fix(connection): gracefully handle missing method (#2351)

lighthouse-core/gather/connections/connection.js

@@ -93,7 +93,7 @@ class Connection {
     const object = JSON.parse(message);
     // Remote debugging protocol is JSON RPC 2.0 compiant. In terms of that transport,
     // responses to the commands carry "id" property, while notifications do not.
-    if (object.id) {
+    if (this._callbacks.has(object.id)) {
       const callback = this._callbacks.get(object.id);
       this._callbacks.delete(object.id);
 
@@ -108,11 +108,17 @@ class Connection {
           {method: callback.method, params: object.result}, 'verbose');
         return object.result;
       }));
+    } else if (object.id) {
+      // In DevTools we receive responses to commands we did not send which we cannot act on, so we
+      // just log these occurrences.
+      const error = object.error && object.error.message;
+      log.formatProtocol(`disowned method <= browser ${error ? 'ERR' : 'OK'}`,
+          {method: object.method, params: error || object.result}, 'verbose');
+    } else {
+      log.formatProtocol('<= event',
+          {method: object.method, params: object.params}, 'verbose');
+      this.emitNotification(object.method, object.params);
     }
-
-    log.formatProtocol('<= event',
-        {method: object.method, params: object.params}, 'verbose');
-    this.emitNotification(object.method, object.params);
   }
 
   /**

lighthouse-core/lib/log.js

@@ -108,11 +108,12 @@ class Log {
    */
   static formatProtocol(prefix, data, level) {
     const columns = (!process || process.browser) ? Infinity : process.stdout.columns;
-    const maxLength = columns - data.method.length - prefix.length - loggingBufferColumns;
+    const method = data.method || '?????';
+    const maxLength = columns - method.length - prefix.length - loggingBufferColumns;
     // IO.read blacklisted here to avoid logging megabytes of trace data
-    const snippet = (data.params && data.method !== 'IO.read') ?
+    const snippet = (data.params && method !== 'IO.read') ?
       JSON.stringify(data.params).substr(0, maxLength) : '';
-    Log._logToStdErr(`${prefix}:${level || ''}`, [data.method, snippet]);
+    Log._logToStdErr(`${prefix}:${level || ''}`, [method, snippet]);
   }
 
   static log(title, ...args) {