## Changes
- fix(server): keep SSE connection open until explicitly cancelled
- conformance: add logging to test_tool_with_logging and update
troubleshooting documentation
- chore(conformance): remove 5 passing server tests from conformance
baselines:
- tools-call-with-logging
- tools-call-with-progress
- tools-call-sampling
- tools-call-elicitation
- elicitation-sep1034-defaults
## Motivation and Context
Two bugs in StreamableHttpServerTransport caused server-to-client
notifications (e.g. notifications/message during tool calls) to be
silently dropped.
**Bug 1 — GET SSE stream closed immediately**
`handleGetRequest` rejected GET requests with 405 when
`enableJsonResponse = true` (which `mcpStreamableHttp` always sets).
Since the Ktor `sse {}` handler commits response headers before the body
runs, the reject failed silently and the function returned, causing Ktor
to close the SSE stream. There was also no `awaitCancellation()` to keep
the connection alive.
**Bug 2 — Notifications discarded in JSON mode**
In `send()`, notifications with a relatedRequestId entered the
POST-stream path but hit `if (!isTerminated) return` without being
forwarded anywhere.
**Fix**
- Remove the enableJsonResponse guard from handleGetRequest. The GET SSE
stream is an always-required notification channel, orthogonal to how
POST responses are delivered.
- Add `awaitCancellation()` to keep the GET SSE connection open until
the client disconnects or the transport closes.
- In `send()`, route notifications with a relatedRequestId to the
standalone GET SSE stream when `enableJsonResponse = true`.
## How Has This Been Tested?
Verified against the MCP conformance test suite — the
ToolsCallWithLogging scenario now passes. ngrep confirms the `GET /mcp`
stream stays open and `notifications/message` events arrive before the
`tools/call` response.
## Breaking Changes
<!-- Will users need to update their code or configurations? -->
## Types of changes
<!-- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->
- [x] 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
<!-- Go over all the following points, and put an `x` in all the boxes
that apply. -->
- [x] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [x] 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
Fixes #587
Requires #585 to be merged first.
---------
Co-authored-by: devcrocod <devcrocod@gmail.com>
This commit is contained in:
Konstantin Pavlov
GitHub
parent
e88b34170c
commit
736efe9dc0
4 changed files with 37 additions and 24 deletions
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@ -114,16 +114,11 @@ Tests the conformance server against all server scenarios:
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8 scenarios are expected to fail due to current SDK limitations (tracked in [
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`conformance-baseline.yml`](conformance-baseline.yml).
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| Scenario | Suite | Root Cause |
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|---------------------------------------|--------|--------------------------------------------------------------------------------------------------------------------------------------------------------|
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| `tools-call-with-logging` | server | Notifications from tool handlers have no `relatedRequestId`; transport routes them to the standalone SSE stream instead of the request-specific stream |
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| `tools-call-with-progress` | server | *(same as above)* |
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| `tools-call-sampling` | server | *(same as above)* |
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| `tools-call-elicitation` | server | *(same as above)* |
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| `elicitation-sep1034-defaults` | server | *(same as above)* |
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| `elicitation-sep1330-enums` | server | *(same as above)* |
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| `resources-templates-read` | server | SDK does not implement `addResourceTemplate()` with URI pattern matching; resources are looked up by exact URI |
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| `elicitation-sep1034-client-defaults` | client | SDK does not fill in `default` values from the elicitation request schema before sending the response |
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| Scenario | Suite | Root Cause |
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|---------------------------------------|--------|----------------------------------------------------------------------------------------------------------------|
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| `elicitation-sep1330-enums` | server | *(same as above)* |
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| `resources-templates-read` | server | SDK does not implement `addResourceTemplate()` with URI pattern matching; resources are looked up by exact URI |
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| `elicitation-sep1034-client-defaults` | client | SDK does not fill in `default` values from the elicitation request schema before sending the response |
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These failures reveal SDK gaps and are intentionally not fixed in this module.
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@ -1,11 +1,6 @@
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# Conformance test baseline - expected failures
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# Add entries here as tests are identified as known SDK limitations
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server:
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- tools-call-with-logging
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- tools-call-with-progress
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- tools-call-sampling
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- tools-call-elicitation
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- elicitation-sep1034-defaults
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- elicitation-sep1330-enums
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- resources-templates-read
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@ -1,5 +1,6 @@
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package io.modelcontextprotocol.kotlin.sdk.conformance
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import io.github.oshai.kotlinlogging.KotlinLogging
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import io.modelcontextprotocol.kotlin.sdk.server.Server
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import io.modelcontextprotocol.kotlin.sdk.types.AudioContent
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import io.modelcontextprotocol.kotlin.sdk.types.CallToolResult
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@ -33,6 +34,8 @@ internal const val PNG_BASE64 =
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// Minimal WAV (base64)
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internal const val WAV_BASE64 = "UklGRiYAAABXQVZFZm10IBAAAAABAAEAQB8AAAB9AAACABAAZGF0YQIAAAA="
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private val logger = KotlinLogging.logger {}
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@Suppress("LongMethod")
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fun Server.registerConformanceTools() {
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// 1. Simple text
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@ -429,6 +432,7 @@ fun Server.registerConformanceTools() {
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name = "test_tool_with_logging",
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description = "test_tool_with_logging",
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) {
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logger.debug { "[test_tool_with_logging] Sending message 1" }
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sendLoggingMessage(
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LoggingMessageNotification(
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LoggingMessageNotificationParams(
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@ -439,6 +443,7 @@ fun Server.registerConformanceTools() {
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),
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)
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delay(50.milliseconds)
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logger.debug { "[test_tool_with_logging] Sending message #2" }
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sendLoggingMessage(
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LoggingMessageNotification(
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LoggingMessageNotificationParams(
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@ -449,6 +454,7 @@ fun Server.registerConformanceTools() {
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),
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)
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delay(50.milliseconds)
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logger.debug { "[test_tool_with_logging] Sending message 3" }
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sendLoggingMessage(
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LoggingMessageNotification(
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LoggingMessageNotificationParams(
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@ -458,6 +464,7 @@ fun Server.registerConformanceTools() {
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),
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),
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)
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CallToolResult(listOf(TextContent("Simple text content")))
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}
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@ -0,0 +1,9 @@
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# Level of logging for the ROOT logger: ERROR, WARN, INFO, DEBUG, TRACE (default is INFO)
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org.slf4j.simpleLogger.defaultLogLevel=INFO
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org.slf4j.simpleLogger.showThreadName=true
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org.slf4j.simpleLogger.showDateTime=false
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# Log level for specific packages or classes
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org.slf4j.simpleLogger.log.io.ktor.server=DEBUG
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org.slf4j.simpleLogger.log.io.modelcontextprotocol=DEBUG
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org.slf4j.simpleLogger.log.io.modelcontextprotocol.kotlin.sdk.conformance=INFO
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