super simple url shortener #golang

main.go

package main

import (
	"context"
	"encoding/json"
	"fmt"
	"io"
	"log"
	"net/http"
	"os"
	"strings"
	"time"

	"github.com/go-redis/redis/v8"
	"github.com/gorilla/mux"
	"github.com/patrickmn/go-cache"
)

var cash *cache.Cache
var rdb *redis.Client
var ctx = context.Background()

type addResult struct {
	ID  string `json:"id"`
	URL string `json:"url"`
}

func getEnv(key, fallback string) string {
	if value, ok := os.LookupEnv(key); ok {
		return value
	}
	return fallback
}

func getURL(key string) (string, error) {
	if x, found := cash.Get(key); found {
		return x.(string), nil
	}

	url, err := rdb.HGet(ctx, "links", key).Result()

	if err != nil {
		return "", err
	}

	cash.Set(key, url, cache.DefaultExpiration)

	return url, nil
}

func authHandler(next http.Handler) http.HandlerFunc {
	key := os.Getenv("API_TOKEN")

	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		auth := strings.SplitN(r.Header.Get("Authorization"), " ", 2)

		if len(auth) != 2 || auth[0] != "Bearer" || auth[1] != key {
			http.Error(w, "authorization failed", http.StatusUnauthorized)
			return
		}

		next.ServeHTTP(w, r)
	})
}

func addHandler(w http.ResponseWriter, r *http.Request) {
	if err := r.ParseForm(); err != nil {
		log.Fatal(err)
		fmt.Fprintf(w, "error parsing response: %v", err)
		return
	}

	id := r.FormValue("id")
	url := r.FormValue("url")

	if len(url) == 0 || len(id) == 0 {
		http.Error(w, "you must specifly a url and an id", http.StatusBadRequest)
		return
	}

	if err := rdb.HSet(ctx, "links", []string{id, url}).Err(); err != nil {
		log.Fatal(err)
		http.Error(w, "error adding link", http.StatusBadRequest)
		return
	}

	cash.Delete(id)

	w.Header().Set("Content-Type", "application/json")
	result, _ := json.Marshal(addResult{id, url})
	io.WriteString(w, string(result))
}

func rootHandler(w http.ResponseWriter, r *http.Request) {
	http.Redirect(w, r, getEnv("ROOT_REDIRECT", "https://dmt.sh"), 302)
}

func redirectHandler(w http.ResponseWriter, r *http.Request) {
	vars := mux.Vars(r)
	url, err := getURL(vars["id"])

	if err == nil && len(url) > 0 {
		http.Redirect(w, r, url, 302)
		return
	}

	http.Error(w, "not found", http.StatusNotFound)
}

func main() {
	rdb = redis.NewClient(&redis.Options{
		Addr:     getEnv("REDIS_HOST", "localhost:6379"),
		Password: getEnv("REDIS_PASSWORD", ""),
		DB:       0,
	})

	cash = cache.New(5*time.Minute, 10*time.Minute)

	r := mux.NewRouter()
	r.HandleFunc("/", authHandler(http.HandlerFunc(addHandler))).Methods("POST")
	r.HandleFunc("/{id}", redirectHandler).Methods("GET")
	r.HandleFunc("/", rootHandler).Methods("GET")

	http.Handle("/", r)
	http.ListenAndServe(":8000", nil)
}