NetEq: Handle nested RED packets

This CL makes NetEq handle nested RED packets without crashing. Nested
RED packets mean that the block PT (see
https://tools.ietf.org/html/rfc2198.html#section-3) in the RED packet
is also set to the RED PT. This implies a nested RED packet, which is
not supported. Instead, all payloads in a RED packet that have the RED
PT will be discarded.

Bug: chromium:851662
Change-Id: I86ec257e60fb8076e3574ac5a4a1ca50196f6b34
Reviewed-on: https://webrtc-review.googlesource.com/86824
Commit-Queue: Henrik Lundin <henrik.lundin@webrtc.org>
Reviewed-by: Ivo Creusen <ivoc@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23825}

modules/audio_coding/neteq/mock/mock_red_payload_splitter.h

@@ -21,7 +21,7 @@ class MockRedPayloadSplitter : public RedPayloadSplitter {
  public:
   MOCK_METHOD1(SplitRed, bool(PacketList* packet_list));
   MOCK_METHOD2(CheckRedPayloads,
-               int(PacketList* packet_list,
+               void(PacketList* packet_list,
                     const DecoderDatabase& decoder_database));
 };
 

modules/audio_coding/neteq/neteq_impl.cc

@@ -612,6 +612,9 @@ int NetEqImpl::InsertPacketInternal(const RTPHeader& rtp_header,
     // Only accept a few RED payloads of the same type as the main data,
     // DTMF events and CNG.
     red_payload_splitter_->CheckRedPayloads(&packet_list, *decoder_database_);
+    if (packet_list.empty()) {
+      return kRedundancySplitError;
+    }
   }
 
   // Check payload types.

modules/audio_coding/neteq/red_payload_splitter.cc

@@ -130,13 +130,16 @@ bool RedPayloadSplitter::SplitRed(PacketList* packet_list) {
   return ret;
 }
 
-int RedPayloadSplitter::CheckRedPayloads(
+void RedPayloadSplitter::CheckRedPayloads(
     PacketList* packet_list,
     const DecoderDatabase& decoder_database) {
   int main_payload_type = -1;
-  int num_deleted_packets = 0;
   for (auto it = packet_list->begin(); it != packet_list->end(); /* */) {
     uint8_t this_payload_type = it->payload_type;
+    if (decoder_database.IsRed(this_payload_type)) {
+      it = packet_list->erase(it);
+      continue;
+    }
     if (!decoder_database.IsDtmf(this_payload_type) &&
         !decoder_database.IsComfortNoise(this_payload_type)) {
       if (main_payload_type == -1) {
@@ -149,14 +152,12 @@ int RedPayloadSplitter::CheckRedPayloads(
           // moves the iterator |it| to the next packet in the list. Thus, we
           // do not have to increment it manually.
           it = packet_list->erase(it);
-          ++num_deleted_packets;
           continue;
         }
       }
     }
     ++it;
   }
-  return num_deleted_packets;
 }
 
 }  // namespace webrtc

modules/audio_coding/neteq/red_payload_splitter.h

@@ -38,9 +38,8 @@ class RedPayloadSplitter {
 
   // Checks all packets in |packet_list|. Packets that are DTMF events or
   // comfort noise payloads are kept. Except that, only one single payload type
-  // is accepted. Any packet with another payload type is discarded.  Returns
-  // the number of discarded packets.
-  virtual int CheckRedPayloads(PacketList* packet_list,
+  // is accepted. Any packet with another payload type is discarded.
+  virtual void CheckRedPayloads(PacketList* packet_list,
                                 const DecoderDatabase& decoder_database);
 
  private:

modules/audio_coding/neteq/red_payload_splitter_unittest.cc

@@ -319,6 +319,30 @@ TEST(RedPayloadSplitter, CheckRedPayloads) {
   EXPECT_TRUE(packet_list.empty());
 }
 
+// This test creates a RED packet where the payloads also have the payload type
+// for RED. That is, some kind of weird nested RED packet. This is not supported
+// and the splitter should discard all packets.
+TEST(RedPayloadSplitter, CheckRedPayloadsRecursiveRed) {
+  PacketList packet_list;
+  for (uint8_t i = 0; i <= 3; ++i) {
+    // Create packet with RED payload type, payload length 10 bytes, all 0.
+    packet_list.push_back(CreatePacket(kRedPayloadType, 10, 0));
+  }
+
+  // Use a real DecoderDatabase object here instead of a mock, since it is
+  // easier to just register the payload types and let the actual implementation
+  // do its job.
+  DecoderDatabase decoder_database(
+      new rtc::RefCountedObject<MockAudioDecoderFactory>, absl::nullopt);
+  decoder_database.RegisterPayload(kRedPayloadType, NetEqDecoder::kDecoderRED,
+                                   "red");
+
+  RedPayloadSplitter splitter;
+  splitter.CheckRedPayloads(&packet_list, decoder_database);
+
+  EXPECT_TRUE(packet_list.empty());  // Should have dropped all packets.
+}
+
 // Packet A is split into A1, A2 and A3. But the length parameter is off, so
 // the last payloads should be discarded.
 TEST(RedPayloadSplitter, WrongPayloadLength) {