1// Package mcp provides functionality for managing Model Context Protocol (MCP)
2// clients within the Crush application.
3package mcp
4
5import (
6 "cmp"
7 "context"
8 "errors"
9 "fmt"
10 "io"
11 "log/slog"
12 "maps"
13 "net/http"
14 "os"
15 "os/exec"
16 "strings"
17 "sync"
18 "time"
19
20 "github.com/charmbracelet/crush/internal/config"
21 "github.com/charmbracelet/crush/internal/csync"
22 "github.com/charmbracelet/crush/internal/home"
23 "github.com/charmbracelet/crush/internal/permission"
24 "github.com/charmbracelet/crush/internal/pubsub"
25 "github.com/charmbracelet/crush/internal/version"
26 "github.com/modelcontextprotocol/go-sdk/mcp"
27)
28
29var (
30 sessions = csync.NewMap[string, *mcp.ClientSession]()
31 states = csync.NewMap[string, ClientInfo]()
32 broker = pubsub.NewBroker[Event]()
33)
34
35// State represents the current state of an MCP client
36type State int
37
38const (
39 StateDisabled State = iota
40 StateStarting
41 StateConnected
42 StateError
43)
44
45func (s State) String() string {
46 switch s {
47 case StateDisabled:
48 return "disabled"
49 case StateStarting:
50 return "starting"
51 case StateConnected:
52 return "connected"
53 case StateError:
54 return "error"
55 default:
56 return "unknown"
57 }
58}
59
60// EventType represents the type of MCP event
61type EventType string
62
63const (
64 EventStateChanged EventType = "state_changed"
65 EventToolsListChanged EventType = "tools_list_changed"
66 EventPromptsListChanged EventType = "prompts_list_changed"
67)
68
69// Event represents an event in the MCP system
70type Event struct {
71 Type EventType
72 Name string
73 State State
74 Error error
75 Counts Counts
76}
77
78// Counts number of available tools, prompts, etc.
79type Counts struct {
80 Tools int
81 Prompts int
82}
83
84// ClientInfo holds information about an MCP client's state
85type ClientInfo struct {
86 Name string
87 State State
88 Error error
89 Client *mcp.ClientSession
90 Counts Counts
91 ConnectedAt time.Time
92}
93
94// SubscribeEvents returns a channel for MCP events
95func SubscribeEvents(ctx context.Context) <-chan pubsub.Event[Event] {
96 return broker.Subscribe(ctx)
97}
98
99// GetStates returns the current state of all MCP clients
100func GetStates() map[string]ClientInfo {
101 return maps.Collect(states.Seq2())
102}
103
104// GetState returns the state of a specific MCP client
105func GetState(name string) (ClientInfo, bool) {
106 return states.Get(name)
107}
108
109// Close closes all MCP clients. This should be called during application shutdown.
110func Close() error {
111 var errs []error
112 for name, c := range sessions.Seq2() {
113 if err := c.Close(); err != nil &&
114 !errors.Is(err, io.EOF) &&
115 !errors.Is(err, context.Canceled) &&
116 err.Error() != "signal: killed" {
117 errs = append(errs, fmt.Errorf("close mcp: %s: %w", name, err))
118 }
119 }
120 broker.Shutdown()
121 return errors.Join(errs...)
122}
123
124// Initialize initializes MCP clients based on the provided configuration.
125func Initialize(ctx context.Context, permissions permission.Service, cfg *config.Config) {
126 var wg sync.WaitGroup
127 // Initialize states for all configured MCPs
128 for name, m := range cfg.MCP {
129 if m.Disabled {
130 updateState(name, StateDisabled, nil, nil, Counts{})
131 slog.Debug("skipping disabled mcp", "name", name)
132 continue
133 }
134
135 // Set initial starting state
136 updateState(name, StateStarting, nil, nil, Counts{})
137
138 wg.Add(1)
139 go func(name string, m config.MCPConfig) {
140 defer func() {
141 wg.Done()
142 if r := recover(); r != nil {
143 var err error
144 switch v := r.(type) {
145 case error:
146 err = v
147 case string:
148 err = fmt.Errorf("panic: %s", v)
149 default:
150 err = fmt.Errorf("panic: %v", v)
151 }
152 updateState(name, StateError, err, nil, Counts{})
153 slog.Error("panic in mcp client initialization", "error", err, "name", name)
154 }
155 }()
156
157 ctx, cancel := context.WithTimeout(ctx, mcpTimeout(m))
158 defer cancel()
159
160 session, err := createSession(ctx, name, m, cfg.Resolver())
161 if err != nil {
162 return
163 }
164
165 tools, err := getTools(ctx, session)
166 if err != nil {
167 slog.Error("error listing tools", "error", err)
168 updateState(name, StateError, err, nil, Counts{})
169 session.Close()
170 return
171 }
172
173 prompts, err := getPrompts(ctx, session)
174 if err != nil {
175 slog.Error("error listing prompts", "error", err)
176 updateState(name, StateError, err, nil, Counts{})
177 session.Close()
178 return
179 }
180
181 updateTools(name, tools)
182 updatePrompts(name, prompts)
183 sessions.Set(name, session)
184
185 updateState(name, StateConnected, nil, session, Counts{
186 Tools: len(tools),
187 Prompts: len(prompts),
188 })
189 }(name, m)
190 }
191 wg.Wait()
192}
193
194func getOrRenewClient(ctx context.Context, name string) (*mcp.ClientSession, error) {
195 sess, ok := sessions.Get(name)
196 if !ok {
197 return nil, fmt.Errorf("mcp '%s' not available", name)
198 }
199
200 cfg := config.Get()
201 m := cfg.MCP[name]
202 state, _ := states.Get(name)
203
204 timeout := mcpTimeout(m)
205 pingCtx, cancel := context.WithTimeout(ctx, timeout)
206 defer cancel()
207 err := sess.Ping(pingCtx, nil)
208 if err == nil {
209 return sess, nil
210 }
211 updateState(name, StateError, maybeTimeoutErr(err, timeout), nil, state.Counts)
212
213 sess, err = createSession(ctx, name, m, cfg.Resolver())
214 if err != nil {
215 return nil, err
216 }
217
218 updateState(name, StateConnected, nil, sess, state.Counts)
219 sessions.Set(name, sess)
220 return sess, nil
221}
222
223// updateState updates the state of an MCP client and publishes an event
224func updateState(name string, state State, err error, client *mcp.ClientSession, counts Counts) {
225 info := ClientInfo{
226 Name: name,
227 State: state,
228 Error: err,
229 Client: client,
230 Counts: counts,
231 }
232 switch state {
233 case StateConnected:
234 info.ConnectedAt = time.Now()
235 case StateError:
236 updateTools(name, nil)
237 sessions.Del(name)
238 }
239 states.Set(name, info)
240
241 // Publish state change event
242 broker.Publish(pubsub.UpdatedEvent, Event{
243 Type: EventStateChanged,
244 Name: name,
245 State: state,
246 Error: err,
247 Counts: counts,
248 })
249}
250
251func createSession(ctx context.Context, name string, m config.MCPConfig, resolver config.VariableResolver) (*mcp.ClientSession, error) {
252 timeout := mcpTimeout(m)
253 mcpCtx, cancel := context.WithCancel(ctx)
254 cancelTimer := time.AfterFunc(timeout, cancel)
255
256 transport, err := createTransport(mcpCtx, m, resolver)
257 if err != nil {
258 updateState(name, StateError, err, nil, Counts{})
259 slog.Error("error creating mcp client", "error", err, "name", name)
260 cancel()
261 cancelTimer.Stop()
262 return nil, err
263 }
264
265 client := mcp.NewClient(
266 &mcp.Implementation{
267 Name: "crush",
268 Version: version.Version,
269 Title: "Crush",
270 },
271 &mcp.ClientOptions{
272 ToolListChangedHandler: func(context.Context, *mcp.ToolListChangedRequest) {
273 broker.Publish(pubsub.UpdatedEvent, Event{
274 Type: EventToolsListChanged,
275 Name: name,
276 })
277 },
278 PromptListChangedHandler: func(context.Context, *mcp.PromptListChangedRequest) {
279 broker.Publish(pubsub.UpdatedEvent, Event{
280 Type: EventPromptsListChanged,
281 Name: name,
282 })
283 },
284 LoggingMessageHandler: func(_ context.Context, req *mcp.LoggingMessageRequest) {
285 slog.Info("mcp log", "name", name, "data", req.Params.Data)
286 },
287 KeepAlive: time.Minute * 10,
288 },
289 )
290
291 session, err := client.Connect(mcpCtx, transport, nil)
292 if err != nil {
293 err = maybeStdioErr(err, transport)
294 updateState(name, StateError, maybeTimeoutErr(err, timeout), nil, Counts{})
295 slog.Error("error starting mcp client", "error", err, "name", name)
296 cancel()
297 cancelTimer.Stop()
298 return nil, err
299 }
300
301 cancelTimer.Stop()
302 slog.Info("Initialized mcp client", "name", name)
303 return session, nil
304}
305
306// maybeStdioErr if a stdio mcp prints an error in non-json format, it'll fail
307// to parse, and the cli will then close it, causing the EOF error.
308// so, if we got an EOF err, and the transport is STDIO, we try to exec it
309// again with a timeout and collect the output so we can add details to the
310// error.
311// this happens particularly when starting things with npx, e.g. if node can't
312// be found or some other error like that.
313func maybeStdioErr(err error, transport mcp.Transport) error {
314 if !errors.Is(err, io.EOF) {
315 return err
316 }
317 ct, ok := transport.(*mcp.CommandTransport)
318 if !ok {
319 return err
320 }
321 if err2 := stdioCheck(ct.Command); err2 != nil {
322 err = errors.Join(err, err2)
323 }
324 return err
325}
326
327func maybeTimeoutErr(err error, timeout time.Duration) error {
328 if errors.Is(err, context.Canceled) {
329 return fmt.Errorf("timed out after %s", timeout)
330 }
331 return err
332}
333
334func createTransport(ctx context.Context, m config.MCPConfig, resolver config.VariableResolver) (mcp.Transport, error) {
335 switch m.Type {
336 case config.MCPStdio:
337 command, err := resolver.ResolveValue(m.Command)
338 if err != nil {
339 return nil, fmt.Errorf("invalid mcp command: %w", err)
340 }
341 if strings.TrimSpace(command) == "" {
342 return nil, fmt.Errorf("mcp stdio config requires a non-empty 'command' field")
343 }
344 cmd := exec.CommandContext(ctx, home.Long(command), m.Args...)
345 cmd.Env = append(os.Environ(), m.ResolvedEnv()...)
346 return &mcp.CommandTransport{
347 Command: cmd,
348 }, nil
349 case config.MCPHttp:
350 if strings.TrimSpace(m.URL) == "" {
351 return nil, fmt.Errorf("mcp http config requires a non-empty 'url' field")
352 }
353 client := &http.Client{
354 Transport: &headerRoundTripper{
355 headers: m.ResolvedHeaders(),
356 },
357 }
358 return &mcp.StreamableClientTransport{
359 Endpoint: m.URL,
360 HTTPClient: client,
361 }, nil
362 case config.MCPSSE:
363 if strings.TrimSpace(m.URL) == "" {
364 return nil, fmt.Errorf("mcp sse config requires a non-empty 'url' field")
365 }
366 client := &http.Client{
367 Transport: &headerRoundTripper{
368 headers: m.ResolvedHeaders(),
369 },
370 }
371 return &mcp.SSEClientTransport{
372 Endpoint: m.URL,
373 HTTPClient: client,
374 }, nil
375 default:
376 return nil, fmt.Errorf("unsupported mcp type: %s", m.Type)
377 }
378}
379
380type headerRoundTripper struct {
381 headers map[string]string
382}
383
384func (rt headerRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
385 for k, v := range rt.headers {
386 req.Header.Set(k, v)
387 }
388 return http.DefaultTransport.RoundTrip(req)
389}
390
391func mcpTimeout(m config.MCPConfig) time.Duration {
392 return time.Duration(cmp.Or(m.Timeout, 15)) * time.Second
393}
394
395func stdioCheck(old *exec.Cmd) error {
396 ctx, cancel := context.WithTimeout(context.Background(), time.Second*5)
397 defer cancel()
398 cmd := exec.CommandContext(ctx, old.Path, old.Args...)
399 cmd.Env = old.Env
400 out, err := cmd.CombinedOutput()
401 if err == nil || errors.Is(ctx.Err(), context.DeadlineExceeded) {
402 return nil
403 }
404 return fmt.Errorf("%w: %s", err, string(out))
405}