feat(MCPServer): send log message notifications to specific client #301

cryo-zd · 2025-05-18T04:16:45Z

Description

This PR enables MCPServer to send log message notifications to specific client according to the specification

Type of Change

Bug fix (non-breaking change that fixes an issue)
New feature (non-breaking change that adds functionality)
MCP spec compatibility implementation
Breaking change (fix or feature that would cause existing functionality to not work as expected)
Documentation update
Code refactoring (no functional changes)
Performance improvement
Tests only (no functional changes)
Other (please describe):

Checklist

My code follows the code style of this project
I have performed a self-review of my own code
I have added tests that prove my fix is effective or that my feature works
I have updated the documentation accordingly

MCP Spec Compliance

This PR implements a feature defined in the MCP specification
Link to relevant spec section: Link text
Implementation follows the specification exactly

Additional Information

Summary by CodeRabbit

New Features
- Introduced server-to-client log message notifications, allowing clients to receive log messages based on their configured log level.
Bug Fixes
- Improved error handling and validation for sending log messages to clients.
- Clarified error message regarding session support for logging level operations.
Tests
- Added comprehensive tests covering various scenarios for sending log messages to clients, including filtering by log level and error conditions.

coderabbitai · 2025-05-18T04:16:50Z

"""

Walkthrough

The changes introduce a new server-to-client logging notification mechanism. This includes defining a new MCP method constant, mapping logging levels to RFC-5424 severity codes, and adding logic to determine if a message should be sent based on client subscription level. A method is added to the server for sending log notifications, and comprehensive tests are implemented to verify this functionality under various scenarios. Additionally, an error message was clarified to reflect support for both setting and getting logging levels.

Changes

File(s)	Change Summary
mcp/types.go	Added `MethodNotificationMessage` constant, mapping from logging level strings to RFC-5424 severity codes, and the `Allows` method to determine if a log message should be sent based on subscription level.
mcp/utils.go	Modified `NewLoggingMessageNotification` to use the new `MethodNotificationMessage` constant instead of a hardcoded string for the method name.
server/session.go	Added `SendLogMessageToClient` method to `MCPServer` for sending log message notifications to clients, with logic for capability checking, session validation, level filtering, and error handling.
server/session_test.go	Added tests for the new log message sending functionality, including scenarios for disabled logging, invalid sessions, invalid messages, channel blocking, and log level filtering. Also included minor formatting and error message improvements.
server/errors.go	Updated error message for `ErrSessionDoesNotSupportLogging` to clarify support for both setting and getting logging level.

Possibly related PRs

feat(MCPServer): support logging/setlevel request #276: Adds support for setting the client log level via a logging/setLevel request, complementing this PR's focus on sending log message notifications and filtering by severity.

Suggested labels

type: enhancement, area: mcp spec
"""

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mcp/types.go

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…ication

pottekkat

Looks good. We can merge this.

mcp/types.go

dugenkui03 · 2025-05-23T07:07:29Z

hi @pottekkat @cryo-zd It's a great idea to support this feature, but this implement is not what I think.

for example, how develops use this function, they can not access SendLogMessageToClient in their tool_function.

I think the python-sdk is a good reference example, it allow develop send log message in tool function:

@mcp.tool()
async def long_task(files: list[str], ctx: Context) -> str:
   """Process multiple files with progress tracking"""
   for i, file in enumerate(files):
       ctx.info(f"Processing {file}")
       await ctx.report_progress(i, len(files))
       data, mime_type = await ctx.read_resource(f"file://{file}")
   return "Processing complete"

dugenkui03 · 2025-05-23T07:21:24Z

Also, we need to consider compatibility with both cancelled_notification and progress_notification, maybe there are some design ideas they could share.

pottekkat · 2025-05-23T14:51:14Z

Relaying the discussion we had in the Discord server. The current implementation has limitations that make it difficult for developers to use the log notifications effectively within tool handlers. Ideally, we want to implement a more idiomatic way to handle these logs, maybe similar to the logging package in the standard library where the SDK does the heavy lifting and offer neat abstractions for Go developers that are intuitive and familiar.

We can merge this PR and open a new issue to track this improvement because it will be a breaking change. We have to plan out how to implement this and @dugenkui03 can include his thoughts.

dugenkui03 · 2025-05-23T17:42:54Z

@pottekkat I agree with that and create another issue #321.

And I left another comment for this pr: how about change the type of LoggingLevel from string to int

cryo-zd · 2025-05-24T04:01:09Z

@pottekkat I agree with that and create another issue #321.

And I left another comment for this pr: how about change the type of LoggingLevel from string to int

picked from: https://github.com/modelcontextprotocol/modelcontextprotocol/blob/main/schema/2025-03-26/schema.json

        "LoggingLevel": {
            "description": "The severity of a log message.\n\nThese map to syslog message severities, as specified in RFC-5424:\nhttps://datatracker.ietf.org/doc/html/rfc5424#section-6.2.1",
            "enum": [
                "alert",
                "critical",
                "debug",
                "emergency",
                "error",
                "info",
                "notice",
                "warning"
            ],
            "type": "string"
        },

May be string is better for consistency?

dugenkui03 · 2025-05-24T05:54:04Z

@cryo-zd thank you present more details, and I agree with you.

pottekkat · 2025-05-29T11:43:02Z

Ok, so we are reimplementing this as per the new proposal in #329 and this was closed.

feat(MCPServer): send log messages to specific client

19fe996

pottekkat requested review from pottekkat and rwjblue-glean and removed request for pottekkat May 18, 2025 04:18

cryo-zd marked this pull request as ready for review May 19, 2025 09:08

cryo-zd and others added 2 commits May 19, 2025 09:13

chore(MCPServer): reuse func SendNotificationToClient() to send notif…

a7b38b8

…ication

Merge branch 'main' into feat/sendlog

d0e3734

pottekkat approved these changes May 23, 2025

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mcp/types.go Show resolved Hide resolved

chore(mcp/types): format types.go

de45823

pottekkat approved these changes May 23, 2025

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dugenkui03 mentioned this pull request May 23, 2025

feature: Support log/cancelled/progress notification #321

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cryo-zd closed this May 26, 2025

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Description

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MCP Spec Compliance

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