Downloading of binary files stalls at 0/0 bytes in Tor Browser based on ESR52 with e10s off

A user reported in #21340that downloading of zip file stalls reliably at 0 bytes with

[04-07 10:07:18] Torbutton INFO: External app requested
http channel Listener OnDataAvailable contract violation

Stalling happens as well for other binaries that need the external helper dialog, e.g. https://dist.torproject.org/torbrowser/6.5.1/TorBrowser-6.5.1-osx64_ar.dmg.

A workaround is to cancel the download and restart it on the about:downloads page.

added GeorgKoppen201705 TorBrowserTeam201705 component::applications/tor browser ff52-esr owner::gk priority::high resolution::fixed severity::normal sponsor::4 status::closed tbb-7.0-must tbb-usability type::defect labels

Trac:
Component: Applications to Applications/Tor Browser
Status: new to assigned
Owner: N/A to tbb-team

esr52 made #18778 (moved) more obvious.

Might be related to #21766 (moved) (as comment:14:ticket:21340 mentions).

Trac:
Summary: Downloading of binary filles stalls at 0/0 bytes in Tor Browser based on ESR52 to Downloading of binary files stalls at 0/0 bytes in Tor Browser based on ESR52
Cc: N/A to mcs, brade

Trac:
Priority: Medium to High
Keywords: tbb-7.0-must deleted, tbb-7.0-must-alpha added

Trac:
Keywords: N/A deleted, GeorgKoppen201704 added

After looking a bit closer at it I think this is highly related to #21766 (moved). mcs/brade: would it be helpful to deal with that bug by looking closer at this issue? Or do you feel you have a solution for #21766 (moved)? If so you could test whether my assumption is right and this bug gets fixed with it, too.

Trac:
Status: assigned to needs_information

Replying to gk:

After looking a bit closer at it I think this is highly related to #21766 (moved). mcs/brade: would it be helpful to deal with that bug by looking closer at this issue? We will look at this one at the same time as #21766 (moved).

Or do you feel you have a solution for #21766 (moved)? If so you could test whether my assumption is right and this bug gets fixed with it, too. We do not have a solution yet but are planning to work on that bug tomorrow.

Oh, I did not mean to put that on your plate. I was just trying to avoid different folks working on the same issue. :) But I am fine if you look at that one as well while wrapping your head around #21766 (moved).

Trac:
Status: needs_information to assigned
Keywords: GeorgKoppen201704 deleted, N/A added
Owner: tbb-team to mcs

Kathy and I can not reproduce this bug when Tor Browser is running in multiprocess mode. When multiprocess mode is enabled, we always see a tab crash, which is #21766 (moved). Also, if the pref extensions.torbutton.launch_warning is set to false, neither this bug nor #21766 (moved) occur.

I wanted to mention our experience in case someone is seeing different behavior.

Replying to mcs:

Kathy and I can not reproduce this bug when Tor Browser is running in multiprocess mode. When multiprocess mode is enabled, we always see a tab crash, which is #21766 (moved). Also, if the pref extensions.torbutton.launch_warning is set to false, neither this bug nor #21766 (moved) occur.

I wanted to mention our experience in case someone is seeing different behavior.

No, this ticket got filed before we had e10s enabled in Tor Browser. And I only see the bug once I have e10s off.

Trac:
Summary: Downloading of binary files stalls at 0/0 bytes in Tor Browser based on ESR52 to Downloading of binary files stalls at 0/0 bytes in Tor Browser based on ESR52 with e10s off

Moving more tickets on our May 2015 radar.

Trac:
Keywords: N/A deleted, TorBrowserTeam201705 added

Replying to mcs:

Replying to gk:

After looking a bit closer at it I think this is highly related to #21766 (moved). mcs/brade: would it be helpful to deal with that bug by looking closer at this issue? We will look at this one at the same time as #21766 (moved).

Or do you feel you have a solution for #21766 (moved)? If so you could test whether my assumption is right and this bug gets fixed with it, too. We do not have a solution yet but are planning to work on that bug tomorrow.

mcs/brade: This bug is not related to #21766 (moved) it seems. I'll put it back on my plate, feel free to focus (again) on #21766 (moved). I think I can figure our what is going wrong here tomorrow.

Trac:
Keywords: N/A deleted, GeorgKoppen201705 added

Trac:
Owner: mcs to gk

Replying to gk:

mcs/brade: This bug is not related to #21766 (moved) it seems. I'll put it back on my plate, feel free to focus (again) on #21766 (moved). I think I can figure our what is going wrong here tomorrow.

That's fine. Kathy and I will be interested to see what you have learned. We just came up with a patch that seems to fix this ticket but not #21766 (moved). I will post it as an attachment for reference, although you may have a different fix in mind.

Trac:
tor-21886.patch

a possible fix (work in progress)

Update: Kathy and I have a patch that fixes both this ticket and #21766 (moved), at least on OSX. I am going to test it on Linux before I post it here. We will also need to test it on Windows, although I will probably wait for a new nightly build.

Unfortunately, the patch does not seem to fix either problem on Linux, at least not without introducing other problems :( Here it is in case someone else wants to take a look: https://gitweb.torproject.org/user/brade/tor-browser.git/commit/?h=bug21766-01&id=e8ed33bbb5ad632acc173ab5be3880fc08eab681

FWIW: modal dialogs are forbidden in e10s. And what's happened with https://dxr.mozilla.org/mozilla-esr52/source/uriloader/exthandler/nsExternalHelperAppService.cpp#753?