Listener indicated async response by returning true, but channel was closed

[twschiller]

Context

• User reports this starting in 1.6.3, and it's still happening in 1.6.4
• When using the @pixiebrix/wait/element brick
• https://pixiebrixcommunity.slack.com/archives/C02TS1K83EX/p1654198610485169

Discussion

• Potentially related to The content script is injected twice (editor open, click browser action) #3510

[fregante]

Copying this message from Slack:

Could that be simply a closed tab? The message is basically saying:

• the onMessage listener didn't resolve before the tab was closed

It should be replicable with a raw:

a: browser.tabs.sendMessage(1, 'msg')

b: browser.runtime.onMessage
  .addListener(() => new Promise(console.warn))

This will never resolve, so if you close the context B, you'll get that error on A

Confirmed:

[fregante]

This issue is similar to:

• Incorrect "connection lost" message for multi-page flows #2902

Related:

• Documentation: How sendMessage responds webext-messenger#66

I opened:

• A listener indicated an asynchronous response by returning true, but the message channel closed before a response was received mozilla/webextension-polyfill#384
• Handle new "tab closed" response from Chrome mozilla/webextension-polyfill#385

[twschiller]

Moving to 1.7.1. With the 1.7.0 release, will confirm if #3510 solved the problem or not

[twschiller]

We haven't seen this recently and have been updating related messenger code. Will re-open as necessary

[fregante]

Likely it has been fixed/hidden by:

• Handle closed tabs better while attempting to message them #3572

The underlying issue is being tracked in:

• If a tab is closed before the method responds, the Messenger throws "Could not establish connection" webext-messenger#67