1600512 - BroadcastChannel.onmessage not working

Status: NEW

(Core :: DOM: Security, defect, P3)

Description

[Hugues]

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.108 Safari/537.36

Steps to reproduce:

I need to share some information between 2 tabs of the same browser pointing at the .html files on my local disk. I'm using the BroadcastChannel.onmessage event handler as detailed here: https://developer.mozilla.org/en-US/docs/Web/API/BroadcastChannel/onmessage

In the sender tab javascript code I defined:

var bc = new BroadcastChannel('my_bc_channel');

bc.postMessage(i); //where i is simply a consecutive number i want to share

And in the receiving tab:

var bc = new BroadcastChannel('my_bc_channel');

//then use this to receive the incoming messages:

bc.onmessage = function (ev) {

last_line = ev.data
}

My code works fine in Chrome, but it does not do anything in Firefox (latest version 70 freshly installed under windows). The compatibility chart in the link I gave above says it should be working from Firefox version 38.

I don't have any error messages in the console. I don't know if it's the sender code that does not send anything. But clearly the receiving code is not triggered so I guess the .onmessage event is not detected.

I have asked for support here:
https://support.mozilla.org/en-US/questions/1273938
It was proposed that it might relate to bug 1356546. But i have modified my code to send only one number once to be sure it is not the same bug, but the modification failed to solve my problem.

Actual results:

No message received in receiving tab. Not sure if message sent from sending tab.

Expected results:

Message is sent from sending tab and received in receiving tab.

Comment 1

[Olli Pettay [:smaug][[e-mail]]]

A minimal testcase here would be really nice, attached to this bug.

Comment 2

[Hugues]

Attachment: receive.html

Comment 3

[Hugues]

Attachment: send.html

Comment 4

[Hugues]

(In reply to Olli Pettay [:smaug] from comment #1)

A minimal testcase here would be really nice, attached to this bug.

I have now attached 2 .html files to my bug report:

• send.html with a javascript that is simply sending "test" using .postmessage
• receive.html with a javascript to receive the message and alert user with a popup on screen

Procedure to replicate:

• open receive.html in one tab
• open send.html in another tab
• at this point the Alert with "Test" should show up in the receive tab
• at least that's how it behaves in Chrome, but in Firefox nothing happens, no error message.

Comment 5

[Olli Pettay [:smaug][[e-mail]]]

When I open receive.html in one tab and send.html in another tab, alert is opened in the tab which has receive.html loaded, when loaded from this bug.
I tested both Firefox 70.0.1 and recent Nightly.

But ok, I see, this is about local files. Same origin handling on local files isn't consistent across browsers.

Comment 6

[Hugues]

I confirm that BroadcastChannel.onmessage works if I'm pulling my code from a remote server, the problem appears to be only when i load the files from my local drive.

Comment 7

[Daniel Veditz [:dveditz]]

So Chrome treats file:/// urls as unique origins for direct access, but same origin for purposes of BroadcastChannel? That's not very consistent and I'm not sure it's supportable. But file:/// is a weird specless wasteland of guessing what the right thing to do is.

For your own development purposes, does setting the pref privacy.file_unique_origin to false fix the bug for you? Does this have to be deployable as a file:/// url solution or is that a good enough work around for your own personal development?

Comment 8

[Hugues]

(In reply to Daniel Veditz [:dveditz] from comment #7)

So Chrome treats file:/// urls as unique origins for direct access, but same origin for purposes of BroadcastChannel? That's not very consistent and I'm not sure it's supportable. But file:/// is a weird specless wasteland of guessing what the right thing to do is.

For your own development purposes, does setting the pref privacy.file_unique_origin to false fix the bug for you? Does this have to be deployable as a file:/// url solution or is that a good enough work around for your own personal development?

• started firefox
• opened about:config url
• looked for privacy.file_unique_origin
• changed to false
• restarted Firefox, to be sure
• checked that above flag is still false
• loaded my 2 .html files from local drive
• unfortunately problem is still there, receiving code .onmessage event is not detected.

Comment 9

[Justin Peter]

Unfortunately this seems to make local development of sites using BroadcastChannel impossible.