micro--go-micro/gateway/mcp/stdio.go

package mcp

import (
	"bufio"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"log"
	"os"
	"strings"
	"sync"
	"time"

	"go-micro.dev/v6/auth"
	"go-micro.dev/v6/metadata"

	"github.com/google/uuid"
	"go.opentelemetry.io/otel/attribute"
)

// StdioTransport implements MCP JSON-RPC 2.0 over stdio
// This is used by Claude Code and other local AI tools
type StdioTransport struct {
	server   *Server
	reader   *bufio.Reader
	writer   *bufio.Writer
	writerMu sync.Mutex
	ctx      context.Context
	cancel   context.CancelFunc
}

// JSONRPCRequest represents a JSON-RPC 2.0 request
type JSONRPCRequest struct {
	JSONRPC string          `json:"jsonrpc"`
	ID      interface{}     `json:"id,omitempty"`
	Method  string          `json:"method"`
	Params  json.RawMessage `json:"params,omitempty"`
}

// JSONRPCResponse represents a JSON-RPC 2.0 response
type JSONRPCResponse struct {
	JSONRPC string      `json:"jsonrpc"`
	ID      interface{} `json:"id,omitempty"`
	Result  interface{} `json:"result,omitempty"`
	Error   *RPCError   `json:"error,omitempty"`
}

// RPCError represents a JSON-RPC error
type RPCError struct {
	Code    int         `json:"code"`
	Message string      `json:"message"`
	Data    interface{} `json:"data,omitempty"`
}

// Standard JSON-RPC error codes
const (
	ParseError     = -32700
	InvalidRequest = -32600
	MethodNotFound = -32601
	InvalidParams  = -32602
	InternalError  = -32603
)

// NewStdioTransport creates a new stdio transport for the MCP server
func NewStdioTransport(server *Server) *StdioTransport {
	ctx, cancel := context.WithCancel(context.Background())
	return &StdioTransport{
		server: server,
		reader: bufio.NewReader(os.Stdin),
		writer: bufio.NewWriter(os.Stdout),
		ctx:    ctx,
		cancel: cancel,
	}
}

// Serve starts the stdio transport and processes JSON-RPC requests
func (t *StdioTransport) Serve() error {
	t.server.opts.Logger.Printf("[mcp] MCP server started (stdio transport)")

	// Read and process requests from stdin
	for {
		select {
		case <-t.ctx.Done():
			return nil
		default:
		}

		// Read one line (JSON-RPC request)
		line, err := t.reader.ReadBytes('\n')
		if err != nil {
			if err == io.EOF {
				return nil
			}
			return fmt.Errorf("failed to read request: %w", err)
		}

		// Parse JSON-RPC request
		var req JSONRPCRequest
		if err := json.Unmarshal(line, &req); err != nil {
			t.sendError(nil, ParseError, "Parse error", err.Error())
			continue
		}

		// Validate JSON-RPC version
		if req.JSONRPC != "2.0" {
			t.sendError(req.ID, InvalidRequest, "Invalid request", "jsonrpc must be '2.0'")
			continue
		}

		// Handle request
		go t.handleRequest(&req)
	}
}

// handleRequest processes a single JSON-RPC request
func (t *StdioTransport) handleRequest(req *JSONRPCRequest) {
	switch req.Method {
	case "initialize":
		t.handleInitialize(req)
	case "tools/list":
		t.handleToolsList(req)
	case "tools/call":
		t.handleToolsCall(req)
	default:
		t.sendError(req.ID, MethodNotFound, "Method not found", req.Method)
	}
}

// handleInitialize handles the initialize request
func (t *StdioTransport) handleInitialize(req *JSONRPCRequest) {
	result := map[string]interface{}{
		"protocolVersion": "2024-11-05",
		"capabilities": map[string]interface{}{
			"tools": map[string]interface{}{},
		},
		"serverInfo": map[string]interface{}{
			"name":    "go-micro-mcp",
			"version": "1.0.0",
		},
	}

	t.sendResponse(req.ID, result)
}

// handleToolsList handles the tools/list request
func (t *StdioTransport) handleToolsList(req *JSONRPCRequest) {
	t.server.toolsMu.RLock()
	tools := make([]interface{}, 0, len(t.server.tools))
	for _, tool := range t.server.tools {
		tools = append(tools, map[string]interface{}{
			"name":        tool.Name,
			"description": tool.Description,
			"inputSchema": tool.InputSchema,
		})
	}
	t.server.toolsMu.RUnlock()

	result := map[string]interface{}{
		"tools": tools,
	}

	t.sendResponse(req.ID, result)
}

// handleToolsCall handles the tools/call request
func (t *StdioTransport) handleToolsCall(req *JSONRPCRequest) {
	// Parse params
	var params struct {
		Name      string                 `json:"name"`
		Arguments map[string]interface{} `json:"arguments"`
		// Token allows callers to pass a bearer token for auth via the
		// JSON-RPC params (since stdio has no HTTP headers).
		Token string `json:"_token,omitempty"`
	}
	if err := json.Unmarshal(req.Params, &params); err != nil {
		t.sendError(req.ID, InvalidParams, "Invalid params", err.Error())
		return
	}

	// Get tool info
	t.server.toolsMu.RLock()
	tool, exists := t.server.tools[params.Name]
	t.server.toolsMu.RUnlock()

	if !exists {
		t.sendError(req.ID, InvalidParams, "Tool not found", params.Name)
		return
	}

	// Generate trace ID
	traceID := uuid.New().String()

	// Start OTel span (noop if TraceProvider is nil)
	ctx, span := t.server.startToolSpan(t.ctx, params.Name, "stdio", traceID)
	defer span.End()

	// Authenticate and authorize (if Auth is configured)
	var account *auth.Account
	if t.server.opts.Auth != nil {
		token := params.Token
		if token == "" {
			span.SetAttributes(attribute.Bool(AttrAuthAllowed, false), attribute.String(AttrAuthDeniedReason, "missing token"))
			setSpanError(span, fmt.Errorf("missing token"))
			t.server.audit(AuditRecord{TraceID: traceID, Timestamp: time.Now(), Tool: params.Name, Allowed: false, DeniedReason: "missing token"})
			t.sendError(req.ID, InvalidParams, "Unauthorized", "missing _token in params")
			return
		}
		token = strings.TrimPrefix(token, "Bearer ")
		acc, err := t.server.opts.Auth.Inspect(token)
		if err != nil {
			span.SetAttributes(attribute.Bool(AttrAuthAllowed, false), attribute.String(AttrAuthDeniedReason, "invalid token"))
			setSpanError(span, fmt.Errorf("invalid token"))
			t.server.audit(AuditRecord{TraceID: traceID, Timestamp: time.Now(), Tool: params.Name, Allowed: false, DeniedReason: "invalid token"})
			t.sendError(req.ID, InvalidParams, "Unauthorized", "invalid token")
			return
		}
		account = acc
		span.SetAttributes(attribute.String(AttrAccountID, account.ID))

		// Check per-tool scopes
		if len(tool.Scopes) > 0 {
			span.SetAttributes(attribute.StringSlice(AttrScopesRequired, tool.Scopes))
			if !hasScope(account.Scopes, tool.Scopes) {
				span.SetAttributes(attribute.Bool(AttrAuthAllowed, false), attribute.String(AttrAuthDeniedReason, "insufficient scopes"))
				setSpanError(span, fmt.Errorf("insufficient scopes"))
				t.server.audit(AuditRecord{
					TraceID: traceID, Timestamp: time.Now(), Tool: params.Name,
					AccountID: account.ID, ScopesRequired: tool.Scopes,
					Allowed: false, DeniedReason: "insufficient scopes",
				})
				t.sendError(req.ID, InvalidParams, "Forbidden", "insufficient scopes")
				return
			}
		}
	}

	// Rate limit check
	if err := t.server.allowRate(params.Name); err != nil {
		span.SetAttributes(attribute.Bool(AttrRateLimited, true))
		setSpanError(span, err)
		accountID := ""
		if account != nil {
			accountID = account.ID
		}
		t.server.audit(AuditRecord{
			TraceID: traceID, Timestamp: time.Now(), Tool: params.Name,
			AccountID: accountID, Allowed: false, DeniedReason: "rate limited",
		})
		t.sendError(req.ID, InternalError, "Rate limit exceeded", params.Name)
		return
	}

	span.SetAttributes(attribute.Bool(AttrAuthAllowed, true))

	// Convert arguments to JSON bytes for RPC call
	inputBytes, err := json.Marshal(params.Arguments)
	if err != nil {
		t.sendError(req.ID, InternalError, "Failed to marshal arguments", err.Error())
		return
	}

	// Build context with tracing metadata
	// OTel trace context was already injected by startToolSpan; add MCP metadata.
	md, _ := metadata.FromContext(ctx)
	if md == nil {
		md = make(metadata.Metadata)
	}
	md.Set(TraceIDKey, traceID)
	md.Set(ToolNameKey, params.Name)
	if account != nil {
		md.Set(AccountIDKey, account.ID)
	}
	ctx = metadata.NewContext(ctx, md)

	// Make RPC call
	start := time.Now()
	rpcReq := t.server.opts.Client.NewRequest(tool.Service, tool.Endpoint, &struct {
		Data []byte
	}{Data: inputBytes})

	var rsp struct {
		Data []byte
	}

	if err := t.server.opts.Client.Call(ctx, rpcReq, &rsp); err != nil {
		setSpanError(span, err)
		accountID := ""
		if account != nil {
			accountID = account.ID
		}
		t.server.audit(AuditRecord{
			TraceID: traceID, Timestamp: time.Now(), Tool: params.Name,
			AccountID: accountID, ScopesRequired: tool.Scopes,
			Allowed: true, Duration: time.Since(start), Error: err.Error(),
		})
		// A tool-execution failure is reported as an isError result, not a
		// JSON-RPC protocol error (per the MCP spec), so the agent can read it.
		t.sendResponse(req.ID, mcpToolError(traceID, "tool call failed: "+err.Error()))
		return
	}

	setSpanOK(span)

	// Audit successful call
	accountID := ""
	if account != nil {
		accountID = account.ID
	}
	t.server.audit(AuditRecord{
		TraceID: traceID, Timestamp: time.Now(), Tool: params.Name,
		AccountID: accountID, ScopesRequired: tool.Scopes,
		Allowed: true, Duration: time.Since(start),
	})

	// The downstream response is JSON — return it as JSON text, not %v.
	t.sendResponse(req.ID, mcpToolResult(traceID, rsp.Data))
}

// sendResponse sends a JSON-RPC response
func (t *StdioTransport) sendResponse(id interface{}, result interface{}) {
	resp := JSONRPCResponse{
		JSONRPC: "2.0",
		ID:      id,
		Result:  result,
	}

	t.writeJSON(resp)
}

// sendError sends a JSON-RPC error response
func (t *StdioTransport) sendError(id interface{}, code int, message string, data interface{}) {
	resp := JSONRPCResponse{
		JSONRPC: "2.0",
		ID:      id,
		Error: &RPCError{
			Code:    code,
			Message: message,
			Data:    data,
		},
	}

	t.writeJSON(resp)
}

// writeJSON writes a JSON-RPC message to stdout
func (t *StdioTransport) writeJSON(v interface{}) {
	t.writerMu.Lock()
	defer t.writerMu.Unlock()

	data, err := json.Marshal(v)
	if err != nil {
		log.Printf("[mcp] Failed to marshal response: %v", err)
		return
	}

	if _, err := t.writer.Write(data); err != nil {
		log.Printf("[mcp] Failed to write response: %v", err)
		return
	}

	if _, err := t.writer.Write([]byte("\n")); err != nil {
		log.Printf("[mcp] Failed to write newline: %v", err)
		return
	}

	if err := t.writer.Flush(); err != nil {
		log.Printf("[mcp] Failed to flush writer: %v", err)
	}
}

// Stop gracefully stops the stdio transport
func (t *StdioTransport) Stop() error {
	t.cancel()
	return nil
}