Fix POSTUN scriptlet on RPM upgrade and uninstall

[rosahaj]

As mentioned in httptoolkit/httptoolkit-website#85 (comment), upgrading or uninstalling the HttpToolkit RPM package produces the same messages as in this issue: IsmaelMartinez/teams-for-linux#958.

I was curious how other projects addressed this problem and stumbled upon pulsar-edit/pulsar@a47da8e. I combined Pulsar's upgrade check with the POSTUN scriptlet produced by electron-builder to create a custom post-uninstall script for RPM packages.

I tested the fix on Fedora 40 by

1. building two RPM packages with increasing version numbers
2. installing the package with the lower version number, then upgrading to the package with the higher version number
3. uninstalling the latter package

All of these actions succeeded without any issues. Upgrading does not remove the symlink from /usr/bin/httptoolkit to /opt/HTTP Toolkit/httptoolkit. Removing the package removes the /usr/bin/httptoolkit symlink as expected.

[rosahaj]

This check was copied from pulsar-edit/pulsar@a47da8e. I'm not sure how they came up with this solution, but it works.

[rosahaj]

I adopted the POSTUN script created by electron-builder (as verified by recreating the SPEC file):

#!/bin/bash

# Delete the link to the binary
if type update-alternatives >/dev/null 2>&1; then
    update-alternatives --remove 'httptoolkit' '/usr/bin/httptoolkit'
else
    rm -f '/usr/bin/httptoolkit'
fi

[rosahaj]

As explained here, the second argument to update-alternatives --remove should be /opt/HTTP Toolkit/toolkit, not /usr/bin/toolkit.

[rosahaj]

If update-alternatives is not installed, the /usr/bin/httptoolkit is removed directly. The %post script created by electron-builder does the same thing on installs and upgrades:

#!/bin/bash

if type update-alternatives 2>/dev/null >&1; then
    # Remove previous link if it doesn't use update-alternatives
    if [ -L '/usr/bin/httptoolkit' -a -e '/usr/bin/httptoolkit' -a "`readlink '/usr/bin/httptoolkit'`" != '/etc/alternatives/httptoolkit' ]; then
        rm -f '/usr/bin/httptoolkit'
    fi
    update-alternatives --install '/usr/bin/httptoolkit' 'httptoolkit' '/opt/HTTP Toolkit/httptoolkit' 100 || ln -sf '/opt/HTTP Toolkit/httptoolkit' '/usr/bin/httptoolkit'
else
    ln -sf '/opt/HTTP Toolkit/httptoolkit' '/usr/bin/httptoolkit'
fi

[pimterry]

Awesome work @rosahaj! Thanks for digging into this, great stuff.

I'll merge now. This won't be live immediately and I don't think it's urgent, but I'm planning to do a release next week so it'll be included there.

By the way, in case you're not aware, HTTP Toolkit Pro is totally free for all contributors. Is that something you'd be interested in? If so just let me know what email you'd like for your account - either here or by email at tim @ httptoolkit.com.