WebGUI doesn't work with snap sandboxing

[Axel-Naumann]

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Description

Hi,

starting the webgui (new TBrowser) opens a chromium window which complains:

Your file couldn’t be accessed
It may have been moved, edited, or deleted.
ERR_FILE_NOT_FOUND

I guess this corresponds to the following process:

axel       17508    3604  4 15:51 pts/0    00:00:01     /snap/chromium/2950/usr/lib/chromium-browser/chrome --password-store --disable-features=TFLiteLanguageDetectionEnabled --window-size=1200,700 --new-window --app=file:///tmp/root_start_t9pNYd.html

Note that this is a snap package; the browser might not be allowed to access files in /tmp as per https://forum.snapcraft.io/t/can-browsers-open-local-files/3016

(I can work around this, but I thought it'd still be worthwhile to report this.)

Cheers, Axel

Reproducer

new TBrowser with web gui.

ROOT version

master

Installation method

source

Operating system

Ubuntu 24.04

Additional context

No response

[linev]

Hi Axel,

Can you try to add --allow-file-access-from-files to the command line? It can be done with the following entry in .rootrc file:

WebGui.ChromeInteractive: $prog $geometry --new-window  --allow-file-access-from-files --app='$url'  &

[ferdymercury]

WebGui.ChromeInteractive: $prog $geometry --new-window --allow-file-access-from-files --app='$url' &

@linev I confirm that this solves the issue.

Question: should this be documented? Or should we just close this issue as Won't fix, considering that it's not a safe flag? See https://stackoverflow.com/a/33801287/7471760

I think a better solution would be to allow to define a Variable in the .rootrc file, something like WebGui.TempFolder, which is /tmp by default, but can be modified to /home/user/mytmp so that it works fine with snap sandboxing.

[linev]

That is value for you in WebGui.Chrome in etc/system.rootrc file? I already implement workaround for snap chromium - if its name "/snap/bin/chromium".

See https://github.com/root-project/root/pull/18311

Probably another name variants can be tested.

And you always can redefine shell variable TMPDIR before running ROOT.

[ferdymercury]

hat is value for you in WebGui.Chrome in etc/system.rootrc file?

It's empty.

Chromium is not my default browser. What I do is the following:

root --web=on
gROOT->SetWebDisplay("chromium-browser");
new TBrowser

This starts the following process: /snap/chromium/3218/usr/lib/chromium-browser/chrome --password-store --gtk-version=3 --disable-features=TFLiteLanguageDetectionEnabled file:///tmp/root_start_zTlQy9.html

/usr/bin/chromium-browser is a shell script that starts /snap/bin/chromium with different flags depending on the desktop.

Probably another name variants can be tested. Hmm, I am not sure if this makes sense, since /usr/bin/chromium-browser could point to an APT installation that is not in snap.

And you always can redefine shell variable TMPDIR before running ROOT.

I confirm that this works, thanks for pointing. Could this trick be documented here: https://root.cern/doc/master/group__webdisplay.html?

[linev]

Try to run root --web=chrome -e 'new TBrowser'.

Current ROOT master should test snap chromium and will activate workaround.

[ferdymercury]

This works:

Try to run root --web=chrome -e 'new TBrowser'.

/snap/chromium/3218/usr/lib/chromium-browser/chrome --password-store --gtk-version=3 --disable-features=TFLiteLanguageDetectionEnabled --window-size=1200,700 --new-window --app=file:///home/user/root_start_Us0Yl8.html

This fails:

Try to run root --web=chromium-browser -e 'new TBrowser'.

/snap/chromium/3218/usr/lib/chromium-browser/chrome --password-store --gtk-version=3 --disable-features=TFLiteLanguageDetectionEnabled file:///tmp/root_start_AhgOb2.html

[linev]

So workaround works correctly when --web=chrome is set. In my mind, https://github.com/root-project/root/pull/18311 fixes the problem. And one can add few words about TMPDIR in documentation for RWebWindowsManager::ShowWindow method

[linev]

Fixed by #18311

[ferdymercury]

So workaround works correctly when --web=chrome is set.

Thanks. Do you know why it fails if --web=chromium-browser, even if it still understands that I want to use the chromium-browser and starts it?

[linev]

If fails with chromium-browser while it is not detected as snap version of chrome and therefore workaround is not applied.