1385720 - When downloading more than 6 files at the same time causes the downloads greater than 5 or 6 not to download or be displayed in the download panel

Status: NEW

(Firefox :: Downloads Panel, defect, P3)

Description

[Robert Strong (they/them - no direct email)]

While working on the oak branch I needed to download the installers and mar files for all of the builds. After doing so I noticed that I was missing some files. I needed to do this again the next day and I noticed it again.

Note: I'm not certain whether the number of simultaneous downloads is 5 or 6 so when you try to reproduce start with a number greater than 6

Comment 1

[:Paolo Amadini]

Hi Brindusa, can you help with verifying the steps to reproduce for this bug? I don't see how this could happen with the current front-end architecture, but may be a back-end issue.

Robert, if you have any details that can help QA, like add-ons installed and so on, feel free to add them to the bug.

Comment 2

[Hani Yacoub, Desktop QA]

Hi,
So I tried to do 8 simultaneous downloads, and I noticed that only 5 downloads are displayed in the download panel, but in download library I can see the rest of the downloads are correctly displayed.

I'm not sure if all the downloads should be displayed in the download panel or not, but I can confirm that the rest of the downloads that were not displayed in download panel, are displayed in library and were correctly downloaded.

please see the screenshots attached and let me know your thoughts.
Thanks

Comment 3

[Hani Yacoub, Desktop QA]

Attachment: during downlaod.png

Comment 4

[Hani Yacoub, Desktop QA]

Attachment: library downlaods.png

Comment 5

[Robert Strong (they/them - no direct email)]

On Windows launch Nightly Firefox with a new profile
Open Tools -> Options and scroll down to Downloads.
Change to "Always ask you where to save files"
Open https://archive.mozilla.org/pub/firefox/nightly/latest-mozilla-central/
Using the context menu and "Save Link As" download files that will take awhile to download. I went with files that were around 50 MB and larger.
For the first file I selected c:\moz\_download_check as the location to save the file and all of the remaining files will default to that same directory.
List of files that I tried to download:
firefox-56.0a1.en-US.linux-i686.common.tests.zip
firefox-56.0a1.en-US.linux-i686.complete.mar
firefox-56.0a1.en-US.linux-i686.crashreporter-symbols.zip
firefox-56.0a1.en-US.linux-i686.mochitest.tests.zip
firefox-56.0a1.en-US.linux-i686.reftest.tests.zip
firefox-56.0a1.en-US.linux-i686.tar.bz2
firefox-56.0a1.en-US.linux-i686.web-platform.tests.tar.gz
firefox-56.0a1.en-US.linux-x86_64.common.tests.zip
firefox-56.0a1.en-US.linux-x86_64.complete.mar
firefox-56.0a1.en-US.linux-x86_64.crashreporter-symbols.zip

Only the first 6 links for the files listed above changed color to denote that they have been visited (see screenshot 1)
After the first 6 it took several seconds for the UI to be displayed.
If I recall correctly there is a 6 simultaneous download limit and I recall it queuing the downloads in the distant past.
Only the first 6 files were downloaded to c:\moz\_download_check (see screenshot 2)

Comment 6

[Robert Strong (they/them - no direct email)]

Attachment: Screenshot 1

Comment 7

[Robert Strong (they/them - no direct email)]

Attachment: Scr5eenshot 2

Comment 8

[Robert Strong (they/them - no direct email)]

In case it is Windows version specific I am using Windows 10 with the Creators update

Comment 9

[Robert Strong (they/them - no direct email)]

Note: "Using the context menu and "Save Link As" download files" was used to start each download. I have no idea if it affects other ways to download files but this and the steps I listed definitely reproduce it for me consistently.

Comment 10

[:Paolo Amadini]

I suspect either Firefox or the operating system is limiting the number of network connections we can do from the same domain. Maybe this causes the later downloads to time out after a while.

We don't have a queuing feature to handle this case, and I'm not sure we'd like to implement one into Firefox, given the added complexity and the fact that telemetry shows that only a very small percentage of sessions have more than three simultaneous downloads in the general user population.

Although some major download managers will stop working with Firefox 57, I believe it would be possible to implement some form of queuing using the WebExtensions API for downloads, so this is still something that could be implemented by an add-on.

Comment 11

[Robert Strong (they/them - no direct email)]

From what I recall from many years ago that the downloads would queue... if I am recalling correctly I remember seeing it in one of the old Firefox download UI's. I also recall that there was a limit of 6 simultaneous downloads via Firefox. Found the pref
https://support.mozilla.org/en-US/questions/992338

At the very least this should display information to the client that the downloads aren't going to happen. For anyone that does this every few years it is extremely off putting and confusing not to see the files that Firefox presented UI to download.

It also seems from comment #2 that this works when using different steps and I wouldn't be surprised if it were just the save link as case that is broken since I recall this working many years ago.

Comment 12

[:Paolo Amadini]

This confirms network is not starting the connection, and is internally still waiting for the other downloads to complete. We should likely investigate which code paths are affected by lowering "network.http.max-persistent-connections-per-server", and ensure we display a sensible user interface in various cases.

Comment 13

[Robert Strong (they/them - no direct email)]

I just verified that this did work with Firefox 4 so adding regression keyword

Comment 14

[Robert Strong (they/them - no direct email)]

Attachment: Firefox 4 screenshot

Using the same steps this shows the downloads being queued.

Comment 15

[Robert Strong (they/them - no direct email)]

Attachment: Firefox 4 screenshot

Using the same steps this shows the queued downloads being downloaded.