window.print() is blocked until XMLHttpRequest completes

• Component: Printing
• Status: NEW ---

[Andrew Paprotsky]

If there's an active XMLHttpRequest window.print() is blocked; print dialog appears only when the request is completed. This is a problem for cases when XMLHttpRequest is used for long-polling.

Steps to reproduce:
1. Extract the attached archive to a PHP enabled web server
2. Visit the index.php.
3. Click the button to see the result.

[Andrew Paprotsky]

Created attachment 237302 [details]
reproducible test case

[Alexey Proskuryakov]

Thank you for the bug report.

I think that this is unintentional (and a consequence of delaying a print() that's called from an inline script), yet this still looks like a correct behavior.

If XHR progress events were displayed under a modal print dialog, that would cause many undesirable effects (e.g. what if event handler tried to do a window.close() while the window was being printed). And if we stopped progress events, that would cause correctness issues on websites that expect them to be handled in a timely manner.

[Andrew Paprotsky]

Thanks for the quick reply.

The problem is that if I want to print something using window.print() then I have to wait until active XHR is completed. So if I have a long-polling request with 10 minutes timeout then in worst case I'd have to wait 10 minutes until the print dialog appears.

[Philipp Spiess]

This is still an issue. Chrome seems to have fixed this [1], are there any plans for Safari to do the same as well?

This makes it impossible to use the print API for websites that rely on long-polling to get real time updates.

[1] https://bugs.chromium.org/p/chromium/issues/detail?id=173140

[Radar WebKit Bug Importer]

<rdar://problem/35035119>