feat: add hooks for sse client

client/transport/sse.go

@@ -17,6 +17,18 @@ import (
 	"github.com/mark3labs/mcp-go/mcp"
 )
 
+// OnBeforeRequestFunc is called before sending the request, with context.
+type OnBeforeRequestFunc func(ctx context.Context, req *http.Request)
+
+// OnAfterResponseFunc is called after receiving the response, with context. (Regardless of error, when err is not nil resp may be nil.) The req parameter is included.
+type OnAfterResponseFunc func(ctx context.Context, req *http.Request, resp *http.Response, err error)
+
+// SSEHooks supports multiple before and after processing functions.
+type SSEHooks struct {
+	OnBeforeRequest []OnBeforeRequestFunc
+	OnAfterResponse []OnAfterResponseFunc
+}
+
 // SSE implements the transport layer of the MCP protocol using Server-Sent Events (SSE).
 // It maintains a persistent HTTP connection to receive server-pushed events
 // while sending requests over regular HTTP POST calls. The client handles
@@ -32,6 +44,8 @@ type SSE struct {
 	endpointChan   chan struct{}
 	headers        map[string]string
 
+	hooks SSEHooks
+
 	started         atomic.Bool
 	closed          atomic.Bool
 	cancelSSEStream context.CancelFunc
@@ -45,6 +59,13 @@ func WithHeaders(headers map[string]string) ClientOption {
 	}
 }
 
+// Register a set of hooks (overwrites existing hooks)
+func WithSSEHooks(hooks SSEHooks) ClientOption {
+	return func(sc *SSE) {
+		sc.hooks = hooks
+	}
+}
+
 // NewSSE creates a new SSE-based MCP client with the given base URL.
 // Returns an error if the URL is invalid.
 func NewSSE(baseURL string, options ...ClientOption) (*SSE, error) {
@@ -261,6 +282,13 @@ func (c *SSE) SendRequest(
 		req.Header.Set(k, v)
 	}
 
+	// hooks: before request
+	for _, hook := range c.hooks.OnBeforeRequest {
+		if hook != nil {
+			hook(ctx, req)
+		}
+	}
+
 	// Register response channel
 	responseChan := make(chan *JSONRPCResponse, 1)
 	c.mu.Lock()
@@ -274,6 +302,14 @@ func (c *SSE) SendRequest(
 
 	// Send request
 	resp, err := c.httpClient.Do(req)
+
+	// hooks: after response
+	for _, hook := range c.hooks.OnAfterResponse {
+		if hook != nil {
+			hook(ctx, req, resp, err)
+		}
+	}
+
 	if err != nil {
 		deleteResponseChan()
 		return nil, fmt.Errorf("failed to send request: %w", err)
@@ -348,7 +384,22 @@ func (c *SSE) SendNotification(ctx context.Context, notification mcp.JSONRPCNoti
 		req.Header.Set(k, v)
 	}
 
+	// hooks: before request
+	for _, hook := range c.hooks.OnBeforeRequest {
+		if hook != nil {
+			hook(ctx, req)
+		}
+	}
+
 	resp, err := c.httpClient.Do(req)
+
+	// hooks: after response
+	for _, hook := range c.hooks.OnAfterResponse {
+		if hook != nil {
+			hook(ctx, req, resp, err)
+		}
+	}
+
 	if err != nil {
 		return fmt.Errorf("failed to send notification: %w", err)
 	}