[Bug]Handle SFU events for missing participant (#996)

Author: ipavlidakis

CHANGELOG.md

@@ -4,7 +4,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 # Upcoming
 
-### 🔄 Changed
+### 🐞 Fixed
+- Ensure SFU track and participant updates create missing participants. [#996](https://github.com/GetStream/stream-video-swift/pull/996)
 
 # [1.35.0](https://github.com/GetStream/stream-video-swift/releases/tag/1.35.0)
 _November 05, 2025_

Sources/StreamVideo/WebRTC/v2/SFU/SFUEventAdapter.swift

@@ -330,9 +330,7 @@ final class SFUEventAdapter: @unchecked Sendable {
         await stateAdapter.enqueue { participants in
             var updatedParticipants = participants
 
-            guard let participant = updatedParticipants[sessionID] else {
-                return participants
-            }
+            let participant = updatedParticipants[sessionID] ?? event.participant.toCallParticipant()
 
             switch event.type {
             case .audio:
@@ -390,9 +388,7 @@ final class SFUEventAdapter: @unchecked Sendable {
         await stateAdapter.enqueue { participants in
             var updatedParticipants = participants
 
-            guard let participant = updatedParticipants[sessionID] else {
-                return participants
-            }
+            let participant = updatedParticipants[sessionID] ?? event.participant.toCallParticipant()
 
             switch event.type {
             case .audio:
@@ -484,19 +480,20 @@ final class SFUEventAdapter: @unchecked Sendable {
         await stateAdapter.enqueue { participants in
             var updatedParticipants = participants
 
-            guard
-                let participant = updatedParticipants[event.participant.sessionID]
-            else {
-                return participants
+            if let participant = updatedParticipants[event.participant.sessionID] {
+                updatedParticipants[event.participant.sessionID] = event
+                    .participant
+                    .toCallParticipant()
+                    .withUpdated(showTrack: participant.showTrack)
+                    .withUpdated(pin: participant.pin)
+                    .withUpdated(track: participant.track)
+                    .withUpdated(screensharingTrack: participant.screenshareTrack)
+            } else {
+                updatedParticipants[event.participant.sessionID] = event
+                    .participant
+                    .toCallParticipant()
             }
 
-            updatedParticipants[event.participant.sessionID] = event
-                .participant
-                .toCallParticipant()
-                .withUpdated(showTrack: participant.showTrack)
-                .withUpdated(pin: participant.pin)
-                .withUpdated(track: participant.track)
-                .withUpdated(screensharingTrack: participant.screenshareTrack)
             return updatedParticipants
         }
     }

StreamVideoTests/WebRTC/SFU/SFUEventAdapter_Tests.swift

@@ -406,6 +406,22 @@ final class SFUEventAdapter_Tests: XCTestCase, @unchecked Sendable {
         }
     }
 
+    func test_handleTrackPublished_givenAudioEvent_participantDoesNotExist_whenPublished_thenAddsAndUpdatesParticipantAudioStatus(
+    ) async throws {
+        let participant = CallParticipant.dummy()
+        var event = Stream_Video_Sfu_Event_TrackPublished()
+        event.sessionID = participant.sessionId
+        event.type = .audio
+
+        try await assert(
+            event,
+            wrappedEvent: .sfuEvent(.trackPublished(event)),
+            initialState: [:]
+        ) {
+            $0.count == 1 && $0[participant.sessionId]?.hasAudio == true
+        }
+    }
+
     // MARK: trackUnpublished
 
     func test_handleTrackUnpublished_givenAudioEvent_whenPublished_thenUpdatesParticipantAudioStatus() async throws {
@@ -507,6 +523,22 @@ final class SFUEventAdapter_Tests: XCTestCase, @unchecked Sendable {
         }
     }
 
+    func test_handleTrackUnpublished_givenAudioEvent_participantDoesNotExist_whenPublished_thenAddsAndUpdatesParticipantAudioStatus(
+    ) async throws {
+        let participant = CallParticipant.dummy(hasAudio: true)
+        var event = Stream_Video_Sfu_Event_TrackUnpublished()
+        event.sessionID = participant.sessionId
+        event.type = .audio
+
+        try await assert(
+            event,
+            wrappedEvent: .sfuEvent(.trackUnpublished(event)),
+            initialState: [:]
+        ) {
+            $0.count == 1 && $0[participant.sessionId]?.hasAudio == false
+        }
+    }
+
     // MARK: pinsChanged
 
     func test_handlePinsChanged_givenEvent_whenPublished_thenUpdatesPinnedParticipants() async throws {
@@ -587,6 +619,23 @@ final class SFUEventAdapter_Tests: XCTestCase, @unchecked Sendable {
         }
     }
 
+    func test_handleParticipantUpdated_givenEvent_participantDoesNotExist_whenPublished_thenUAddsAndpdatesParticipant(
+    ) async throws {
+        var event = Stream_Video_Sfu_Event_ParticipantUpdated()
+        // We add the showTrack and audioLevels to match what the `event.participant.toCallParticipant()`
+        // does (defaults to showTrack:True and uses the audioLevel to create an array for the audioLevels.)
+        let expectedParticipant = CallParticipant.dummy(showTrack: true, audioLevels: [0])
+        event.participant = .init(expectedParticipant)
+
+        try await assert(
+            event,
+            wrappedEvent: .sfuEvent(.participantUpdated(event)),
+            initialState: [:]
+        ) {
+            $0.count == 1 && $0[expectedParticipant.sessionId] == expectedParticipant
+        }
+    }
+
     // MARK: publishOptionsChanged
 
     func test_handleChangePublishOptions_givenEvent_whenPublished_thenUpdatesPublishOptions() async throws {