Add MCP notifications/message for log streaming to clients by anushakolan · Pull Request #3484 · Azure/data-api-builder

anushakolan · 2026-04-29T20:18:55Z

Why make this change?

Enables MCP clients (like MCP Inspector, Claude Desktop, VS Code Copilot) to receive real-time log output via MCP notifications/message.

Related: #3274 (depends on PR #3419)

What is this change?

When logging/setLevel is called with a level other than "none", logs are sent to MCP clients as JSON-RPC notifications:

{
  "jsonrpc": "2.0",
  "method": "notifications/message",
  "params": {
    "level": "info",
    "logger": "Azure.DataApiBuilder.Service.Startup",
    "data": "Starting Data API builder..."
  }
}

New files:

McpLogNotificationWriter.cs - Writes logs as MCP notifications to stdout
McpLogger.cs / McpLoggerProvider.cs - ILogger implementation for .NET logging pipeline
McpLogNotificationTests.cs - Unit tests (8 tests)

Modified files:

Program.cs - Registers McpNotificationWriter and McpLoggerProvider for MCP mode
McpStdioServer.cs - Enables notifications when logging/setLevel is called

How was this tested?

Unit tests: 6 tests covering level mapping, enable/disable, JSON format
Manual testing with MCP Inspector: verified notifications appear when logging/setLevel is sent

Note

This PR targets dev/anushakolan/set-log-level (PR #3419) as it depends on the logging/setLevel implementation.

Aniruddh25

Left some suggestions for code reuse.

The base branch was changed.

Copilot

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds support for streaming server logs to MCP clients via notifications/message, enabling real-time log consumption after logging/setLevel is invoked.

Changes:

Introduces MCP-specific logging components (McpLogger, McpLoggerProvider, McpLogNotificationWriter) that emit logs as JSON-RPC notifications to stdout.
Centralizes MCP↔.NET log level mapping in McpLogLevelConverter and wires it into dynamic log level handling.
Updates MCP stdio server to enable/disable log notifications based on logging/setLevel and standardizes JSON-RPC version usage.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
src/Service/Telemetry/DynamicLogLevelProvider.cs	Switches MCP level parsing to shared converter.
src/Service/Program.cs	Registers MCP notification writer/provider and clears default log providers in MCP stdio mode.
src/Service.Tests/UnitTests/McpLogNotificationTests.cs	Adds unit tests around MCP logger/provider enabled behavior.
src/Core/Telemetry/McpLogLevelConverter.cs	Adds shared MCP↔.NET log level conversion utility.
src/Azure.DataApiBuilder.Mcp/Telemetry/McpLoggerProvider.cs	Adds logger provider that caches per-category MCP loggers.
src/Azure.DataApiBuilder.Mcp/Telemetry/McpLogger.cs	Adds `ILogger` implementation that forwards logs to MCP notifications.
src/Azure.DataApiBuilder.Mcp/Telemetry/McpLogNotificationWriter.cs	Adds stdout JSON-RPC notification writer + interface for toggling.
src/Azure.DataApiBuilder.Mcp/Model/McpStdioJsonRpcErrorCodes.cs	Introduces shared JSON-RPC version constant.
src/Azure.DataApiBuilder.Mcp/Core/McpStdioServer.cs	Enables notifications on `logging/setLevel` and uses shared JSON-RPC version constant.

aaronburtle · 2026-05-06T03:27:28Z

+    private void InitializeWriter()
+    {
+        // Use the same approach as McpStdioServer - get raw stdout
+        Stream stdout = Console.OpenStandardOutput();


This StreamWriter is on the same stdout as we use in McpStdioServer.cs in RunAsync

using Stream stdout = Console.OpenStandardOutput();

I think this will have concurrency/race conditions. Maybe we can factor these two uses into a helper with a lock?

aaronburtle · 2026-05-06T03:32:09Z

+            // when the client requests logging. They'll get logs at the overridden level.
            bool isLoggingEnabled = !string.Equals(level, "none", StringComparison.OrdinalIgnoreCase);
-            if (updated && isLoggingEnabled)
+            if (isLoggingEnabled)


without the guard from updated, won't this result in us resetting stderr in the case where it was initially set to none re-introducing noisy logs when someone set log level to none on startup?

aaronburtle · 2026-05-06T03:48:18Z

+            IMcpLogNotificationWriter? notificationWriter = _serviceProvider.GetService<IMcpLogNotificationWriter>();
+            if (notificationWriter != null)
+            {
+                notificationWriter.IsEnabled = isLoggingEnabled;


This makes the IsEnabled flag in McpLogger.cs redudant, and gives us 2 gates. Should refactor this so that we have 1 source of truth. I dont think the 2 gates always agree currently.

aaronburtle · 2026-05-06T03:49:45Z

+    {
+        // Use the same approach as McpStdioServer - get raw stdout
+        Stream stdout = Console.OpenStandardOutput();
+        _writer = new StreamWriter(stdout, new UTF8Encoding(encoderShouldEmitUTF8Identifier: false))


We probably need to implement IDisposable and properly dispose of the StreamWriter.

aaronburtle · 2026-05-06T04:00:22Z

+        // Include exception details if present
+        if (exception != null)
+        {
+            message = $"{message} Exception: {exception.GetType().Name}: {exception.Message}";


Do we intentionally drop the stack trace, inner exceptions, etc here? Do MCP clients expect to see this?

aaronburtle · 2026-05-06T04:01:29Z

+    }
+
+    /// <inheritdoc />
+    public IDisposable? BeginScope<TState>(TState state) where TState : notnull


Consider supporting external scopes ie: implement ISupportExternalScope as a future task.

aaronburtle · 2026-05-06T04:02:58Z

+    }
+
+    /// <inheritdoc />
+    public ILogger CreateLogger(string categoryName)


shouldnt we check _disposed to avoid creating a new McpLogger with a stale reference?

aaronburtle · 2026-05-06T04:19:15Z

+    /// </summary>
+    /// <param name="writer">The notification writer to use for sending log messages.</param>
+    /// <param name="levelFilter">A function to filter log levels. Returns true if the level should be logged.</param>
+    public McpLoggerProvider(IMcpLogNotificationWriter writer, Func<LogLevel, bool> levelFilter)


this delegate is from LogLevelProvider.ShouldLog in Program.cs, but Program.cs has already used LogLevelProvider.ShouldLog in the previous AddFilter calls, so by the time McpLogger.Lo is reached LogLevelProvider.ShouldLog is already true. The _levelFilter parameter then on the McpLoggerProvider/McpLogger is then calling the same delegate with the same shared state and gets the same answer.

Id recommend dropping this delegate and updating IsEnabled to something like

public bool IsEnabled(LogLevel logLevel) => _writer.IsEnabled && logLevel != LogLevel.None;

aaronburtle

Looks good once comments are resolved.

anushakolan requested review from Alekhya-Polavarapu, Aniruddh25, JerryNixon, RubenCerna2079, aaronburtle, rusamant, sourabh1007, souvikghosh04, stuartpa and vadeveka as code owners April 29, 2026 20:18

anushakolan added the assign-for-review label Apr 29, 2026

github-actions Bot assigned aaronburtle and Aniruddh25 Apr 29, 2026

github-actions Bot removed the assign-for-review label Apr 29, 2026

Aniruddh25 reviewed May 1, 2026

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Comment thread src/Service/Program.cs Outdated

Aniruddh25 reviewed May 1, 2026

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Comment thread src/Azure.DataApiBuilder.Mcp/Telemetry/McpLogNotificationWriter.cs Outdated

Aniruddh25 reviewed May 1, 2026

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Comment thread src/Azure.DataApiBuilder.Mcp/Telemetry/McpLogNotificationWriter.cs Outdated

Aniruddh25 reviewed May 1, 2026

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Comment thread src/Service.Tests/UnitTests/McpLogNotificationTests.cs Outdated

Aniruddh25 previously approved these changes May 1, 2026

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Base automatically changed from dev/anushakolan/set-log-level to main May 2, 2026 00:28

anushakolan mentioned this pull request May 4, 2026

[Bug] --mcp-stdio mode writes startup log lines to stdout, corrupting the MCP JSON stream #3427

Closed

Copilot AI review requested due to automatic review settings May 4, 2026 20:01

anushakolan force-pushed the dev/anushakolan/mcp-notifications branch from 3b658ef to e2a1ee8 Compare May 4, 2026 20:01

Copilot AI reviewed May 4, 2026

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Copilot started reviewing on behalf of anushakolan May 4, 2026 20:32 View session

Aniruddh25 approved these changes May 5, 2026

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Add MCP notifications/message for log streaming to clients

350a4b5

anushakolan force-pushed the dev/anushakolan/mcp-notifications branch from bc9426d to 350a4b5 Compare May 5, 2026 06:45

Aniruddh25 approved these changes May 5, 2026

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anushakolan enabled auto-merge (squash) May 5, 2026 20:58

This was referenced May 5, 2026

Fix MCP CLI logging: apply colors and respect config log-level #3508

Open

[Bug] MCP stdio mode: CLI logs lack colors and are suppressed when log level is set via config #3509

Open

Merge branch 'main' into dev/anushakolan/mcp-notifications

5ee46e8

aaronburtle reviewed May 6, 2026

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aaronburtle approved these changes May 6, 2026

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anushakolan commented Apr 29, 2026 •

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