Super simple URL unshortener in Go

unshortener.go

// Package unshortener takes a single parameter (url) and sends back an unshortened version.
//
// This version is in vanilla go, and requires no packages to be installed.
package main

import (
	"encoding/json"
	"io"
	"log"
	"net/http"
	"net/url"
)

// Handler function looks for a "url" query parameter in the request, and uses
// it to make a request and ultimately resolve an unshortened URL.
func Handler(w http.ResponseWriter, r *http.Request) {
	vals, err := url.ParseQuery(r.URL.RawQuery)

	if err != nil {
		http.Error(w, "No query parameters.", 400)
		return
	}

	// Get the short URL from the query parameters.
	urlParam := vals.Get("url")

	if urlParam == "" {
		http.Error(w, "No URL given.", 400)
		return
	}

	// Make a request with the URL
	res, err := http.Head(urlParam)

	if err != nil {
		http.Error(w, "Received error from external server.", 500)
		return
	}

	// Close the response body later.
	defer res.Body.Close()

	resolvedUrl := res.Request.URL.String()

	log.Printf("Unshortened %q to %q", urlParam, resolvedUrl)

	// Build a response containing the original and resolved URLs.
	reponse, err := json.Marshal(map[string]string{"original": urlParam, "resolved": resolvedUrl})

	if err != nil {
		http.Error(w, "Unable to marshal response.", 500)
	}

	// Set the response header and respond with JSON.
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	io.WriteString(w, string(reponse))
}

func main() {
	http.HandleFunc("/", Handler)

	log.Printf("Server listening...")
	log.Fatal(http.ListenAndServe("localhost:8080", nil))
}

Extremely crude, but does the job. I wanted to compare it to a similar utility I wrote in Node.js today. Example use (the url parameter is http://youtu.be/JPBRbIvs5lc encoded):

GET localhost:8080?url=http%3A%2F%2Fyoutu.be%2FJPBRbIvs5lc

which responds with

{
    "original": "http://youtu.be/JPBRbIvs5lc",
    "resolved": "http://www.youtube.com/watch?v=JPBRbIvs5lc&feature=youtu.be"
}