sb_size;
if (avail == 0)
{
if (RTMPSockBuf_Fill(&r->m_sb) < 1)
{
if (!r->m_sb.sb_timedout)
RTMP_Close(r);
return 0;
}
avail = r->m_sb.sb_size;
}
}
nRead = ((n < avail) n : avail);
if (nRead > 0)
{
memcpy(ptr, r->m_sb.sb_start, nRead);
r->m_sb.sb_start += nRead;
r->m_sb.sb_size -= nRead;
nBytes = nRead;
r->m_nBytesIn += nRead;
if (r->m_bSendCounter
&& r->m_nBytesIn > r->m_nBytesInSent + r->m_nClientBW / 2)
SendBytesReceived(r);
}
/*RTMP_Log(RTMP_LOGDEBUG, "%s: %d bytes\n", __FUNCTION__, nBytes); */
#ifdef _DEBUG
fwrite(ptr, 1, nBytes, netstackdump_read);
#endif
if (nBytes == 0)
{
RTMP_Log(RTMP_LOGDEBUG, "%s, RTMP socket closed by peer", __FUNCTION__);
/*goto again; */
RTMP_Close(r);
break;
}
if (r->Link.protocol & RTMP_FEATURE_HTTP)
r->m_resplen -= nBytes;
#ifdef CRYPTO
if (r->Link.rc4keyIn)
{
RC4_encrypt((RC4_KEY *)r->Link.rc4keyIn, nBytes, ptr);
}
#endif
n -= nBytes;
ptr += nBytes;
}
return nOriginalSize - n;
}
ReadN()中实现从Socket中接收数据的函数是RTMPSockBuf_Fi