Add a basic Url rewrite modifier.

[favalos]

Wrote a very simple and basic Url Rewrite functionality.

With the test configuration I tested doing:

http://localhost:8080/rewrite/blog/

Hope this could be the beginning of a contribution to this project, any feedback or improvements please let me know.

Thanks!

[jamesmunns]

Hey there! I think this looks reasonable, from a quick first glance:

• It would be good to remove any unwraps, at least during the proxying stage (it's more okay at configuration/setup time as those will fire at startup). This isn't a hard blocker, but it'll help me out later when I go to cleanup the other existing unwrap/expects!
• It would be good to add this to the user manual, e.g. https://github.com/memorysafety/river/blob/main/user-manual/src/config/kdl.md#servicesnamepath-control

One perf note is that it might be faster to do the replace, then figure out if we replaced anything, instead of looking for the match and then replacing. The docs say:

If no match is found, then the haystack is returned unchanged. In that case, this implementation will likely return a Cow::Borrowed value such that no allocation is performed.

When a Cow::Borrowed is returned, the value returned is guaranteed to be equivalent to the haystack given.

That being said: I'm just guessing (and that's not a good basis for requesting a perf change!) that it'd be faster to do a replace and then check if the result is Borrowed or Owned, instead of doing a match and then conditionally a replace, so maybe just a comment that we could consider benchmarking this in the future would be fine.

Basically suggesting:

// instead of this:
if is_match() {
    replace()
}

// this
let res = replace()
if !res.is_borrowed() {
    // set the new URI here
}

[jamesmunns]

Made some nits, the one blocker is that I'd like to see the docs updated, then we can merge this!

[Szpadel]

My 2 cents about performance
Instead of

filter kind="url-rewrite" regex="^/rewrite/(.*)$" rewrite="/${1}"

Doing

filter kind="url-rewrite" regex="^/rewrite/" rewrite="/"

So removing capture group would switch replacen , with replace is wrapping, to fast path with significally better performance.
(I think that this could be documented)

if !res.is_borrowed() {
    // set the new URI here
}

I feel here more readable would be res.is_owned() instead. Or match if we want to avoid nightly only feature.