mcp: NewClient and NewServer take Implementation

jba · jba · commit 6556ce57976c · 2025-07-09T13:36:28.000-04:00
Change the name and version arguments to NewClient and NewServer to a *Implementation, to future-proof against the spec. Fixes #109.
diff --git a/examples/completion/main.go b/examples/completion/main.go
@@ -40,7 +40,7 @@ func main() {
 
 	// Create the MCP Server instance and assign the handler.
 	// No server running, just showing the configuration.
-	_ = mcp.NewServer("myServer", "v1.0.0", &mcp.ServerOptions{
+	_ = mcp.NewServer(nil, &mcp.ServerOptions{
 		CompletionHandler: myCompletionHandler,
 	})
 
diff --git a/examples/hello/main.go b/examples/hello/main.go
@@ -42,7 +42,7 @@ func PromptHi(ctx context.Context, ss *mcp.ServerSession, params *mcp.GetPromptP
 func main() {
 	flag.Parse()
 
-	server := mcp.NewServer("greeter", "v0.0.1", nil)
+	server := mcp.NewServer(&mcp.Implementation{Name: "greeter"}, nil)
 	mcp.AddTool(server, &mcp.Tool{Name: "greet", Description: "say hi"}, SayHi)
 	server.AddPrompt(&mcp.Prompt{Name: "greet"}, PromptHi)
 	server.AddResource(&mcp.Resource{
diff --git a/examples/memory/main.go b/examples/memory/main.go
@@ -91,7 +91,7 @@ func main() {
 	kb := knowledgeBase{s: kbStore}
 
 	// Setup MCP server with knowledge base tools
-	server := mcp.NewServer("memory", "v0.0.1", nil)
+	server := mcp.NewServer(nil, nil)
 	mcp.AddTool(server, &mcp.Tool{
 		Name:        "create_entities",
 		Description: "Create multiple new entities in the knowledge graph",
diff --git a/examples/sse/main.go b/examples/sse/main.go
@@ -34,10 +34,10 @@ func main() {
 		log.Fatal("http address not set")
 	}
 
-	server1 := mcp.NewServer("greeter1", "v0.0.1", nil)
+	server1 := mcp.NewServer(&mcp.Implementation{Name: "greeter1"}, nil)
 	mcp.AddTool(server1, &mcp.Tool{Name: "greet1", Description: "say hi"}, SayHi)
 
-	server2 := mcp.NewServer("greeter2", "v0.0.1", nil)
+	server2 := mcp.NewServer(&mcp.Implementation{Name: "greeter2"}, nil)
 	mcp.AddTool(server2, &mcp.Tool{Name: "greet2", Description: "say hello"}, SayHi)
 
 	log.Printf("MCP servers serving at %s", *httpAddr)
diff --git a/internal/readme/client/client.go b/internal/readme/client/client.go
@@ -17,7 +17,7 @@ func main() {
 	ctx := context.Background()
 
 	// Create a new client, with no features.
-	client := mcp.NewClient("mcp-client", "v1.0.0", nil)
+	client := mcp.NewClient(nil, nil)
 
 	// Connect to a server over stdin/stdout
 	transport := mcp.NewCommandTransport(exec.Command("myserver"))
diff --git a/internal/readme/server/server.go b/internal/readme/server/server.go
@@ -24,7 +24,7 @@ func SayHi(ctx context.Context, cc *mcp.ServerSession, params *mcp.CallToolParam
 
 func main() {
 	// Create a server with a single tool.
-	server := mcp.NewServer("greeter", "v1.0.0", nil)
+	server := mcp.NewServer(&mcp.Implementation{Name: "greeter", Version: "v1.0.0"}, nil)
 
 	mcp.AddTool(server, &mcp.Tool{Name: "greet", Description: "say hi"}, SayHi)
 	// Run the server over stdin/stdout, until the client disconnects
diff --git a/mcp/client.go b/mcp/client.go
@@ -17,8 +17,7 @@ import (
 // A Client is an MCP client, which may be connected to an MCP server
 // using the [Client.Connect] method.
 type Client struct {
-	name                    string
-	version                 string
+	impl                    *Implementation
 	opts                    ClientOptions
 	mu                      sync.Mutex
 	roots                   *featureSet[*Root]
@@ -27,15 +26,18 @@ type Client struct {
 	receivingMethodHandler_ MethodHandler[*ClientSession]
 }
 
-// NewClient creates a new Client.
+// NewClient creates a new [Client].
 //
 // Use [Client.Connect] to connect it to an MCP server.
 //
+// If impl is nil, a default name and version are used, and the title is left empty.
 // If non-nil, the provided options configure the Client.
-func NewClient(name, version string, opts *ClientOptions) *Client {
+func NewClient(impl *Implementation, opts *ClientOptions) *Client {
+	if impl == nil {
+		impl = &Implementation{Name: "Go MCP SDK Client", Version: "v0.1.0"}
+	}
 	c := &Client{
-		name:                    name,
-		version:                 version,
+		impl:                    impl,
 		roots:                   newFeatureSet(func(r *Root) string { return r.URI }),
 		sendingMethodHandler_:   defaultSendingMethodHandler[*ClientSession],
 		receivingMethodHandler_: defaultReceivingMethodHandler[*ClientSession],
@@ -106,7 +108,7 @@ func (c *Client) Connect(ctx context.Context, t Transport) (cs *ClientSession, e
 	}
 
 	params := &InitializeParams{
-		ClientInfo:      &implementation{Name: c.name, Version: c.version},
+		ClientInfo:      c.impl,
 		Capabilities:    caps,
 		ProtocolVersion: "2025-03-26",
 	}
diff --git a/mcp/cmd_test.go b/mcp/cmd_test.go
@@ -30,7 +30,7 @@ func TestMain(m *testing.M) {
 func runServer() {
 	ctx := context.Background()
 
-	server := mcp.NewServer("greeter", "v0.0.1", nil)
+	server := mcp.NewServer(nil, nil)
 	mcp.AddTool(server, &mcp.Tool{Name: "greet", Description: "say hi"}, SayHi)
 	if err := server.Run(ctx, mcp.NewStdioTransport()); err != nil {
 		log.Fatal(err)
@@ -56,7 +56,7 @@ func TestCmdTransport(t *testing.T) {
 	cmd := exec.Command(exe)
 	cmd.Env = append(os.Environ(), runAsServer+"=true")
 
-	client := mcp.NewClient("client", "v0.0.1", nil)
+	client := mcp.NewClient(nil, nil)
 	session, err := client.Connect(ctx, mcp.NewCommandTransport(cmd))
 	if err != nil {
 		log.Fatal(err)
diff --git a/mcp/example_progress_test.go b/mcp/example_progress_test.go
@@ -16,7 +16,7 @@ var nextProgressToken atomic.Int64
 // This middleware function adds a progress token to every outgoing request
 // from the client.
 func Example_progressMiddleware() {
-	c := mcp.NewClient("test", "v1", nil)
+	c := mcp.NewClient(nil, nil)
 	c.AddSendingMiddleware(addProgressToken[*mcp.ClientSession])
 	_ = c
 }
diff --git a/mcp/mcp_test.go b/mcp/mcp_test.go
@@ -64,7 +64,7 @@ func TestEndToEnd(t *testing.T) {
 			notificationChans["progress_server"] <- 0
 		},
 	}
-	s := NewServer("testServer", "v1.0.0", sopts)
+	s := NewServer(nil, sopts)
 	AddTool(s, &Tool{
 		Name:        "greet",
 		Description: "say hi",
@@ -125,7 +125,7 @@ func TestEndToEnd(t *testing.T) {
 			notificationChans["progress_client"] <- 0
 		},
 	}
-	c := NewClient("testClient", "v1.0.0", opts)
+	c := NewClient(nil, opts)
 	rootAbs, err := filepath.Abs(filepath.FromSlash("testdata/files"))
 	if err != nil {
 		t.Fatal(err)
@@ -510,7 +510,7 @@ func basicConnection(t *testing.T, config func(*Server)) (*ServerSession, *Clien
 	ctx := context.Background()
 	ct, st := NewInMemoryTransports()
 
-	s := NewServer("testServer", "v1.0.0", nil)
+	s := NewServer(nil, nil)
 	if config != nil {
 		config(s)
 	}
@@ -519,7 +519,7 @@ func basicConnection(t *testing.T, config func(*Server)) (*ServerSession, *Clien
 		t.Fatal(err)
 	}
 
-	c := NewClient("testClient", "v1.0.0", nil)
+	c := NewClient(nil, nil)
 	cs, err := c.Connect(ctx, ct)
 	if err != nil {
 		t.Fatal(err)
@@ -562,13 +562,13 @@ func TestBatching(t *testing.T) {
 	ctx := context.Background()
 	ct, st := NewInMemoryTransports()
 
-	s := NewServer("testServer", "v1.0.0", nil)
+	s := NewServer(nil, nil)
 	_, err := s.Connect(ctx, st)
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	c := NewClient("testClient", "v1.0.0", nil)
+	c := NewClient(nil, nil)
 	// TODO: this test is broken, because increasing the batch size here causes
 	// 'initialize' to block. Therefore, we can only test with a size of 1.
 	// Since batching is being removed, we can probably just delete this.
@@ -632,7 +632,7 @@ func TestMiddleware(t *testing.T) {
 	ctx := context.Background()
 	ct, st := NewInMemoryTransports()
 
-	s := NewServer("testServer", "v1.0.0", nil)
+	s := NewServer(nil, nil)
 	ss, err := s.Connect(ctx, st)
 	if err != nil {
 		t.Fatal(err)
@@ -656,7 +656,7 @@ func TestMiddleware(t *testing.T) {
 	s.AddSendingMiddleware(traceCalls[*ServerSession](&sbuf, "S1"), traceCalls[*ServerSession](&sbuf, "S2"))
 	s.AddReceivingMiddleware(traceCalls[*ServerSession](&sbuf, "R1"), traceCalls[*ServerSession](&sbuf, "R2"))
 
-	c := NewClient("testClient", "v1.0.0", nil)
+	c := NewClient(nil, nil)
 	c.AddSendingMiddleware(traceCalls[*ClientSession](&cbuf, "S1"), traceCalls[*ClientSession](&cbuf, "S2"))
 	c.AddReceivingMiddleware(traceCalls[*ClientSession](&cbuf, "R1"), traceCalls[*ClientSession](&cbuf, "R2"))
 
@@ -741,13 +741,13 @@ func TestNoJSONNull(t *testing.T) {
 	var logbuf safeBuffer
 	ct = NewLoggingTransport(ct, &logbuf)
 
-	s := NewServer("testServer", "v1.0.0", nil)
+	s := NewServer(nil, nil)
 	ss, err := s.Connect(ctx, st)
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	c := NewClient("testClient", "v1.0.0", nil)
+	c := NewClient(nil, nil)
 	cs, err := c.Connect(ctx, ct)
 	if err != nil {
 		t.Fatal(err)
@@ -810,7 +810,7 @@ func TestKeepAlive(t *testing.T) {
 	serverOpts := &ServerOptions{
 		KeepAlive: 100 * time.Millisecond,
 	}
-	s := NewServer("testServer", "v1.0.0", serverOpts)
+	s := NewServer(nil, serverOpts)
 	AddTool(s, greetTool(), sayHi)
 
 	ss, err := s.Connect(ctx, st)
@@ -822,7 +822,7 @@ func TestKeepAlive(t *testing.T) {
 	clientOpts := &ClientOptions{
 		KeepAlive: 100 * time.Millisecond,
 	}
-	c := NewClient("testClient", "v1.0.0", clientOpts)
+	c := NewClient(nil, clientOpts)
 	cs, err := c.Connect(ctx, ct)
 	if err != nil {
 		t.Fatal(err)
@@ -855,7 +855,7 @@ func TestKeepAliveFailure(t *testing.T) {
 	ct, st := NewInMemoryTransports()
 
 	// Server without keepalive (to test one-sided keepalive)
-	s := NewServer("testServer", "v1.0.0", nil)
+	s := NewServer(nil, nil)
 	AddTool(s, greetTool(), sayHi)
 	ss, err := s.Connect(ctx, st)
 	if err != nil {
@@ -866,7 +866,7 @@ func TestKeepAliveFailure(t *testing.T) {
 	clientOpts := &ClientOptions{
 		KeepAlive: 50 * time.Millisecond,
 	}
-	c := NewClient("testClient", "v1.0.0", clientOpts)
+	c := NewClient(nil, clientOpts)
 	cs, err := c.Connect(ctx, ct)
 	if err != nil {
 		t.Fatal(err)
diff --git a/mcp/protocol.go b/mcp/protocol.go
@@ -292,7 +292,7 @@ type InitializeParams struct {
 	// attach additional metadata to their responses.
 	Meta         `json:"_meta,omitempty"`
 	Capabilities *ClientCapabilities `json:"capabilities"`
-	ClientInfo   *implementation     `json:"clientInfo"`
+	ClientInfo   *Implementation     `json:"clientInfo"`
 	// The latest version of the Model Context Protocol that the client supports.
 	// The client may decide to support older versions as well.
 	ProtocolVersion string `json:"protocolVersion"`
@@ -318,7 +318,7 @@ type InitializeResult struct {
 	// may not match the version that the client requested. If the client cannot
 	// support this version, it must disconnect.
 	ProtocolVersion string          `json:"protocolVersion"`
-	ServerInfo      *implementation `json:"serverInfo"`
+	ServerInfo      *Implementation `json:"serverInfo"`
 }
 
 type InitializedParams struct {
@@ -863,9 +863,9 @@ func (x *ToolListChangedParams) SetProgressToken(t any) { setProgressToken(x, t)
 
 // TODO(jba): add ElicitRequest and related types.
 
-// Describes the name and version of an MCP implementation, with an optional
+// An Implementation describes the name and version of an MCP implementation, with an optional
 // title for UI representation.
-type implementation struct {
+type Implementation struct {
 	// Intended for programmatic or logical use, but used as a display name in past
 	// specs or fallback (if title isn't present).
 	Name string `json:"name"`
diff --git a/mcp/server.go b/mcp/server.go
@@ -31,9 +31,8 @@ const DefaultPageSize = 1000
 // sessions by using [Server.Start] or [Server.Run].
 type Server struct {
 	// fixed at creation
-	name    string
-	version string
-	opts    ServerOptions
+	impl *Implementation
+	opts ServerOptions
 
 	mu                      sync.Mutex
 	prompts                 *featureSet[*serverPrompt]
@@ -67,13 +66,17 @@ type ServerOptions struct {
 }
 
 // NewServer creates a new MCP server. The resulting server has no features:
-// add features using [Server.AddTools], [Server.AddPrompts] and [Server.AddResources].
+// add features using the various Server.AddXXX methods, and the [AddTool] function.
 //
 // The server can be connected to one or more MCP clients using [Server.Start]
 // or [Server.Run].
 //
+// If impl is nil, a default name and version are used, and the title is left empty.
 // If non-nil, the provided options is used to configure the server.
-func NewServer(name, version string, opts *ServerOptions) *Server {
+func NewServer(impl *Implementation, opts *ServerOptions) *Server {
+	if impl == nil {
+		impl = &Implementation{Name: "Go MCP SDK Server", Version: "v0.1.0"}
+	}
 	if opts == nil {
 		opts = new(ServerOptions)
 	}
@@ -84,8 +87,7 @@ func NewServer(name, version string, opts *ServerOptions) *Server {
 		opts.PageSize = DefaultPageSize
 	}
 	return &Server{
-		name:                    name,
-		version:                 version,
+		impl:                    impl,
 		opts:                    *opts,
 		prompts:                 newFeatureSet(func(p *serverPrompt) string { return p.prompt.Name }),
 		tools:                   newFeatureSet(func(t *serverTool) string { return t.tool.Name }),
@@ -658,10 +660,7 @@ func (ss *ServerSession) initialize(ctx context.Context, params *InitializeParam
 			Logging: &loggingCapabilities{},
 		},
 		Instructions: ss.server.opts.Instructions,
-		ServerInfo: &implementation{
-			Name:    ss.server.name,
-			Version: ss.server.version,
-		},
+		ServerInfo:   ss.server.impl,
 	}, nil
 }
 
diff --git a/mcp/server_example_test.go b/mcp/server_example_test.go
@@ -28,15 +28,15 @@ func ExampleServer() {
 	ctx := context.Background()
 	clientTransport, serverTransport := mcp.NewInMemoryTransports()
 
-	server := mcp.NewServer("greeter", "v0.0.1", nil)
+	server := mcp.NewServer(&mcp.Implementation{Name: "greeter", Version: "v0.0.1"}, nil)
 	mcp.AddTool(server, &mcp.Tool{Name: "greet", Description: "say hi"}, SayHi)
 
 	serverSession, err := server.Connect(ctx, serverTransport)
 	if err != nil {
 		log.Fatal(err)
 	}
 
-	client := mcp.NewClient("client", "v0.0.1", nil)
+	client := mcp.NewClient(nil, nil)
 	clientSession, err := client.Connect(ctx, clientTransport)
 	if err != nil {
 		log.Fatal(err)
@@ -59,8 +59,8 @@ func ExampleServer() {
 
 // createSessions creates and connects an in-memory client and server session for testing purposes.
 func createSessions(ctx context.Context) (*mcp.ClientSession, *mcp.ServerSession, *mcp.Server) {
-	server := mcp.NewServer("server", "v0.0.1", nil)
-	client := mcp.NewClient("client", "v0.0.1", nil)
+	server := mcp.NewServer(nil, nil)
+	client := mcp.NewClient(nil, nil)
 	serverTransport, clientTransport := mcp.NewInMemoryTransports()
 	serverSession, err := server.Connect(ctx, serverTransport)
 	if err != nil {
diff --git a/mcp/sse_example_test.go b/mcp/sse_example_test.go
@@ -27,7 +27,7 @@ func Add(ctx context.Context, cc *mcp.ServerSession, params *mcp.CallToolParamsF
 }
 
 func ExampleSSEHandler() {
-	server := mcp.NewServer("adder", "v0.0.1", nil)
+	server := mcp.NewServer(&mcp.Implementation{Name: "adder"}, nil)
 	mcp.AddTool(server, &mcp.Tool{Name: "add", Description: "add two numbers"}, Add)
 
 	handler := mcp.NewSSEHandler(func(*http.Request) *mcp.Server { return server })
@@ -36,7 +36,7 @@ func ExampleSSEHandler() {
 
 	ctx := context.Background()
 	transport := mcp.NewSSEClientTransport(httpServer.URL, nil)
-	client := mcp.NewClient("test", "v1.0.0", nil)
+	client := mcp.NewClient(nil, nil)
 	cs, err := client.Connect(ctx, transport)
 	if err != nil {
 		log.Fatal(err)
diff --git a/mcp/sse_test.go b/mcp/sse_test.go
@@ -20,7 +20,7 @@ func TestSSEServer(t *testing.T) {
 	for _, closeServerFirst := range []bool{false, true} {
 		t.Run(fmt.Sprintf("closeServerFirst=%t", closeServerFirst), func(t *testing.T) {
 			ctx := context.Background()
-			server := NewServer("testServer", "v1.0.0", nil)
+			server := NewServer(nil, nil)
 			AddTool(server, &Tool{Name: "greet"}, sayHi)
 
 			sseHandler := NewSSEHandler(func(*http.Request) *Server { return server })
@@ -47,7 +47,7 @@ func TestSSEServer(t *testing.T) {
 				HTTPClient: customClient,
 			})
 
-			c := NewClient("testClient", "v1.0.0", nil)
+			c := NewClient(nil, nil)
 			cs, err := c.Connect(ctx, clientTransport)
 			if err != nil {
 				t.Fatal(err)
diff --git a/mcp/streamable_test.go b/mcp/streamable_test.go

Original file line number	Diff line number	Diff line change
`@@ -16,7 +16,7 @@ var nextProgressToken atomic.Int64`
`16`	`16`	`// This middleware function adds a progress token to every outgoing request`
`17`	`17`	`// from the client.`
`18`	`18`	`func Example_progressMiddleware() {`
`19`		`- c := mcp.NewClient("test", "v1", nil)`
	`19`	`+ c := mcp.NewClient(nil, nil)`
`20`	`20`	`c.AddSendingMiddleware(addProgressToken[*mcp.ClientSession])`
`21`	`21`	`_ = c`
`22`	`22`	`}`