fix(streamable_http): ensure graceful shutdown to prevent close reque… #477

sunerpy · 2025-07-09T02:46:09Z

…st errors

func TestExtract(t *testing.T) {
	srv, err := newTestMCPServer()
	if err != nil {
		t.Fatalf("failed to new MCP server: %v", err)
	}
	defer srv.Close()
	t.Logf("Using server URL: %s", srv.URL)
	serverURL := srv.URL + "/mcp"
	t.Logf("Using server URL: %s", serverURL)

	transport, err := transport.NewStreamableHTTP(serverURL)
	if err != nil {
		t.Fatalf("failed to create transport: %v", err)
	}
	client := client.NewClient(transport)
	defer srv.Close()
	client.OnNotification(func(notification mm.JSONRPCNotification) {
		t.Logf("Received notification: %+v", notification)
	})

	ctx := context.Background()
	client.Start(ctx)

	var ret any

	ret, err = client.Initialize(ctx, mm.InitializeRequest{})
	if err != nil {
		t.Fatalf("failed to initialize client: %v", err)
	}
	t.Logf("Client initialized: %v", ret)

	ret, err = client.ListTools(ctx, mm.ListToolsRequest{})
	if err != nil {
		t.Fatalf("failed to initialize client: %v", err)
	}
	t.Logf("Client initialized: %v", ret)

	call := mm.CallToolRequest{}
	call.Params.Name = "extract"
	call.Params.Arguments = map[string]any{
		"extractor": "demo",
		// "input":       "Hello, world",
		// "input_type":  "text",
		// "output_type": "text",
	}
	ret, err = client.CallTool(ctx, call)
	if err != nil {
		t.Fatalf("failed to initialize client: %v", err)
	}
	t.Logf("Client initialized: %v", ret)
}

newTestMCPServer return a *httptest.Server like:

	srv := server.NewTestStreamableHTTPServer(raw,
		server.WithEndpointPath("/mcp"),
	)

console errors:
2025/07/09 10:32:34 ERROR: failed to send close request: Delete "http://127.0.0.1:43485/mcp": dial tcp 127.0.0.1:43485: connect: connection refused

Description

Added sync.WaitGroup to wait for asynchronous session cleanup goroutine to finish

wg.Add(1) is used before spawning the goroutine; wg.Done() is called upon completion

wg.Wait() ensures Close() blocks until the cleanup finishes, preserving correct shutdown order

Fixes an issue in tests where closing the client and server in quick succession could lead to connection refused errors due to the client's asynchronous close attempting to reach a server that has already shut down

Removed redundant blank lines to streamline the code structure

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

Additional Information

This PR fixes a race condition in StreamableHTTP.Close() where the asynchronous close request may be sent after the server is already shut down, leading to connection refused errors in tests.

Summary by CodeRabbit

Bug Fixes
- Improved reliability of session closure by ensuring that notifications to the server complete before closing.
Style
- Removed unnecessary blank lines for cleaner code formatting.

…st errors Added sync.WaitGroup to wait for asynchronous session cleanup goroutine to finish wg.Add(1) is used before spawning the goroutine; wg.Done() is called upon completion wg.Wait() ensures Close() blocks until the cleanup finishes, preserving correct shutdown order Fixes an issue in tests where closing the client and server in quick succession could lead to connection refused errors due to the client's asynchronous close attempting to reach a server that has already shut down Removed redundant blank lines to streamline the code structure

coderabbitai · 2025-07-09T02:46:15Z

Walkthrough

A sync.WaitGroup field was introduced to the StreamableHTTP struct to synchronize the completion of a session close notification goroutine in the Close() method. The Close() method now waits for the notification goroutine to finish before returning. Several unnecessary blank lines were also removed from various methods.

Changes

File(s)	Change Summary
client/transport/streamable_http.go	Added sync.WaitGroup field to StreamableHTTP; synchronized session close notification in Close(); removed extraneous blank lines from several methods.

Suggested reviewers

ezynda3
dugenkui03
pottekkat

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coderabbitai

Actionable comments posted: 0

🧹 Nitpick comments (1)

client/transport/streamable_http.go (1)

186-206: Close() now blocks correctly, but the wait group is very specific

The added wg.Add/Done/Wait pattern correctly serialises the async DELETE, 👍.
Two nits you may want to address:

Scope: the WG only tracks the session-close goroutine; other long-lived goroutines (listenForever, SSE readers) can still be alive when Close() returns and may leak if the caller expects full shutdown.

Clarity: naming the field closeWg (or similar) would make its intent crystal clear.

Neither issue is blocking, but clarifying would improve maintainability.

📜 Review details

Configuration used: CodeRabbit UI
Review profile: CHILL
Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 56f2501 and bee9f90.

📒 Files selected for processing (1)

client/transport/streamable_http.go (3 hunks)

🔇 Additional comments (1)

client/transport/streamable_http.go (1)

117-118: Beware of struct copying after embedding a sync.WaitGroup

Embedding wg sync.WaitGroup directly makes the whole StreamableHTTP struct non-copyable after first use (the sync package panics on WaitGroup misuse when copied). The current API always hands out a *StreamableHTTP, but nothing prevents downstream code from taking a value copy (e.g., val := *client).
Consider documenting this explicitly or embedding a pointer (wg *sync.WaitGroup) to hard-prevent accidental copies.

pottekkat

Thank you for fixing this @sunerpy

coderabbitai bot reviewed Jul 9, 2025

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pottekkat approved these changes Jul 9, 2025

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pottekkat merged commit 2d479bb into mark3labs:main Jul 9, 2025
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