1 files changed, 36 insertions, 0 deletions
diff --git a/browser/extensions/webcompat/lib/messaging_helper.js b/browser/extensions/webcompat/lib/messaging_helper.js
new file mode 100644
index 0000000000..d978ed384f
--- /dev/null
+++ b/browser/extensions/webcompat/lib/messaging_helper.js
@@ -0,0 +1,36 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+/* globals browser */
+
+// By default, only the first handler for browser.runtime.onMessage which
+// returns a value will get to return one. As such, we need to let them all
+// receive the message, and all have a chance to return a response (with the
+// first non-undefined result being the one that is ultimately returned).
+// This way, about:compat and the shims library can both get a chance to
+// process a message, and just return undefined if they wish to ignore it.
+
+const onMessageFromTab = (function () {
+  const handlers = new Set();
+
+  browser.runtime.onMessage.addListener((msg, sender) => {
+    const promises = [...handlers.values()].map(fn => fn(msg, sender));
+    return Promise.allSettled(promises).then(results => {
+      for (const { reason, value } of results) {
+        if (reason) {
+          console.error(reason);
+        } else if (value !== undefined) {
+          return value;
+        }
+      }
+      return undefined;
+    });
+  });
+
+  return function (handler) {
+    handlers.add(handler);
+  };
+})();