fix(server): notifications not delivered over Streamable HTTP (#587) by kpavlov · Pull Request #599 · modelcontextprotocol/kotlin-sdk

kpavlov · 2026-03-12T08:06:10Z

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

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

Fixes #587
Requires #585 to be merged first.

…ce tests

…eline file for expected test failures

…etup

…esponse format in ConformanceTools

…ation scenarios

…covery logic

…th flows

…deFlow implementation

… directory resolution and disabling redundant shellcheck warning

…bump conformance tool version to 0.1.15

…ow implementation

fixes #589 ## How Has This Been Tested? conformance tests ## Breaking Changes NaN ## Types of changes - [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 - [x] I have read the [MCP Documentation](https://modelcontextprotocol.io) - [x] My code follows the repository's style guidelines - [x] New and existing tests pass locally - [ ] I have added appropriate error handling - [ ] I have added or updated documentation as needed

fixes #588 ## How Has This Been Tested? conformance test ## Breaking Changes NaN ## Types of changes - [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 - [x] I have read the [MCP Documentation](https://modelcontextprotocol.io) - [x] My code follows the repository's style guidelines - [x] New and existing tests pass locally - [ ] I have added appropriate error handling - [ ] I have added or updated documentation as needed

…est handling

…ared factory method

…rios to matrix, and update conformance test baseline

…fine JWT assertion audience handling

Add configurable SSE reconnection with exponential backoff and server-driven retry delays to `StreamableHttpClientTransport` closes #590 closes #420 ## How Has This Been Tested? New unit tests and pass conformance test ## Breaking Changes old constructors are Deprecated `close` no longer calls `terminateSession` ## Types of changes - [x] Bug fix (non-breaking change which fixes an issue) - [x] New feature (non-breaking change which adds functionality) - [ ] Breaking change (fix or feature that would cause existing functionality to change) - [ ] Documentation update ## Checklist - [x] I have read the [MCP Documentation](https://modelcontextprotocol.io) - [x] My code follows the repository's style guidelines - [x] New and existing tests pass locally - [x] I have added appropriate error handling - [x] I have added or updated documentation as needed

- Introduced `list` command in `run-conformance.sh` to display available scenarios. - Updated README with details about the new `list` command and its purpose.

… troubleshooting documentation - Integrate KotlinLogging for debug messages in `test_tool_with_logging`. - Add logging configuration via `simplelogger.properties`. - Expand README with network traffic capture tools and usage examples.

- Add `awaitCancellation()` to prevent premature stream closure in SSE handler.

…selines Following tests are now passing: - tools-call-with-logging - tools-call-with-progress - tools-call-sampling - tools-call-elicitation - elicitation-sep1034-defaults

codecov-commenter · 2026-03-12T08:27:12Z

Codecov Report

❌ Patch coverage is 20.00000% with 4 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...kotlin/sdk/server/StreamableHttpServerTransport.kt	20.00%	3 Missing and 1 partial ⚠️

📢 Thoughts on this report? Let us know!

conformance-test/README.md

…th retry support (#596) (#585) Adds a comprehensive conformance test suite for the Kotlin MCP SDK, covering core protocol operations, tool calls, elicitation, resources, prompts, and 20 OAuth/auth scenarios - Conformance server and client implementations - OAuth/auth test scenarios: JWT, authorization code flow, client credentials, PKCE, scope handling, cross-app access, client registration - CI workflow - Baseline file for tracking expected failures - Shell script fixes: - #592 - #593 - #596 ## Remaining known failures (tracked issues, will be fixed directly in `main`) - [x] `tools-call-with-logging`, `tools-call-with-progress`, `tools-call-sampling`, `tools-call-elicitation`, `elicitation-sep1034-defaults`- see #599, - [x] `elicitation-sep1330-enums` - #587 #600 - [x] `initialize` - #588 - [x] `tools_call`, `auth/scope-step-up`, `auth/scope-retry-limit` - #589 - [ ] `elicitation-sep1034-client-defaults` - #414 - [x] `sse-retry` - #590 - [ ] `resources-templates-read` - #591 ## Breaking Changes from #596 - `StreamableHttpClientTransport` and `mcpStreamableHttp`/`mcpStreamableHttpTransport`: old constructors accepting `Duration` timeout are now `@Deprecated` — use the new overloads with `ReconnectionOptions` instead - `StreamableHttpClientTransport.close()` no longer calls `terminateSession()` automatically ## Types of changes - [x] Bug fix (non-breaking change which fixes an issue) - [x] New feature (non-breaking change which adds functionality) - [x] Breaking change (fix or feature that would cause existing functionality to change) - [ ] Documentation update ## Checklist - [x] I have read the [MCP Documentation](https://modelcontextprotocol.io) - [x] My code follows the repository's style guidelines - [x] New and existing tests pass locally - [x] I have added appropriate error handling - [x] I have added or updated documentation as needed --------- Co-authored-by: Konstantin Pavlov <1517853+kpavlov@users.noreply.github.com>

# Conflicts: # conformance-test/conformance-baseline.yml # conformance-test/src/main/kotlin/io/modelcontextprotocol/kotlin/sdk/conformance/ConformanceTools.kt # conformance-test/src/main/resources/simplelogger.properties

…scenarios - Removed 5 server tests (`tools-call-with-logging`, `tools-call-with-progress`, `tools-call-sampling`, `tools-call-elicitation`, `elicitation-sep1034-defaults`) that now pass.

devcrocod

lgtm

devcrocod · 2026-03-12T14:42:55Z

conformance-test/README.md

@@ -114,16 +114,11 @@ Tests the conformance server against all server scenarios:
 8 scenarios are expected to fail due to current SDK limitations (tracked in [


Please reduce the number of expected failed scenarios

Will do it in the next PR

…ep1330_enums (#600) ## Correct SEP-1330 enum schemas in test_elicitation_sep1330_enums **NB! This PR contains changes from #599 and should be rebased and merged after #599 is merged.** Update conformance test according to [test requirements](https://github.com/modelcontextprotocol/conformance/blob/main/src/scenarios/server/elicitation-enums.ts#L14C1-L35C9). - Fix legacyEnum: was using `oneOf` with const/title pairs; now correctly uses `enum` + `enumNames` arrays per LegacyEnumSchema spec - Fix titledMulti: items were using `oneOf` with extra `type:"string"`; now correctly uses `anyOf` per TitledMultiSelectEnumSchema spec - Fix return text format to match expected "Elicitation completed: action=..., content=..." - Remove _elicitation-sep1330-enums_ from conformance baseline (test now passes) ## How Has This Been Tested? ```shell ./conformance-test/run-conformance.sh server ``` ## Breaking Changes No ## Types of changes - [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  - [x] I have read the [MCP Documentation](https://modelcontextprotocol.io) - [x] My code follows the repository's style guidelines - [x] New and existing tests pass locally - [ ] I have added appropriate error handling - [ ] I have added or updated documentation as needed --------- Co-authored-by: devcrocod <devcrocod@gmail.com>

devcrocod and others added 30 commits March 6, 2026 18:32

add conformance tests for server and client

3c36239

rewrite conformance tests, rework server-client implementation

42d14f0

add OAuth authorization and client credentials scenarios to conforman…

21846f5

…ce tests

add OAuth authorization and client credentials scenarios to conforman…

c241bda

…ce tests

replace System.err with KotlinLogging in ConformanceClient, add bas…

4c7900a

…eline file for expected test failures

remove toolLists from basic client

aebff7a

update protocol version constants

6e30638

remove unused allowedOrigins configuration from ConformanceServer s…

09ff656

…etup

add support for baseline file of expected failures in conformance tests

0e80c11

update elicitation schema to include username and email, adjust r…

b37f568

…esponse format in ConformanceTools

delete results directory during clean task in conformance-test build

70ace75

conditionally apply Detekt plugin to exclude conformance-test

928c68e

add resource parameter support and pre-registration in OAuth authoriz…

30ab88e

…ation scenarios

remove OAuth authorization handler and simplify resource metadata dis…

914b531

…covery logic

add CSRF state parameter validation and enhance error handling in OAu…

1ba27f8

…th flows

remove redundant non-null assertions in authCodeFlow implementation

7c3b6ce

add new expected failures to conformance test baseline

d0c0d96

specify explicit types for cached discovery and credentials in authCo…

5369a57

…deFlow implementation

improve error handling in run-conformance.sh by adding fallback for…

451940f

… directory resolution and disabling redundant shellcheck warning

update README to reflect 18 OAuth scenarios in client-auth suite and …

94dfe80

…bump conformance tool version to 0.1.15

add Cross-App Access scenario and validate PRM resource in authCodeFl…

c465ffe

…ow implementation

add HTTP timeout configuration to ConformanceClient for improved requ…

5ef15e9

…est handling

refactor ConformanceClient to centralize HTTP client creation with sh…

6e9c082

…ared factory method

parameterize JDK and Node.js versions in workflow, add new auth scena…

7c1a1cf

…rios to matrix, and update conformance test baseline

add support for additional auth scenarios in conformance tests and re…

4892b7c

…fine JWT assertion audience handling

feat(conformance): add list command to conformance test script

6f1ae61

- Introduced `list` command in `run-conformance.sh` to display available scenarios. - Updated README with details about the new `list` command and its purpose.

kpavlov added 2 commits March 12, 2026 09:52

fix(server): keep SSE connection open until explicitly cancelled

c1f1818

- Add `awaitCancellation()` to prevent premature stream closure in SSE handler.

chore(conformance): remove 5 passing server tests from conformance ba…

7ec51bd

…selines Following tests are now passing: - tools-call-with-logging - tools-call-with-progress - tools-call-sampling - tools-call-elicitation - elicitation-sep1034-defaults

kpavlov changed the base branch from devcrocod/conformance-tests to main March 12, 2026 08:10

kpavlov changed the title ~~Kpavlov/fix sse notifications~~ fix(server): notifications not delivered over Streamable HTTP Mar 12, 2026

kpavlov changed the base branch from main to devcrocod/conformance-tests March 12, 2026 08:28

kpavlov requested a review from e5l March 12, 2026 09:46

kpavlov changed the title ~~fix(server): notifications not delivered over Streamable HTTP~~ fix(server): notifications not delivered over Streamable HTTP (#587) Mar 12, 2026

devcrocod reviewed Mar 12, 2026

View reviewed changes

conformance-test/README.md Outdated Show resolved Hide resolved

e5l removed their request for review March 12, 2026 12:08

remove network traffic capture examples from README

b883af6

Base automatically changed from devcrocod/conformance-tests to main March 12, 2026 13:45

Merge branch 'main' into kpavlov/fix-sse-notifications

145c173

# Conflicts: # conformance-test/conformance-baseline.yml # conformance-test/src/main/kotlin/io/modelcontextprotocol/kotlin/sdk/conformance/ConformanceTools.kt # conformance-test/src/main/resources/simplelogger.properties

kpavlov marked this pull request as ready for review March 12, 2026 13:50

chore(conformance): remove outdated server tests from README failure …

92eecc8

…scenarios - Removed 5 server tests (`tools-call-with-logging`, `tools-call-with-progress`, `tools-call-sampling`, `tools-call-elicitation`, `elicitation-sep1034-defaults`) that now pass.

kpavlov requested a review from devcrocod March 12, 2026 14:10

kpavlov added the bugfix Something was fixed 🎉 label Mar 12, 2026

devcrocod approved these changes Mar 12, 2026

View reviewed changes

kpavlov merged commit 736efe9 into main Mar 12, 2026
24 of 25 checks passed

kpavlov deleted the kpavlov/fix-sse-notifications branch March 12, 2026 14:52

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fix(server): notifications not delivered over Streamable HTTP (#587)#599

fix(server): notifications not delivered over Streamable HTTP (#587)#599
kpavlov merged 35 commits intomainfrom
kpavlov/fix-sse-notifications

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		@@ -114,16 +114,11 @@ Tests the conformance server against all server scenarios:
		8 scenarios are expected to fail due to current SDK limitations (tracked in [

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