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mcp: refactor notification of subscribed sessions (#1018)

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This PR improves the notification of subscribed sessions removing
duplicated part
This commit is contained in:
Guglielmo Colombo 2026-06-23 11:50:33 +02:00 • committed by GitHub
commit 01847b35b3
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1 changed files with 30 additions and 21 deletions
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53
mcp/server.go
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@ -726,18 +726,31 @@ func (s *Server) notifySessions(n string) {
}
s.mu.Unlock() // Don't hold the lock during notification: it causes deadlock.
// Notify legacy sessions on the shared session channel regardless of
// their subscription status.
notifySessions(legacySessions, n, changeNotificationParams[n](), s.opts.Logger)
// Sessions receive the notification only if they opened a
// subscriptions/listen stream that opted in to this notification type.
// Notify modern sessions only if they have an active subscription for
// this notification type.
s.notifySubscribedSessions(subscribers, n, changeNotificationParams[n])
}
// notifySubscribedSessions delivers a list-changed or resource-updated
// notification to each session in subscribers, stamping the session's
// listen-request ID into the params' _meta so the receiving client can demultiplex
// notifications belonging to different concurrent listens.
func (s *Server) notifySubscribedSessions(subscribers map[*ServerSession]jsonrpc.ID, method string, makeParams func() Params) {
if len(subscribers) == 0 {
return
}
ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
defer cancel()
for sess, reqID := range subscribers {
params := changeNotificationParams[n]()
params := makeParams()
injectMetaSubscriptionID(params, reqID)
req := newRequest(sess, params)
if err := handleNotify(ctx, n, req); err != nil {
s.opts.Logger.Warn(fmt.Sprintf("calling %s: %v", n, err))
if err := handleNotify(ctx, method, req); err != nil {
s.opts.Logger.Warn(fmt.Sprintf("calling %s: %v", method, err))
}
}
}
@ -1067,32 +1080,28 @@ func fileResourceHandler(dir string) ResourceHandler {
func (s *Server) ResourceUpdated(ctx context.Context, params *ResourceUpdatedNotificationParams) error {
s.mu.Lock()
subscribedSessions := s.resourceSubscriptions[params.URI]
sessions := slices.Collect(maps.Keys(subscribedSessions))
s.mu.Unlock()
// Only add legacy sessions for the notification, new ones use the new notification mechanism.
var legacySessions []*ServerSession
var newSessions []*ServerSession
for _, sess := range sessions {
newSessions := make(map[*ServerSession]jsonrpc.ID)
for sess, reqID := range subscribedSessions {
if sess.InitializeParams().isNil() || sess.InitializeParams().ProtocolVersion < protocolVersion20260728 {
legacySessions = append(legacySessions, sess)
} else {
newSessions = append(newSessions, sess)
newSessions[sess] = reqID
}
}
notifySessions(legacySessions, notificationResourceUpdated, params, s.opts.Logger)
s.opts.Logger.Info("resource updated notification sent", "uri", params.URI, "subscriber_count", len(sessions))
s.mu.Unlock()
ctx, cancel := context.WithTimeout(ctx, 10*time.Second)
defer cancel()
for _, sess := range newSessions {
reqID := subscribedSessions[sess]
notifySessions(legacySessions, notificationResourceUpdated, params, s.opts.Logger)
// Notify modern sessions, injecting the per-session subscription ID into the notification's metadata.
s.notifySubscribedSessions(newSessions, notificationResourceUpdated, func() Params {
p := *params
injectMetaSubscriptionID(&p, reqID)
req := newRequest(sess, &p)
if err := handleNotify(ctx, notificationResourceUpdated, req); err != nil {
s.opts.Logger.Warn(fmt.Sprintf("calling %s: %v", notificationResourceUpdated, err))
}
}
return &p
})
s.opts.Logger.Info("resource updated notification sent",
"uri", params.URI,
"subscriber_count", len(legacySessions)+len(newSessions))
return nil
}