feat: add MCP HTTP server with JSON-RPC 2.0 transport

internal/mcp/server.go

@@ -0,0 +1,98 @@
+package mcp
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+
+	"github.com/mathiasbq/supervisor/internal/registry"
+)
+
+type request struct {
+	JSONRPC string          `json:"jsonrpc"`
+	ID      any             `json:"id"`
+	Method  string          `json:"method"`
+	Params  json.RawMessage `json:"params"`
+}
+
+type response struct {
+	JSONRPC string    `json:"jsonrpc"`
+	ID      any       `json:"id,omitempty"`
+	Result  any       `json:"result,omitempty"`
+	Error   *rpcError `json:"error,omitempty"`
+}
+
+type rpcError struct {
+	Code    int    `json:"code"`
+	Message string `json:"message"`
+}
+
+// Server is an HTTP handler implementing the MCP JSON-RPC protocol.
+type Server struct {
+	reg *registry.Registry
+}
+
+func NewServer(reg *registry.Registry) *Server {
+	return &Server{reg: reg}
+}
+
+func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	var req request
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeError(w, nil, -32700, "parse error")
+		return
+	}
+
+	var result any
+	var rpcErr *rpcError
+
+	switch req.Method {
+	case "initialize":
+		result = map[string]any{
+			"protocolVersion": "2024-11-05",
+			"capabilities":    map[string]any{"tools": map[string]any{}},
+			"serverInfo":      map[string]any{"name": "supervisor", "version": "0.1.0"},
+		}
+
+	case "tools/list":
+		result = map[string]any{"tools": s.reg.Tools()}
+
+	case "tools/call":
+		var p struct {
+			Name      string          `json:"name"`
+			Arguments json.RawMessage `json:"arguments"`
+		}
+		if err := json.Unmarshal(req.Params, &p); err != nil {
+			rpcErr = &rpcError{Code: -32602, Message: "invalid params"}
+			break
+		}
+		out, err := s.reg.Dispatch(context.Background(), p.Name, p.Arguments)
+		if err != nil {
+			rpcErr = &rpcError{Code: -32000, Message: err.Error()}
+			break
+		}
+		result = map[string]any{
+			"content": []map[string]any{{"type": "text", "text": string(out)}},
+		}
+
+	default:
+		rpcErr = &rpcError{Code: -32601, Message: "method not found: " + req.Method}
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(response{
+		JSONRPC: "2.0",
+		ID:      req.ID,
+		Result:  result,
+		Error:   rpcErr,
+	})
+}
+
+func writeError(w http.ResponseWriter, id any, code int, msg string) {
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(response{
+		JSONRPC: "2.0",
+		ID:      id,
+		Error:   &rpcError{Code: code, Message: msg},
+	})
+}

internal/mcp/server_test.go

@@ -0,0 +1,78 @@
+package mcp_test
+
+import (
+	"bytes"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/mathiasbq/supervisor/internal/mcp"
+	"github.com/mathiasbq/supervisor/internal/registry"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func jsonBody(t *testing.T, v any) *bytes.Buffer {
+	t.Helper()
+	b, err := json.Marshal(v)
+	require.NoError(t, err)
+	return bytes.NewBuffer(b)
+}
+
+func TestMCPInitialize(t *testing.T) {
+	reg := registry.New()
+	srv := mcp.NewServer(reg)
+
+	req := httptest.NewRequest(http.MethodPost, "/mcp", jsonBody(t, map[string]any{
+		"jsonrpc": "2.0",
+		"id":      1,
+		"method":  "initialize",
+		"params":  map[string]any{},
+	}))
+	req.Header.Set("Content-Type", "application/json")
+	rr := httptest.NewRecorder()
+
+	srv.ServeHTTP(rr, req)
+
+	assert.Equal(t, http.StatusOK, rr.Code)
+	var resp map[string]any
+	require.NoError(t, json.Unmarshal(rr.Body.Bytes(), &resp))
+	result := resp["result"].(map[string]any)
+	assert.Equal(t, "2024-11-05", result["protocolVersion"])
+}
+
+func TestMCPToolsList(t *testing.T) {
+	reg := registry.New()
+	srv := mcp.NewServer(reg)
+
+	req := httptest.NewRequest(http.MethodPost, "/mcp", jsonBody(t, map[string]any{
+		"jsonrpc": "2.0", "id": 2, "method": "tools/list", "params": map[string]any{},
+	}))
+	req.Header.Set("Content-Type", "application/json")
+	rr := httptest.NewRecorder()
+	srv.ServeHTTP(rr, req)
+
+	assert.Equal(t, http.StatusOK, rr.Code)
+	var resp map[string]any
+	require.NoError(t, json.Unmarshal(rr.Body.Bytes(), &resp))
+	result := resp["result"].(map[string]any)
+	assert.NotNil(t, result["tools"])
+}
+
+func TestMCPUnknownMethod(t *testing.T) {
+	reg := registry.New()
+	srv := mcp.NewServer(reg)
+
+	req := httptest.NewRequest(http.MethodPost, "/mcp", jsonBody(t, map[string]any{
+		"jsonrpc": "2.0", "id": 3, "method": "unknown/method", "params": map[string]any{},
+	}))
+	req.Header.Set("Content-Type", "application/json")
+	rr := httptest.NewRecorder()
+	srv.ServeHTTP(rr, req)
+
+	assert.Equal(t, http.StatusOK, rr.Code)
+	var resp map[string]any
+	require.NoError(t, json.Unmarshal(rr.Body.Bytes(), &resp))
+	assert.NotNil(t, resp["error"])
+}