link/main.go

// A URL Shortener called Link.
// Copyright (C) 2021 i@fsh.ee
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.
package main

import (
	"crypto/md5"
	_ "embed"
	"errors"
	"flag"
	"fmt"
	"hash/maphash"
	"io/ioutil"
	"log"
	"net/http"
	"net/url"
	"os"
	"strconv"
	"strings"
	"time"

	"gorm.io/driver/sqlite"
	"gorm.io/gorm"
	"gorm.io/gorm/logger"
)

//go:embed index.html
var indexTemplate string

type DB struct {
	*gorm.DB
	log      *log.Logger
	hashSeed string
}

func NewDB(l *log.Logger, dbFilePath, hashSeed string) (DB, error) {
	_, err := os.Stat(dbFilePath)
	if os.IsNotExist(err) {
		err := ioutil.WriteFile(dbFilePath, []byte{}, 0600)
		if err != nil {
			return DB{}, err
		}
	}
	db, err := gorm.Open(sqlite.Open(dbFilePath), &gorm.Config{
		NowFunc: func() time.Time { return time.Now().UTC() },
		Logger:  logger.Default.LogMode(logger.Silent),
	})
	if err != nil {
		return DB{}, err
	}
	return DB{db, l, hashSeed}, db.AutoMigrate(&Link{})
}

type Link struct {
	gorm.Model
	Big  string
	Smol string `gorm:"unique"`
	Del  string `gorm:"unique"`
}

func (db DB) getHashShortLink(s fmt.Stringer) string {
	h := maphash.Hash{}
	h.WriteString(s.String())
	return strings.TrimSpace(strings.TrimLeft(fmt.Sprintf("%#x\n", h.Sum64()), "0x"))
}

func (db DB) getHashDeleteKey(s fmt.Stringer) string {
	return strings.TrimSpace(fmt.Sprintf("%x", md5.Sum([]byte(db.hashSeed+s.String()+strconv.FormatInt(time.Now().Unix(), 10)))))
}

func (db DB) NewLink(u *url.URL) (Link, error) {
	return db.NewLinkWithShortLink(u, db.getHashShortLink(u))
}

func (db DB) NewLinkWithShortLink(u *url.URL, hash string) (Link, error) {
	var (
		link = Link{Big: u.String(), Smol: hash, Del: db.getHashDeleteKey(u)}
		err  = db.Create(&link).Error
	)
	// TODO: If error due to unique issue should attempt to retry a few times.
	if err != nil {
		db.log.Println(err)
		return Link{}, err
	}
	return link, nil
}

func (db DB) GetLink(smol string) (l Link, e error) {
	res := db.Where(&Link{Smol: smol}).First(&l)
	return l, res.Error
}

func (db DB) DelLink(smol, del string) error {
	link, err := db.GetLink(smol)
	if err != nil {
		return err
	}
	res := db.Where(&Link{Del: del}).Delete(&link)
	if res.RowsAffected < 1 {
		return gorm.ErrRecordNotFound
	}
	return res.Error
}

type controller struct {
	log *log.Logger
	db  DB
	url string
}

func NewController(logger *log.Logger, db DB, url string) controller {
	return controller{logger, db, strings.TrimRight(url, "/")}
}

func (c controller) Err(rw http.ResponseWriter, r *http.Request, err error) {
	if errors.Is(err, gorm.ErrRecordNotFound) {
		rw.WriteHeader(http.StatusNotFound)
		rw.Write([]byte(err.Error()))
		return
	}
	c.log.Println(err)
	rw.WriteHeader(http.StatusInternalServerError)
	rw.Write([]byte(err.Error()))
}

func (c controller) ServeHTTP(rw http.ResponseWriter, r *http.Request) {
	switch r.Method {

	case http.MethodGet:
		switch strings.TrimRight(r.URL.Path, "/") {

		case "":
			rw.Header().Add("Content-Type", "text/html")
			rw.Write([]byte(fmt.Sprintf(indexTemplate, c.url, c.url, c.url)))
			return

		case "/favicon.ico":
			http.NotFound(rw, r)
			return

		default:
			link, err := c.db.GetLink(strings.TrimLeft(r.URL.Path, "/"))
			if err != nil {
				c.Err(rw, r, err)
				return
			}
			http.Redirect(rw, r, link.Big, http.StatusPermanentRedirect)
			return

		}

	case http.MethodPost:
		b, err := ioutil.ReadAll(r.Body)
		if err != nil {
			c.Err(rw, r, err)
			return
		}
		u, err := url.Parse(string(b))
		if err != nil {
			c.Err(rw, r, err)
			return
		}
		if u.Scheme != "http" && u.Scheme != "https" {
			rw.WriteHeader(http.StatusBadRequest)
			rw.Write([]byte("URL must contain scheme. E.G. missing `http://` or `https://`."))
			return
		}
		var (
			link Link
			h    = strings.Trim(r.URL.Path, "/")
		)
		if h != "" {
			link, err = c.db.NewLinkWithShortLink(u, h)

		} else {
			link, err = c.db.NewLink(u)
		}
		if err != nil {
			c.Err(rw, r, err)
			return
		}
		rw.Header().Set("X-Delete-With", link.Del)
		rw.WriteHeader(http.StatusFound)
		rw.Write([]byte(fmt.Sprintf("%s/%s", c.url, link.Smol)))
		return

	case http.MethodDelete:
		b, err := ioutil.ReadAll(r.Body)
		if err != nil {
			c.Err(rw, r, err)
			return
		}
		if len(b) < 1 {
			rw.WriteHeader(http.StatusBadRequest)
			rw.Write([]byte("Must include deletion key in DELETE body."))
			return
		}
		var (
			smol = strings.TrimSpace(strings.TrimLeft(r.URL.Path, "/"))
			del  = strings.TrimSpace(string(b))
		)
		if err := c.db.DelLink(smol, del); err != nil {
			c.Err(rw, r, err)
			return
		}
		rw.WriteHeader(http.StatusNoContent)
		return

	}

	http.NotFound(rw, r)
}

func main() {
	var (
		logPrefix         = "link: "
		startupLogger     = log.New(os.Stdout, logPrefix, 0)
		applicationLogger = log.New(ioutil.Discard, logPrefix, 0)
		v                 = flag.Bool("v", false, "verbose logging")
		port              = flag.Uint("port", 8080, "port to listen on")
		dbFilePath        = flag.String("db", "", "sqlite database filepath: required")
		url               = flag.String("url", "", "service url: required")
		hashSeed          = flag.String("seed", "", "hash seed: required")
	)
	flag.Parse()
	if *dbFilePath == "" || *url == "" || *hashSeed == "" {
		flag.Usage()
		return
	}
	if *v {
		applicationLogger = log.New(os.Stdout, logPrefix, 0)
	}
	db, err := NewDB(applicationLogger, *dbFilePath, *hashSeed)
	if err != nil {
		startupLogger.Fatal(err)
		return
	}
	http.Handle("/", NewController(applicationLogger, db, *url))
	startupLogger.Println("listening on port", *port)
	startupLogger.Fatal(http.ListenAndServe(fmt.Sprintf(":%d", *port), nil))
}