WebRtc libjingle_PeerConnection层（二） CreateOffer

发起视频通话流程图如下



创建dsp描述符,CreateOffer在流程中位于 OnSignalingMessage(offer)

void CConductor::ConnectToPeer(int peer_id) {

if (peer_connection_.get()) {
LOG(LS_ERROR) <<
"We only support connecting to one peer at a time";
return;
}

if (InitializePeerConnection()) {
peer_connection_->CreateOffer(this, NULL);
}
else {
LOG(LS_ERROR) << "Failed to initialize PeerConnection";
}
}

void CConductor::OnSuccess(webrtc::SessionDescriptionInterface* desc) {
peer_connection_->SetLocalDescription(
DummySetSessionDescriptionObserver::Create(), desc);

std::string sdp;
desc->ToString(&sdp);

// For loopback test. To save some connecting delay.
if (loopback_) {
// Replace message type from "offer" to "answer"
webrtc::SessionDescriptionInterface* session_description(
webrtc::CreateSessionDescription("answer", sdp));
peer_connection_->SetRemoteDescription(
DummySetSessionDescriptionObserver::Create(), session_description);
return;
}

Json::StyledWriter writer;
Json::Value jmessage;
jmessage[kSessionDescriptionTypeName] = desc->type();
jmessage[kSessionDescriptionSdpName] = sdp;
SendMessage(writer.write(jmessage));
}

void CConductor::OnFailure(const std::string& error) {
LOG(LERROR) << error;
}

CreateOffer的第一个参数是webrtc:CreateSessionDescriptionObserver，故CConductor继承自webrtc:CreateSessionDescriptionObserver，重写OnSuccess和OnFailure，当调用CreateOffer成功后，OnSuccess会被函数会被触发，就可以获得sdp信息。

再将sdp传递到外部，有通讯现成发送至RemotPeer。

int main(){
...

rtc::Win32Thread w32_thread;
rtc::ThreadManager::Instance()->SetCurrentThread(&w32_thread);

...

rtc::scoped_refptr<CConductor> conductor(
new rtc::RefCountedObject<CConductor>(&client, &viceo_show));

...

while ((gm = ::GetMessage(&msg, NULL, 0, 0)) != 0 && gm != -1) {
::TranslateMessage(&msg);
::DispatchMessage(&msg);
}

...
}

从调试来看webrtc似乎是用了类似Windows的消息机制，很多命令都是通过DispatchMessage来派发消息。

注意如果没有调用rtc::ThreadManager::Instance()->SetCurrentThread(）函数和DispatchMessage，会导致CreateOffer调用后，无法回调OnSuccess。(掉坑了)

调试的时候。仅需在OnSuccess中打断点即可。

仅含工程代码，无webrtc项目源码

http://download.csdn.net/detail/q339659207/9104747