Enhance HTTP and MCP session logging

src/ModelContextProtocol.AspNetCore/StreamableHttpHandler.cs

@@ -18,7 +18,7 @@
 
 namespace ModelContextProtocol.AspNetCore;
 
-internal sealed class StreamableHttpHandler(
+internal sealed partial class StreamableHttpHandler(
     IOptions<McpServerOptions> mcpServerOptionsSnapshot,
     IOptionsFactory<McpServerOptions> mcpServerOptionsFactory,
     IOptions<HttpServerTransportOptions> httpServerTransportOptions,
@@ -28,6 +28,20 @@ internal sealed class StreamableHttpHandler(
 {
     private const string McpSessionIdHeaderName = "Mcp-Session-Id";
     private static readonly JsonTypeInfo<JsonRpcError> s_errorTypeInfo = GetRequiredJsonTypeInfo<JsonRpcError>();
+
+    private readonly ILogger _logger = loggerFactory.CreateLogger<StreamableHttpHandler>();
+
+    // Headers that are safe and relevant to log for MCP over HTTP
+    private static readonly HashSet<string> SafeHeadersToLog = new(StringComparer.OrdinalIgnoreCase)
+    {
+        "Accept",
+        "Content-Type",
+        "Content-Length",
+        "User-Agent",
+        McpSessionIdHeaderName,
+        "X-Request-ID",
+        "X-Correlation-ID"
+    };
 
     public ConcurrentDictionary<string, HttpMcpSession<StreamableHttpServerTransport>> Sessions { get; } = new(StringComparer.Ordinal);
 
@@ -37,6 +51,9 @@ internal sealed class StreamableHttpHandler(
 
     public async Task HandlePostRequestAsync(HttpContext context)
     {
+        // Log request headers for debugging
+        LogHttpRequestHeadersIfEnabled(context);
+
         // The Streamable HTTP spec mandates the client MUST accept both application/json and text/event-stream.
         // ASP.NET Core Minimal APIs mostly try to stay out of the business of response content negotiation,
         // so we have to do this manually. The spec doesn't mandate that servers MUST reject these requests,
@@ -83,6 +100,9 @@ await WriteJsonRpcErrorAsync(context,
 
     public async Task HandleGetRequestAsync(HttpContext context)
     {
+        // Log request headers for debugging
+        LogHttpRequestHeadersIfEnabled(context);
+
         if (!context.Request.GetTypedHeaders().Accept.Any(MatchesTextEventStreamMediaType))
         {
             await WriteJsonRpcErrorAsync(context,
@@ -118,6 +138,9 @@ await WriteJsonRpcErrorAsync(context,
 
     public async Task HandleDeleteRequestAsync(HttpContext context)
     {
+        // Log request headers for debugging
+        LogHttpRequestHeadersIfEnabled(context);
+
         var sessionId = context.Request.Headers[McpSessionIdHeaderName].ToString();
         if (Sessions.TryRemove(sessionId, out var session))
         {
@@ -336,6 +359,27 @@ private static bool MatchesApplicationJsonMediaType(MediaTypeHeaderValue acceptH
     private static bool MatchesTextEventStreamMediaType(MediaTypeHeaderValue acceptHeaderValue)
         => acceptHeaderValue.MatchesMediaType("text/event-stream");
 
+    private void LogHttpRequestHeadersIfEnabled(HttpContext context)
+    {
+        if (_logger.IsEnabled(LogLevel.Trace))
+        {
+            var safeHeaders = new Dictionary<string, string>();
+
+            foreach (var header in context.Request.Headers)
+            {
+                if (SafeHeadersToLog.Contains(header.Key))
+                {
+                    safeHeaders[header.Key] = header.Value.ToString();
+                }
+            }
+
+            LogHttpRequestHeaders(context.Request.Method, context.Request.Path, safeHeaders);
+        }
+    }
+
+    [LoggerMessage(Level = LogLevel.Trace, Message = "HTTP {Method} {Path} - Headers: {Headers}")]
+    private partial void LogHttpRequestHeaders(string method, string path, Dictionary<string, string> headers);
+
     private sealed class HttpDuplexPipe(HttpContext context) : IDuplexPipe
     {
         public PipeReader Input => context.Request.BodyReader;

src/ModelContextProtocol.Core/McpSession.cs

@@ -95,6 +95,7 @@ public McpSession(
         _requestHandlers = requestHandlers;
         _notificationHandlers = notificationHandlers;
         _logger = logger ?? NullLogger.Instance;
+        LogSessionCreated(EndpointName, _sessionId, _transportKind);
     }
 
     /// <summary>
@@ -108,6 +109,7 @@ public McpSession(
     /// </summary>
     public async Task ProcessMessagesAsync(CancellationToken cancellationToken)
     {
+        LogSessionConnected(EndpointName, _sessionId, _transportKind);
         try
         {
             await foreach (var message in _transport.MessageReader.ReadAllAsync(cancellationToken).ConfigureAwait(false))
@@ -609,9 +611,9 @@ private static void AddExceptionTags(ref TagList tags, Activity? activity, Excep
             e = ae.InnerException;
         }
 
-        int? intErrorCode = 
+        int? intErrorCode =
             (int?)((e as McpException)?.ErrorCode) is int errorCode ? errorCode :
-            e is JsonException ? (int)McpErrorCode.ParseError : 
+            e is JsonException ? (int)McpErrorCode.ParseError :
             null;
 
         string? errorType = intErrorCode?.ToString() ?? e.GetType().FullName;
@@ -692,6 +694,7 @@ public void Dispose()
         }
 
         _pendingRequests.Clear();
+        LogSessionDisposed(EndpointName, _sessionId, _transportKind);
     }
 
 #if !NET
@@ -774,4 +777,13 @@ private static TimeSpan GetElapsed(long startingTimestamp) =>
 
     [LoggerMessage(Level = LogLevel.Trace, Message = "{EndpointName} sending message. Message: '{Message}'.")]
     private partial void LogSendingMessageSensitive(string endpointName, string message);
+
+    [LoggerMessage(Level = LogLevel.Debug, Message = "{EndpointName} session {SessionId} created with transport {TransportKind}")]
+    private partial void LogSessionCreated(string endpointName, string sessionId, string transportKind);
+
+    [LoggerMessage(Level = LogLevel.Debug, Message = "{EndpointName} session {SessionId} connected and processing messages with transport {TransportKind}")]
+    private partial void LogSessionConnected(string endpointName, string sessionId, string transportKind);
+
+    [LoggerMessage(Level = LogLevel.Debug, Message = "{EndpointName} session {SessionId} disposed with transport {TransportKind}")]
+    private partial void LogSessionDisposed(string endpointName, string sessionId, string transportKind);
 }