rejects clients joining full dkg sessions

if the maximum number of participants (according to the session config) have
already joined a DKG session then the server prevents new clients from joining
the session and returns an error message

Author: Hugh Cunningham

src/errors.ts

@@ -11,6 +11,7 @@ export const MultisigBrokerErrorCodes = {
   INVALID_SIGNING_SESSION_ID: 4,
   IDENTITY_NOT_ALLOWED: 5,
   NON_SESSION_CLIENT: 6,
+  DKG_SESSION_FULL: 7,
 }
 
 export class MessageMalformedError extends Error {

src/server.ts

@@ -567,6 +567,16 @@ export class MultisigServer {
       return
     }
 
+    if (isDkgSession(session) && session.clientIds.size >= session.status.maxSigners) {
+      this.sendErrorMessage(
+        client,
+        message.id,
+        'DKG session is full',
+        MultisigBrokerErrorCodes.DKG_SESSION_FULL,
+      )
+      return
+    }
+
     this.logger.debug(`Client ${client.id} joined session ${message.sessionId}`)
 
     this.addClientToSession(client, message.sessionId)