Support more schemes and other commands

[rusty-snake]

# schemeapps.conf
# ===============
#
# This file contains a mapping of schemes to command-line for fireurl::open.
#
# Format
# ------
#
# * Leading and trailing whitespace characters are ignored.
# * Empty lines are ignored.
# * Lines starting with a "#" are comments (and ignored).
# * Everything else is expected to be an mapping of an scheme to a command line
#   in the form of `<scheme>: <command-line>`.
# * The command-line can contain a "%u" that will be substituted with the uri.
#   If the "%u" is missing it is implicitly added at the end.
# * The command-line is split at every whitespace character.
#   No quoting. No escaping.
# * If there is more than one mapping for a scheme the behavior is undefined.
# * If there is more than one "%u" in the command-line the behavior is undefined.
# * The format may change in the future.

http: firefox
https: firefox %u

[rusty-snake]

for line in schemeapps_conf {
    let line = line.trim();
    if line.is_empty() || line.starts_with('#') {
        continue;
    }
    
    let (scheme, cmd) = if let Some(scheme_cmd) = line.split_once(':') {
        scheme_cmd
    } else {
        eprintln!("ERROR: Invalid line in schemeapps.conf: {line}");
        continue;
    };
    let mut cmd = cmd.split_whitespace()
        ...
}

[topimiettinen]

How about using a regexp or fnmatch patterns and also explicit allow/deny:

allow http:https://*.example.com/* firefox %u
deny *

For more flexibility (for example, if client authentication is considered in the future), the syntax could be

allow url=https://*.example.com/* cmd='firefox %u' client='mutt'
allow url=https:* client='firefox*'
deny url=http:*
# default deny
deny

[rusty-snake]

• regexp/fnmatch/glob: Require some dependencies. If we to integrate fireurl into firejail's build system this is much more complicated (ATM it would be two calls to rustc). However if everything we need is a zero/one-or-more placeholder this can be implemented easily in fireurl.
• Restricts for specific clients make sense. But global restrictions do not seem very useful to me.
• One file for everything? Maybe it would be easier/better to have one file mapping schemes to commands and one defining policies.