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mcp: allow requests before notifications/initialized

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Upon a closer reading of the spec, it is OK for the server to response
to client requests before it has received notifications/initialized (as
long as it has received initialize). This effectively rolls back the fix
from #225.

Some hooks are left for enforcing strictness around server->client
requests prior to initialized. These will be revisited in subsequent
CLs.

For #395
This commit is contained in:
Rob Findley 2025-09-05 01:10:52 +00:00 • committed by Robert Findley
commit 5ccd97fafc
1 changed files with 53 additions and 6 deletions
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38
mcp/server.go
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@ -844,6 +844,33 @@ func (ss *ServerSession) updateState(mut func(*ServerSessionState)) {
}
}
// hasInitialized reports whether the server has received the initialized
// notification.
//
// TODO(findleyr): use this to prevent change notifications.
func (ss *ServerSession) hasInitialized() bool {
ss.mu.Lock()
defer ss.mu.Unlock()
return ss.state.InitializedParams != nil
}
// checkInitialized returns a formatted error if the server has not yet
// received the initialized notification.
func (ss *ServerSession) checkInitialized(method string) error {
if !ss.hasInitialized() {
// TODO(rfindley): enable this check.
// Right now is is flaky, because server tests don't await the initialized notification.
// Perhaps requests should simply block until they have received the initialized notification
// if strings.HasPrefix(method, "notifications/") {
// return fmt.Errorf("must not send %q before %q is received", method, notificationInitialized)
// } else {
// return fmt.Errorf("cannot call %q before %q is received", method, notificationInitialized)
// }
}
return nil
}
func (ss *ServerSession) ID() string {
if c, ok := ss.mcpConn.(hasSessionID); ok {
return c.SessionID()
@ -859,11 +886,17 @@ func (ss *ServerSession) Ping(ctx context.Context, params *PingParams) error {
// ListRoots lists the client roots.
func (ss *ServerSession) ListRoots(ctx context.Context, params *ListRootsParams) (*ListRootsResult, error) {
if err := ss.checkInitialized(methodListRoots); err != nil {
return nil, err
}
return handleSend[*ListRootsResult](ctx, methodListRoots, newServerRequest(ss, orZero[Params](params)))
}
// CreateMessage sends a sampling request to the client.
func (ss *ServerSession) CreateMessage(ctx context.Context, params *CreateMessageParams) (*CreateMessageResult, error) {
if err := ss.checkInitialized(methodCreateMessage); err != nil {
return nil, err
}
if params == nil {
params = &CreateMessageParams{Messages: []*SamplingMessage{}}
}
@ -877,6 +910,9 @@ func (ss *ServerSession) CreateMessage(ctx context.Context, params *CreateMessag
// Elicit sends an elicitation request to the client asking for user input.
func (ss *ServerSession) Elicit(ctx context.Context, params *ElicitParams) (*ElicitResult, error) {
if err := ss.checkInitialized(methodElicit); err != nil {
return nil, err
}
return handleSend[*ElicitResult](ctx, methodElicit, newServerRequest(ss, orZero[Params](params)))
}
@ -978,7 +1014,7 @@ func (ss *ServerSession) getConn() *jsonrpc2.Connection { return ss.conn }
// handle invokes the method described by the given JSON RPC request.
func (ss *ServerSession) handle(ctx context.Context, req *jsonrpc.Request) (any, error) {
ss.mu.Lock()
initialized := ss.state.InitializedParams != nil
initialized := ss.state.InitializeParams != nil
ss.mu.Unlock()
// From the spec: