Darwin Streaming Server 支援UDP打洞
RTSP客戶端點播Darwin 視訊時，SDP協商後的客戶端埠可能是在NAT後面，所以需要Darwin支援NAT打洞的功能，從Darwin的原始碼看，官方的原始碼是不支援這個能力的。
通過抓取VLC客戶端的包發現，VLC在播放RTSP流時，兩次SETUP（音訊流和視訊分別協商埠）之後，會發送4個UDP打洞的包，但Darwin沒有接收這些包，並且根據這些包來源的埠修改遠端RTP和RTCP的埠。
文章Darwin Streaming Server 支援UDP穿透中給出了修改方法，嘗試之後，發現有兩個問題：
1、兩次SETUP協商後，Darwin給返回的伺服器的RTP和RTCP埠兩次都一樣
2、客戶端傳送的打洞的RTP和RTCP打洞的包，並沒有接收完全。
針對問題1的修改就是將兩次SETUP協商後,Darwin返回的埠不同並且唯一
問題2的修改方法是，在接收到SETUP協商後，開啟一個執行緒接收發送到伺服器的RTP和RTCP埠的包，並根據接收到的包的源埠更新遠端的RTP和RTCP埠，即使沒有收到打洞的包，不做任何處理，還是使用之前協商的埠往外發包。
第一個問題是將RTPStream::Setup方法中的：
fSockets = QTSServerInterface::GetServer()->GetSocketPool()->GetUDPSocketPair(sourceAddr, 0, fRemoteAddr,
fRemoteRTCPPort);
修改為：
fSockets = QTSServerInterface::GetServer()->GetSocketPool()->CreateUDPSocketPair(sourceAddr, 0);
並將UDPSocketPool::CreateUDPSocketPair方法中兩個變數的初值修改為如下：
UInt16 curPort = kLowestUDPPort + usedNum++;
UInt16 stopPort = kHighestUDPPort -1; // prevent roll over when iterating over port nums
UInt16 socketBPort = curPort + 1;
第二個問題修改，標頭檔案增加下面的方法和變數：
void start_thread_for_nat();
void setRemoteRTPPort(int value){fRemoteRTPPort = value; }
void setRemoteRTCPPort(int value){fRemoteRTCPPort = value;}
UInt16 getRemoteRTPPort(){return fRemoteRTPPort;}
UInt32 getRemoteRTPAddr(){return fRemoteAddr;}
Bool16 getQuitValue(){return bQuit;}
Bool16 getRunningValue(){return bRunning;}
void setRunningValue(Bool16 value){ bRunning = value;}
UInt16 getRemoteRTCPPort(){return fRemoteRTCPPort;}
UDPSocketPair* getUDPSocketPair(){ return fSockets;}
Bool16 bQuit;
Bool16 bRunning;在setup方法最後啟動一個監聽執行緒：
this->start_thread_for_nat();
//errors should only be returned if there is a routing problem, there should be none
Assert(err == QTSS_NoErr);
return QTSS_NoErr;
}實現：
#include <pthread.h>
void* thread_for_nat(void *parms){
Bool16 fUpdateRtpPort = false;
Bool16 fUpdateRtcpPort = false;
SInt64 currentTime = OS::Milliseconds();
RTPStream *pRTPStream = (RTPStream *)parms;
if (pRTPStream == NULL){
return NULL;
}
if (pRTPStream->getUDPSocketPair() == NULL){
return NULL;
}
if (pRTPStream->getUDPSocketPair()->GetSocketA() == NULL ||
pRTPStream->getUDPSocketPair()->GetSocketB() == NULL){
return NULL;
}
qtss_printf("thread_for_nat enter, pRTPStream:%08x, rtp_port:%d\n", pRTPStream, pRTPStream->getRemoteRTPPort());
pRTPStream->setRunningValue(true);
while(1){
UInt32 iRemoteAddr = 0;
UInt16 iRemotePort = 0;
char szBuff[64];
UInt32 iBufLen = sizeof(szBuff);
UInt32 iRecvLen = 0;
if (pRTPStream->getQuitValue()){
break;
}
if (!fUpdateRtpPort){
OS_Error iRet = pRTPStream->getUDPSocketPair()->GetSocketA()->RecvFrom(&iRemoteAddr, &iRemotePort, szBuff, iBufLen, &iRecvLen);
if (OS_NoErr == iRet){
if (iRemoteAddr == pRTPStream->getRemoteRTPAddr()
&& iRemotePort != pRTPStream->getRemoteRTPPort()
&& iRecvLen > 0){
qtss_printf("thread_for_nat update GetSocketA iRet:%d, fRemoteRTPPort:%d, fRemoteRTCPPort:%d, iRemotePort:%d\n", iRet, pRTPStream->getRemoteRTPPort(),
pRTPStream->getRemoteRTCPPort(), iRemotePort);
pRTPStream->setRemoteRTPPort(iRemotePort);
fUpdateRtpPort = true;
}else{
qtss_printf("thread_for_nat update GetSocketA received the same port value, fRemoteRTPPort:%d, fRemoteRTCPPort:%d\n", pRTPStream->getRemoteRTPPort(),
pRTPStream->getRemoteRTCPPort());
fUpdateRtpPort = true;
}
}else{
//qtss_printf("Setup update GetSocketA iRet:%d, fRemoteRTPPort:%d, fRemoteRTCPPort:%d\n", iRet, fRemoteRTPPort, fRemoteRTCPPort);
}
}
if (!fUpdateRtcpPort){
OS_Error iRet = pRTPStream->getUDPSocketPair()->GetSocketB()->RecvFrom(&iRemoteAddr, &iRemotePort, szBuff, iBufLen, &iRecvLen);
if (OS_NoErr == iRet){
if (iRemoteAddr == pRTPStream->getRemoteRTPAddr()
&& iRemotePort != pRTPStream->getRemoteRTCPPort()
&& iRecvLen > 0){
qtss_printf("thread_for_nat update GetSocketB iRet:%d, fRemoteRTPPort:%d, fRemoteRTCPPort:%d, iRemotePort:%d\n", iRet, pRTPStream->getRemoteRTPPort(),
pRTPStream->getRemoteRTCPPort(), iRemotePort);
pRTPStream->setRemoteRTCPPort(iRemotePort);
fUpdateRtcpPort = true;
} else{
qtss_printf("thread_for_nat update GetSocketB received the same port value, fRemoteRTPPort:%d, fRemoteRTCPPort:%d\n", pRTPStream->getRemoteRTPPort(),
pRTPStream->getRemoteRTCPPort());
fUpdateRtcpPort = true;
}
}else{
//wait.
//qtss_printf("Setup update GetSocketB iRet:%d, fRemoteRTPPort:%d, fRemoteRTCPPort:%d\n", iRet, fRemoteRTPPort, fRemoteRTCPPort);
}
}
if (fUpdateRtcpPort && fUpdateRtpPort){
qtss_printf("thread_for_nat exit for update end, break, pRTPStream:%08x, rtp_port:%d\n", pRTPStream, pRTPStream->getRemoteRTPPort());
break;
}
if ( (OS::Milliseconds() - currentTime ) > 2000){
qtss_printf("thread_for_nat exaust 2000 ms, break, pRTPStream:%08x, rtp_port:%d\n", pRTPStream, pRTPStream->getRemoteRTPPort());
break;
}
}
pRTPStream->setRunningValue(false);
gid_thread = -1;
return NULL;
}
void RTPStream::start_thread_for_nat(){
int ret=pthread_create(&gid_thread, NULL, thread_for_nat, (void*)this);
if (ret != 0){
qtss_printf("err:%d\n", ret);
}else{
qtss_printf("start_thread_for_nat create OK\n");
}
}