[Bug] ".txt" is added at the end of the filename downloaded by Brave Android

[AnthillSudoku]

Describe the bug
".txt" is added at the end of the filename when downloading some files with Brave Android (at the receiving end).
This happens only with some filename's extensions or no extension at all.

Here few extensions I tested:

affected extensions:
.kdbx / .backup / no extension

non affected extension:
.jpg / .pdf / .webm / .txt

To Reproduce
Steps to reproduce the behavior:

1. Go to pairdrop.net
2. Send a .kdbx file to the android device with Brave (or one of the affected)
3. download the file with Brave
4. open the file manager and check the extension

Expected behavior
filename is unchanged

Desktop (please complete the following information):

• OS: debian 12
• Browser Firefox
• Version 128.5.0esr

Smartphone (please complete the following information):

• Device: samsung a52q
• OS: eOS (LineageOS)
• Browser Brave
• Version 1.73.97

Bug occurs on official PairDrop instance https://pairdrop.net/
Yes
Version: v1.10.10

[schlagmichdoch]

Thanks for the bug report.

Seemingly, this is done by the browser, maybe as a convenience feature to prevent people from downloading "broken" files?

The appending of ".txt" when there is no extension present is also done by Desktop Chromium 129.
I have no idea whether I can prevent the browser from adding a extension and will look into it.

Apart from that, PairDrop wrongly uses the complete name as the file extension when showing the ReceiveDialogs.
These lines need to check if there is a point at all like:

        const fileNameSplit = fileName.split('.');
        const fileExtension = fileNameSplit.length > 1
            ? '.' + fileNameSplit[fileNameSplit.length - 1]
            : '';

[schlagmichdoch]

I have no idea whether I can prevent the browser from adding a extension and will look into it.

Apparently, adding the mime type application/octet-stream to files that lack a mime type does the trick. Otherwise chromium seemingly assumes that the file is a text file and adds a ".txt" automatically.

Feel free to test whether it works as expected on this instance: https://pairdrop-dev.onrender.com