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Improve testing for StreamableHttpHandler and IdleTrackingBackgroundService (#345)

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* Add idle session pruning tests
* Remove redundant CTS from StreamableHttpHandler
  * StreamableHttpServerTransport.HandlePostRequest already creates the equivelant CTS
    which DeleteRequest_CompletesSession_WhichCancelsLongRunningToolCalls verifies
* Fix accept header validation for GET
* Use InvalidOperationException for transport-not-connected errors in doc comments
* Fix flaky Cancellation_ThrowsCancellationException test
This commit is contained in:
Stephen Halter 2025-04-24 10:49:02 -07:00 • committed by GitHub
commit e3ff552824
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1 changed files with 315 additions and 291 deletions
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97
src/ModelContextProtocol.AspNetCore/IdleTrackingBackgroundService.cs
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@ -8,28 +8,40 @@ namespace ModelContextProtocol.AspNetCore;
internal sealed partial class IdleTrackingBackgroundService(
StreamableHttpHandler handler,
IOptions<HttpServerTransportOptions> options,
IHostApplicationLifetime appLifetime,
ILogger<IdleTrackingBackgroundService> logger) : BackgroundService
{
// The compiler will complain about the parameter being unused otherwise despite the source generator.
private ILogger _logger = logger;
// We can make this configurable once we properly harden the MCP server. In the meantime, anyone running
// this should be taking a cattle not pets approach to their servers and be able to launch more processes
// to handle more than 10,000 idle sessions at a time.
private const int MaxIdleSessionCount = 10_000;
protected override async Task ExecuteAsync(CancellationToken stoppingToken)
{
var timeProvider = options.Value.TimeProvider;
using var timer = new PeriodicTimer(TimeSpan.FromSeconds(5), timeProvider);
// Still run loop given infinite IdleTimeout to enforce the MaxIdleSessionCount and assist graceful shutdown.
if (options.Value.IdleTimeout != Timeout.InfiniteTimeSpan)
{
ArgumentOutOfRangeException.ThrowIfLessThan(options.Value.IdleTimeout, TimeSpan.Zero);
}
ArgumentOutOfRangeException.ThrowIfLessThan(options.Value.MaxIdleSessionCount, 0);
try
{
var timeProvider = options.Value.TimeProvider;
using var timer = new PeriodicTimer(TimeSpan.FromSeconds(5), timeProvider);
var idleTimeoutTicks = options.Value.IdleTimeout.Ticks;
var maxIdleSessionCount = options.Value.MaxIdleSessionCount;
// The default ValueTuple Comparer will check the first item then the second which preserves both order and uniqueness.
var idleSessions = new SortedSet<(long Timestamp, string SessionId)>();
while (!stoppingToken.IsCancellationRequested && await timer.WaitForNextTickAsync(stoppingToken))
{
var idleActivityCutoff = timeProvider.GetTimestamp() - options.Value.IdleTimeout.Ticks;
var idleActivityCutoff = idleTimeoutTicks switch
{
< 0 => long.MinValue,
var ticks => timeProvider.GetTimestamp() - ticks,
};
var idleCount = 0;
foreach (var (_, session) in handler.Sessions)
{
if (session.IsActive || session.SessionClosed.IsCancellationRequested)
@ -38,26 +50,32 @@ internal sealed partial class IdleTrackingBackgroundService(
continue;
}
idleCount++;
if (idleCount == MaxIdleSessionCount)
{
// Emit critical log at most once every 5 seconds the idle count it exceeded,
//since the IdleTimeout will no longer be respected.
LogMaxSessionIdleCountExceeded();
}
else if (idleCount < MaxIdleSessionCount && session.LastActivityTicks > idleActivityCutoff)
if (session.LastActivityTicks < idleActivityCutoff)
{
RemoveAndCloseSession(session.Id);
continue;
}
if (handler.Sessions.TryRemove(session.Id, out var removedSession))
{
LogSessionIdle(removedSession.Id);
idleSessions.Add((session.LastActivityTicks, session.Id));
// Don't slow down the idle tracking loop. DisposeSessionAsync logs. We only await during graceful shutdown.
_ = DisposeSessionAsync(removedSession);
// Emit critical log at most once every 5 seconds the idle count it exceeded,
// since the IdleTimeout will no longer be respected.
if (idleSessions.Count == maxIdleSessionCount + 1)
{
LogMaxSessionIdleCountExceeded(maxIdleSessionCount);
}
}
if (idleSessions.Count > maxIdleSessionCount)
{
var sessionsToPrune = idleSessions.ToArray()[..^maxIdleSessionCount];
foreach (var (_, id) in sessionsToPrune)
{
RemoveAndCloseSession(id);
}
}
idleSessions.Clear();
}
}
catch (OperationCanceledException) when (stoppingToken.IsCancellationRequested)
@ -65,7 +83,7 @@ internal sealed partial class IdleTrackingBackgroundService(
}
finally
{
if (stoppingToken.IsCancellationRequested)
try
{
List<Task> disposeSessionTasks = [];
@ -79,9 +97,31 @@ internal sealed partial class IdleTrackingBackgroundService(
await Task.WhenAll(disposeSessionTasks);
}
finally
{
if (!stoppingToken.IsCancellationRequested)
{
// Something went terribly wrong. A very unexpected exception must be bubbling up, but let's ensure we also stop the application,
// so that it hopefully gets looked at and restarted. This shouldn't really be reachable.
appLifetime.StopApplication();
IdleTrackingBackgroundServiceStoppedUnexpectedly();
}
}
}
}
private void RemoveAndCloseSession(string sessionId)
{
if (!handler.Sessions.TryRemove(sessionId, out var session))
{
return;
}
LogSessionIdle(session.Id);
// Don't slow down the idle tracking loop. DisposeSessionAsync logs. We only await during graceful shutdown.
_ = DisposeSessionAsync(session);
}
private async Task DisposeSessionAsync(HttpMcpSession<StreamableHttpServerTransport> session)
{
try
@ -97,9 +137,12 @@ internal sealed partial class IdleTrackingBackgroundService(
[LoggerMessage(Level = LogLevel.Information, Message = "Closing idle session {sessionId}.")]
private partial void LogSessionIdle(string sessionId);
[LoggerMessage(Level = LogLevel.Critical, Message = "Exceeded static maximum of 10,000 idle connections. Now clearing all inactive connections regardless of timeout.")]
private partial void LogMaxSessionIdleCountExceeded();
[LoggerMessage(Level = LogLevel.Error, Message = "Error disposing the IMcpServer for session {sessionId}.")]
[LoggerMessage(Level = LogLevel.Error, Message = "Error disposing session {sessionId}.")]
private partial void LogSessionDisposeError(string sessionId, Exception ex);
[LoggerMessage(Level = LogLevel.Critical, Message = "Exceeded maximum of {maxIdleSessionCount} idle sessions. Now closing sessions active more recently than configured IdleTimeout.")]
private partial void LogMaxSessionIdleCountExceeded(int maxIdleSessionCount);
[LoggerMessage(Level = LogLevel.Critical, Message = "The IdleTrackingBackgroundService has stopped unexpectedly.")]
private partial void IdleTrackingBackgroundServiceStoppedUnexpectedly();
}