Routing Group like interface not exposed in router

[someone1]

A Routing Group like interface from the dimfeld/httptreemux package used for kami's router is not exposed on the kami.Mux object. This would simplify larger projects when building URLs.

For example, if I wanted to setup my application with multiple API versions, I could have my code split between server/endpoint logic as follows:

package server - > holds a simple main.go that imports packages from various API imports, sets up a user auth middleware on the context
package api/foo/v1 -> has a LoadRoutes(ctx context.Context, prefix *kami.Mux) function that adds its own group of routes building on the prefix supplied by the prefix router passed in. (e.g. if the group router that was passed in is for '/api/', this adds the group of routes for '/v1/' which when added to the group translates to '/api/v1')
package api/foo/v2 -> has a LoadRoutes(ctx context.Context, prefix *kami.Mux) that is the same as v1 except adds the group of routes for v2

A quick (not thought out) example:
main.go:

package server

import (
    //...

    " api/foo/v1"
    " api/foo/v2"

    "github.com/guregu/kami"
)

func init() {
    // Setup Auth middleware and other things
    kami.Use('/', Login)
    // ... Other things...

    group := kami.NewGroup('/api')
    v1.LoadRoutes(kami.Context, group)
    v2.LoadRoutes(kami.Context, group)
}

api_v1.go:

package v1

import (
    //...
    "github.com/guregu/kami"
)

func LoadRoutes(ctx context.Context, prefix  *kami.Mux) {
    v1Prefix := prefix.NewGroup("/v1")
    v1Prefix.Context = ctx
    v1Prefix.Get('/list', ListHandler)
    // Other routes...
}

api_v2.go:

package v2

import (
    //...
    "github.com/guregu/kami"
)

func LoadRoutes(ctx context.Context, prefix  *kami.Mux) {
    v2Prefix := prefix.NewGroup("/v2")
    v2Prefix.Context = ctx
    v2Prefix.Get('/list', ListHandler)
    // Other routes...
}

I'm interested to hear thoughts on this and see whether or not this feature could be added to kami!

[guregu]

Hello, could you be more specific about how groups would work? Unfortunately we can't merge arbitrary contexts, so it might be impossible to implement.
I can make it easier to use different contexts. I think I will add a way to copy URL params from one context to another. Right now the lack of such a function makes it difficult to use middleware that completely replaces the context.

For routes like:

/api/v1/...
/api/v2/...

You don't really need groups to separate them. You can add common middleware with kami.Use("/api/", mw). Then you can add v1 middleware like kami.Use("/api/v1/", mw) and v2 middleware like kami.Use("/api/v2/", mw). You can add multiple middleware functions to the same route.

I'll also get #21 taken care of so it's easier to run kami from a kami.Mux.