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Align telemetry with OpenTelemetry MCP semantic conventions (#1139)

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>
This commit is contained in:
Copilot 2026-01-13 18:07:49 -08:00 • committed by GitHub
commit d52a7b183d
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1 changed files with 226 additions and 77 deletions
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183
src/ModelContextProtocol.Core/McpSessionHandler.cs
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@ -20,13 +20,13 @@ namespace ModelContextProtocol;
internal sealed partial class McpSessionHandler : IAsyncDisposable
{
private static readonly Histogram<double> s_clientSessionDuration = Diagnostics.CreateDurationHistogram(
"mcp.client.session.duration", "Measures the duration of a client session.", longBuckets: true);
"mcp.client.session.duration", "The duration of the MCP session as observed on the MCP client.");
private static readonly Histogram<double> s_serverSessionDuration = Diagnostics.CreateDurationHistogram(
"mcp.server.session.duration", "Measures the duration of a server session.", longBuckets: true);
"mcp.server.session.duration", "The duration of the MCP session as observed on the MCP server.");
private static readonly Histogram<double> s_clientOperationDuration = Diagnostics.CreateDurationHistogram(
"mcp.client.operation.duration", "Measures the duration of outbound message.", longBuckets: false);
"mcp.client.operation.duration", "The duration of the MCP request or notification as observed on the sender from the time it was sent until the response or ack is received.");
private static readonly Histogram<double> s_serverOperationDuration = Diagnostics.CreateDurationHistogram(
"mcp.server.operation.duration", "Measures the duration of inbound message processing.", longBuckets: false);
"mcp.server.operation.duration", "MCP request or notification duration as observed on the receiver from the time it was received until the result or ack is sent.");
/// <summary>The latest version of the protocol supported by this implementation.</summary>
internal const string LatestProtocolVersion = "2025-06-18";
@ -59,6 +59,7 @@ internal sealed partial class McpSessionHandler : IAsyncDisposable
// This _sessionId is solely used to identify the session in telemetry and logs.
private readonly string _sessionId = Guid.NewGuid().ToString("N");
private long _lastRequestId;
private CancellationTokenSource? _messageProcessingCts;
@ -85,11 +86,11 @@ internal sealed partial class McpSessionHandler : IAsyncDisposable
_transportKind = transport switch
{
StdioClientSessionTransport or StdioServerTransport => "stdio",
StreamClientSessionTransport or StreamServerTransport => "stream",
SseClientSessionTransport or SseResponseStreamTransport => "sse",
StreamableHttpClientSessionTransport or StreamableHttpServerTransport or StreamableHttpPostTransport => "http",
_ => "unknownTransport"
StdioClientSessionTransport or StdioServerTransport => "pipe",
StreamClientSessionTransport or StreamServerTransport => "pipe",
SseClientSessionTransport or SseResponseStreamTransport => "tcp",
StreamableHttpClientSessionTransport or StreamableHttpServerTransport or StreamableHttpPostTransport => "tcp",
_ => "unknown"
};
_isServer = isServer;
@ -106,6 +107,11 @@ internal sealed partial class McpSessionHandler : IAsyncDisposable
/// </summary>
public string EndpointName { get; set; }
/// <summary>
/// Gets or sets the negotiated MCP protocol version for telemetry.
/// </summary>
public string? NegotiatedProtocolVersion { get; set; }
/// <summary>
/// Starts processing messages from the transport. This method will block until the transport is disconnected.
/// This is generally started in a background task or thread from the initialization logic of the derived class.
@ -260,13 +266,17 @@ internal sealed partial class McpSessionHandler : IAsyncDisposable
long? startingTimestamp = durationMetric.Enabled ? Stopwatch.GetTimestamp() : null;
Activity? activity = Diagnostics.ShouldInstrumentMessage(message) ?
Diagnostics.ActivitySource.StartActivity(
CreateActivityName(method),
Activity? activity = null;
string? target = null;
if (Diagnostics.ShouldInstrumentMessage(message))
{
target = ExtractTargetFromMessage(message, method);
activity = Diagnostics.ActivitySource.StartActivity(
CreateActivityName(method, target),
ActivityKind.Server,
parentContext: _propagator.ExtractActivityContext(message),
links: Diagnostics.ActivityLinkFromCurrent()) :
null;
links: Diagnostics.ActivityLinkFromCurrent());
}
TagList tags = default;
bool addTags = activity is { IsAllDataRequested: true } || startingTimestamp is not null;
@ -274,7 +284,7 @@ internal sealed partial class McpSessionHandler : IAsyncDisposable
{
if (addTags)
{
AddTags(ref tags, activity, message, method);
AddTags(ref tags, activity, message, method, target);
}
switch (message)
@ -420,9 +430,25 @@ internal sealed partial class McpSessionHandler : IAsyncDisposable
string method = request.Method;
long? startingTimestamp = durationMetric.Enabled ? Stopwatch.GetTimestamp() : null;
using Activity? activity = Diagnostics.ShouldInstrumentMessage(request) ?
Diagnostics.ActivitySource.StartActivity(McpSessionHandler.CreateActivityName(method), ActivityKind.Client) :
null;
// If outer GenAI instrumentation is already tracing the tool execution,
// add MCP attributes to that activity instead of creating a new one.
Activity? activity = null;
bool usingOuterActivity = false;
string? target = null;
if (Diagnostics.ShouldInstrumentMessage(request))
{
target = ExtractTargetFromMessage(request, method);
if (method == RequestMethods.ToolsCall && Diagnostics.TryGetOuterToolExecutionActivity(out var outerActivity))
{
activity = outerActivity;
usingOuterActivity = true;
}
else
{
activity = Diagnostics.ActivitySource.StartActivity(CreateActivityName(method, target), ActivityKind.Client);
}
}
// Set request ID
if (request.Id.Id is null)
@ -441,7 +467,7 @@ internal sealed partial class McpSessionHandler : IAsyncDisposable
{
if (addTags)
{
AddTags(ref tags, activity, request, method);
AddTags(ref tags, activity, request, method, target);
}
if (_logger.IsEnabled(LogLevel.Trace))
@ -502,7 +528,7 @@ internal sealed partial class McpSessionHandler : IAsyncDisposable
finally
{
_pendingRequests.TryRemove(request.Id, out _);
FinalizeDiagnostics(activity, startingTimestamp, durationMetric, ref tags);
FinalizeDiagnostics(activity, startingTimestamp, durationMetric, ref tags, disposeActivity: !usingOuterActivity);
}
}
@ -516,9 +542,14 @@ internal sealed partial class McpSessionHandler : IAsyncDisposable
string method = GetMethodName(message);
long? startingTimestamp = durationMetric.Enabled ? Stopwatch.GetTimestamp() : null;
using Activity? activity = Diagnostics.ShouldInstrumentMessage(message) ?
Diagnostics.ActivitySource.StartActivity(McpSessionHandler.CreateActivityName(method), ActivityKind.Client) :
null;
Activity? activity = null;
string? target = null;
if (Diagnostics.ShouldInstrumentMessage(message))
{
target = ExtractTargetFromMessage(message, method);
activity = Diagnostics.ActivitySource.StartActivity(CreateActivityName(method, target), ActivityKind.Client);
}
TagList tags = default;
bool addTags = activity is { IsAllDataRequested: true } || startingTimestamp is not null;
@ -530,7 +561,7 @@ internal sealed partial class McpSessionHandler : IAsyncDisposable
{
if (addTags)
{
AddTags(ref tags, activity, message, method);
AddTags(ref tags, activity, message, method, target);
}
if (_logger.IsEnabled(LogLevel.Trace))
@ -585,6 +616,38 @@ internal sealed partial class McpSessionHandler : IAsyncDisposable
private static string CreateActivityName(string method) => method;
/// <summary>
/// Creates a span name according to semantic conventions: "{mcp.method.name} {target}" where
/// target is the tool name, prompt name, or resource URI when applicable.
/// </summary>
private static string CreateActivityName(string method, string? target) =>
target is null ? method : $"{method} {target}";
/// <summary>
/// Extracts the target (tool name, prompt name, or resource URI) from a message for use in span naming.
/// </summary>
private static string? ExtractTargetFromMessage(JsonRpcMessage message, string method)
{
JsonObject? paramsObj = message switch
{
JsonRpcRequest request => request.Params as JsonObject,
JsonRpcNotification notification => notification.Params as JsonObject,
_ => null
};
if (paramsObj is null)
{
return null;
}
return method switch
{
RequestMethods.ToolsCall or RequestMethods.PromptsGet => GetStringProperty(paramsObj, "name"),
// Note: resource URI is not included in span name by default due to high cardinality per semantic conventions
_ => null
};
}
private static string GetMethodName(JsonRpcMessage message) =>
message switch
{
@ -593,46 +656,45 @@ internal sealed partial class McpSessionHandler : IAsyncDisposable
_ => "unknownMethod"
};
private void AddTags(ref TagList tags, Activity? activity, JsonRpcMessage message, string method)
private void AddTags(ref TagList tags, Activity? activity, JsonRpcMessage message, string method, string? target)
{
tags.Add("mcp.method.name", method);
tags.Add("network.transport", _transportKind);
// TODO: When using SSE transport, add:
// - server.address and server.port on client spans and metrics
// - client.address and client.port on server spans (not metrics because of cardinality) when using SSE transport
if (_transportKind is "tcp")
{
tags.Add("network.protocol.name", "http");
}
if (NegotiatedProtocolVersion is not null)
{
tags.Add("mcp.protocol.version", NegotiatedProtocolVersion);
}
if (activity is { IsAllDataRequested: true })
{
// session and request id have high cardinality, so not applying to metric tags
activity.AddTag("mcp.session.id", _sessionId);
if (message is JsonRpcMessageWithId withId)
{
activity.AddTag("mcp.request.id", withId.Id.Id?.ToString());
activity.AddTag("jsonrpc.request.id", withId.Id.Id?.ToString());
}
}
JsonObject? paramsObj = message switch
{
JsonRpcRequest request => request.Params as JsonObject,
JsonRpcNotification notification => notification.Params as JsonObject,
_ => null
};
if (paramsObj == null)
{
return;
}
string? target = null;
switch (method)
{
case RequestMethods.ToolsCall:
case RequestMethods.PromptsGet:
target = GetStringProperty(paramsObj, "name");
if (target is not null)
{
tags.Add(method == RequestMethods.ToolsCall ? "mcp.tool.name" : "mcp.prompt.name", target);
tags.Add("gen_ai.tool.name", target);
tags.Add("gen_ai.operation.name", "execute_tool");
}
break;
case RequestMethods.PromptsGet:
if (target is not null)
{
tags.Add("gen_ai.prompt.name", target);
}
break;
@ -640,18 +702,21 @@ internal sealed partial class McpSessionHandler : IAsyncDisposable
case RequestMethods.ResourcesSubscribe:
case RequestMethods.ResourcesUnsubscribe:
case NotificationMethods.ResourceUpdatedNotification:
target = GetStringProperty(paramsObj, "uri");
if (target is not null)
{
tags.Add("mcp.resource.uri", target);
JsonObject? paramsObj = message switch
{
JsonRpcRequest request => request.Params as JsonObject,
JsonRpcNotification notification => notification.Params as JsonObject,
_ => null
};
string? uri = paramsObj is not null ? GetStringProperty(paramsObj, "uri") : null;
if (uri is not null)
{
tags.Add("mcp.resource.uri", uri);
}
}
break;
}
if (activity is { IsAllDataRequested: true })
{
activity.DisplayName = target == null ? method : $"{method} {target}";
}
}
private static void AddExceptionTags(ref TagList tags, Activity? activity, Exception e)
@ -670,7 +735,7 @@ internal sealed partial class McpSessionHandler : IAsyncDisposable
tags.Add("error.type", errorType);
if (intErrorCode is not null)
{
tags.Add("rpc.jsonrpc.error_code", errorType);
tags.Add("rpc.response.status_code", errorType);
}
if (activity is { IsAllDataRequested: true })
@ -701,7 +766,7 @@ internal sealed partial class McpSessionHandler : IAsyncDisposable
}
private static void FinalizeDiagnostics(
Activity? activity, long? startingTimestamp, Histogram<double> durationMetric, ref TagList tags)
Activity? activity, long? startingTimestamp, Histogram<double> durationMetric, ref TagList tags, bool disposeActivity = true)
{
try
{
@ -720,7 +785,11 @@ internal sealed partial class McpSessionHandler : IAsyncDisposable
}
finally
{
activity?.Dispose();
// Only dispose the activity if we created it (not when reusing an outer GenAI activity)
if (disposeActivity)
{
activity?.Dispose();
}
}
}