refactor: decouple MCP header utilities from http.Request by accepting http.Header instead

Author: guglielmo-san

mcp/mcp_http_headers.go

@@ -44,32 +44,32 @@ func extractName(method string, params json.RawMessage) (string, bool) {
 	return "", false
 }
 
-func setStandardHeaders(httpReq *http.Request, msg jsonrpc.Message) {
+func setStandardHeaders(header http.Header, msg jsonrpc.Message) {
 	if msg == nil {
 		return
 	}
-	if httpReq.Header.Get(ProtocolVersionHeader) == "" || httpReq.Header.Get(ProtocolVersionHeader) < MinVersionForStandardHeaders {
+	if header.Get(ProtocolVersionHeader) == "" || header.Get(ProtocolVersionHeader) < MinVersionForStandardHeaders {
 		return
 	}
 
 	switch msg := msg.(type) {
 	case *jsonrpc.Request:
-		httpReq.Header.Set(MethodHeader, msg.Method)
+		header.Set(MethodHeader, msg.Method)
 		if name, ok := extractName(msg.Method, msg.Params); ok {
-			httpReq.Header.Set(NameHeader, name)
+			header.Set(NameHeader, name)
 		}
 	}
 }
 
-func validateMcpHeaders(req *http.Request, msg jsonrpc.Message) error {
-	protocolVersion := req.Header.Get(ProtocolVersionHeader)
+func validateMcpHeaders(header http.Header, msg jsonrpc.Message) error {
+	protocolVersion := header.Get(ProtocolVersionHeader)
 	if protocolVersion == "" || protocolVersion < MinVersionForStandardHeaders {
 		return nil
 	}
 
 	switch msg := msg.(type) {
 	case *jsonrpc.Request:
-		methodInHeader := req.Header.Get(MethodHeader)
+		methodInHeader := header.Get(MethodHeader)
 		if methodInHeader == "" {
 			return errors.New("missing required Mcp-Method header")
 		}
@@ -78,7 +78,7 @@ func validateMcpHeaders(req *http.Request, msg jsonrpc.Message) error {
 		}
 
 		if msg.Method == "tools/call" || msg.Method == "resources/read" || msg.Method == "prompts/get" {
-			nameInHeader := req.Header.Get(NameHeader)
+			nameInHeader := header.Get(NameHeader)
 			if nameInHeader == "" {
 				return fmt.Errorf("missing required Mcp-Name header for method %q", msg.Method)
 			}

mcp/mcp_http_headers_test.go

@@ -193,20 +193,17 @@ func TestSetStandardHeaders(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			httpReq, err := http.NewRequest("POST", "http://localhost/mcp", nil)
-			if err != nil {
-				t.Fatal(err)
-			}
+			header := http.Header{}
 			if tt.protocolVersion != "" {
-				httpReq.Header.Set(ProtocolVersionHeader, tt.protocolVersion)
+				header.Set(ProtocolVersionHeader, tt.protocolVersion)
 			}
 
-			setStandardHeaders(httpReq, tt.msg)
+			setStandardHeaders(header, tt.msg)
 
-			if got := httpReq.Header.Get(MethodHeader); got != tt.wantMethodHeader {
+			if got := header.Get(MethodHeader); got != tt.wantMethodHeader {
 				t.Errorf("MethodHeader = %q, want %q", got, tt.wantMethodHeader)
 			}
-			if got := httpReq.Header.Get(NameHeader); got != tt.wantNameHeader {
+			if got := header.Get(NameHeader); got != tt.wantNameHeader {
 				t.Errorf("NameHeader = %q, want %q", got, tt.wantNameHeader)
 			}
 		})
@@ -406,21 +403,18 @@ func TestValidateMcpHeaders(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			httpReq, err := http.NewRequest("POST", "http://localhost/mcp", nil)
-			if err != nil {
-				t.Fatal(err)
-			}
+			header := http.Header{}
 			if tt.version != "" {
-				httpReq.Header.Set(ProtocolVersionHeader, tt.version)
+				header.Set(ProtocolVersionHeader, tt.version)
 			}
 			if tt.methodHeader != "" {
-				httpReq.Header.Set(MethodHeader, tt.methodHeader)
+				header.Set(MethodHeader, tt.methodHeader)
 			}
 			if tt.nameHeader != "" {
-				httpReq.Header.Set(NameHeader, tt.nameHeader)
+				header.Set(NameHeader, tt.nameHeader)
 			}
 
-			err = validateMcpHeaders(httpReq, tt.msg)
+			err := validateMcpHeaders(header, tt.msg)
 			if tt.wantErr {
 				if err == nil {
 					t.Fatalf("validateMcpHeaders() = nil, want error containing %q", tt.wantErrContain)

mcp/streamable.go

@@ -1187,7 +1187,7 @@ func (c *streamableServerConn) servePOST(w http.ResponseWriter, req *http.Reques
 
 	// Validate MCP standard headers (Mcp-Method, Mcp-Name)
 	if !isBatch && len(incoming) == 1 {
-		if err := validateMcpHeaders(req, incoming[0]); err != nil {
+		if err := validateMcpHeaders(req.Header, incoming[0]); err != nil {
 			resp := &jsonrpc.Response{
 				Error: jsonrpc2.NewError(CodeHeaderMismatch, err.Error()),
 			}
@@ -1809,7 +1809,7 @@ func (c *streamableClientConn) Write(ctx context.Context, msg jsonrpc.Message) e
 			// and permanently break the connection.
 			return nil, nil, fmt.Errorf("%s: %w: %w", requestSummary, jsonrpc2.ErrRejected, err)
 		}
-		setStandardHeaders(req, msg)
+		setStandardHeaders(req.Header, msg)
 		resp, err := c.client.Do(req)
 		if err != nil {
 			// Any error from client.Do means the request didn't reach the server.