[Server] Implemented MCP logging specification with auto-injection #104

Adebayo120 · 2025-10-10T04:52:54Z

This PR implements the Model Context Protocol (MCP) logging specification, providing centralized logging capabilities with auto-injection support for capability handlers. This enables developers to debug across multiple MCP servers from a single client interface, addressing the challenge of distributed logging in MCP ecosystems.

Motivation and Context

Fixes #70

This implementation addresses the missing logging functionality as outlined in the MCP logging specification.

Problem solved:

Developers working with 10-15 MCP servers struggle with debugging across distributed logs
No centralized logging mechanism for MCP servers
Missing client-controlled log level filtering
No easy way to access logging within tools/resources/prompts

Key benefits:

Centralized logging: All server logs flow to the client for unified debugging
Client-controlled filtering: Clients can set log levels to reduce noise
Auto-injection: Zero-configuration logger access in capability handlers
Fallback support: Compatible with existing external PSR-3 loggers

How Has This Been Tested?

Comprehensive test coverage:

✅ 360 unit tests with 1530 assertions - all passing
✅ 0 PHPStan errors - full static analysis compliance
✅ 0 PHP CS Fixer issues - code style compliance

Test scenarios:

Auto-injection of McpLogger into tools, resources, and prompts
Client log level filtering (debug → emergency levels)
Fallback to external PSR-3 loggers when MCP transport unavailable
Notification serialization and transport integration
Error handling and graceful degradation
Builder configuration and server lifecycle integration

Working examples:

examples/stdio-logging-showcase/ - Complete demonstration of auto-injection
Updated calculator example with comprehensive logging

Breaking Changes

None. This implementation maintains full backward compatibility:

Existing servers continue to work without modification
Logging is opt-in via ->enableMcpLogging()
No changes to existing method signatures
Auto-injection only occurs when McpLogger or LoggerInterface parameters are declared

Types of changes

Bug fix (non-breaking change which fixes an issue)
New feature (non-breaking change which adds functionality)
Breaking change (fix or feature that would cause existing functionality to change)
Documentation update

Checklist

I have read the MCP Documentation
My code follows the repository's style guidelines
New and existing tests pass locally
I have added appropriate error handling
I have added or updated documentation as needed

Additional context

Implementation highlights:

Core Components:

McpLogger: PSR-3 compliant logger with MCP notification transport
NotificationSender: Handles delivery of log messages to clients
SetLogLevelHandler: Processes client log level configuration requests
LoggingLevel enum: RFC-5424 compliant severity levels with indexing

Auto-injection mechanism:

#[McpTool(name: 'my_tool')]
public function myTool(string $input, McpLogger $logger): array {
    $logger->info('Tool called', ['input' => $input]);
    // Logger automatically injected - no configuration needed!
    return ['result' => 'processed'];
}

giacomomasseron · 2025-10-10T21:13:22Z

Why you use Yoda style?

Is it necessary?

Adebayo120 · 2025-10-11T07:59:27Z

I was only trying to follow the project convention and ensure the PR focuses on the feature, rather than refactoring. The Yoda style is not necessary, but that's what the project mostly uses at the moment. I believe refactoring is an implementation that is worthy of its own PR

@giacomomasseron

chr-hertel

Hi @Adebayo120 - thanks a lot for giving this a try!

I did a first round of review, and didn't tackle all yet - since this is a larger feature, i guess we will need a couple of rounds and discussions - also with @CodeWithKyrian.
Just want to be transparent about that from the start, but we'll guide you through it, if you're up for that.

Please have a look at my comments, and also have a look at the examples here with Inspector:

at first glance i found two issues here:

the logger appears as tool argument in the schema
setting a higher log level raises errors

let me know if you have some questions!

README.md

docs/mcp-logging.md

examples/stdio-discovery-calculator/McpElements.php

src/Capability/Logger/McpLogger.php

src/Capability/Registry.php

Adebayo120 · 2025-10-12T11:31:58Z

Going through comments and updating, thank you so much @chr-hertel

Adebayo120 · 2025-10-13T23:21:39Z

Hi @Adebayo120 - thanks a lot for giving this a try!

I did a first round of review, and didn't tackle all yet - since this is a larger feature, i guess we will need a couple of rounds and discussions - also with @CodeWithKyrian. Just want to be transparent about that from the start, but we'll guide you through it, if you're up for that.

Please have a look at my comments, and also have a look at the examples here with Inspector:

at first glance i found two issues here:

the logger appears as tool argument in the schema

setting a higher log level raises errors

let me know if you have some questions!

I have added implementation to excluded autoInjected ClientLogger
setting a higher log level raises errors: As far as I can see in the implementation, we don't throw an error when a higher log level is called; we only log a message on the server

Adebayo120 · 2025-10-19T23:08:01Z

@chr-hertel, I have updated the PR as suggested and tested as shown in the attached screenshot. It works great for me
. Please let me know if there are any updates I need to make to the PR

chr-hertel · 2025-10-20T21:15:36Z

@Adebayo120 thanks for following up - can you extend one of the HTTP examples to include client logging as well?

chr-hertel · 2025-10-20T21:17:32Z

src/Capability/Discovery/SchemaGenerator.php

+        return 'Mcp\\Capability\\Logger\\ClientLogger' === $typeName
+            || 'Psr\\Log\\LoggerInterface' === $typeName;


please use ::class instead

actually you could simplify this to sth like

Suggested change

return 'Mcp\\Capability\\Logger\\ClientLogger' === $typeName

|| 'Psr\\Log\\LoggerInterface' === $typeName;

return in_array($type->getName(), [ClientLogger::class, LoggerInterface::class], true);

chr-hertel · 2025-10-20T21:22:18Z

tests/Unit/Capability/Discovery/SchemaGeneratorFixture.php

+     * @param string                              $message The message to process
+     * @param \Mcp\Capability\Logger\ClientLogger $logger  Auto-injected logger
+     */
+    public function withClientLogger(string $message, \Mcp\Capability\Logger\ClientLogger $logger): string


use an import instead of FQCN inline

chr-hertel · 2025-10-20T21:22:46Z

tests/Unit/Capability/Discovery/SchemaGeneratorTest.php

+        // Should include the message parameter
+        $this->assertArrayHasKey('message', $schema['properties']);
+        $this->assertEquals(['type' => 'string', 'description' => 'The message to process'], $schema['properties']['message']);
+
+        // Should NOT include the logger parameter
+        $this->assertArrayNotHasKey('logger', $schema['properties']);
+
+        // Required array should only contain client parameters
+        $this->assertEquals(['message'], $schema['required']);


those comments are not needed - just make it look like vibe coded

chr-hertel · 2025-10-21T21:25:13Z

@Adebayo120 please wait before continuing here - with #109 there is a competing solution that also covers other client-facing features - doesn't really make sense to work on the same thing.

Or do I miss something @CodeWithKyrian that your PR wouldn't cover? also addresses the STDIO vs HTTP question that is rather unsolved here, right?

Adebayo120 · 2025-10-27T16:54:01Z

@CodeWithKyrian could you please help here

chr-hertel · 2025-10-30T13:20:34Z

There is still something in the PR we could need - mostly the SetLogLevelHandler. but it requires some rebase on adoption of the ClientGateway instead of the ClientLogger

@Adebayo120 are you still up for that?

Adebayo120 requested review from CodeWithKyrian, Nyholm and chr-hertel as code owners October 10, 2025 04:52

Adebayo120 force-pushed the feature/mcp-logging-specification branch from 34ae3c3 to 035b75e Compare October 10, 2025 05:39

Adebayo120 force-pushed the feature/mcp-logging-specification branch from 953aca7 to 30f8f42 Compare October 11, 2025 20:00

chr-hertel requested changes Oct 11, 2025

View reviewed changes

Adebayo120 added 13 commits October 19, 2025 23:08

Implemented MCP logging specification with auto-injection

c51af7e

Added doc

4a1b62c

Modified doc

77a774f

Fixed lint issues

eb998cf

Fixed issues found in pipeline

9362f6c

Fixed issue with McpLogger compatibility with LoggerInterface

cd27bac

Updated with latest Server method interface

2fdb8d8

Exclude Auto injected client logger from generated input-schema

4a8b33e

Streamlined examples/stdio-logging-showcase

b701bb1

Simplified docs

11cfb16

Renamed McpLogger to ClientLogger

4614dc5

Enabled logging by default

e21a81d

Resolved conflict

0eecd64

Adebayo120 force-pushed the feature/mcp-logging-specification branch from e6e49b3 to 0eecd64 Compare October 19, 2025 22:25

Rmoved unnecessary line of codes

e082fd3

chr-hertel reviewed Oct 20, 2025

View reviewed changes

chr-hertel changed the title ~~Implemented MCP logging specification with auto-injection~~ [Server] Implemented MCP logging specification with auto-injection Oct 20, 2025

chr-hertel added the Server Issues & PRs related to the Server component label Oct 20, 2025

		return 'Mcp\\Capability\\Logger\\ClientLogger' === $typeName
		\|\| 'Psr\\Log\\LoggerInterface' === $typeName;

	return 'Mcp\\Capability\\Logger\\ClientLogger' === $typeName
	\|\| 'Psr\\Log\\LoggerInterface' === $typeName;
	return in_array($type->getName(), [ClientLogger::class, LoggerInterface::class], true);

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Adebayo120 commented Oct 10, 2025

Motivation and Context

How Has This Been Tested?

Breaking Changes

Types of changes

Checklist

Additional context

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giacomomasseron commented Oct 10, 2025

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Adebayo120 commented Oct 11, 2025

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