chrome.tabs.sendMessage throw error

[Aleksej Todorovic]

Hello all,

I've noticed that my extension as of Chrome 99 throws an error if something goes wrong with chrome.tabs.sendMessage(tabId, message) (eg. listener in tab not set/ready, or no content script, etc).

I've checked in the earliest version, and it looks like chrome.runtime.lastError was silently processed if no callback set.

The message that I see is: "Uncaught (in promise) Error: Could not establish connection. Receiving end does not exist.”

Is this on purpose or not? 

[wOxxOm]

Reported as https://crbug.com/1304272.

The reason is that sendMessage is now promisified internally, so we can `await` it, but the byproduct is that when we don't specify a callback ourselves, it is added internally anyway in order for the call to return a Promise, which means that since we don't call sendResponse in onMessage, the API will think that it was us who made a mistake of using a callback and not providing a response, and report it as such.

Two workarounds for extensions:

1. Always call sendResponse() inside chrome.runtime.onMessage.

// sender
chrome.runtime.sendMessage('test');

// receiver
chrome.runtime.onMessage.addListener((msg, sender, sendResponse) => {
doSomethingWithoutResponding(msg);
sendResponse();
});

2. Suppress this specific error.
Also patch the API's inherent lack of a callstack prior to the call (a bug in itself BTW).

// sender
sendMessage('foo');
sendMessage('foo').then(res => whatever(res));
await sendMessage('foo');

function sendMessage(msg, options) {
const err1 = new Error('Callstack before sendMessage:');
return new Promise((resolve, reject) => {
chrome.runtime.sendMessage(undefined, msg, options, res => {
let err2 = chrome.runtime.lastError;
if (!err2 || err2.message.startsWith('The message port closed before')) {
resolve(res);
} else {
err2 = new Error(err2.message);
err2.stack += err1.stack.replace(/^Error:\s*/, '');
reject(err2);
}
});
});
}

[Alexey Makhrov]

@w0xx0m - it looks like you code snippet addresses a different error ("The message port closed before ...").

The OP asks about "Could not establish connection. Receiving end does not exist.".

I also started observing this one recently. I'm getting it even though I'm using an empty "sendResponse()" call as per your first workaround

[wOxxOm]

Report it on https://crbug.com.

[Jackie Han]

To suppress "Could not establish connection. Receiving end does not exist." error in MV3, I would like to write like this:

// I know there is most likely no extension pages listening for messages

chrome.runtime.sendMessage(msg, () => chrome.runtime.lastError);

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