webrtc/api/webrtcsessiondescriptionfactory.cc - src - Git at Google

 /*
  *  Copyright 2013 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */

 #include "webrtc/api/webrtcsessiondescriptionfactory.h"

 #include <utility>

 #include "webrtc/api/jsep.h"
 #include "webrtc/api/jsepsessiondescription.h"
 #include "webrtc/api/mediaconstraintsinterface.h"
 #include "webrtc/api/webrtcsession.h"
 #include "webrtc/base/sslidentity.h"

 using cricket::MediaSessionOptions;

 namespace webrtc {
 namespace {
 static const char kFailedDueToIdentityFailed[] =
     " failed because DTLS identity request failed";
 static const char kFailedDueToSessionShutdown[] =
     " failed because the session was shut down";

 static const uint64_t kInitSessionVersion = 2;

 static bool CompareStream(const MediaSessionOptions::Stream& stream1,
                           const MediaSessionOptions::Stream& stream2) {
   return stream1.id < stream2.id;
 }

 static bool SameId(const MediaSessionOptions::Stream& stream1,
                    const MediaSessionOptions::Stream& stream2) {
   return stream1.id == stream2.id;
 }

 // Checks if each Stream within the |streams| has unique id.
 static bool ValidStreams(const MediaSessionOptions::Streams& streams) {
   MediaSessionOptions::Streams sorted_streams = streams;
   std::sort(sorted_streams.begin(), sorted_streams.end(), CompareStream);
   MediaSessionOptions::Streams::iterator it =
       std::adjacent_find(sorted_streams.begin(), sorted_streams.end(),
                          SameId);
   return it == sorted_streams.end();
 }

 enum {
   MSG_CREATE_SESSIONDESCRIPTION_SUCCESS,
   MSG_CREATE_SESSIONDESCRIPTION_FAILED,
   MSG_USE_CONSTRUCTOR_CERTIFICATE
 };

 struct CreateSessionDescriptionMsg : public rtc::MessageData {
   explicit CreateSessionDescriptionMsg(
       webrtc::CreateSessionDescriptionObserver* observer)
       : observer(observer) {
   }

   rtc::scoped_refptr<webrtc::CreateSessionDescriptionObserver> observer;
   std::string error;
   std::unique_ptr<webrtc::SessionDescriptionInterface> description;
 };
 }  // namespace

 void WebRtcCertificateGeneratorCallback::OnFailure() {
   SignalRequestFailed();
 }

 void WebRtcCertificateGeneratorCallback::OnSuccess(
     const rtc::scoped_refptr<rtc::RTCCertificate>& certificate) {
   SignalCertificateReady(certificate);
 }

 // static
 void WebRtcSessionDescriptionFactory::CopyCandidatesFromSessionDescription(
     const SessionDescriptionInterface* source_desc,
     const std::string& content_name,
     SessionDescriptionInterface* dest_desc) {
   if (!source_desc) {
     return;
   }
   const cricket::ContentInfos& contents =
       source_desc->description()->contents();
   const cricket::ContentInfo* cinfo =
       source_desc->description()->GetContentByName(content_name);
   if (!cinfo) {
     return;
   }
   size_t mediasection_index = static_cast<int>(cinfo - &contents[0]);
   const IceCandidateCollection* source_candidates =
       source_desc->candidates(mediasection_index);
   const IceCandidateCollection* dest_candidates =
       dest_desc->candidates(mediasection_index);
   if (!source_candidates || !dest_candidates) {
     return;
   }
   for (size_t n = 0; n < source_candidates->count(); ++n) {
     const IceCandidateInterface* new_candidate = source_candidates->at(n);
     if (!dest_candidates->HasCandidate(new_candidate)) {
       dest_desc->AddCandidate(source_candidates->at(n));
     }
   }
 }

 // Private constructor called by other constructors.
 WebRtcSessionDescriptionFactory::WebRtcSessionDescriptionFactory(
     rtc::Thread* signaling_thread,
     cricket::ChannelManager* channel_manager,
     WebRtcSession* session,
     const std::string& session_id,
     std::unique_ptr<rtc::RTCCertificateGeneratorInterface> cert_generator,
     const rtc::scoped_refptr<rtc::RTCCertificate>& certificate)
     : signaling_thread_(signaling_thread),
       session_desc_factory_(channel_manager, &transport_desc_factory_),
       // RFC 4566 suggested a Network Time Protocol (NTP) format timestamp
       // as the session id and session version. To simplify, it should be fine
       // to just use a random number as session id and start version from
       // |kInitSessionVersion|.
       session_version_(kInitSessionVersion),
       cert_generator_(std::move(cert_generator)),
       session_(session),
       session_id_(session_id),
       certificate_request_state_(CERTIFICATE_NOT_NEEDED) {
   RTC_DCHECK(signaling_thread_);
   session_desc_factory_.set_add_legacy_streams(false);
   bool dtls_enabled = cert_generator_ || certificate;
   // SRTP-SDES is disabled if DTLS is on.
   SetSdesPolicy(dtls_enabled ? cricket::SEC_DISABLED : cricket::SEC_REQUIRED);
   if (!dtls_enabled) {
     LOG(LS_VERBOSE) << "DTLS-SRTP disabled.";
     return;
   }

   if (certificate) {
     // Use |certificate|.
     certificate_request_state_ = CERTIFICATE_WAITING;

     LOG(LS_VERBOSE) << "DTLS-SRTP enabled; has certificate parameter.";
     // We already have a certificate but we wait to do |SetIdentity|; if we do
     // it in the constructor then the caller has not had a chance to connect to
     // |SignalCertificateReady|.
     signaling_thread_->Post(
         RTC_FROM_HERE, this, MSG_USE_CONSTRUCTOR_CERTIFICATE,
         new rtc::ScopedRefMessageData<rtc::RTCCertificate>(certificate));
   } else {
     // Generate certificate.
     certificate_request_state_ = CERTIFICATE_WAITING;

     rtc::scoped_refptr<WebRtcCertificateGeneratorCallback> callback(
         new rtc::RefCountedObject<WebRtcCertificateGeneratorCallback>());
     callback->SignalRequestFailed.connect(
         this, &WebRtcSessionDescriptionFactory::OnCertificateRequestFailed);
     callback->SignalCertificateReady.connect(
         this, &WebRtcSessionDescriptionFactory::SetCertificate);

     rtc::KeyParams key_params = rtc::KeyParams();
     LOG(LS_VERBOSE) << "DTLS-SRTP enabled; sending DTLS identity request (key "
                     << "type: " << key_params.type() << ").";

     // Request certificate. This happens asynchronously, so that the caller gets
     // a chance to connect to |SignalCertificateReady|.
     cert_generator_->GenerateCertificateAsync(
         key_params, rtc::Optional<uint64_t>(), callback);
   }
 }

 WebRtcSessionDescriptionFactory::WebRtcSessionDescriptionFactory(
     rtc::Thread* signaling_thread,
     cricket::ChannelManager* channel_manager,
     WebRtcSession* session,
     const std::string& session_id,
     std::unique_ptr<rtc::RTCCertificateGeneratorInterface> cert_generator)
     : WebRtcSessionDescriptionFactory(
           signaling_thread,
           channel_manager,
           session,
           session_id,
           std::move(cert_generator),
           nullptr) {
 }

 WebRtcSessionDescriptionFactory::WebRtcSessionDescriptionFactory(
     rtc::Thread* signaling_thread,
     cricket::ChannelManager* channel_manager,
     WebRtcSession* session,
     const std::string& session_id,
     const rtc::scoped_refptr<rtc::RTCCertificate>& certificate)
     : WebRtcSessionDescriptionFactory(signaling_thread,
                                       channel_manager,
                                       session,
                                       session_id,
                                       nullptr,
                                       certificate) {
   RTC_DCHECK(certificate);
 }

 WebRtcSessionDescriptionFactory::~WebRtcSessionDescriptionFactory() {
   ASSERT(signaling_thread_->IsCurrent());

   // Fail any requests that were asked for before identity generation completed.
   FailPendingRequests(kFailedDueToSessionShutdown);

   // Process all pending notifications in the message queue.  If we don't do
   // this, requests will linger and not know they succeeded or failed.
   rtc::MessageList list;
   signaling_thread_->Clear(this, rtc::MQID_ANY, &list);
   for (auto& msg : list) {
     if (msg.message_id != MSG_USE_CONSTRUCTOR_CERTIFICATE) {
       OnMessage(&msg);
     } else {
       // Skip MSG_USE_CONSTRUCTOR_CERTIFICATE because we don't want to trigger
       // SetIdentity-related callbacks in the destructor. This can be a problem
       // when WebRtcSession listens to the callback but it was the WebRtcSession
       // destructor that caused WebRtcSessionDescriptionFactory's destruction.
       // The callback is then ignored, leaking memory allocated by OnMessage for
       // MSG_USE_CONSTRUCTOR_CERTIFICATE.
       delete msg.pdata;
     }
   }
 }

 void WebRtcSessionDescriptionFactory::CreateOffer(
     CreateSessionDescriptionObserver* observer,
     const PeerConnectionInterface::RTCOfferAnswerOptions& options,
     const cricket::MediaSessionOptions& session_options) {
   std::string error = "CreateOffer";
   if (certificate_request_state_ == CERTIFICATE_FAILED) {
     error += kFailedDueToIdentityFailed;
     LOG(LS_ERROR) << error;
     PostCreateSessionDescriptionFailed(observer, error);
     return;
   }

   if (!ValidStreams(session_options.streams)) {
     error += " called with invalid media streams.";
     LOG(LS_ERROR) << error;
     PostCreateSessionDescriptionFailed(observer, error);
     return;
   }

   CreateSessionDescriptionRequest request(
       CreateSessionDescriptionRequest::kOffer, observer, session_options);
   if (certificate_request_state_ == CERTIFICATE_WAITING) {
     create_session_description_requests_.push(request);
   } else {
     ASSERT(certificate_request_state_ == CERTIFICATE_SUCCEEDED ||
            certificate_request_state_ == CERTIFICATE_NOT_NEEDED);
     InternalCreateOffer(request);
   }
 }

 void WebRtcSessionDescriptionFactory::CreateAnswer(
     CreateSessionDescriptionObserver* observer,
     const cricket::MediaSessionOptions& session_options) {
   std::string error = "CreateAnswer";
   if (certificate_request_state_ == CERTIFICATE_FAILED) {
     error += kFailedDueToIdentityFailed;
     LOG(LS_ERROR) << error;
     PostCreateSessionDescriptionFailed(observer, error);
     return;
   }
   if (!session_->remote_description()) {
     error += " can't be called before SetRemoteDescription.";
     LOG(LS_ERROR) << error;
     PostCreateSessionDescriptionFailed(observer, error);
     return;
   }
   if (session_->remote_description()->type() !=
       JsepSessionDescription::kOffer) {
     error += " failed because remote_description is not an offer.";
     LOG(LS_ERROR) << error;
     PostCreateSessionDescriptionFailed(observer, error);
     return;
   }

   if (!ValidStreams(session_options.streams)) {
     error += " called with invalid media streams.";
     LOG(LS_ERROR) << error;
     PostCreateSessionDescriptionFailed(observer, error);
     return;
   }

   CreateSessionDescriptionRequest request(
       CreateSessionDescriptionRequest::kAnswer, observer, session_options);
   if (certificate_request_state_ == CERTIFICATE_WAITING) {
     create_session_description_requests_.push(request);
   } else {
     ASSERT(certificate_request_state_ == CERTIFICATE_SUCCEEDED ||
            certificate_request_state_ == CERTIFICATE_NOT_NEEDED);
     InternalCreateAnswer(request);
   }
 }

 void WebRtcSessionDescriptionFactory::SetSdesPolicy(
     cricket::SecurePolicy secure_policy) {
   session_desc_factory_.set_secure(secure_policy);
 }

 cricket::SecurePolicy WebRtcSessionDescriptionFactory::SdesPolicy() const {
   return session_desc_factory_.secure();
 }

 void WebRtcSessionDescriptionFactory::OnMessage(rtc::Message* msg) {
   switch (msg->message_id) {
     case MSG_CREATE_SESSIONDESCRIPTION_SUCCESS: {
       CreateSessionDescriptionMsg* param =
           static_cast<CreateSessionDescriptionMsg*>(msg->pdata);
       param->observer->OnSuccess(param->description.release());
       delete param;
       break;
     }
     case MSG_CREATE_SESSIONDESCRIPTION_FAILED: {
       CreateSessionDescriptionMsg* param =
           static_cast<CreateSessionDescriptionMsg*>(msg->pdata);
       param->observer->OnFailure(param->error);
       delete param;
       break;
     }
     case MSG_USE_CONSTRUCTOR_CERTIFICATE: {
       rtc::ScopedRefMessageData<rtc::RTCCertificate>* param =
           static_cast<rtc::ScopedRefMessageData<rtc::RTCCertificate>*>(
               msg->pdata);
       LOG(LS_INFO) << "Using certificate supplied to the constructor.";
       SetCertificate(param->data());
       delete param;
       break;
     }
     default:
       ASSERT(false);
       break;
   }
 }

 void WebRtcSessionDescriptionFactory::InternalCreateOffer(
     CreateSessionDescriptionRequest request) {
   cricket::SessionDescription* desc(session_desc_factory_.CreateOffer(
       request.options, session_->local_description()
                            ? session_->local_description()->description()
                            : nullptr));
   // RFC 3264
   // When issuing an offer that modifies the session,
   // the "o=" line of the new SDP MUST be identical to that in the
   // previous SDP, except that the version in the origin field MUST
   // increment by one from the previous SDP.

   // Just increase the version number by one each time when a new offer
   // is created regardless if it's identical to the previous one or not.
   // The |session_version_| is a uint64_t, the wrap around should not happen.
   ASSERT(session_version_ + 1 > session_version_);
   JsepSessionDescription* offer(new JsepSessionDescription(
       JsepSessionDescription::kOffer));
   if (!offer->Initialize(desc, session_id_,
                          rtc::ToString(session_version_++))) {
     delete offer;
     PostCreateSessionDescriptionFailed(request.observer,
                                        "Failed to initialize the offer.");
     return;
   }
   if (session_->local_description()) {
     for (const cricket::ContentInfo& content :
          session_->local_description()->description()->contents()) {
       // Include all local ICE candidates in the SessionDescription unless
       // the remote peer has requested an ICE restart.
       if (!request.options.transport_options[content.name].ice_restart) {
         CopyCandidatesFromSessionDescription(session_->local_description(),
                                              content.name, offer);
       }
     }
   }
   PostCreateSessionDescriptionSucceeded(request.observer, offer);
 }

 void WebRtcSessionDescriptionFactory::InternalCreateAnswer(
     CreateSessionDescriptionRequest request) {
   if (session_->remote_description()) {
     for (const cricket::ContentInfo& content :
          session_->remote_description()->description()->contents()) {
       // According to http://tools.ietf.org/html/rfc5245#section-9.2.1.1
       // an answer should also contain new ICE ufrag and password if an offer
       // has been received with new ufrag and password.
       request.options.transport_options[content.name].ice_restart =
           session_->IceRestartPending(content.name);
       // We should pass the current SSL role to the transport description
       // factory, if there is already an existing ongoing session.
       rtc::SSLRole ssl_role;
       if (session_->GetSslRole(session_->GetChannel(content.name), &ssl_role)) {
         request.options.transport_options[content.name].prefer_passive_role =
             (rtc::SSL_SERVER == ssl_role);
       }
     }
   }

   cricket::SessionDescription* desc(session_desc_factory_.CreateAnswer(
       session_->remote_description()
           ? session_->remote_description()->description()
           : nullptr,
       request.options, session_->local_description()
                            ? session_->local_description()->description()
                            : nullptr));
   // RFC 3264
   // If the answer is different from the offer in any way (different IP
   // addresses, ports, etc.), the origin line MUST be different in the answer.
   // In that case, the version number in the "o=" line of the answer is
   // unrelated to the version number in the o line of the offer.
   // Get a new version number by increasing the |session_version_answer_|.
   // The |session_version_| is a uint64_t, the wrap around should not happen.
   ASSERT(session_version_ + 1 > session_version_);
   JsepSessionDescription* answer(new JsepSessionDescription(
       JsepSessionDescription::kAnswer));
   if (!answer->Initialize(desc, session_id_,
                           rtc::ToString(session_version_++))) {
     delete answer;
     PostCreateSessionDescriptionFailed(request.observer,
                                        "Failed to initialize the answer.");
     return;
   }
   if (session_->local_description()) {
     for (const cricket::ContentInfo& content :
          session_->local_description()->description()->contents()) {
       // Include all local ICE candidates in the SessionDescription unless
       // the remote peer has requested an ICE restart.
       if (!request.options.transport_options[content.name].ice_restart) {
         CopyCandidatesFromSessionDescription(session_->local_description(),
                                              content.name, answer);
       }
     }
   }
   PostCreateSessionDescriptionSucceeded(request.observer, answer);
 }

 void WebRtcSessionDescriptionFactory::FailPendingRequests(
     const std::string& reason) {
   ASSERT(signaling_thread_->IsCurrent());
   while (!create_session_description_requests_.empty()) {
     const CreateSessionDescriptionRequest& request =
         create_session_description_requests_.front();
     PostCreateSessionDescriptionFailed(request.observer,
         ((request.type == CreateSessionDescriptionRequest::kOffer) ?
             "CreateOffer" : "CreateAnswer") + reason);
     create_session_description_requests_.pop();
   }
 }

 void WebRtcSessionDescriptionFactory::PostCreateSessionDescriptionFailed(
     CreateSessionDescriptionObserver* observer, const std::string& error) {
   CreateSessionDescriptionMsg* msg = new CreateSessionDescriptionMsg(observer);
   msg->error = error;
   signaling_thread_->Post(RTC_FROM_HERE, this,
                           MSG_CREATE_SESSIONDESCRIPTION_FAILED, msg);
   LOG(LS_ERROR) << "Create SDP failed: " << error;
 }

 void WebRtcSessionDescriptionFactory::PostCreateSessionDescriptionSucceeded(
     CreateSessionDescriptionObserver* observer,
     SessionDescriptionInterface* description) {
   CreateSessionDescriptionMsg* msg = new CreateSessionDescriptionMsg(observer);
   msg->description.reset(description);
   signaling_thread_->Post(RTC_FROM_HERE, this,
                           MSG_CREATE_SESSIONDESCRIPTION_SUCCESS, msg);
 }

 void WebRtcSessionDescriptionFactory::OnCertificateRequestFailed() {
   ASSERT(signaling_thread_->IsCurrent());

   LOG(LS_ERROR) << "Asynchronous certificate generation request failed.";
   certificate_request_state_ = CERTIFICATE_FAILED;

   FailPendingRequests(kFailedDueToIdentityFailed);
 }

 void WebRtcSessionDescriptionFactory::SetCertificate(
     const rtc::scoped_refptr<rtc::RTCCertificate>& certificate) {
   RTC_DCHECK(certificate);
   LOG(LS_VERBOSE) << "Setting new certificate.";

   certificate_request_state_ = CERTIFICATE_SUCCEEDED;
   SignalCertificateReady(certificate);

   transport_desc_factory_.set_certificate(certificate);
   transport_desc_factory_.set_secure(cricket::SEC_ENABLED);

   while (!create_session_description_requests_.empty()) {
     if (create_session_description_requests_.front().type ==
         CreateSessionDescriptionRequest::kOffer) {
       InternalCreateOffer(create_session_description_requests_.front());
     } else {
       InternalCreateAnswer(create_session_description_requests_.front());
     }
     create_session_description_requests_.pop();
   }
 }
 }  // namespace webrtc
	/*
	* Copyright 2013 The WebRTC project authors. All Rights Reserved.
	*
	* Use of this source code is governed by a BSD-style license
	* that can be found in the LICENSE file in the root of the source
	* tree. An additional intellectual property rights grant can be found
	* in the file PATENTS. All contributing project authors may
	* be found in the AUTHORS file in the root of the source tree.
	*/

	#include "webrtc/api/webrtcsessiondescriptionfactory.h"

	#include <utility>

	#include "webrtc/api/jsep.h"
	#include "webrtc/api/jsepsessiondescription.h"
	#include "webrtc/api/mediaconstraintsinterface.h"
	#include "webrtc/api/webrtcsession.h"
	#include "webrtc/base/sslidentity.h"

	using cricket::MediaSessionOptions;

	namespace webrtc {
	namespace {
	static const char kFailedDueToIdentityFailed[] =
	" failed because DTLS identity request failed";
	static const char kFailedDueToSessionShutdown[] =
	" failed because the session was shut down";

	static const uint64_t kInitSessionVersion = 2;

	static bool CompareStream(const MediaSessionOptions::Stream& stream1,
	const MediaSessionOptions::Stream& stream2) {
	return stream1.id < stream2.id;
	}

	static bool SameId(const MediaSessionOptions::Stream& stream1,
	const MediaSessionOptions::Stream& stream2) {
	return stream1.id == stream2.id;
	}

	// Checks if each Stream within the \|streams\| has unique id.
	static bool ValidStreams(const MediaSessionOptions::Streams& streams) {
	MediaSessionOptions::Streams sorted_streams = streams;
	std::sort(sorted_streams.begin(), sorted_streams.end(), CompareStream);
	MediaSessionOptions::Streams::iterator it =
	std::adjacent_find(sorted_streams.begin(), sorted_streams.end(),
	SameId);
	return it == sorted_streams.end();
	}

	enum {
	MSG_CREATE_SESSIONDESCRIPTION_SUCCESS,
	MSG_CREATE_SESSIONDESCRIPTION_FAILED,
	MSG_USE_CONSTRUCTOR_CERTIFICATE
	};

	struct CreateSessionDescriptionMsg : public rtc::MessageData {
	explicit CreateSessionDescriptionMsg(
	webrtc::CreateSessionDescriptionObserver* observer)
	: observer(observer) {
	}

	rtc::scoped_refptr<webrtc::CreateSessionDescriptionObserver> observer;
	std::string error;
	std::unique_ptr<webrtc::SessionDescriptionInterface> description;
	};
	} // namespace

	void WebRtcCertificateGeneratorCallback::OnFailure() {
	SignalRequestFailed();
	}

	void WebRtcCertificateGeneratorCallback::OnSuccess(
	const rtc::scoped_refptr<rtc::RTCCertificate>& certificate) {
	SignalCertificateReady(certificate);
	}

	// static
	void WebRtcSessionDescriptionFactory::CopyCandidatesFromSessionDescription(
	const SessionDescriptionInterface* source_desc,
	const std::string& content_name,
	SessionDescriptionInterface* dest_desc) {
	if (!source_desc) {
	return;
	}
	const cricket::ContentInfos& contents =
	source_desc->description()->contents();
	const cricket::ContentInfo* cinfo =
	source_desc->description()->GetContentByName(content_name);
	if (!cinfo) {
	return;
	}
	size_t mediasection_index = static_cast<int>(cinfo - &contents[0]);
	const IceCandidateCollection* source_candidates =
	source_desc->candidates(mediasection_index);
	const IceCandidateCollection* dest_candidates =
	dest_desc->candidates(mediasection_index);
	if (!source_candidates \|\| !dest_candidates) {
	return;
	}
	for (size_t n = 0; n < source_candidates->count(); ++n) {
	const IceCandidateInterface* new_candidate = source_candidates->at(n);
	if (!dest_candidates->HasCandidate(new_candidate)) {
	dest_desc->AddCandidate(source_candidates->at(n));
	}
	}
	}

	// Private constructor called by other constructors.
	WebRtcSessionDescriptionFactory::WebRtcSessionDescriptionFactory(
	rtc::Thread* signaling_thread,
	cricket::ChannelManager* channel_manager,
	WebRtcSession* session,
	const std::string& session_id,
	std::unique_ptr<rtc::RTCCertificateGeneratorInterface> cert_generator,
	const rtc::scoped_refptr<rtc::RTCCertificate>& certificate)
	: signaling_thread_(signaling_thread),
	session_desc_factory_(channel_manager, &transport_desc_factory_),
	// RFC 4566 suggested a Network Time Protocol (NTP) format timestamp
	// as the session id and session version. To simplify, it should be fine
	// to just use a random number as session id and start version from
	// \|kInitSessionVersion\|.
	session_version_(kInitSessionVersion),
	cert_generator_(std::move(cert_generator)),
	session_(session),
	session_id_(session_id),
	certificate_request_state_(CERTIFICATE_NOT_NEEDED) {
	RTC_DCHECK(signaling_thread_);
	session_desc_factory_.set_add_legacy_streams(false);
	bool dtls_enabled = cert_generator_ \|\| certificate;
	// SRTP-SDES is disabled if DTLS is on.
	SetSdesPolicy(dtls_enabled ? cricket::SEC_DISABLED : cricket::SEC_REQUIRED);
	if (!dtls_enabled) {
	LOG(LS_VERBOSE) << "DTLS-SRTP disabled.";
	return;
	}

	if (certificate) {
	// Use \|certificate\|.
	certificate_request_state_ = CERTIFICATE_WAITING;

	LOG(LS_VERBOSE) << "DTLS-SRTP enabled; has certificate parameter.";
	// We already have a certificate but we wait to do \|SetIdentity\|; if we do
	// it in the constructor then the caller has not had a chance to connect to
	// \|SignalCertificateReady\|.
	signaling_thread_->Post(
	RTC_FROM_HERE, this, MSG_USE_CONSTRUCTOR_CERTIFICATE,
	new rtc::ScopedRefMessageData<rtc::RTCCertificate>(certificate));
	} else {
	// Generate certificate.
	certificate_request_state_ = CERTIFICATE_WAITING;

	rtc::scoped_refptr<WebRtcCertificateGeneratorCallback> callback(
	new rtc::RefCountedObject<WebRtcCertificateGeneratorCallback>());
	callback->SignalRequestFailed.connect(
	this, &WebRtcSessionDescriptionFactory::OnCertificateRequestFailed);
	callback->SignalCertificateReady.connect(
	this, &WebRtcSessionDescriptionFactory::SetCertificate);

	rtc::KeyParams key_params = rtc::KeyParams();
	LOG(LS_VERBOSE) << "DTLS-SRTP enabled; sending DTLS identity request (key "
	<< "type: " << key_params.type() << ").";

	// Request certificate. This happens asynchronously, so that the caller gets
	// a chance to connect to \|SignalCertificateReady\|.
	cert_generator_->GenerateCertificateAsync(
	key_params, rtc::Optional<uint64_t>(), callback);
	}
	}

	WebRtcSessionDescriptionFactory::WebRtcSessionDescriptionFactory(
	rtc::Thread* signaling_thread,
	cricket::ChannelManager* channel_manager,
	WebRtcSession* session,
	const std::string& session_id,
	std::unique_ptr<rtc::RTCCertificateGeneratorInterface> cert_generator)
	: WebRtcSessionDescriptionFactory(
	signaling_thread,
	channel_manager,
	session,
	session_id,
	std::move(cert_generator),
	nullptr) {
	}

	WebRtcSessionDescriptionFactory::WebRtcSessionDescriptionFactory(
	rtc::Thread* signaling_thread,
	cricket::ChannelManager* channel_manager,
	WebRtcSession* session,
	const std::string& session_id,
	const rtc::scoped_refptr<rtc::RTCCertificate>& certificate)
	: WebRtcSessionDescriptionFactory(signaling_thread,
	channel_manager,
	session,
	session_id,
	nullptr,
	certificate) {
	RTC_DCHECK(certificate);
	}

	WebRtcSessionDescriptionFactory::~WebRtcSessionDescriptionFactory() {
	ASSERT(signaling_thread_->IsCurrent());

	// Fail any requests that were asked for before identity generation completed.
	FailPendingRequests(kFailedDueToSessionShutdown);

	// Process all pending notifications in the message queue. If we don't do
	// this, requests will linger and not know they succeeded or failed.
	rtc::MessageList list;
	signaling_thread_->Clear(this, rtc::MQID_ANY, &list);
	for (auto& msg : list) {
	if (msg.message_id != MSG_USE_CONSTRUCTOR_CERTIFICATE) {
	OnMessage(&msg);
	} else {
	// Skip MSG_USE_CONSTRUCTOR_CERTIFICATE because we don't want to trigger
	// SetIdentity-related callbacks in the destructor. This can be a problem
	// when WebRtcSession listens to the callback but it was the WebRtcSession
	// destructor that caused WebRtcSessionDescriptionFactory's destruction.
	// The callback is then ignored, leaking memory allocated by OnMessage for
	// MSG_USE_CONSTRUCTOR_CERTIFICATE.
	delete msg.pdata;
	}
	}
	}

	void WebRtcSessionDescriptionFactory::CreateOffer(
	CreateSessionDescriptionObserver* observer,
	const PeerConnectionInterface::RTCOfferAnswerOptions& options,
	const cricket::MediaSessionOptions& session_options) {
	std::string error = "CreateOffer";
	if (certificate_request_state_ == CERTIFICATE_FAILED) {
	error += kFailedDueToIdentityFailed;
	LOG(LS_ERROR) << error;
	PostCreateSessionDescriptionFailed(observer, error);
	return;
	}

	if (!ValidStreams(session_options.streams)) {
	error += " called with invalid media streams.";
	LOG(LS_ERROR) << error;
	PostCreateSessionDescriptionFailed(observer, error);
	return;
	}

	CreateSessionDescriptionRequest request(
	CreateSessionDescriptionRequest::kOffer, observer, session_options);
	if (certificate_request_state_ == CERTIFICATE_WAITING) {
	create_session_description_requests_.push(request);
	} else {
	ASSERT(certificate_request_state_ == CERTIFICATE_SUCCEEDED \|\|
	certificate_request_state_ == CERTIFICATE_NOT_NEEDED);
	InternalCreateOffer(request);
	}
	}

	void WebRtcSessionDescriptionFactory::CreateAnswer(
	CreateSessionDescriptionObserver* observer,
	const cricket::MediaSessionOptions& session_options) {
	std::string error = "CreateAnswer";
	if (certificate_request_state_ == CERTIFICATE_FAILED) {
	error += kFailedDueToIdentityFailed;
	LOG(LS_ERROR) << error;
	PostCreateSessionDescriptionFailed(observer, error);
	return;
	}
	if (!session_->remote_description()) {
	error += " can't be called before SetRemoteDescription.";
	LOG(LS_ERROR) << error;
	PostCreateSessionDescriptionFailed(observer, error);
	return;
	}
	if (session_->remote_description()->type() !=
	JsepSessionDescription::kOffer) {
	error += " failed because remote_description is not an offer.";
	LOG(LS_ERROR) << error;
	PostCreateSessionDescriptionFailed(observer, error);
	return;
	}

	if (!ValidStreams(session_options.streams)) {
	error += " called with invalid media streams.";
	LOG(LS_ERROR) << error;
	PostCreateSessionDescriptionFailed(observer, error);
	return;
	}

	CreateSessionDescriptionRequest request(
	CreateSessionDescriptionRequest::kAnswer, observer, session_options);
	if (certificate_request_state_ == CERTIFICATE_WAITING) {
	create_session_description_requests_.push(request);
	} else {
	ASSERT(certificate_request_state_ == CERTIFICATE_SUCCEEDED \|\|
	certificate_request_state_ == CERTIFICATE_NOT_NEEDED);
	InternalCreateAnswer(request);
	}
	}

	void WebRtcSessionDescriptionFactory::SetSdesPolicy(
	cricket::SecurePolicy secure_policy) {
	session_desc_factory_.set_secure(secure_policy);
	}

	cricket::SecurePolicy WebRtcSessionDescriptionFactory::SdesPolicy() const {
	return session_desc_factory_.secure();
	}

	void WebRtcSessionDescriptionFactory::OnMessage(rtc::Message* msg) {
	switch (msg->message_id) {
	case MSG_CREATE_SESSIONDESCRIPTION_SUCCESS: {
	CreateSessionDescriptionMsg* param =
	static_cast<CreateSessionDescriptionMsg*>(msg->pdata);
	param->observer->OnSuccess(param->description.release());
	delete param;
	break;
	}
	case MSG_CREATE_SESSIONDESCRIPTION_FAILED: {
	CreateSessionDescriptionMsg* param =
	static_cast<CreateSessionDescriptionMsg*>(msg->pdata);
	param->observer->OnFailure(param->error);
	delete param;
	break;
	}
	case MSG_USE_CONSTRUCTOR_CERTIFICATE: {
	rtc::ScopedRefMessageData<rtc::RTCCertificate>* param =
	static_cast<rtc::ScopedRefMessageData<rtc::RTCCertificate>*>(
	msg->pdata);
	LOG(LS_INFO) << "Using certificate supplied to the constructor.";
	SetCertificate(param->data());
	delete param;
	break;
	}
	default:
	ASSERT(false);
	break;
	}
	}

	void WebRtcSessionDescriptionFactory::InternalCreateOffer(
	CreateSessionDescriptionRequest request) {
	cricket::SessionDescription* desc(session_desc_factory_.CreateOffer(
	request.options, session_->local_description()
	? session_->local_description()->description()
	: nullptr));
	// RFC 3264
	// When issuing an offer that modifies the session,
	// the "o=" line of the new SDP MUST be identical to that in the
	// previous SDP, except that the version in the origin field MUST
	// increment by one from the previous SDP.

	// Just increase the version number by one each time when a new offer
	// is created regardless if it's identical to the previous one or not.
	// The \|session_version_\| is a uint64_t, the wrap around should not happen.
	ASSERT(session_version_ + 1 > session_version_);
	JsepSessionDescription* offer(new JsepSessionDescription(
	JsepSessionDescription::kOffer));
	if (!offer->Initialize(desc, session_id_,
	rtc::ToString(session_version_++))) {
	delete offer;
	PostCreateSessionDescriptionFailed(request.observer,
	"Failed to initialize the offer.");
	return;
	}
	if (session_->local_description()) {
	for (const cricket::ContentInfo& content :
	session_->local_description()->description()->contents()) {
	// Include all local ICE candidates in the SessionDescription unless
	// the remote peer has requested an ICE restart.
	if (!request.options.transport_options[content.name].ice_restart) {
	CopyCandidatesFromSessionDescription(session_->local_description(),
	content.name, offer);
	}
	}
	}
	PostCreateSessionDescriptionSucceeded(request.observer, offer);
	}

	void WebRtcSessionDescriptionFactory::InternalCreateAnswer(
	CreateSessionDescriptionRequest request) {
	if (session_->remote_description()) {
	for (const cricket::ContentInfo& content :
	session_->remote_description()->description()->contents()) {
	// According to http://tools.ietf.org/html/rfc5245#section-9.2.1.1
	// an answer should also contain new ICE ufrag and password if an offer
	// has been received with new ufrag and password.
	request.options.transport_options[content.name].ice_restart =
	session_->IceRestartPending(content.name);
	// We should pass the current SSL role to the transport description
	// factory, if there is already an existing ongoing session.
	rtc::SSLRole ssl_role;
	if (session_->GetSslRole(session_->GetChannel(content.name), &ssl_role)) {
	request.options.transport_options[content.name].prefer_passive_role =
	(rtc::SSL_SERVER == ssl_role);
	}
	}
	}

	cricket::SessionDescription* desc(session_desc_factory_.CreateAnswer(
	session_->remote_description()
	? session_->remote_description()->description()
	: nullptr,
	request.options, session_->local_description()
	? session_->local_description()->description()
	: nullptr));
	// RFC 3264
	// If the answer is different from the offer in any way (different IP
	// addresses, ports, etc.), the origin line MUST be different in the answer.
	// In that case, the version number in the "o=" line of the answer is
	// unrelated to the version number in the o line of the offer.
	// Get a new version number by increasing the \|session_version_answer_\|.
	// The \|session_version_\| is a uint64_t, the wrap around should not happen.
	ASSERT(session_version_ + 1 > session_version_);
	JsepSessionDescription* answer(new JsepSessionDescription(
	JsepSessionDescription::kAnswer));
	if (!answer->Initialize(desc, session_id_,
	rtc::ToString(session_version_++))) {
	delete answer;
	PostCreateSessionDescriptionFailed(request.observer,
	"Failed to initialize the answer.");
	return;
	}
	if (session_->local_description()) {
	for (const cricket::ContentInfo& content :
	session_->local_description()->description()->contents()) {
	// Include all local ICE candidates in the SessionDescription unless
	// the remote peer has requested an ICE restart.
	if (!request.options.transport_options[content.name].ice_restart) {
	CopyCandidatesFromSessionDescription(session_->local_description(),
	content.name, answer);
	}
	}
	}
	PostCreateSessionDescriptionSucceeded(request.observer, answer);
	}

	void WebRtcSessionDescriptionFactory::FailPendingRequests(
	const std::string& reason) {
	ASSERT(signaling_thread_->IsCurrent());
	while (!create_session_description_requests_.empty()) {
	const CreateSessionDescriptionRequest& request =
	create_session_description_requests_.front();
	PostCreateSessionDescriptionFailed(request.observer,
	((request.type == CreateSessionDescriptionRequest::kOffer) ?
	"CreateOffer" : "CreateAnswer") + reason);
	create_session_description_requests_.pop();
	}
	}

	void WebRtcSessionDescriptionFactory::PostCreateSessionDescriptionFailed(
	CreateSessionDescriptionObserver* observer, const std::string& error) {
	CreateSessionDescriptionMsg* msg = new CreateSessionDescriptionMsg(observer);
	msg->error = error;
	signaling_thread_->Post(RTC_FROM_HERE, this,
	MSG_CREATE_SESSIONDESCRIPTION_FAILED, msg);
	LOG(LS_ERROR) << "Create SDP failed: " << error;
	}

	void WebRtcSessionDescriptionFactory::PostCreateSessionDescriptionSucceeded(
	CreateSessionDescriptionObserver* observer,
	SessionDescriptionInterface* description) {
	CreateSessionDescriptionMsg* msg = new CreateSessionDescriptionMsg(observer);
	msg->description.reset(description);
	signaling_thread_->Post(RTC_FROM_HERE, this,
	MSG_CREATE_SESSIONDESCRIPTION_SUCCESS, msg);
	}

	void WebRtcSessionDescriptionFactory::OnCertificateRequestFailed() {
	ASSERT(signaling_thread_->IsCurrent());

	LOG(LS_ERROR) << "Asynchronous certificate generation request failed.";
	certificate_request_state_ = CERTIFICATE_FAILED;

	FailPendingRequests(kFailedDueToIdentityFailed);
	}

	void WebRtcSessionDescriptionFactory::SetCertificate(
	const rtc::scoped_refptr<rtc::RTCCertificate>& certificate) {
	RTC_DCHECK(certificate);
	LOG(LS_VERBOSE) << "Setting new certificate.";

	certificate_request_state_ = CERTIFICATE_SUCCEEDED;
	SignalCertificateReady(certificate);

	transport_desc_factory_.set_certificate(certificate);
	transport_desc_factory_.set_secure(cricket::SEC_ENABLED);

	while (!create_session_description_requests_.empty()) {
	if (create_session_description_requests_.front().type ==
	CreateSessionDescriptionRequest::kOffer) {
	InternalCreateOffer(create_session_description_requests_.front());
	} else {
	InternalCreateAnswer(create_session_description_requests_.front());
	}
	create_session_description_requests_.pop();
	}
	}
	} // namespace webrtc