Add the ability to provide a custom HTTP client for SSE connections

Author: andrey-star

internal/mcp/sse.go

@@ -310,19 +310,30 @@ func (s sseServerStream) Close() error {
 // https://modelcontextprotocol.io/specification/2024-11-05/basic/transports
 type SSEClientTransport struct {
 	sseEndpoint *url.URL
+	httpClient  *http.Client
 }
 
 // NewSSEClientTransport returns a new client transport that connects to the
-// SSE server at the provided URL.
+// SSE server at the provided URL using the default HTTP client.
 //
 // NewSSEClientTransport panics if the given URL is invalid.
 func NewSSEClientTransport(baseURL string) *SSEClientTransport {
+	// Use the default HTTP client.
+	return NewSSEClientTransportWithHTTPClient(baseURL, http.DefaultClient)
+}
+
+// NewSSEClientTransportWithHTTPClient returns a new client transport that connects to the
+// SSE server at the provided URL using the provided HTTP client.
+//
+// NewSSEClientTransportWithHTTPClient panics if the given URL is invalid.
+func NewSSEClientTransportWithHTTPClient(baseURL string, httpClient *http.Client) *SSEClientTransport {
 	url, err := url.Parse(baseURL)
 	if err != nil {
 		panic(fmt.Sprintf("invalid base url: %v", err))
 	}
 	return &SSEClientTransport{
 		sseEndpoint: url,
+		httpClient:  httpClient,
 	}
 }
 
@@ -333,7 +344,7 @@ func (c *SSEClientTransport) Connect(ctx context.Context) (Stream, error) {
 		return nil, err
 	}
 	req.Header.Set("Accept", "text/event-stream")
-	resp, err := http.DefaultClient.Do(req)
+	resp, err := c.httpClient.Do(req)
 	if err != nil {
 		return nil, err
 	}
@@ -404,6 +415,7 @@ func (c *SSEClientTransport) Connect(ctx context.Context) (Stream, error) {
 	// From here on, the stream takes ownership of resp.Body.
 	s := &sseClientStream{
 		sseEndpoint: c.sseEndpoint,
+		httpClient:  c.httpClient,
 		msgEndpoint: msgEndpoint,
 		incoming:    make(chan []byte, 100),
 		body:        resp.Body,
@@ -435,9 +447,10 @@ func (c *SSEClientTransport) Connect(ctx context.Context) (Stream, error) {
 //   - Reads are SSE 'message' events, and pushes them onto a buffered channel.
 //   - Close terminates the GET request.
 type sseClientStream struct {
-	sseEndpoint *url.URL    // SSE endpoint for the GET
-	msgEndpoint *url.URL    // session endpoint for POSTs
-	incoming    chan []byte // queue of incoming messages
+	sseEndpoint *url.URL     // SSE endpoint for the GET
+	msgEndpoint *url.URL     // session endpoint for POSTs
+	httpClient  *http.Client // HTTP client to use for requests
+	incoming    chan []byte  // queue of incoming messages
 
 	mu     sync.Mutex
 	body   io.ReadCloser // body of the hanging GET
@@ -484,7 +497,7 @@ func (c *sseClientStream) Write(ctx context.Context, msg jsonrpc2.Message) error
 		return err
 	}
 	req.Header.Set("Content-Type", "application/json")
-	resp, err := http.DefaultClient.Do(req)
+	resp, err := c.httpClient.Do(req)
 	if err != nil {
 		return err
 	}