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Fix silent hang in message processing loop when deserialization fails #15578

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Fix silent hang in message processing loop when deserialization fails #15578

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764b674
Fix silent hang in message processing loop when deserialization fails
nohwnd Mar 24, 2026
ad81f8a
retrigger CI
nohwnd Mar 24, 2026
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12 changes: 12 additions & 0 deletions src/Microsoft.TestPlatform.Client/DesignMode/DesignModeClient.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -291,6 +291,18 @@ private void ProcessRequests(ITestRequestManager testRequestManager)
catch (Exception ex)
{
EqtTrace.Error("DesignModeClient: Error processing request: {0}", ex);

// Notify the caller (IDE) about the error so it does not hang
// waiting for a response that will never come.
try
{
_communicationManager.SendMessage(MessageType.ProtocolError, ex.Message);
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Copilot AI Mar 24, 2026

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Using ex.Message alone can be empty and loses the exception type/context, which makes the ProtocolError less actionable for the IDE/user. Consider including at least the exception type + message (e.g., ${ex.GetType().FullName}: ${ex.Message}) or a structured error payload, while being mindful of not sending overly large data (stack traces) over the protocol unless explicitly desired.

Suggested change
_communicationManager.SendMessage(MessageType.ProtocolError, ex.Message);
_communicationManager.SendMessage(
MessageType.ProtocolError,
string.Format(
CultureInfo.InvariantCulture,
"{0}: {1}",
ex.GetType().FullName,
ex.Message));

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}
catch (Exception sendEx)
{
EqtTrace.Error("DesignModeClient: Failed to send ProtocolError to client: {0}", sendEx);
}
Comment on lines +295 to +304
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Copilot AI Mar 24, 2026

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This introduces a repeated pattern (log error → try send ProtocolError → log send failure). Since similar logic now exists on both sides (testhost + vstest.console), consider extracting a small helper (per component) like TrySendProtocolError(Exception ex) to keep exception paths consistent and reduce future drift (e.g., message formatting, telemetry, or fallback behavior).

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Stop();
}
}
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26 changes: 26 additions & 0 deletions src/Microsoft.TestPlatform.CrossPlatEngine/EventHandlers/TestRequestHandler.cs
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Expand Up @@ -323,6 +323,32 @@ public bool AttachDebuggerToProcess(AttachDebuggerInfo attachDebuggerInfo)
}

public void OnMessageReceived(object? sender, MessageReceivedEventArgs messageReceivedArgs)
{
try
{
OnMessageReceivedCore(messageReceivedArgs);
}
catch (Exception ex)
{
EqtTrace.Error("TestRequestHandler.OnMessageReceived: Failed to process message, sending ProtocolError and closing session: {0}", ex);

// Notify the caller about the error so it does not hang
// waiting for a response that will never come.
try
{
SendData(_dataSerializer.SerializePayload(MessageType.ProtocolError, ex.Message));
}
catch (Exception sendEx)
{
EqtTrace.Error("TestRequestHandler.OnMessageReceived: Failed to send ProtocolError: {0}", sendEx);
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Copilot AI Mar 24, 2026

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The PR description calls out failures due to missing System.Text.Json dependencies during deserialization. In that failure mode, _dataSerializer.SerializePayload(...) is likely to fail for the same reason, which would prevent ProtocolError from being sent and can reintroduce the hang. Consider a fallback error-notification path that does not depend on the JSON serializer (e.g., sending a minimal pre-serialized frame / raw transport-level error message if supported), or ensure the communication layer can emit ProtocolError even when payload serialization fails.

Suggested change
EqtTrace.Error("TestRequestHandler.OnMessageReceived: Failed to send ProtocolError: {0}", sendEx);
EqtTrace.Error("TestRequestHandler.OnMessageReceived: Failed to send ProtocolError using serializer: {0}", sendEx);
// Fallback: attempt to send a minimal, serializer-independent error message
try
{
var fallbackMessage = "ProtocolError: " + ex.ToString();
EqtTrace.Verbose("TestRequestHandler.OnMessageReceived: Sending fallback ProtocolError message without serializer: {0}", fallbackMessage);
SendData(fallbackMessage);
}
catch (Exception fallbackEx)
{
EqtTrace.Error("TestRequestHandler.OnMessageReceived: Failed to send fallback ProtocolError message: {0}", fallbackEx);
}

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}

_sessionCompleted.Set();
Close();
}
}

private void OnMessageReceivedCore(MessageReceivedEventArgs messageReceivedArgs)
{
var message = _dataSerializer.DeserializeMessage(messageReceivedArgs.Data!);
EqtTrace.Info("TestRequestHandler.OnMessageReceived: received message: {0}", message);
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