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mcp/streamable: add persistent SSE GET listener (#206)

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This CL adds the optional persistent SSE GET listener as specified in
section 2.2.
https://modelcontextprotocol.io/specification/2025-06-18/basic/transports#listening-for-messages-from-the-server

This enables server initiated SSE streams.

For #10
This commit is contained in:
Sam Thanawalla 2025-07-30 17:00:50 -04:00 • committed by GitHub
commit a9a503f74a
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1 changed files with 57 additions and 15 deletions
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39
mcp/streamable_test.go
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@ -168,7 +168,7 @@ func TestClientReplay(t *testing.T) {
clientSession.CallTool(ctx, &CallToolParams{Name: "multiMessageTool"})
// 4. Read and verify messages until the server signals it's ready for the proxy kill.
receivedNotifications := readProgressNotifications(t, ctx, notifications, 2)
receivedNotifications := readNotifications(t, ctx, notifications, 2)
wantReceived := []string{"msg1", "msg2"}
if diff := cmp.Diff(wantReceived, receivedNotifications); diff != "" {
@ -201,7 +201,7 @@ func TestClientReplay(t *testing.T) {
// 7. Continue reading from the same connection object.
// Its internal logic should successfully retry, reconnect to the new proxy,
// and receive the replayed messages.
recoveredNotifications := readProgressNotifications(t, ctx, notifications, 2)
recoveredNotifications := readNotifications(t, ctx, notifications, 2)
// 8. Verify the correct messages were received on the recovered connection.
wantRecovered := []string{"msg3", "msg4"}
@ -211,8 +211,39 @@ func TestClientReplay(t *testing.T) {
}
}
// Helper to read a specific number of progress notifications.
func readProgressNotifications(t *testing.T, ctx context.Context, notifications chan string, count int) []string {
// TestServerInitiatedSSE verifies that the persistent SSE connection remains
// open and can receive server-initiated events.
func TestServerInitiatedSSE(t *testing.T) {
notifications := make(chan string)
server := NewServer(testImpl, nil)
httpServer := httptest.NewServer(NewStreamableHTTPHandler(func(*http.Request) *Server { return server }, nil))
defer httpServer.Close()
ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
defer cancel()
client := NewClient(testImpl, &ClientOptions{ToolListChangedHandler: func(ctx context.Context, cc *ClientSession, params *ToolListChangedParams) {
notifications <- "toolListChanged"
},
})
clientSession, err := client.Connect(ctx, NewStreamableClientTransport(httpServer.URL, nil))
if err != nil {
t.Fatalf("client.Connect() failed: %v", err)
}
defer clientSession.Close()
server.AddTool(&Tool{Name: "testTool", InputSchema: &jsonschema.Schema{}},
func(ctx context.Context, ss *ServerSession, params *CallToolParamsFor[map[string]any]) (*CallToolResult, error) {
return &CallToolResult{}, nil
})
receivedNotifications := readNotifications(t, ctx, notifications, 1)
wantReceived := []string{"toolListChanged"}
if diff := cmp.Diff(wantReceived, receivedNotifications); diff != "" {
t.Errorf("Received notifications mismatch (-want +got):\n%s", diff)
}
}
// Helper to read a specific number of notifications.
func readNotifications(t *testing.T, ctx context.Context, notifications chan string, count int) []string {
t.Helper()
var collectedNotifications []string
for {