Support encrypted RTP extensions (RFC 6904)

webrtc/pc/mediasession.cc

Index: webrtc/pc/mediasession.cc
diff --git a/webrtc/pc/mediasession.cc b/webrtc/pc/mediasession.cc
index dbd32566d523d3d67d8ca3be8fee17e7190fcf9f..ac438ba1f85abc2054d84dcf07d218c1beb92b9e 100644
--- a/webrtc/pc/mediasession.cc
+++ b/webrtc/pc/mediasession.cc
@@ -932,16 +932,42 @@ static void FindCodecsToOffer(
 static bool FindByUri(const RtpHeaderExtensions& extensions,
                       const webrtc::RtpExtension& ext_to_match,
                       webrtc::RtpExtension* found_extension) {
+  // We assume that all URIs are given in a canonical format.
+  const webrtc::RtpExtension* found =
+      webrtc::RtpExtension::FindHeaderExtensionByUri(extensions,
+                                                     ext_to_match.uri);
+  if (!found) {
+    return false;
+  }
+  if (found_extension) {
+    *found_extension = *found;
+  }
+  return true;
+}
+
+static bool FindByUriWithEncryptionPreference(
+    const RtpHeaderExtensions& extensions,
+    const webrtc::RtpExtension& ext_to_match, bool encryption_preference,
+    webrtc::RtpExtension* found_extension) {
+  const webrtc::RtpExtension* regular_extension = nullptr;
   for (RtpHeaderExtensions::const_iterator it = extensions.begin();
        it  != extensions.end(); ++it) {
     // We assume that all URIs are given in a canonical format.
     if (it->uri == ext_to_match.uri) {
-      if (found_extension != NULL) {
+      if (!found_extension) {
+        return true;
+      }
+      if (!encryption_preference || it->encrypt) {
         *found_extension = *it;
+        return true;
       }
-      return true;
+      regular_extension = &(*it);
     }
   }
+  if (regular_extension) {
+    *found_extension = *regular_extension;
+    return true;
+  }
   return false;
 }
 
@@ -984,15 +1010,35 @@ static void FindRtpHdrExtsToOffer(
   }
 }
 
+static void AddEncryptedVersionsOfHdrExts(RtpHeaderExtensions* extensions,
+                                          UsedRtpHeaderExtensionIds* used_ids) {
+  RtpHeaderExtensions encrypted_extensions;
+  for (const webrtc::RtpExtension& extension : *extensions) {
+    if (extension.encrypt ||

[Taylor Brandstetter, 2017/03/23 20:10:56]

Could you leave a comment explaining why "extension.encrypt" is checked? I
assume it's because this ensures that the encrypted extension isn't added twice
for a subsequent offer.

[joachim, 2017/03/30 22:43:49]

Done and also updated the condition.

+        !webrtc::RtpExtension::IsEncryptionSupported(extension.uri)) {
+      continue;
+    }
+
+    webrtc::RtpExtension encrypted(extension);
+    encrypted.encrypt = true;
+    used_ids->FindAndSetIdUsed(&encrypted);

[Taylor Brandstetter, 2017/03/23 20:10:56]

If the same encrypted extension is used for audio and video, won't this result
in it using different IDs? This could be solved by doing the same thing as in
FindRtpHdrExtsToOffer, using the "all_extensions" list.

[joachim, 2017/03/30 22:43:49]

Done. Also added a test for encrypted id reuse and offer update
("MediaSessionDescriptionFactoryTest::RtpExtensionIdReusedEncrypted").

+    encrypted_extensions.push_back(encrypted);
+  }
+  extensions->insert(extensions->end(), encrypted_extensions.begin(),
+      encrypted_extensions.end());
+}
+
 static void NegotiateRtpHeaderExtensions(
     const RtpHeaderExtensions& local_extensions,
     const RtpHeaderExtensions& offered_extensions,
+    bool enable_encrypted_rtp_header_extensions,
     RtpHeaderExtensions* negotiated_extenstions) {
   RtpHeaderExtensions::const_iterator ours;
   for (ours = local_extensions.begin();
        ours != local_extensions.end(); ++ours) {
     webrtc::RtpExtension theirs;
-    if (FindByUri(offered_extensions, *ours, &theirs)) {
+    if (FindByUriWithEncryptionPreference(offered_extensions, *ours,
+        enable_encrypted_rtp_header_extensions, &theirs)) {
       // We respond with their RTP header extension id.
       negotiated_extenstions->push_back(theirs);
     }
@@ -1027,6 +1073,7 @@ static bool CreateMediaContentAnswer(
     const SecurePolicy& sdes_policy,
     const CryptoParamsVec* current_cryptos,
     const RtpHeaderExtensions& local_rtp_extenstions,
+    bool enable_encrypted_rtp_header_extensions,
     StreamParamsVec* current_streams,
     bool add_legacy_stream,
     bool bundle_enabled,
@@ -1038,6 +1085,7 @@ static bool CreateMediaContentAnswer(
   RtpHeaderExtensions negotiated_rtp_extensions;
   NegotiateRtpHeaderExtensions(local_rtp_extenstions,
                                offer->rtp_header_extensions(),
+                               enable_encrypted_rtp_header_extensions,
                                &negotiated_rtp_extensions);
   answer->set_rtp_header_extensions(negotiated_rtp_extensions);
 
@@ -1605,6 +1653,10 @@ void MediaSessionDescriptionFactory::GetRtpHdrExtsToOffer(
                         &all_extensions, &used_ids);
   FindRtpHdrExtsToOffer(video_rtp_header_extensions(), video_extensions,
                         &all_extensions, &used_ids);
+  if (enable_encrypted_rtp_header_extensions_) {
+    AddEncryptedVersionsOfHdrExts(audio_extensions, &used_ids);
+    AddEncryptedVersionsOfHdrExts(video_extensions, &used_ids);
+  }
 }
 
 bool MediaSessionDescriptionFactory::AddTransportOffer(
@@ -1878,6 +1930,7 @@ bool MediaSessionDescriptionFactory::AddAudioContentForAnswer(
           sdes_policy,
           GetCryptos(GetFirstAudioContentDescription(current_description)),
           audio_rtp_extensions_,
+          enable_encrypted_rtp_header_extensions_,
           current_streams,
           add_legacy_,
           bundle_enabled,
@@ -1934,6 +1987,7 @@ bool MediaSessionDescriptionFactory::AddVideoContentForAnswer(
           sdes_policy,
           GetCryptos(GetFirstVideoContentDescription(current_description)),
           video_rtp_extensions_,
+          enable_encrypted_rtp_header_extensions_,
           current_streams,
           add_legacy_,
           bundle_enabled,
@@ -1995,6 +2049,7 @@ bool MediaSessionDescriptionFactory::AddDataContentForAnswer(
           sdes_policy,
           GetCryptos(GetFirstDataContentDescription(current_description)),
           RtpHeaderExtensions(),
+          enable_encrypted_rtp_header_extensions_,
           current_streams,
           add_legacy_,
           bundle_enabled,