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fix: handle CancellationException in WebSocketTransport #663

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fix: handle CancellationException in WebSocketTransport #663

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c4fa2df
Handle `CancellationException` gracefully and enable ignored tests
devcrocod Apr 1, 2026
c39d4ab
Merge branch 'main' into devcrocod/websocket-transport-cancellation
devcrocod Apr 14, 2026
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8 changes: 4 additions & 4 deletions ...tlin/sdk/client/WebSocketTransportTest.kt → ...tlin/sdk/client/WebSocketTransportTest.kt
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
package io.modelcontextprotocol.kotlin.sdk.client

Check failure on line 1 in integration-test/src/jvmTest/kotlin/io/modelcontextprotocol/kotlin/sdk/client/WebSocketTransportTest.kt

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WebSocketTransportTest.should start then close cleanly()[jvm] 

org.opentest4j.AssertionFailedError: Block failed after 2.000900139s; attempted 71 time(s)
The first error was caused by: expected:<false> but was:<true>
org.opentest4j.AssertionFailedError: expected:<false> but was:<true>
	at io.modelcontextprotocol.kotlin.sdk.shared.BaseTransportTest$testTransportOpenClose$4.invokeSuspend(BaseTransportTest.kt:27)
	at io.modelcontextprotocol.kotlin.sdk.shared.BaseTransportTest$testTransportOpenClose$4.invoke(BaseTransportTest.kt)
	at io.modelcontextprotocol.kotlin.sdk.shared.BaseTransportTest$testTransportOpenClose$4.invoke(BaseTransportTest.kt)
	at io.kotest.assertions.nondeterministic.EventuallyKt.runIterations(eventually.kt:114)
	at io.kotest.assertions.nondeterministic.EventuallyKt.access$runIterations(eventually.kt:1)
	at io.kotest.assertions.nondeterministic.EventuallyKt$eventually$6.invokeSuspend(eventually.kt:92)
	at io.kotest.assertions.nondeterministic.EventuallyKt$eventually$6.invoke(eventually.kt)
	at io.kotest.assertions.nondeterministic.EventuallyKt$eventually$6.invoke(eventually.kt)
	at io.kotest.common.WithNonVirtualTimeoutKt$withWallClockTimeout$2$blockDeferred$1.invokeSuspend(withNonVirtualTimeout.kt:50)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:34)
	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:100)
	at kotlinx.coroutines.internal.LimitedDispatcher$Worker.run(LimitedDispatcher.kt:124)
	at kotlinx.coroutines.scheduling.TaskImpl.run(Tasks.kt:89)
	at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:586)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:829)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:717)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:704)

The last error was caused by: expected:<false> but was:<true>
org.opentest4j.AssertionFailedError: expected:<false> but was:<true>
	at io.modelcontextprotocol.kotlin.sdk.shared.BaseTransportTest$testTransportOpenClose$4.invokeSuspend(BaseTransportTest.kt:27)
	at io.modelcontextprotocol.kotlin.sdk.shared.BaseTransportTest$testTransportOpenClose$4.invoke(BaseTransportTest.kt)
	at io.modelcontextprotocol.kotlin.sdk.shared.BaseTransportTest$testTransportOpenClose$4.invoke(BaseTransportTest.kt)
	at io.kotest.assertions.nondeterministic.EventuallyKt.runIterations(eventually.kt:114)
	at io.kotest.assertions.nondeterministic.EventuallyKt.access$runIterations(eventually.kt:1)
	at io.kotest.assertions.nondeterministic.EventuallyKt$runIterations$1.invokeSuspend(eventually.kt)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:34)
	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:100)
	at kotlinx.coroutines.internal.LimitedDispatcher$Worker.run(LimitedDispatcher.kt:124)
	at kotlinx.coroutines.scheduling.TaskImpl.run(Tasks.kt:89)
	at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:586)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:829)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:717)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:704)

import io.ktor.server.testing.testApplication
import io.ktor.server.websocket.WebSockets
Expand All @@ -6,12 +6,13 @@
import io.modelcontextprotocol.kotlin.sdk.server.mcpWebSocketTransport
import io.modelcontextprotocol.kotlin.sdk.shared.BaseTransportTest
import kotlinx.coroutines.CompletableDeferred
import kotlin.test.Ignore
import kotlin.test.Test
import org.junit.jupiter.api.Test
import org.junit.jupiter.api.Timeout
import java.util.concurrent.TimeUnit

@Timeout(30, unit = TimeUnit.SECONDS)
class WebSocketTransportTest : BaseTransportTest() {
@Test
@Ignore // "Test disabled for investigation #17"
fun `should start then close cleanly`() = testApplication {
install(WebSockets)
routing {
Expand All @@ -26,7 +27,6 @@
}

@Test
@Ignore // "Test disabled for investigation #17"
fun `should read messages`() = testApplication {
val clientFinished = CompletableDeferred<Unit>()

Expand Down
5 changes: 2 additions & 3 deletions .../src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/shared/WebSocketMcpTransport.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -7,9 +7,9 @@ import io.ktor.websocket.close
import io.ktor.websocket.readText
import io.modelcontextprotocol.kotlin.sdk.types.JSONRPCMessage
import io.modelcontextprotocol.kotlin.sdk.types.McpJson
import kotlinx.coroutines.CancellationException
import kotlinx.coroutines.CoroutineName
Comment on lines 8 to 11
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Copilot AI Apr 10, 2026

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CancellationException is imported from kotlinx.coroutines here, but other commonMain code in this module uses kotlin.coroutines.cancellation.CancellationException (e.g., AbstractClientTransport). Consider switching to the stdlib import for consistency and to avoid confusion with java.util.concurrent.CancellationException on JVM.

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import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.InternalCoroutinesApi
import kotlinx.coroutines.SupervisorJob
import kotlinx.coroutines.channels.ClosedReceiveChannelException
import kotlinx.coroutines.job
Expand Down Expand Up @@ -81,9 +81,8 @@ public abstract class WebSocketMcpTransport : AbstractTransport() {
}
}

@OptIn(InternalCoroutinesApi::class)
session.coroutineContext.job.invokeOnCompletion {
if (it != null) {
if (it != null && it !is CancellationException) {
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@kpavlov kpavlov Apr 1, 2026

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Shouldn’t the CancellationException be also rethrown?

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@devcrocod devcrocod Apr 10, 2026

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No, rethrowing here would be incorrect

_onError.invoke(it)
} else {
invokeOnCloseCallback()
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