A simple redirect manager

main.go

package main

import (
	"fmt"
	"io/ioutil"
	"log"
	"net/http"
	"strings"

	"github.com/alecthomas/template"
	"github.com/pkg/errors"
)

// Redirects is a map backed up by a file
type Redirects map[string]string

func (r Redirects) Read() error {
	file, err := ioutil.ReadFile("redirects.txt")
	if err != nil {
		return errors.Wrapf(err, "redirects read")
	}

	lines := strings.Split(string(file), "\n")
	for _, line := range lines {
		if line == "" {
			continue
		}
		parts := strings.Split(line, " ")
		if len(parts) != 2 {
			return fmt.Errorf("redirects read: couldn't parse line '%s'", line)
		}

		r[parts[0]] = parts[1]
	}

	return nil
}

func (r Redirects) Write() error {
	out := ""
	for key, value := range r {
		out = out + key + " " + value + "\n"
	}

	err := ioutil.WriteFile("redirects.txt", []byte(out), 0644)
	if err != nil {
		return errors.Wrapf(err, "redirects write")
	}

	return nil
}

func main() {
	redirs := Redirects{}
	err := redirs.Read()
	if err != nil {
		err = redirs.Write()
		if err != nil {
			panic(err.Error())
		}
	}

	form := `<h1>Add redirects</h1>
		<form method="post">
		<input type="submit">
		<table>
		<tr><th>From</th><th>To</th></tr>
		<tr><td><input type="text" name="key" value=""></td><td><input type="text" name="value" value=""></td></tr>
		{{ range $key, $value := . }}
		<tr><td><input type="text" name="key" value="{{ $key }}"></td><td><input type="text" name="value" value="{{ $value }}"></td></tr>
		{{ end }}
		</table>
		</form>
		`

	t, err := template.New("form").Parse(form)
	if err != nil {
		panic(err.Error())
	}

	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		if redir, ok := redirs[r.URL.Path]; ok {
			http.Redirect(w, r, redir, 301)
			return
		}
		http.NotFound(w, r)
	})

	http.HandleFunc("/redirect", func(w http.ResponseWriter, r *http.Request) {
		r.ParseForm()
		if keys, ok := r.Form["key"]; ok {
			if values, ok := r.Form["value"]; ok {
				for i := range keys {
					if keys[i] == "" || values[i] == "" {
						continue
					}
					redirs[keys[i]] = values[i]
				}

				err := redirs.Write()
				if err != nil {
					log.Printf("%+v", err)
				}
			}
		}

		t.Execute(w, redirs)

	})

	http.ListenAndServe(":8080", nil)
}