Routing with Go on Google Cloud Functions

Couple of days ago Google cloud functions got official support for go 1.11. I got interested in how to handle routing in cloud functions in go, so after couple of experiments I came up with a solution based on http.ServeMux.

To get started with cloud functions you can follow this simple tutorial.

One of many neat things about cloud functions is that they can be built from existing Github repository. You simply have to define Google source repository that mirrors one on Github and use this repository as the source repository for your newly defined cloud function.

It feels like go code you upload to cloud function gets loaded by some generated code as a dependency.

Ultimately we can simply define our own router using NewServeMux like this:

package function

import (
	"net/http"
)

var mux = newMux()

//F represents cloud function entry point
func F(w http.ResponseWriter, r *http.Request) {
	mux.ServeHTTP(w, r)
}

func newMux() *http.ServeMux {
	mux := http.NewServeMux()
	mux.HandleFunc("/one", one)
	mux.HandleFunc("/two", two)
	mux.HandleFunc("/subroute/three", three)

	return mux
}

func one(w http.ResponseWriter, r *http.Request) {
	w.Write([]byte("hello from one"))
}

func two(w http.ResponseWriter, r *http.Request) {
	w.Write([]byte("hello from two"))
}

func three(w http.ResponseWriter, r *http.Request) {
	w.Write([]byte("hello from three"))
}

Now you can access your handlers by appending /one, /two or /subroute/three to URL that cloud functions will have in triggers section of the UI like this: https://us-central1-my-test-project-123456.cloudfunctions.net/my-function-1/one.

This works because your cloud function receives request with prefix stripped away from the URL. This is very handy since allows one to port existing http server in to cloud function without changing it too much.

I hope this helps, and happy hacking on cloud functions with go!

Example code can be found here.