Package verbs provides a simple method to filter request method with the net/http ServeMux

verbs.go

// Copyright 2015 Guillermo Alvarez. All rights reserved.
// Use of this source code is governed by standard BSD license.

/*
Package verbs provides a simple method to filter request method with the net/http ServeMux

	func createUser(w http.ResponseWriter, r *http.Request) {
		...
	}
	mux := http.NewServeMux()
	mux.Handle("/users", Verbs{Post: createUser})
	
*/
package verbs

import "net/http"

type Verbs struct {
	Get    http.HandlerFunc
	Post   http.HandlerFunc
	Put    http.HandlerFunc
	Delete http.HandlerFunc
	Patch  http.HandlerFunc
	Head   http.HandlerFunc
}

func (v Verbs) ServeHTTP(w http.ResponseWriter, r *http.Request) {

	switch r.Method {
	case "GET":
		if v.Get != nil {
			v.Get(w, r)
			return
		}
	case "POST":
		if v.Post != nil {
			v.Post(w, r)
			return
		}
	case "PUT":
		if v.Put != nil {
			v.Put(w, r)
			return
		}
	case "DELETE":
		if v.Delete != nil {
			v.Delete(w, r)
			return
		}
	case "PATCH":
		if v.Patch != nil {
			v.Patch(w, r)
			return
		}
	case "HEAD":
		if v.Head != nil {
			v.Head(w, r)
			return
		}
	}

	http.Error(w, http.StatusText(http.StatusMethodNotAllowed), http.StatusMethodNotAllowed)
}

The origin server MUST generate an
Allow header field in a 405 response containing a list of the target
resource's currently supported methods.
— Source: https://tools.ietf.org/html/rfc7231#section-6.5.5

So the last line should actually read something like:

var allow []string
if v.Get != nil {
	allow = append(allow, "GET")
}
if v.Post != nil {
	allow = append(allow, "POST")
}
if v.Put != nil {
	allow = append(allow, "PUT")
}
if v.Delete != nil {
	allow = append(allow, "DELETE")
}
if v.Patch != nil {
	allow = append(allow, "PATCH")
}
if v.Head != nil {
	allow = append(allow, "HEAD")
}
w.Header().Set("Allow", strings.Join(allow, ",")) // technically could also w.Header()["Allow"] = allow, more verbose on the wire though
w.WriteHeader(http.StatusMethodNotAllowed) // or use http.Error here

(ouch! much less readable)