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davidliu merged 2 commits into from
Nov 25, 2025
Merged

Model MockPeerConnection signaling state behavior closer to WebRTC spec #815

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3fc8df7
Model MockPeerConnection signaling state behavior closer to WebRTC spec
davidliu Nov 24, 2025
1fec1ce
more tests
davidliu Nov 25, 2025
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137 changes: 100 additions & 37 deletions livekit-android-test/src/main/java/io/livekit/android/test/mock/MockPeerConnection.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -47,39 +47,48 @@ class MockPeerConnection(
var localDesc: SessionDescription? = null
var remoteDesc: SessionDescription? = null

private val signalStateMachine = SignalStateMachine { newState ->
observer?.onSignalingChange(newState)
}

private val transceivers = mutableListOf<RtpTransceiver>()

override fun getLocalDescription(): SessionDescription? = localDesc
override fun setLocalDescription(observer: SdpObserver?, sdp: SessionDescription?) {
if (sdp?.description?.isEmpty() == true) {
observer?.onSetFailure("empty local description")
override fun setLocalDescription(observer: SdpObserver, sdp: SessionDescription) {
if (sdp.description.isEmpty()) {
observer.onSetFailure("empty local description")
return
}

// https://w3c.github.io/webrtc-pc/#fig-non-normative-signaling-state-transitions-diagram-method-calls-abbreviated
if (signalingState() == SignalingState.STABLE) {
remoteDesc = null
try {
signalStateMachine.handleSetMethod(Location.LOCAL, sdp.type)
} catch (e: IllegalStateException) {
observer.onSetFailure(e.message)
}

localDesc = sdp
observer?.onSetSuccess()
observer.onSetSuccess()

if (signalingState() == SignalingState.STABLE) {
moveToIceConnectionState(IceConnectionState.CONNECTED)
}
}

override fun getRemoteDescription(): SessionDescription? = remoteDesc
override fun setRemoteDescription(observer: SdpObserver?, sdp: SessionDescription?) {
if (sdp?.description?.isEmpty() == true) {
observer?.onSetFailure("empty remote description")
override fun setRemoteDescription(observer: SdpObserver, sdp: SessionDescription) {
if (sdp.description.isEmpty()) {
observer.onSetFailure("empty remote description")
return
}

// https://w3c.github.io/webrtc-pc/#fig-non-normative-signaling-state-transitions-diagram-method-calls-abbreviated
if (signalingState() == SignalingState.STABLE) {
localDesc = null
try {
signalStateMachine.handleSetMethod(Location.REMOTE, sdp.type)
} catch (e: IllegalStateException) {
observer.onSetFailure(e.message)
}

remoteDesc = sdp
observer?.onSetSuccess()
observer.onSetSuccess()

if (signalingState() == SignalingState.STABLE) {
moveToIceConnectionState(IceConnectionState.CONNECTED)
Expand Down Expand Up @@ -211,29 +220,7 @@ class MockPeerConnection(
override fun stopRtcEventLog() {
}

override fun signalingState(): SignalingState {
if (closed) {
return SignalingState.CLOSED
}

if ((localDesc?.type == null && remoteDesc?.type == null) ||
(localDesc?.type == SessionDescription.Type.OFFER &&
remoteDesc?.type == SessionDescription.Type.ANSWER) ||
(localDesc?.type == SessionDescription.Type.ANSWER &&
remoteDesc?.type == SessionDescription.Type.OFFER)
) {
return SignalingState.STABLE
}

if (localDesc?.type == SessionDescription.Type.OFFER && remoteDesc?.type == null) {
return SignalingState.HAVE_LOCAL_OFFER
}
if (remoteDesc?.type == SessionDescription.Type.OFFER && localDesc?.type == null) {
return SignalingState.HAVE_REMOTE_OFFER
}

throw IllegalStateException("Illegal signalling state? localDesc: $localDesc, remoteDesc: $remoteDesc")
}
override fun signalingState(): SignalingState = signalStateMachine.state

private var iceConnectionState = IceConnectionState.NEW
set(value) {
Expand Down Expand Up @@ -312,10 +299,86 @@ class MockPeerConnection(
override fun dispose() {
iceConnectionState = IceConnectionState.CLOSED
closed = true
signalStateMachine.close()

transceivers.forEach { t -> t.dispose() }
transceivers.clear()
}

override fun getNativePeerConnection(): Long = 0L
}

private class SignalStateMachine(
var changeListener: ((PeerConnection.SignalingState) -> Unit)? = null,
) {
var state = PeerConnection.SignalingState.STABLE
set(value) {
val changed = field != value
field = value
if (changed) {
changeListener?.invoke(field)
}
}

/**
* Throws if would go to invalid state.
*
* Does not handle PRANSWER or ROLLBACK.
*
* State machine as shown here:
* https://w3c.github.io/webrtc-pc/#fig-non-normative-signaling-state-transitions-diagram-method-calls-abbreviated
*/
@Throws(IllegalStateException::class)
fun handleSetMethod(location: Location, type: SessionDescription.Type) {
fun throwException() {
throw IllegalStateException("Illegal set of $location with $type on signal state $state")
}
when (state) {
PeerConnection.SignalingState.STABLE -> {
// Can only accept offers from stable
if (type != SessionDescription.Type.OFFER) {
throwException()
}
state = when (location) {
Location.LOCAL -> PeerConnection.SignalingState.HAVE_LOCAL_OFFER
Location.REMOTE -> PeerConnection.SignalingState.HAVE_REMOTE_OFFER
}
}

PeerConnection.SignalingState.HAVE_LOCAL_OFFER -> {
if (location == Location.LOCAL && type == SessionDescription.Type.OFFER) {
// legal, does not change state.
} else if (location == Location.REMOTE && type == SessionDescription.Type.ANSWER) {
state = PeerConnection.SignalingState.STABLE
} else {
throwException()
}
}

PeerConnection.SignalingState.HAVE_REMOTE_OFFER -> {
if (location == Location.REMOTE && type == SessionDescription.Type.OFFER) {
// legal, does not change state.
} else if (location == Location.LOCAL && type == SessionDescription.Type.ANSWER) {
state = PeerConnection.SignalingState.STABLE
} else {
throwException()
}
}

PeerConnection.SignalingState.HAVE_LOCAL_PRANSWER -> TODO()
PeerConnection.SignalingState.HAVE_REMOTE_PRANSWER -> TODO()
PeerConnection.SignalingState.CLOSED -> {
throw IllegalStateException("Closed")
}
}
}

fun close() {
state = PeerConnection.SignalingState.CLOSED
}
}

private enum class Location {
LOCAL,
REMOTE
}
168 changes: 168 additions & 0 deletions livekit-android-test/src/test/java/io/livekit/android/test/mock/MockPeerConnectionTest.kt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,168 @@
/*
* Copyright 2025 LiveKit, Inc.
*
* 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.
*/

package io.livekit.android.test.mock

import livekit.org.webrtc.PeerConnection
import livekit.org.webrtc.SdpObserver
import livekit.org.webrtc.SessionDescription
import org.junit.Assert.assertEquals
import org.junit.Before
import org.junit.Test
import org.mockito.Mockito.mock
import org.mockito.kotlin.any
import org.mockito.kotlin.times
import org.mockito.kotlin.verify

class MockPeerConnectionTest {

lateinit var pc: MockPeerConnection

@Before
fun setup() {
pc = MockPeerConnection(PeerConnection.RTCConfiguration(emptyList()), null)
}

@Test
fun publisherNegotiation() {
run {
val observer = mock<SdpObserver>()
pc.setLocalDescription(
observer,
SessionDescription(SessionDescription.Type.OFFER, "local_offer"),
)
verify(observer, times(1)).onSetSuccess()
assertEquals(PeerConnection.SignalingState.HAVE_LOCAL_OFFER, pc.signalingState())
}
run {
val observer = mock<SdpObserver>()
pc.setRemoteDescription(
observer,
SessionDescription(SessionDescription.Type.ANSWER, "remote_answer"),
)
verify(observer, times(1)).onSetSuccess()
assertEquals(PeerConnection.SignalingState.STABLE, pc.signalingState())
}
}

@Test
fun subscriberNegotiation() {
run {
val observer = mock<SdpObserver>()
pc.setRemoteDescription(
observer,
SessionDescription(SessionDescription.Type.OFFER, "remote_offer"),
)
verify(observer, times(1)).onSetSuccess()
assertEquals(PeerConnection.SignalingState.HAVE_REMOTE_OFFER, pc.signalingState())
}
run {
val observer = mock<SdpObserver>()
pc.setLocalDescription(
observer,
SessionDescription(SessionDescription.Type.ANSWER, "local_answer"),
)
verify(observer, times(1)).onSetSuccess()
assertEquals(PeerConnection.SignalingState.STABLE, pc.signalingState())
}
}

@Test
fun cannotSetAnswerOnStable() {
run {
val observer = mock<SdpObserver>()
pc.setLocalDescription(
observer,
SessionDescription(SessionDescription.Type.ANSWER, "local_answer"),
)
verify(observer, times(1)).onSetFailure(any())
assertEquals(PeerConnection.SignalingState.STABLE, pc.signalingState())
}
run {
val observer = mock<SdpObserver>()
pc.setRemoteDescription(
observer,
SessionDescription(SessionDescription.Type.ANSWER, "remote_answer"),
)
verify(observer, times(1)).onSetFailure(any())
assertEquals(PeerConnection.SignalingState.STABLE, pc.signalingState())
}
}

@Test
fun cannotIllegalSetOnHaveLocalOffer() {
run {
val observer = mock<SdpObserver>()
pc.setLocalDescription(
observer,
SessionDescription(SessionDescription.Type.OFFER, "local_offer"),
)
assertEquals(PeerConnection.SignalingState.HAVE_LOCAL_OFFER, pc.signalingState())
}

run {
val observer = mock<SdpObserver>()
pc.setLocalDescription(
observer,
SessionDescription(SessionDescription.Type.ANSWER, "local_answer"),
)
verify(observer, times(1)).onSetFailure(any())
assertEquals(PeerConnection.SignalingState.HAVE_LOCAL_OFFER, pc.signalingState())
}

run {
val observer = mock<SdpObserver>()
pc.setRemoteDescription(
observer,
SessionDescription(SessionDescription.Type.OFFER, "remote_offer"),
)
verify(observer, times(1)).onSetFailure(any())
assertEquals(PeerConnection.SignalingState.HAVE_LOCAL_OFFER, pc.signalingState())
}
}

@Test
fun cannotIllegalSetOnHaveRemoteOffer() {
run {
val observer = mock<SdpObserver>()
pc.setRemoteDescription(
observer,
SessionDescription(SessionDescription.Type.OFFER, "remote_offer"),
)
assertEquals(PeerConnection.SignalingState.HAVE_REMOTE_OFFER, pc.signalingState())
}

run {
val observer = mock<SdpObserver>()
pc.setLocalDescription(
observer,
SessionDescription(SessionDescription.Type.OFFER, "local_offer"),
)
verify(observer, times(1)).onSetFailure(any())
assertEquals(PeerConnection.SignalingState.HAVE_REMOTE_OFFER, pc.signalingState())
}

run {
val observer = mock<SdpObserver>()
pc.setRemoteDescription(
observer,
SessionDescription(SessionDescription.Type.ANSWER, "remote_offer"),
)
verify(observer, times(1)).onSetFailure(any())
assertEquals(PeerConnection.SignalingState.HAVE_REMOTE_OFFER, pc.signalingState())
}
}
}