Add Streamable Http Transport #87

SeanChinJunKai · 2025-04-27T16:17:26Z

Closes #79

Pending:

Client Implementation of StreamableHttp
Unit Tests
Integration Tests

Motivation and Context

How Has This Been Tested?

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

e5l

Hey @SeanChinJunKai, thanks for the PR. Please check the comments.

It also would be great to have some tests

...commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/server/StreamableHttpServerTransport.kt

e5l · 2025-04-30T06:46:39Z

...commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/server/StreamableHttpServerTransport.kt

+        try {
+            val acceptHeader = call.request.headers["Accept"]?.split(",") ?: listOf()
+
+            if (!acceptHeader.contains("text/event-stream") || !acceptHeader.contains("application/json")) {


please use match instead of contains

@e5l do you mean regex match with call.request.headers["Accept"]? Why do you prefer match over contains?

...commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/server/StreamableHttpServerTransport.kt

e5l · 2025-04-30T06:50:16Z

...commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/server/StreamableHttpServerTransport.kt

+        }
+
+        if (sessionId != null) {
+            call.response.header("Mcp-Session-Id", sessionId!!)


Constants should be extracted to the top-level scope with a proper visibility

@e5l I have extracted it into a Constants file in shared module since we might need it in client module

SeanChinJunKai · 2025-04-30T07:42:59Z

Hi @e5l, thanks for the comments. Ill take a look. I have some questions regarding client transport implementation. In particular, when client makes post request to server server can open a sse session but how does client connect to this sse session?

SeanChinJunKai · 2025-05-06T06:49:30Z

Hi @e5l, could i get some help on the above?

e5l · 2025-05-07T06:57:14Z

Sure, let me check

- Clear callMapping in close() method to prevent memory leaks - Add comprehensive KDoc comments for all public APIs - Fix Accept header validation to use proper matching instead of contains - Fix ContentType header key to use HttpHeaders.ContentType - Fix parseBody error message for invalid JSON format - Add unit tests for StreamableHttpServerTransport

- add EventStore and support "Last-Event-ID" - Origin check - thread safety

Copilot

Pull Request Overview

This PR introduces a new streamable HTTP transport for JSON-RPC over Server-Sent Events (SSE) and updates protocol message types.

Bump protocol version and make JSONRPC IDs optional in response/error types
Add StreamableHttpServerTransport and EventStore interface for SSE-based streaming
Update API metadata to expose new transport and error constructors

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/types.kt	Updated `LATEST_PROTOCOL_VERSION`, `SUPPORTED_PROTOCOL_VERSIONS`, and changed `JSONRPCResponse`/`JSONRPCError` signatures to accept nullable IDs
src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/shared/Protocol.kt	Adjusted named parameter for `JSONRPCError` instantiation in fallback error response
src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/server/StreamableHttpServerTransport.kt	Newly added HTTP transport implementation with SSE, session management, and optional resumability
api/kotlin-sdk.api	Reflected changes to `JSONRPCError`, added `EventStore` interface, and `StreamableHttpServerTransport` to public API

Comments suppressed due to low confidence (3)

src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/types.kt:280

Changing JSONRPCError from a data class to a regular class and adding an optional id parameter is a breaking API change (removes copy, destructuring, and equals/hashCode). Document this in the changelog and provide migration guidance.

public class JSONRPCError(

src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/server/StreamableHttpServerTransport.kt:92

This new transport contains complex SSE and HTTP-session logic but no accompanying tests. Add unit and integration tests covering initialization, streaming, error handling, and session resumption.

public class StreamableHttpServerTransport(

src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/server/StreamableHttpServerTransport.kt:206

[nitpick] Consider adding KDoc to handleRequest (and other public methods) explaining the expected HTTP headers and lifecycle to improve readability and maintainability.

    public suspend fun handleRequest(call: ApplicationCall, session: ServerSSESession) {

Copilot · 2025-07-11T14:19:37Z

src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/shared/Protocol.kt

                transport?.send(
                    JSONRPCResponse(
                        id = request.id,
                        error = JSONRPCError(


JSONRPCError is instantiated without passing the original request.id, so clients cannot correlate the method-not-found error with the request. Include id = request.id when constructing JSONRPCError.

Suggested change

error = JSONRPCError(

error = JSONRPCError(

id = request.id,

...commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/server/StreamableHttpServerTransport.kt

…r/StreamableHttpServerTransport.kt Co-authored-by: Copilot <[email protected]>

devcrocod · 2025-07-16T11:16:35Z

Error when testing with Inspector, needs further investigation

There are also issues with the API design and limitations of ktor when creating the server

e5l · 2025-07-23T05:21:53Z

Obsolete

tidbeck · 2025-08-19T09:18:49Z

Obsolete

Can we have some details on why this is obsolete? Is there ongoing work in any other PR?

devcrocod · 2025-08-19T16:33:07Z

Hi @tidbeck
Due to many changes, this PR is challenging to maintain. I’m continuing the work on the streamable transport server

zshea · 2025-08-25T08:39:03Z

Hi @devcrocod , I created a PR #235, hopefully we won't have duplicated work.

e5l requested review from Copilot and e5l April 29, 2025 12:10

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e5l requested changes Apr 30, 2025

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e5l self-assigned this May 7, 2025

michaellatman mentioned this pull request Jun 2, 2025

Fix StreamableHttpServerTransport review comments #112

Closed

wqerrewetw mentioned this pull request Jun 25, 2025

Streamable HTTP 无法使用 rikkahub/rikkahub#127

Closed

devcrocod force-pushed the sean/streamable-http branch from 802d323 to 257929a Compare July 9, 2025 10:47

e5l requested a review from devcrocod July 10, 2025 06:49

SeanChinJunKai and others added 7 commits July 11, 2025 16:17

feat: allow JSONRPCResponse to have nullable id

764d773

feat: add StreamableHttpTransport for server

096b28f

feat: minor refactoring

fe91936

api dump for StreamableHttpTransport

b7937f9

Fix and refactor StreamableHttpTransport

2737ae4

- add EventStore and support "Last-Event-ID" - Origin check - thread safety

Fix accepts headers and workaround for receive Json

abebd98

Fix content type check in StreamableHttpServerTransport

9613cd3

devcrocod force-pushed the sean/streamable-http branch from d0e2593 to 9613cd3 Compare July 11, 2025 14:17

devcrocod requested review from Copilot and e5l July 11, 2025 14:18

devcrocod previously approved these changes Jul 11, 2025

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Copilot AI reviewed Jul 11, 2025

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Update src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/serve…

a9449be

…r/StreamableHttpServerTransport.kt Co-authored-by: Copilot <[email protected]>

devcrocod dismissed their stale review via a9449be July 11, 2025 17:53

devcrocod mentioned this pull request Jul 14, 2025

Add streamable http client transport #147

Merged

9 tasks

This was referenced Jul 21, 2025

Adding Streaming HTTP Transport #79

Open

StreamableHTTP transport: Server implementation #183

Open

e5l closed this Jul 23, 2025

zshea mentioned this pull request Aug 25, 2025

Add Server Streamable Http Transport #235

Open

9 tasks

Add Streamable Http Transport #87

Add Streamable Http Transport #87

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SeanChinJunKai commented Apr 30, 2025

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devcrocod commented Jul 16, 2025

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tidbeck commented Aug 19, 2025

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SeanChinJunKai commented Apr 27, 2025 •

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