Go API versioning

main.go

package main

import (
        "fmt"
        "net/http"

        "github.com/gorilla/mux"
)

// AnotherHandlerLatest is the newest version of AnotherHandler
func AnotherHandlerLatest(w http.ResponseWriter, r *http.Request) {
        fmt.Fprintf(w, "hello from AnotherHandlerLatest.")
}

// ExampleHandlerLatest is the newest version of ExampleHandler
func ExampleHandlerLatest(w http.ResponseWriter, r *http.Request) {
        fmt.Fprintf(w, "hello from ExampleHandlerLatest.")
}

// ExampleHandlerV1 is a v1-compatible version of ExampleHandler
func ExampleHandlerV1(w http.ResponseWriter, r *http.Request) {
        fmt.Fprintf(w, "Hello from ExampleHandlerv1.")
}

// AddV1Routes takes a router or subrouter and adds all the v1
// routes to it
func AddV1Routes(r *mux.Router) {
        r.HandleFunc("/example", ExampleHandlerV1)
        AddRoutes(r)
}

// AddV2Routes takes a router or subrouter and adds all the v2
// routes to it, note that these should probably match
// AddRoutes(r *muxRouter) alternatively you can do
// var AddV2Routes = AddRoutes
func AddV2Routes(r *mux.Router) {
        AddRoutes(r)
}

// AddRoutes takes a router or subrouter and adds all the latest
// routes to it
func AddRoutes(r *mux.Router) {
        r.HandleFunc("/example", ExampleHandlerLatest)
        r.HandleFunc("/example2", AnotherHandlerLatest)
}

func main() {
        router := mux.NewRouter()

        // latest
        AddRoutes(router)

        // v1
        AddV1Routes(router.PathPrefix("/v1").Subrouter())

        // v2
        AddV2Routes(router.PathPrefix("/v2").Subrouter())
}