Fix set_remote_description failing on description with rejected m-lines

lib/ex_webrtc/peer_connection.ex

@@ -1398,10 +1398,8 @@ defmodule ExWebRTC.PeerConnection do
   defp apply_remote_description(%SessionDescription{type: type, sdp: raw_sdp}, state) do
     with {:ok, next_sig_state} <- next_signaling_state(state.signaling_state, :remote, type),
          {:ok, sdp} <- parse_sdp(raw_sdp),
-         :ok <- SDPUtils.ensure_mid(sdp),
-         :ok <- SDPUtils.ensure_bundle(sdp),
-         :ok <- SDPUtils.ensure_rtcp_mux(sdp),
-         {:ok, {ice_ufrag, ice_pwd}} <- SDPUtils.get_ice_credentials(sdp),
+         :ok <- SDPUtils.ensure_valid(sdp),
+         {:ok, ice_creds} <- SDPUtils.get_ice_credentials(sdp),
          {:ok, {:fingerprint, {:sha256, peer_fingerprint}}} <- SDPUtils.get_cert_fingerprint(sdp),
          {:ok, dtls_role} <- SDPUtils.get_dtls_role(sdp) do
       config = Configuration.update(state.config, sdp)
@@ -1420,8 +1418,16 @@ defmodule ExWebRTC.PeerConnection do
       dtls_role = if dtls_role in [:actpass, :passive], do: :active, else: :passive
       DTLSTransport.start_dtls(state.dtls_transport, dtls_role, peer_fingerprint)
 
+      # ice_creds will be nil if all of the mlines in the description are rejected
+      # in such case, if this is the first remote description, connection won't be established
       # TODO: this can result in ICE restart (when it should, e.g. when this is answer)
-      :ok = state.ice_transport.set_remote_credentials(state.ice_pid, ice_ufrag, ice_pwd)
+      case ice_creds do
+        nil ->
+          :ok
+
+        {ice_ufrag, ice_pwd} ->
+          :ok = state.ice_transport.set_remote_credentials(state.ice_pid, ice_ufrag, ice_pwd)
+      end
 
       for candidate <- SDPUtils.get_ice_candidates(sdp) do
         state.ice_transport.add_remote_candidate(state.ice_pid, candidate)

lib/ex_webrtc/sdp_utils.ex

@@ -8,8 +8,24 @@ defmodule ExWebRTC.SDPUtils do
 
   @type extension() :: {Extension.SourceDescription, atom()}
 
-  @spec ensure_mid(ExSDP.t()) :: :ok | {:error, :missing_mid | :duplicated_mid}
-  def ensure_mid(sdp) do
+  @spec ensure_valid(ExSDP.t()) :: :ok | {:error, term()}
+  def ensure_valid(sdp) do
+    with :ok <- ensure_non_empty(sdp),
+         :ok <- ensure_mid(sdp),
+         :ok <- ensure_bundle(sdp) do
+      ensure_rtcp_mux(sdp)
+    end
+  end
+
+  defp ensure_non_empty(sdp) do
+    if Enum.empty?(sdp.media) do
+      {:error, :empty_sdp}
+    else
+      :ok
+    end
+  end
+
+  defp ensure_mid(sdp) do
     sdp.media
     |> Enum.reduce_while({:ok, []}, fn media, {:ok, acc} ->
       case ExSDP.get_attributes(media, :mid) do
@@ -24,14 +40,7 @@ defmodule ExWebRTC.SDPUtils do
     end
   end
 
-  @spec ensure_bundle(ExSDP.t()) ::
-          :ok
-          | {:error,
-             :non_exhaustive_bundle_group
-             | :missing_bundle_group
-             | :multiple_bundle_groups
-             | :invalid_bundle_group}
-  def ensure_bundle(sdp) do
+  defp ensure_bundle(sdp) do
     groups = ExSDP.get_attributes(sdp, ExSDP.Attribute.Group)
 
     mline_mids = get_bundle_mids(sdp.media)
@@ -56,8 +65,7 @@ defmodule ExWebRTC.SDPUtils do
     Enum.filter(groups, fn %ExSDP.Attribute.Group{semantics: name} -> name == to_filter end)
   end
 
-  @spec ensure_rtcp_mux(ExSDP.t()) :: :ok | {:error, :missing_rtcp_mux}
-  def ensure_rtcp_mux(sdp) do
+  defp ensure_rtcp_mux(sdp) do
     sdp.media
     |> Enum.all?(&(ExSDP.get_attribute(&1, :rtcp_mux) == :rtcp_mux))
     |> case do
@@ -116,20 +124,24 @@ defmodule ExWebRTC.SDPUtils do
   end
 
   @spec get_ice_credentials(ExSDP.t()) ::
-          {:ok, {binary(), binary()}}
+          {:ok, {binary(), binary()} | nil}
           | {:error,
              :missing_ice_pwd
              | :missing_ice_ufrag
              | :missing_ice_credentials
              | :conflicting_ice_credentials}
   def get_ice_credentials(sdp) do
     session_creds = do_get_ice_credentials(sdp)
-    mline_creds = Enum.map(sdp.media, fn mline -> do_get_ice_credentials(mline) end)
+
+    mline_creds =
+      sdp.media
+      |> Enum.reject(&rejected?/1)
+      |> Enum.map(&do_get_ice_credentials/1)
 
     case {session_creds, mline_creds} do
       # no session creds and no mlines (empty SDP)
       {{nil, nil}, []} ->
-        {:error, :missing_ice_credentials}
+        {:ok, nil}
 
       # session creds but no mlines (empty SDP)
       {session_creds, []} ->

test/ex_webrtc/peer_connection_test.exs

@@ -467,6 +467,56 @@ defmodule ExWebRTC.PeerConnectionTest do
         assert expected_result == PeerConnection.set_remote_description(pc, offer)
       end)
     end
+
+    test "mline rejected" do
+      {:ok, pc} = PeerConnection.start_link()
+
+      {:ok, _sender} = PeerConnection.add_track(pc, MediaStreamTrack.new(:video))
+      {:ok, _sender} = PeerConnection.add_track(pc, MediaStreamTrack.new(:audio))
+      {:ok, offer} = PeerConnection.create_offer(pc)
+      :ok = PeerConnection.set_local_description(pc, offer)
+
+      # first m-line is rejected = ice ufrag and passwd are random (thats what Chromium seems to do)
+      sdp =
+        """
+        v=0
+        o=- 4455712322662451611 2 IN IP4 127.0.0.1
+        s=-
+        t=0 0
+        a=group:BUNDLE 1
+        a=extmap-allow-mixed
+        a=msid-semantic: WMS
+        m=video 0 UDP/TLS/RTP/SAVPF 0
+        c=IN IP4 0.0.0.0
+        a=rtcp:9 IN IP4 0.0.0.0
+        a=ice-ufrag:oIRa
+        a=ice-pwd:10rPa8NrMCm602mt1OVkUHJs
+        a=ice-options:trickle
+        a=fingerprint:sha-256 C8:06:34:28:7C:5B:55:00:42:61:54:D2:84:29:B5:07:3D:9A:6C:5C:C6:79:B1:B0:A8:12:30:AD:26:36:93:45
+        a=setup:active
+        a=mid:0
+        a=sendonly
+        a=rtcp-mux
+        m=audio 9 UDP/TLS/RTP/SAVPF 111
+        c=IN IP4 0.0.0.0
+        a=rtcp:9 IN IP4 0.0.0.0
+        a=ice-ufrag:Anyh
+        a=ice-pwd:cdaU0jbHlOTf98BNTRoZxMo1
+        a=ice-options:trickle
+        a=fingerprint:sha-256 C8:06:34:28:7C:5B:55:00:42:61:54:D2:84:29:B5:07:3D:9A:6C:5C:C6:79:B1:B0:A8:12:30:AD:26:36:93:45
+        a=setup:active
+        a=mid:1
+        a=recvonly
+        a=rtcp-mux
+        a=rtpmap:111 opus/48000/2
+        a=rtcp-fb:111 transport-cc
+        a=fmtp:111 minptime=10;useinbandfec=1
+        """
+
+      answer = %SessionDescription{type: :answer, sdp: sdp}
+
+      assert :ok = PeerConnection.set_remote_description(pc, answer)
+    end
   end
 
   describe "add_transceiver/3" do