feat: Implement Streamable-HTTP Client Basic #168

leavez · 2025-04-17T15:47:06Z

This PR implements the basic streamable-http transport for the client side.

This implementation follows the specification, including (but not limited to)

upgradable to SSE response
SessionID management
- optional session id
- 404 response handling
- client closes session with a DELETE request

The features below are not supported:

batching (not supported in other transports either)
continuously listening for server notifications when no request is in flight
stream resuming
server -> client request (not supported in other transports either)

Summary by CodeRabbit

New Features
- Introduced a streamable HTTP client supporting JSON-RPC communication with session management and server-sent event (SSE) streaming.
- Added support for sending requests, notifications, and receiving asynchronous server notifications.
- Implemented session handling, graceful shutdown, and customizable HTTP headers and timeouts.
Tests
- Added comprehensive tests covering initialization, request/response handling, notification delivery, concurrency, and error scenarios.

impl basic streamable HTTP transport

coderabbitai · 2025-04-17T15:47:12Z

Walkthrough

This change introduces a new streamable HTTP transport mechanism for JSON-RPC communication within the client package. It adds the StreamableHTTP transport, supporting both standard JSON and server-sent events (SSE) streaming responses, session management, and notification handling. The client package is extended with a function to create clients using this transport. Comprehensive unit tests are included to validate initialization, request/response handling, notifications, concurrency, and error scenarios using a mock HTTP server.

Changes

File(s)	Change Summary
client/http.go	New file providing a constructor function `NewStreamableHttpClient` to create a streamable HTTP-based MCP client.
client/transport/streamable_http.go	New file implementing the `StreamableHTTP` transport for JSON-RPC over HTTP with support for single JSON and SSE streaming, session management, notification handling, graceful shutdown, and configuration options.
client/transport/streamable_http_test.go	New file containing unit tests for `StreamableHTTP`, including a mock server, tests for request/response handling, notifications, concurrency, and error cases.

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client/transport/streamable_http.go (1 hunks)

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client/transport/streamable_http.go

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coderabbitai

Actionable comments posted: 3

🧹 Nitpick comments (4)

client/http.go (1)
11-14: Error message refers to “SSE” while constructing Streamable‑HTTP transport

The constructor returns “failed to create SSE transport”, but the surrounding code and PR terminology call it “streamable‑http”. This can confuse users when debugging.
-		return nil, fmt.Errorf("failed to create SSE transport: %w", err)
+		return nil, fmt.Errorf("failed to create streamable‑http transport: %w", err)
client/transport/streamable_http.go (2)

206-228: Double‑closing resp.Body & partial SSE detection

SendRequest defers resp.Body.Close() (line 179) but hands the same reader to handleSSEResponse, whose readSSE closes it again (line 286). Closing an already‑closed body is safe but signals oversight.

Additionally, only exact text/event-stream is recognised. Apply the same strings.HasPrefix improvement as above to avoid false negatives.

314-330: SSE parser drops messages with multiline data / no explicit event:

The SSE spec allows:

multiple data: lines per event (should be concatenated with “\n”)

events without an event: field (default event name message)

Current logic overrides data on every line and ignores events lacking event: – losing information.

Suggest accumulating data across lines and treating empty event as "message" before dispatching.

Do you want a patched parser implementation?

client/transport/streamable_http_test.go (1)

281-287: Variable errors shadows stdlib package, harming readability

Inside the “MultipleRequests” sub‑test, the slice errors := make([]error, …) hides the imported errors package, which may be needed later and confuses readers.
Rename the slice to e.g. errs to avoid shadowing.

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📥 Commits

Reviewing files that changed from the base of the PR and between 37ac814 and 1f4d6a8.

📒 Files selected for processing (3)

client/http.go (1 hunks)
client/transport/streamable_http.go (1 hunks)
client/transport/streamable_http_test.go (1 hunks)

🧰 Additional context used

🧬 Code Graph Analysis (2)

client/transport/streamable_http_test.go (2)

mcp/types.go (1)

JSONRPCNotification (192-195)

client/transport/streamable_http.go (1)

NewStreamableHTTP (65-84)

client/transport/streamable_http.go (2)

client/client.go (1)

Client (16-24)

mcp/types.go (1)

JSONRPCNotification (192-195)

🔇 Additional comments (2)

client/transport/streamable_http.go (1)

163-169: 🛠️ Refactor suggestion

Content‑Type equality check too strict; real servers usually append charset

Accept / server reply commonly contains application/json; charset=utf-8.
A strict equality test will mis‑route such responses to the “unexpected content type” branch.
-	switch resp.Header.Get("Content-Type") {
+	ct := resp.Header.Get("Content-Type")
+	switch {
+	case strings.HasPrefix(ct, "application/json"):
Remember to import strings.

Likely an incorrect or invalid review comment.
client/transport/streamable_http_test.go (1)

205-224: SendRequestWithTimeout uses a pre‑canceled context – good, but assert type

The assertion checks errors.Is(err, context.Canceled) which is correct, yet if future implementation wraps the error, this might break. Consider using context.Cause (Go 1.20+) or errors.Is on ctx.Err() for resilience.
No change required, just a note.

client/http.go

client/transport/streamable_http.go

deviantony · 2025-04-21T21:26:00Z

Nice, I wonder if we should add more documentation to the README about how to use this

ls0f · 2025-04-22T01:12:08Z

Nice work! Is the server-side implementation coming soon?

leavez · 2025-04-22T16:27:15Z

Nice work! Is the server-side implementation coming soon?

I'm working on it, but very few minutes on it every day. So it will not be very quick.

leavez · 2025-05-12T05:53:43Z

Nice work! Is the server-side implementation coming soon?

I'm working on it, but very few minutes on it every day. So it will not be very quick.

#273

leavez added 8 commits April 17, 2025 22:31

add streamable http transport

8d7440b

doc

29ac8f5

update

f8dccd7

remove default timeout

b94f6ee

Update streamable_http.go

ea2b686

add http client

f406bd6

Update streamable_http.go

838f9a4

Merge pull request #2 from leavez/stream-http-client

1f4d6a8

impl basic streamable HTTP transport

coderabbitai bot reviewed Apr 17, 2025

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leavez added 2 commits April 18, 2025 00:03

add timeout to close request

07568b1

Update http.go

5a3f37a

sks reviewed Apr 18, 2025

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client/transport/streamable_http.go Outdated Show resolved Hide resolved

fix log

eb43178

ezynda3 merged commit dd3210c into mark3labs:main Apr 19, 2025
2 checks passed

coderabbitai bot mentioned this pull request Apr 30, 2025

Implement MCP Streamable HTTP Server #228

Closed

rwjblue-glean mentioned this pull request May 11, 2025

Does this project support streamable HTTP? #219

Closed

coderabbitai bot mentioned this pull request May 11, 2025

Feat: Impl Server-Side Streamable HTTP transport #273

Merged

This was referenced May 25, 2025

feat: client-side streamable-http transport supports continuously listening #317

Open

[SSE][OAuth] Add OAuth support to SSE client #340

Merged

fix: panic when streamable HTTP server sends notification #348

Merged

This was referenced Jun 2, 2025

[streamable-http] Add ability to override the http.Client #359

Merged

feat: client-side streamable-http transport supports resumability #380

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