Merge pull request #1358 from matrix-org/bwindels/fixwaitforeventrace-rc

Handle race between sending and await next event from other party

src/crypto/verification/Base.js

@@ -122,6 +122,11 @@ export class VerificationBase extends EventEmitter {
         if (this._done) {
             return Promise.reject(new Error("Verification is already done"));
         }
+        const existingEvent = this.request.getEventFromOtherParty(type);
+        if (existingEvent) {
+            return Promise.resolve(existingEvent);
+        }
+
         this._expectedEvent = type;
         return new Promise((resolve, reject) => {
             this._resolveEvent = resolve;

src/crypto/verification/request/VerificationRequest.js

@@ -877,4 +877,8 @@ export class VerificationRequest extends EventEmitter {
             this._setPhase(newTransitions[newTransitions.length - 1].phase);
         }
     }
+
+    getEventFromOtherParty(type) {
+        return this._eventsByThem.get(type);
+    }
 }