feat(mcp): Add TCP transport

Fixes #126

pkg/mcp/mcp.go

@@ -82,61 +82,61 @@ func New(opts ...Option) (*Service, error) {
 		}
 	}
 
-	s.registerTools()
+	s.registerTools(s.server)
 	return s, nil
 }
 
 // registerTools adds file operation tools to the MCP server.
-func (s *Service) registerTools() {
+func (s *Service) registerTools(server *mcp.Server) {
 	// File operations
-	mcp.AddTool(s.server, &mcp.Tool{
+	mcp.AddTool(server, &mcp.Tool{
 		Name:        "file_read",
 		Description: "Read the contents of a file",
 	}, s.readFile)
 
-	mcp.AddTool(s.server, &mcp.Tool{
+	mcp.AddTool(server, &mcp.Tool{
 		Name:        "file_write",
 		Description: "Write content to a file",
 	}, s.writeFile)
 
-	mcp.AddTool(s.server, &mcp.Tool{
+	mcp.AddTool(server, &mcp.Tool{
 		Name:        "file_delete",
 		Description: "Delete a file or empty directory",
 	}, s.deleteFile)
 
-	mcp.AddTool(s.server, &mcp.Tool{
+	mcp.AddTool(server, &mcp.Tool{
 		Name:        "file_rename",
 		Description: "Rename or move a file",
 	}, s.renameFile)
 
-	mcp.AddTool(s.server, &mcp.Tool{
+	mcp.AddTool(server, &mcp.Tool{
 		Name:        "file_exists",
 		Description: "Check if a file or directory exists",
 	}, s.fileExists)
 
-	mcp.AddTool(s.server, &mcp.Tool{
+	mcp.AddTool(server, &mcp.Tool{
 		Name:        "file_edit",
 		Description: "Edit a file by replacing old_string with new_string. Use replace_all=true to replace all occurrences.",
 	}, s.editDiff)
 
 	// Directory operations
-	mcp.AddTool(s.server, &mcp.Tool{
+	mcp.AddTool(server, &mcp.Tool{
 		Name:        "dir_list",
 		Description: "List contents of a directory",
 	}, s.listDirectory)
 
-	mcp.AddTool(s.server, &mcp.Tool{
+	mcp.AddTool(server, &mcp.Tool{
 		Name:        "dir_create",
 		Description: "Create a new directory",
 	}, s.createDirectory)
 
 	// Language detection
-	mcp.AddTool(s.server, &mcp.Tool{
+	mcp.AddTool(server, &mcp.Tool{
 		Name:        "lang_detect",
 		Description: "Detect the programming language of a file",
 	}, s.detectLanguage)
 
-	mcp.AddTool(s.server, &mcp.Tool{
+	mcp.AddTool(server, &mcp.Tool{
 		Name:        "lang_list",
 		Description: "Get list of supported programming languages",
 	}, s.getSupportedLanguages)
@@ -566,8 +566,14 @@ func detectLanguageFromPath(path string) string {
 	}
 }
 
-// Run starts the MCP server on stdio.
+// Run starts the MCP server.
+// If MCP_ADDR is set, it starts a TCP server.
+// Otherwise, it starts a Stdio server.
 func (s *Service) Run(ctx context.Context) error {
+	addr := os.Getenv("MCP_ADDR")
+	if addr != "" {
+		return s.ServeTCP(ctx, addr)
+	}
 	return s.server.Run(ctx, &mcp.StdioTransport{})
 }
 

pkg/mcp/transport_tcp.go

@@ -0,0 +1,131 @@
+package mcp
+
+import (
+	"bufio"
+	"context"
+	"fmt"
+	"net"
+	"os"
+
+	"github.com/modelcontextprotocol/go-sdk/jsonrpc"
+	"github.com/modelcontextprotocol/go-sdk/mcp"
+)
+
+// TCPTransport manages a TCP listener for MCP.
+type TCPTransport struct {
+	addr     string
+	listener net.Listener
+}
+
+// NewTCPTransport creates a new TCP transport listener.
+// It listens on the provided address (e.g. "localhost:9100").
+func NewTCPTransport(addr string) (*TCPTransport, error) {
+	listener, err := net.Listen("tcp", addr)
+	if err != nil {
+		return nil, err
+	}
+	return &TCPTransport{addr: addr, listener: listener}, nil
+}
+
+// ServeTCP starts a TCP server for the MCP service.
+// It accepts connections and spawns a new MCP server session for each connection.
+func (s *Service) ServeTCP(ctx context.Context, addr string) error {
+	t, err := NewTCPTransport(addr)
+	if err != nil {
+		return err
+	}
+	defer t.listener.Close()
+
+	if addr == "" {
+		addr = t.listener.Addr().String()
+	}
+	fmt.Fprintf(os.Stderr, "MCP TCP server listening on %s\n", addr)
+
+	for {
+		conn, err := t.listener.Accept()
+		if err != nil {
+			select {
+			case <-ctx.Done():
+				return nil
+			default:
+				fmt.Fprintf(os.Stderr, "Accept error: %v\n", err)
+				continue
+			}
+		}
+
+		go s.handleConnection(ctx, conn)
+	}
+}
+
+func (s *Service) handleConnection(ctx context.Context, conn net.Conn) {
+	// Note: We don't defer conn.Close() here because it's closed by the Server/Transport
+
+	// Create new server instance for this connection
+	impl := &mcp.Implementation{
+		Name:    "core-cli",
+		Version: "0.1.0",
+	}
+	server := mcp.NewServer(impl, nil)
+	s.registerTools(server)
+
+	// Create transport for this connection
+	transport := &connTransport{conn: conn}
+
+	// Run server (blocks until connection closed)
+	// Server.Run calls Connect, then Read loop.
+	if err := server.Run(ctx, transport); err != nil {
+		fmt.Fprintf(os.Stderr, "Connection error: %v\n", err)
+	}
+}
+
+// connTransport adapts net.Conn to mcp.Transport
+type connTransport struct {
+	conn net.Conn
+}
+
+func (t *connTransport) Connect(ctx context.Context) (mcp.Connection, error) {
+	return &connConnection{
+		conn:    t.conn,
+		scanner: bufio.NewScanner(t.conn),
+	}, nil
+}
+
+// connConnection implements mcp.Connection
+type connConnection struct {
+	conn    net.Conn
+	scanner *bufio.Scanner
+}
+
+func (c *connConnection) Read(ctx context.Context) (jsonrpc.Message, error) {
+	// Blocks until line is read
+	if !c.scanner.Scan() {
+		if err := c.scanner.Err(); err != nil {
+			return nil, err
+		}
+		// EOF
+		// Return error to signal closure, as per Scanner contract?
+		// SDK usually expects error on close.
+		return nil, fmt.Errorf("EOF")
+	}
+	line := c.scanner.Bytes()
+	return jsonrpc.DecodeMessage(line)
+}
+
+func (c *connConnection) Write(ctx context.Context, msg jsonrpc.Message) error {
+	data, err := jsonrpc.EncodeMessage(msg)
+	if err != nil {
+		return err
+	}
+	// Append newline for line-delimited JSON
+	data = append(data, '\n')
+	_, err = c.conn.Write(data)
+	return err
+}
+
+func (c *connConnection) Close() error {
+	return c.conn.Close()
+}
+
+func (c *connConnection) SessionID() string {
+	return "tcp-session" // Unique ID might be better, but optional
+}