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 "git.secluded.site/crush/internal/config"
21 "git.secluded.site/crush/internal/csync"
22 "git.secluded.site/crush/internal/home"
23 "git.secluded.site/crush/internal/permission"
24 "git.secluded.site/crush/internal/pubsub"
25 "git.secluded.site/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 uint
62
63const (
64 EventStateChanged EventType = iota
65 EventToolsListChanged
66 EventPromptsListChanged
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, session := range sessions.Seq2() {
113 if err := session.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 // createSession handles its own timeout internally.
158 session, err := createSession(ctx, name, m, cfg.Resolver())
159 if err != nil {
160 return
161 }
162
163 tools, err := getTools(ctx, session)
164 if err != nil {
165 slog.Error("error listing tools", "error", err)
166 updateState(name, StateError, err, nil, Counts{})
167 session.Close()
168 return
169 }
170
171 prompts, err := getPrompts(ctx, session)
172 if err != nil {
173 slog.Error("error listing prompts", "error", err)
174 updateState(name, StateError, err, nil, Counts{})
175 session.Close()
176 return
177 }
178
179 updateTools(name, tools)
180 updatePrompts(name, prompts)
181 sessions.Set(name, session)
182
183 updateState(name, StateConnected, nil, session, Counts{
184 Tools: len(tools),
185 Prompts: len(prompts),
186 })
187 }(name, m)
188 }
189 wg.Wait()
190}
191
192func getOrRenewClient(ctx context.Context, name string) (*mcp.ClientSession, error) {
193 sess, ok := sessions.Get(name)
194 if !ok {
195 return nil, fmt.Errorf("mcp '%s' not available", name)
196 }
197
198 cfg := config.Get()
199 m := cfg.MCP[name]
200 state, _ := states.Get(name)
201
202 timeout := mcpTimeout(m)
203 pingCtx, cancel := context.WithTimeout(ctx, timeout)
204 defer cancel()
205 err := sess.Ping(pingCtx, nil)
206 if err == nil {
207 return sess, nil
208 }
209 updateState(name, StateError, maybeTimeoutErr(err, timeout), nil, state.Counts)
210
211 sess, err = createSession(ctx, name, m, cfg.Resolver())
212 if err != nil {
213 return nil, err
214 }
215
216 updateState(name, StateConnected, nil, sess, state.Counts)
217 sessions.Set(name, sess)
218 return sess, nil
219}
220
221// updateState updates the state of an MCP client and publishes an event
222func updateState(name string, state State, err error, client *mcp.ClientSession, counts Counts) {
223 info := ClientInfo{
224 Name: name,
225 State: state,
226 Error: err,
227 Client: client,
228 Counts: counts,
229 }
230 switch state {
231 case StateConnected:
232 info.ConnectedAt = time.Now()
233 case StateError:
234 sessions.Del(name)
235 }
236 states.Set(name, info)
237
238 // Publish state change event
239 broker.Publish(pubsub.UpdatedEvent, Event{
240 Type: EventStateChanged,
241 Name: name,
242 State: state,
243 Error: err,
244 Counts: counts,
245 })
246}
247
248func createSession(ctx context.Context, name string, m config.MCPConfig, resolver config.VariableResolver) (*mcp.ClientSession, error) {
249 timeout := mcpTimeout(m)
250 mcpCtx, cancel := context.WithCancel(ctx)
251 cancelTimer := time.AfterFunc(timeout, cancel)
252
253 transport, err := createTransport(mcpCtx, m, resolver)
254 if err != nil {
255 updateState(name, StateError, err, nil, Counts{})
256 slog.Error("error creating mcp client", "error", err, "name", name)
257 cancel()
258 cancelTimer.Stop()
259 return nil, err
260 }
261
262 client := mcp.NewClient(
263 &mcp.Implementation{
264 Name: "crush",
265 Version: version.Version,
266 Title: "Crush",
267 },
268 &mcp.ClientOptions{
269 ToolListChangedHandler: func(context.Context, *mcp.ToolListChangedRequest) {
270 broker.Publish(pubsub.UpdatedEvent, Event{
271 Type: EventToolsListChanged,
272 Name: name,
273 })
274 },
275 PromptListChangedHandler: func(context.Context, *mcp.PromptListChangedRequest) {
276 broker.Publish(pubsub.UpdatedEvent, Event{
277 Type: EventPromptsListChanged,
278 Name: name,
279 })
280 },
281 LoggingMessageHandler: func(_ context.Context, req *mcp.LoggingMessageRequest) {
282 slog.Info("mcp log", "name", name, "data", req.Params.Data)
283 },
284 KeepAlive: time.Minute * 10,
285 },
286 )
287
288 session, err := client.Connect(mcpCtx, transport, nil)
289 if err != nil {
290 err = maybeStdioErr(err, transport)
291 updateState(name, StateError, maybeTimeoutErr(err, timeout), nil, Counts{})
292 slog.Error("error starting mcp client", "error", err, "name", name)
293 cancel()
294 cancelTimer.Stop()
295 return nil, err
296 }
297
298 cancelTimer.Stop()
299 slog.Info("Initialized mcp client", "name", name)
300 return session, nil
301}
302
303// maybeStdioErr if a stdio mcp prints an error in non-json format, it'll fail
304// to parse, and the cli will then close it, causing the EOF error.
305// so, if we got an EOF err, and the transport is STDIO, we try to exec it
306// again with a timeout and collect the output so we can add details to the
307// error.
308// this happens particularly when starting things with npx, e.g. if node can't
309// be found or some other error like that.
310func maybeStdioErr(err error, transport mcp.Transport) error {
311 if !errors.Is(err, io.EOF) {
312 return err
313 }
314 ct, ok := transport.(*mcp.CommandTransport)
315 if !ok {
316 return err
317 }
318 if err2 := stdioCheck(ct.Command); err2 != nil {
319 err = errors.Join(err, err2)
320 }
321 return err
322}
323
324func maybeTimeoutErr(err error, timeout time.Duration) error {
325 if errors.Is(err, context.Canceled) {
326 return fmt.Errorf("timed out after %s", timeout)
327 }
328 return err
329}
330
331func createTransport(ctx context.Context, m config.MCPConfig, resolver config.VariableResolver) (mcp.Transport, error) {
332 switch m.Type {
333 case config.MCPStdio:
334 command, err := resolver.ResolveValue(m.Command)
335 if err != nil {
336 return nil, fmt.Errorf("invalid mcp command: %w", err)
337 }
338 if strings.TrimSpace(command) == "" {
339 return nil, fmt.Errorf("mcp stdio config requires a non-empty 'command' field")
340 }
341 cmd := exec.CommandContext(ctx, home.Long(command), m.Args...)
342 cmd.Env = append(os.Environ(), m.ResolvedEnv()...)
343 return &mcp.CommandTransport{
344 Command: cmd,
345 }, nil
346 case config.MCPHttp:
347 if strings.TrimSpace(m.URL) == "" {
348 return nil, fmt.Errorf("mcp http config requires a non-empty 'url' field")
349 }
350 client := &http.Client{
351 Transport: &headerRoundTripper{
352 headers: m.ResolvedHeaders(),
353 },
354 }
355 return &mcp.StreamableClientTransport{
356 Endpoint: m.URL,
357 HTTPClient: client,
358 }, nil
359 case config.MCPSSE:
360 if strings.TrimSpace(m.URL) == "" {
361 return nil, fmt.Errorf("mcp sse config requires a non-empty 'url' field")
362 }
363 client := &http.Client{
364 Transport: &headerRoundTripper{
365 headers: m.ResolvedHeaders(),
366 },
367 }
368 return &mcp.SSEClientTransport{
369 Endpoint: m.URL,
370 HTTPClient: client,
371 }, nil
372 default:
373 return nil, fmt.Errorf("unsupported mcp type: %s", m.Type)
374 }
375}
376
377type headerRoundTripper struct {
378 headers map[string]string
379}
380
381func (rt headerRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
382 for k, v := range rt.headers {
383 req.Header.Set(k, v)
384 }
385 return http.DefaultTransport.RoundTrip(req)
386}
387
388func mcpTimeout(m config.MCPConfig) time.Duration {
389 return time.Duration(cmp.Or(m.Timeout, 15)) * time.Second
390}
391
392func stdioCheck(old *exec.Cmd) error {
393 ctx, cancel := context.WithTimeout(context.Background(), time.Second*5)
394 defer cancel()
395 cmd := exec.CommandContext(ctx, old.Path, old.Args...)
396 cmd.Env = old.Env
397 out, err := cmd.CombinedOutput()
398 if err == nil || errors.Is(ctx.Err(), context.DeadlineExceeded) {
399 return nil
400 }
401 return fmt.Errorf("%w: %s", err, string(out))
402}