Hi,

The problem is the following: Chrome calls xdg-open, which calls kde-open5, which uses KIO::OpenUrlJob internally. That uses QUrl everywhere to parse and store urls. The problem is that QUrl internally sanitizes the hostname part of the url (anything between the slack:// and the next /) and thereby converts it to lowercase. Whether that behavior makes sense can probably debated a lot, but it makes some kind of sense when thinking about the hostname in terms of a DNS name.

Firefox does not use xdg-open for this and instead implements the opening itself, which is why it works fine there.

I can think of three approaches to address this problem:
1. QUrl is changed to preserve uppercase letters in the hostname. Should be technically doable, but my gut feeling tells me such a change would not be accepted by the QUrl maintainers since the behavior makes some kind of sense. Also it would take quite a while for the fix to arrive at end users
2. Rewrite OpenUrlJob to not use QUrl for this. This would require touching a lot of code, including public API, and be quite complex, so I'd really like to avoid that
3. Slack is changed to not use uppercase letters in the hostname part of the URL or compares the received URL case-insensitively. This is IMHO the most pragmatic and straight-forward solution, and there might be other systems that behave like KDE does. However it's out of my control so I can't judge how feasible it is

I agree with Nicolas (amazing investigation, BTW!). Slack itself should be fixed here. If not, trying a Qt fix would be the better option that changing openUrlJob and everything that uses it.

(In reply to Nate Graham from comment #2)
> I agree with Nicolas (amazing investigation, BTW!). Slack itself should be
> fixed here. If not, trying a Qt fix would be the better option that changing
> openUrlJob and everything that uses it.

Here is a work-around. Drop it in /usr/local/bin/xdg-open so it gets opened first. You will need to make it executable.

    #!/bin/bash

    # Wrapper for xdg-open which fixes auth for Slack URLs
    #
    if [[ "${1:-}" =~ ^slack:// ]]; then
      exec /usr/lib/slack/slack "$@";
    fi
    exec /usr/bin/xdg-open "$@";

Since the favourite solution involves a change in Slack, has the company of Slack been notified of this issue?

I've submitted "Support request #4634800" to slack for this.

Is there any update on the submitted support request? It seems I still have this problem.

A simple experiment demonstrates how xdg-open works:

[code]
$ xdg-mime query default x-scheme-handler/mock
mock.desktop
$ cat .local/share/applications/mock.desktop
[Desktop Entry]
Name=Mock URI Handler
Exec=echo %u >> ~/mockfile
Type=Application
MimeType=x-scheme-handler/mock
$ xdg-open mock://SLACKISBUGGY
$ xdg-open mock:/SLACKISBUGGY
$ xdg-open mock:SLACKISBUGGY
$ cat mockfile
mock://slackisbuggy
mock:/SLACKISBUGGY
mock:SLACKISBUGGY
[/code]

RFC 3986 defines whats between "//" and "/" as an authority (*The host subcomponent is case-insensitive. The presence of a host subcomponent within a URI does not imply that the scheme requires access to the given host on the Internet.* and *Although host is case-insensitive, producers and normalizers should use lowercase for registered names and hexadecimal addresses for the sake of uniformity, while only using uppercase letters for percent-encodings.*).

As such, Slack, as a consumer of an URI needs to handle the host part of the authority component case-insensitive. Or opt into other URI forms that don't rely on authority component e.g. "slack:" or "slack:/".

Also, notice the verbiage used (normalizers SHOULD use lowercase). If QUrl did not lowercase hostnames, that wouldn't make QUrl less conformant to the RFC as the final consumer should be guaranteeing that.

TLDR; Slack is clearly non-complaint to URI RFC, QUrl doesn't need to be so strict and is it even necessary to rely on QUrl to figure out the scheme handler?