A simple WebMod:

using web
using webmod
using wisp
using concurrent

class Webby {
    static Void main() {
        WispService() {
            it.port = 8080
            it.root = HelloMod()
        }.start
        Actor.sleep(Duration.maxVal)
    }
}

const class HelloMod : WebMod {
    override Void onGet() {
        res.headers["Content-Type"] = "text/plain; charset=utf-8"
        res.out.print("modBase=`${req.modBase}`   modRel=`${req.modRel}`")
    }
}

When pointed at http://localhost:8080/index, returns:

modBase=`/`   modRel=`/index`'

But when I use a RouteMod:

static Void main() {
    WispService() {
        it.port = 8080
        it.root = RouteMod() { routes = ["wotever": HelloMod()] }
    }.start
    Actor.sleep(Duration.maxVal)
}

And point at http://localhost:8080/wotever/index, the modRel looses its leading slash:

modBase=`/wotever/`   modRel=`index`

I know Brian explained that is how the Uri.getRange() method is supposed to work, but from an API consumer point of view, it doesn't feel right. For to write a WebMod that can be used anywhere (in a RouteMod or not), you have to have to cater for both scenarios.

(I think I touched upon this in this topic also.)

That is the really the special case when there is no base mod nor relative URI to such. So it actually seems correct to me have the modRel be absolute (because its not actually relative to anything). In general you use modBase to construct URIs to within your mod, and modRel to parse your internal URI structure. The leading slash shouldn't effect that does it?

use modBase to construct URIs to within your mod

Indeed. But what when you use modRel to construct your URIs? As in:

// with RouteMod  
uri := req.modBase + req.modRel  // --> /wotever/index

// without RouteMod
uri := req.modBase + req.modRel  // --> //index

Which, at best, leads to ugly URIs (and may causes errors at worst). Okay, I know I can re-code as:

uri := (req.modBase == `/`) ? req.modRel : req.modBase + req.modRel // --> /index

Or I could also use req.uri - But then I have to know not to use modRel in the above manner. It just seems needlessly error prone.

modRel to parse your internal URI structure. The leading slash shouldn't effect that does it?

Well, it means I have to be careful about what I'm comparing it with:

if (req.modRel == `/index` || req.modRel == `index`) ...

Again, I don't think the WebMod should have to code for both scenarios, for why should it care where it is in the module stack? If it really needs to know, well, it can check modBase!

isRootMod := (req.modBase == `/`)

I don't think the API should return different values dependent on the context of usage; for that either limits its re-use, or complicates the code.

// without RouteMod uri := req.modBase + req.modRel // --> //index

If the URIs were added together like that then it would be a bug. It should be handled by the URI class:

fansh> `/` + `/index`
/index

Well, it means I have to be careful about what I'm comparing it with: if (req.modRel == /index || req.modRel == index) ...

I think the proper way to handle that is like this:

req.modRel.path.first == "index"

It just doesn't seem like something we should make a special case considering how Uri getRange works.