Fix unknown SID from local track (#270)

* Add test coverage

* Update SID after publication complete

* Clean up

* Make setSID protected

* Also test audio track

Author: ladvoc

include/livekit/local_audio_track.h

@@ -116,6 +116,9 @@ class LIVEKIT_API LocalAudioTrack : public Track {
   /// the association.
   void setPublication(const std::shared_ptr<LocalTrackPublication>& publication) noexcept override {
     local_publication_ = publication;
+    if (publication) {
+      setSid(publication->sid());
+    }
   }
 
 private:

include/livekit/local_video_track.h

@@ -89,6 +89,9 @@ class LIVEKIT_API LocalVideoTrack : public Track {
   /// a true move but is a API-breaking change hence left for a future revision.
   void setPublication(const std::shared_ptr<LocalTrackPublication>& publication) noexcept override {
     local_publication_ = publication;
+    if (publication) {
+      setSid(publication->sid());
+    }
   }
 
 private:

include/livekit/track.h

@@ -122,6 +122,8 @@ class LIVEKIT_API Track {
   Track(FfiHandle handle, std::string sid, std::string name, TrackKind kind, StreamState state, bool muted,
         bool remote);
 
+  void setSid(std::string sid) noexcept { sid_ = std::move(sid); }
+
   void setPublicationFields(std::optional<TrackSource> source, std::optional<bool> simulcasted,
                             std::optional<uint32_t> width, std::optional<uint32_t> height,
                             std::optional<std::string> mime_type);

src/tests/integration/test_local_track_publish_sid.cpp

@@ -0,0 +1,76 @@
+/*
+ * Copyright 2026 LiveKit
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <gtest/gtest.h>
+
+#include <memory>
+#include <string>
+
+#include "../common/audio_utils.h"
+#include "../common/test_common.h"
+
+namespace livekit::test {
+namespace {
+
+void expectTrackSidAssigned(const Track& track, const LocalTrackPublication& publication) {
+  const std::string& track_sid = track.sid();
+  const std::string& publication_sid = publication.sid();
+  EXPECT_NE(track_sid, "TR_unknown");
+  EXPECT_FALSE(track_sid.empty());
+  EXPECT_EQ(track_sid, publication_sid);
+}
+
+} // namespace
+
+class LocalTrackPublishSidTest : public LiveKitTestBase {};
+
+TEST_F(LocalTrackPublishSidTest, PublishVideoTrackAssignsSid) {
+  failIfNotConfigured();
+
+  Room room;
+  const RoomOptions room_options;
+  ASSERT_TRUE(room.connect(config_.url, config_.token_a, room_options));
+
+  auto source = std::make_shared<EncodedVideoSource>(VideoCodec::H264, 16, 16);
+  std::shared_ptr<LocalVideoTrack> track;
+  ASSERT_NO_THROW(
+      track = lockLocalParticipant(room)->publishVideoTrack("video-sid-check", source, TrackSource::SOURCE_CAMERA));
+  ASSERT_NE(track, nullptr);
+  ASSERT_NE(track->publication(), nullptr);
+
+  expectTrackSidAssigned(*track, *track->publication());
+  lockLocalParticipant(room)->unpublishTrack(track->publication()->sid());
+}
+
+TEST_F(LocalTrackPublishSidTest, PublishAudioTrackAssignsSid) {
+  failIfNotConfigured();
+
+  Room room;
+  const RoomOptions room_options;
+  ASSERT_TRUE(room.connect(config_.url, config_.token_a, room_options));
+
+  auto source = std::make_shared<AudioSource>(kDefaultAudioSampleRate, kDefaultAudioChannels, 0);
+  std::shared_ptr<LocalAudioTrack> track;
+  ASSERT_NO_THROW(
+      track = lockLocalParticipant(room)->publishAudioTrack("audio-sid-check", source, TrackSource::SOURCE_MICROPHONE));
+  ASSERT_NE(track, nullptr);
+  ASSERT_NE(track->publication(), nullptr);
+
+  expectTrackSidAssigned(*track, *track->publication());
+  lockLocalParticipant(room)->unpublishTrack(track->publication()->sid());
+}
+
+} // namespace livekit::test