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mcp/stream: fix prevent potential goroutine leak on blocked incoming channel #123

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53 changes: 53 additions & 0 deletions mcp/streamable_test.go
Original file line number Diff line number Diff line change
Expand Up @@ -14,10 +14,12 @@ import (
"net/http/cookiejar"
"net/http/httptest"
"net/url"
"runtime"
"strings"
"sync"
"sync/atomic"
"testing"
"time"

"github.com/google/go-cmp/cmp"
"github.com/google/go-cmp/cmp/cmpopts"
Expand Down Expand Up @@ -597,3 +599,54 @@ func TestEventID(t *testing.T) {
})
}
}

func TestStreamableClientConnSSEGoroutineLeak(t *testing.T) {
// Initialize a streamableClientConn instance with channels
conn := &streamableClientConn{
incoming: make(chan []byte, 1),
done: make(chan struct{}),
}

// Construct mock SSE response data
var builder strings.Builder
for range 3 {
builder.WriteString("data: hello world\n\n")
}
resp := &http.Response{
Body: io.NopCloser(strings.NewReader(builder.String())),
}

// Start the handleSSE goroutine manually
var wg sync.WaitGroup
wg.Add(1)
go func() {
conn.handleSSE(resp)
wg.Done()
}()

// Wait until incoming channel is filled
deadlineCtx, cancelFunc := context.WithTimeout(context.Background(), 100*time.Millisecond)
defer cancelFunc()
for len(conn.incoming) < cap(conn.incoming) { // Ensure enough events are written
select {
case <-deadlineCtx.Done():
t.Fatalf("timeout when waiting for streamableClientConn.incoming to be full: %v", deadlineCtx.Err())
default:
// Continue checking until the channel is full
}
}

// Now simulate calling Close() and blocking the goroutine
close(conn.done)
wg.Wait()

// Check if "scanEvents" goroutine is still running
leakKey := "scanEvents"
buf := make([]byte, 1024*1024)
n := runtime.Stack(buf, true)
stack := string(buf[:n])

if idx := strings.Index(stack, leakKey); idx != -1 {
t.Fatalf("goroutine leak detected: %s still active", leakKey)
}
}
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