Program: CWE-79
Project: CVE-2021-33496
Buggy source:
/*
The MIT License (MIT)

Copyright (c) 2014-2017 DutchCoders [https://github.com/dutchcoders/]

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/

package server

import (
	// _ "transfer.sh/app/handlers"
	// _ "transfer.sh/app/utils"

	"archive/tar"
	"archive/zip"
	"bytes"
	"compress/gzip"
	"encoding/json"
	"errors"
	"fmt"
	blackfriday "github.com/russross/blackfriday/v2"
	"html"
	html_template "html/template"
	"io"
	"io/ioutil"
	"log"
	"mime"
	"net/http"
	"net/url"
	"os"
	"path"
	"path/filepath"
	"strconv"
	"strings"
	"sync"
	text_template "text/template"
	"time"

	"net"

	"encoding/base64"
	web "github.com/dutchcoders/transfer.sh-web"
	"github.com/gorilla/mux"
	"github.com/microcosm-cc/bluemonday"
	"github.com/skip2/go-qrcode"
)

const getPathPart = "get"

var (
	htmlTemplates = initHTMLTemplates()
	textTemplates = initTextTemplates()
)

func stripPrefix(path string) string {
	return strings.Replace(path, web.Prefix+"/", "", -1)
}

func initTextTemplates() *text_template.Template {
	templateMap := text_template.FuncMap{"format": formatNumber}

	// Templates with functions available to them
	var templates = text_template.New("").Funcs(templateMap)
	return templates
}

func initHTMLTemplates() *html_template.Template {
	templateMap := html_template.FuncMap{"format": formatNumber}

	// Templates with functions available to them
	var templates = html_template.New("").Funcs(templateMap)

	return templates
}

func healthHandler(w http.ResponseWriter, r *http.Request) {
	fmt.Fprintf(w, "Approaching Neutral Zone, all systems normal and functioning.")
}

/* The preview handler will show a preview of the content for browsers (accept type text/html), and referer is not transfer.sh */
func (s *Server) previewHandler(w http.ResponseWriter, r *http.Request) {
	vars := mux.Vars(r)

	token := vars["token"]
	filename := vars["filename"]

	metadata, err := s.CheckMetadata(token, filename, false)

	if err != nil {
		log.Printf("Error metadata: %s", err.Error())
		http.Error(w, http.StatusText(http.StatusNotFound), http.StatusNotFound)
		return
	}

	contentType := metadata.ContentType
	contentLength, err := s.storage.Head(token, filename)
	if err != nil {
		http.Error(w, http.StatusText(404), 404)
		return
	}

	var templatePath string
	var content html_template.HTML

	switch {
	case strings.HasPrefix(contentType, "image/"):
		templatePath = "download.image.html"
	case strings.HasPrefix(contentType, "video/"):
		templatePath = "download.video.html"
	case strings.HasPrefix(contentType, "audio/"):
		templatePath = "download.audio.html"
	case strings.HasPrefix(contentType, "text/"):
		templatePath = "download.markdown.html"

		var reader io.ReadCloser
		if reader, _, err = s.storage.Get(token, filename); err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}

		var data []byte
		data = make([]byte, _5M)
		if _, err = reader.Read(data); err != io.EOF && err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}

		if strings.HasPrefix(contentType, "text/x-markdown") || strings.HasPrefix(contentType, "text/markdown") {
			unsafe := blackfriday.Run(data)
			output := bluemonday.UGCPolicy().SanitizeBytes(unsafe)
			content = html_template.HTML(output)
		} else if strings.HasPrefix(contentType, "text/plain") {
			content = html_template.HTML(fmt.Sprintf("<pre>%s</pre>", html.EscapeString(string(data))))
		} else {
			templatePath = "download.sandbox.html"
		}

	default:
		templatePath = "download.html"
	}

	relativeURL, _ := url.Parse(path.Join(s.proxyPath, token, filename))
	resolvedURL := resolveURL(r, relativeURL, s.proxyPort)
	relativeURLGet, _ := url.Parse(path.Join(s.proxyPath, getPathPart, token, filename))
	resolvedURLGet := resolveURL(r, relativeURLGet, s.proxyPort)
	var png []byte
	png, err = qrcode.Encode(resolvedURL, qrcode.High, 150)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	qrCode := base64.StdEncoding.EncodeToString(png)

	hostname := getURL(r, s.proxyPort).Host
	webAddress := resolveWebAddress(r, s.proxyPath, s.proxyPort)

	data := struct {
		ContentType    string
		Content        html_template.HTML
		Filename       string
		Url            string
		UrlGet         string
		UrlRandomToken string
		Hostname       string
		WebAddress     string
		ContentLength  uint64
		GAKey          string
		UserVoiceKey   string
		QRCode         string
	}{
		contentType,
		content,
		filename,
		resolvedURL,
		resolvedURLGet,
		token,
		hostname,
		webAddress,
		contentLength,
		s.gaKey,
		s.userVoiceKey,
		qrCode,
	}

	if err := htmlTemplates.ExecuteTemplate(w, templatePath, data); err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

}

// this handler will output html or text, depending on the
// support of the client (Accept header).

func (s *Server) viewHandler(w http.ResponseWriter, r *http.Request) {
	// vars := mux.Vars(r)

	hostname := getURL(r, s.proxyPort).Host
	webAddress := resolveWebAddress(r, s.proxyPath, s.proxyPort)

	data := struct {
		Hostname     string
		WebAddress   string
		GAKey        string
		UserVoiceKey string
	}{
		hostname,
		webAddress,
		s.gaKey,
		s.userVoiceKey,
	}

	if acceptsHTML(r.Header) {
		if err := htmlTemplates.ExecuteTemplate(w, "index.html", data); err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}
	} else {
		if err := textTemplates.ExecuteTemplate(w, "index.txt", data); err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}
	}
}

func (s *Server) notFoundHandler(w http.ResponseWriter, r *http.Request) {
	http.Error(w, http.StatusText(404), 404)
}

func sanitize(fileName string) string {
	return path.Clean(path.Base(fileName))
}

func (s *Server) postHandler(w http.ResponseWriter, r *http.Request) {
	if err := r.ParseMultipartForm(_24K); nil != err {
		log.Printf("%s", err.Error())
		http.Error(w, "Error occurred copying to output stream", 500)
		return
	}

	token := Encode(INIT_SEED, s.randomTokenLength)

	w.Header().Set("Content-Type", "text/plain")

	for _, fheaders := range r.MultipartForm.File {
		for _, fheader := range fheaders {
			filename := sanitize(fheader.Filename)
			contentType := fheader.Header.Get("Content-Type")

			if contentType == "" {
				contentType = mime.TypeByExtension(filepath.Ext(fheader.Filename))
			}

			var f io.Reader
			var err error

			if f, err = fheader.Open(); err != nil {
				log.Printf("%s", err.Error())
				http.Error(w, err.Error(), 500)
				return
			}

			var b bytes.Buffer

			n, err := io.CopyN(&b, f, _24K+1)
			if err != nil && err != io.EOF {
				log.Printf("%s", err.Error())
				http.Error(w, err.Error(), 500)
				return
			}

			var file *os.File
			var reader io.Reader

			if n > _24K {
				file, err = ioutil.TempFile(s.tempPath, "transfer-")
				if err != nil {
					log.Fatal(err)
				}

				n, err = io.Copy(file, io.MultiReader(&b, f))
				if err != nil {
					cleanTmpFile(file)

					log.Printf("%s", err.Error())
					http.Error(w, err.Error(), 500)
					return
				}

				reader, err = os.Open(file.Name())
			} else {
				reader = bytes.NewReader(b.Bytes())
			}

			contentLength := n

			if s.maxUploadSize > 0 && contentLength > s.maxUploadSize {
				log.Print("Entity too large")
				http.Error(w, http.StatusText(http.StatusRequestEntityTooLarge), http.StatusRequestEntityTooLarge)
				return
			}

			metadata := MetadataForRequest(contentType, s.randomTokenLength, r)

			buffer := &bytes.Buffer{}
			if err := json.NewEncoder(buffer).Encode(metadata); err != nil {
				log.Printf("%s", err.Error())
				http.Error(w, errors.New("Could not encode metadata").Error(), 500)

				cleanTmpFile(file)
				return
			} else if err := s.storage.Put(token, fmt.Sprintf("%s.metadata", filename), buffer, "text/json", uint64(buffer.Len())); err != nil {
				log.Printf("%s", err.Error())
				http.Error(w, errors.New("Could not save metadata").Error(), 500)

				cleanTmpFile(file)
				return
			}

			log.Printf("Uploading %s %s %d %s", token, filename, contentLength, contentType)

			if err = s.storage.Put(token, filename, reader, contentType, uint64(contentLength)); err != nil {
				log.Printf("Backend storage error: %s", err.Error())
				http.Error(w, err.Error(), 500)
				return

			}

			filename = url.PathEscape(filename)
			relativeURL, _ := url.Parse(path.Join(s.proxyPath, token, filename))
			fmt.Fprintln(w, getURL(r, s.proxyPort).ResolveReference(relativeURL).String())

			cleanTmpFile(file)
		}
	}
}

func cleanTmpFile(f *os.File) {
	if f != nil {
		err := f.Close()
		if err != nil {
			log.Printf("Error closing tmpfile: %s (%s)", err, f.Name())
		}

		err = os.Remove(f.Name())
		if err != nil {
			log.Printf("Error removing tmpfile: %s (%s)", err, f.Name())
		}
	}
}

type Metadata struct {
	// ContentType is the original uploading content type
	ContentType string
	// Secret as knowledge to delete file
	// Secret string
	// Downloads is the actual number of downloads
	Downloads int
	// MaxDownloads contains the maximum numbers of downloads
	MaxDownloads int
	// MaxDate contains the max age of the file
	MaxDate time.Time
	// DeletionToken contains the token to match against for deletion
	DeletionToken string
}

func MetadataForRequest(contentType string, randomTokenLength int64, r *http.Request) Metadata {
	metadata := Metadata{
		ContentType:   strings.ToLower(contentType),
		MaxDate:       time.Time{},
		Downloads:     0,
		MaxDownloads:  -1,
		DeletionToken: Encode(INIT_SEED, randomTokenLength) + Encode(INIT_SEED, randomTokenLength),
	}

	if v := r.Header.Get("Max-Downloads"); v == "" {
	} else if v, err := strconv.Atoi(v); err != nil {
	} else {
		metadata.MaxDownloads = v
	}

	if v := r.Header.Get("Max-Days"); v == "" {
	} else if v, err := strconv.Atoi(v); err != nil {
	} else {
		metadata.MaxDate = time.Now().Add(time.Hour * 24 * time.Duration(v))
	}

	return metadata
}

func (s *Server) putHandler(w http.ResponseWriter, r *http.Request) {
	vars := mux.Vars(r)

	filename := sanitize(vars["filename"])

	contentLength := r.ContentLength

	var reader io.Reader

	reader = r.Body

	defer r.Body.Close()

	if contentLength == -1 {
		// queue file to disk, because s3 needs content length
		var err error
		var f io.Reader

		f = reader

		var b bytes.Buffer

		n, err := io.CopyN(&b, f, _24K+1)
		if err != nil && err != io.EOF {
			log.Printf("Error putting new file: %s", err.Error())
			http.Error(w, err.Error(), 500)
			return
		}

		var file *os.File

		if n > _24K {
			file, err = ioutil.TempFile(s.tempPath, "transfer-")
			if err != nil {
				log.Printf("%s", err.Error())
				http.Error(w, err.Error(), 500)
				return
			}

			defer cleanTmpFile(file)

			n, err = io.Copy(file, io.MultiReader(&b, f))
			if err != nil {
				log.Printf("%s", err.Error())
				http.Error(w, err.Error(), 500)
				return
			}

			reader, err = os.Open(file.Name())
		} else {
			reader = bytes.NewReader(b.Bytes())
		}

		contentLength = n
	}

	if s.maxUploadSize > 0 && contentLength > s.maxUploadSize {
		log.Print("Entity too large")
		http.Error(w, http.StatusText(http.StatusRequestEntityTooLarge), http.StatusRequestEntityTooLarge)
		return
	}

	if contentLength == 0 {
		log.Print("Empty content-length")
		http.Error(w, errors.New("Could not upload empty file").Error(), 400)
		return
	}

	contentType := r.Header.Get("Content-Type")

	if contentType == "" {
		contentType = mime.TypeByExtension(filepath.Ext(vars["filename"]))
	}

	token := Encode(INIT_SEED, s.randomTokenLength)

	metadata := MetadataForRequest(contentType, s.randomTokenLength, r)

	buffer := &bytes.Buffer{}
	if err := json.NewEncoder(buffer).Encode(metadata); err != nil {
		log.Printf("%s", err.Error())
		http.Error(w, errors.New("Could not encode metadata").Error(), 500)
		return
	} else if err := s.storage.Put(token, fmt.Sprintf("%s.metadata", filename), buffer, "text/json", uint64(buffer.Len())); err != nil {
		log.Printf("%s", err.Error())
		http.Error(w, errors.New("Could not save metadata").Error(), 500)
		return
	}

	log.Printf("Uploading %s %s %d %s", token, filename, contentLength, contentType)

	var err error

	if err = s.storage.Put(token, filename, reader, contentType, uint64(contentLength)); err != nil {
		log.Printf("Error putting new file: %s", err.Error())
		http.Error(w, errors.New("Could not save file").Error(), 500)
		return
	}

	// w.Statuscode = 200

	w.Header().Set("Content-Type", "text/plain")

	filename = url.PathEscape(filename)
	relativeURL, _ := url.Parse(path.Join(s.proxyPath, token, filename))
	deleteURL, _ := url.Parse(path.Join(s.proxyPath, token, filename, metadata.DeletionToken))

	w.Header().Set("X-Url-Delete", resolveURL(r, deleteURL, s.proxyPort))

	fmt.Fprint(w, resolveURL(r, relativeURL, s.proxyPort))
}

func resolveURL(r *http.Request, u *url.URL, proxyPort string) string {
	r.URL.Path = ""

	return getURL(r, proxyPort).ResolveReference(u).String()
}

func resolveKey(key, proxyPath string) string {
	if strings.HasPrefix(key, "/") {
		key = key[1:]
	}

	if strings.HasPrefix(key, proxyPath) {
		key = key[len(proxyPath):]
	}

	key = strings.Replace(key, "\\", "/", -1)

	return key
}

func resolveWebAddress(r *http.Request, proxyPath string, proxyPort string) string {
	url := getURL(r, proxyPort)

	var webAddress string

	if len(proxyPath) == 0 {
		webAddress = fmt.Sprintf("%s://%s/",
			url.ResolveReference(url).Scheme,
			url.ResolveReference(url).Host)
	} else {
		webAddress = fmt.Sprintf("%s://%s/%s",
			url.ResolveReference(url).Scheme,
			url.ResolveReference(url).Host,
			proxyPath)
	}

	return webAddress
}

// Similar to the logic found here:
// https://github.com/golang/go/blob/release-branch.go1.14/src/net/http/clone.go#L22-L33
func cloneURL(u *url.URL) *url.URL {
	c := &url.URL{}
	*c = *u

	if u.User != nil {
		c.User = &url.Userinfo{}
		*c.User = *u.User
	}

	return c
}

func getURL(r *http.Request, proxyPort string) *url.URL {
	u := cloneURL(r.URL)

	if r.TLS != nil {
		u.Scheme = "https"
	} else if proto := r.Header.Get("X-Forwarded-Proto"); proto != "" {
		u.Scheme = proto
	} else {
		u.Scheme = "http"
	}

	if u.Host == "" {
		host, port, err := net.SplitHostPort(r.Host)
		if err != nil {
			host = r.Host
			port = ""
		}
		if len(proxyPort) != 0 {
			port = proxyPort
		}
		if len(port) == 0 {
			u.Host = host
		} else {
			if port == "80" && u.Scheme == "http" {
				u.Host = host
			} else if port == "443" && u.Scheme == "https" {
				u.Host = host
			} else {
				u.Host = net.JoinHostPort(host, port)
			}
		}
	}

	return u
}

func (metadata Metadata) remainingLimitHeaderValues() (remainingDownloads, remainingDays string) {
	if metadata.MaxDate.IsZero() {
		remainingDays = "n/a"
	} else {
		timeDifference := metadata.MaxDate.Sub(time.Now())
		remainingDays = strconv.Itoa(int(timeDifference.Hours()/24) + 1)
	}

	if metadata.MaxDownloads == -1 {
		remainingDownloads = "n/a"
	} else {
		remainingDownloads = strconv.Itoa(metadata.MaxDownloads - metadata.Downloads)
	}

	return remainingDownloads, remainingDays
}

func (s *Server) Lock(token, filename string) error {
	key := path.Join(token, filename)

	if _, ok := s.locks[key]; !ok {
		s.locks[key] = &sync.Mutex{}
	}

	s.locks[key].Lock()

	return nil
}

func (s *Server) Unlock(token, filename string) error {
	key := path.Join(token, filename)
	s.locks[key].Unlock()

	return nil
}

func (s *Server) CheckMetadata(token, filename string, increaseDownload bool) (Metadata, error) {
	s.Lock(token, filename)
	defer s.Unlock(token, filename)

	var metadata Metadata

	r, _, err := s.storage.Get(token, fmt.Sprintf("%s.metadata", filename))
	if err != nil {
		return metadata, err
	}

	defer r.Close()

	if err := json.NewDecoder(r).Decode(&metadata); err != nil {
		return metadata, err
	} else if metadata.MaxDownloads != -1 && metadata.Downloads >= metadata.MaxDownloads {
		return metadata, errors.New("MaxDownloads expired.")
	} else if !metadata.MaxDate.IsZero() && time.Now().After(metadata.MaxDate) {
		return metadata, errors.New("MaxDate expired.")
	} else if metadata.MaxDownloads != -1 && increaseDownload {
		// todo(nl5887): mutex?

		// update number of downloads
		metadata.Downloads++

		buffer := &bytes.Buffer{}
		if err := json.NewEncoder(buffer).Encode(metadata); err != nil {
			return metadata, errors.New("Could not encode metadata")
		} else if err := s.storage.Put(token, fmt.Sprintf("%s.metadata", filename), buffer, "text/json", uint64(buffer.Len())); err != nil {
			return metadata, errors.New("Could not save metadata")
		}
	}

	return metadata, nil
}

func (s *Server) CheckDeletionToken(deletionToken, token, filename string) error {
	s.Lock(token, filename)
	defer s.Unlock(token, filename)

	var metadata Metadata

	r, _, err := s.storage.Get(token, fmt.Sprintf("%s.metadata", filename))
	if s.storage.IsNotExist(err) {
		return nil
	} else if err != nil {
		return err
	}

	defer r.Close()

	if err := json.NewDecoder(r).Decode(&metadata); err != nil {
		return err
	} else if metadata.DeletionToken != deletionToken {
		return errors.New("Deletion token doesn't match.")
	}

	return nil
}

func (s *Server) purgeHandler() {
	ticker := time.NewTicker(s.purgeInterval)
	go func() {
		for {
			select {
			case <-ticker.C:
				err := s.storage.Purge(s.purgeDays)
				log.Printf("error cleaning up expired files: %v", err)
			}
		}
	}()
}

func (s *Server) deleteHandler(w http.ResponseWriter, r *http.Request) {
	vars := mux.Vars(r)

	token := vars["token"]
	filename := vars["filename"]
	deletionToken := vars["deletionToken"]

	if err := s.CheckDeletionToken(deletionToken, token, filename); err != nil {
		log.Printf("Error metadata: %s", err.Error())
		http.Error(w, http.StatusText(http.StatusNotFound), http.StatusNotFound)
		return
	}

	err := s.storage.Delete(token, filename)
	if s.storage.IsNotExist(err) {
		http.Error(w, http.StatusText(http.StatusNotFound), http.StatusNotFound)
		return
	} else if err != nil {
		log.Printf("%s", err.Error())
		http.Error(w, "Could not delete file.", 500)
		return
	}
}

func (s *Server) zipHandler(w http.ResponseWriter, r *http.Request) {
	vars := mux.Vars(r)

	files := vars["files"]

	zipfilename := fmt.Sprintf("transfersh-%d.zip", uint16(time.Now().UnixNano()))

	w.Header().Set("Content-Type", "application/zip")
	w.Header().Set("Content-Disposition", fmt.Sprintf("attachment; filename=\"%s\"", zipfilename))
	w.Header().Set("Connection", "close")

	zw := zip.NewWriter(w)

	for _, key := range strings.Split(files, ",") {
		key = resolveKey(key, s.proxyPath)

		token := strings.Split(key, "/")[0]
		filename := sanitize(strings.Split(key, "/")[1])

		if _, err := s.CheckMetadata(token, filename, true); err != nil {
			log.Printf("Error metadata: %s", err.Error())
			continue
		}

		reader, _, err := s.storage.Get(token, filename)

		if err != nil {
			if s.storage.IsNotExist(err) {
				http.Error(w, "File not found", 404)
				return
			} else {
				log.Printf("%s", err.Error())
				http.Error(w, "Could not retrieve file.", 500)
				return
			}
		}

		defer reader.Close()

		header := &zip.FileHeader{
			Name:         strings.Split(key, "/")[1],
			Method:       zip.Store,
			ModifiedTime: uint16(time.Now().UnixNano()),
			ModifiedDate: uint16(time.Now().UnixNano()),
		}

		fw, err := zw.CreateHeader(header)

		if err != nil {
			log.Printf("%s", err.Error())
			http.Error(w, "Internal server error.", 500)
			return
		}

		if _, err = io.Copy(fw, reader); err != nil {
			log.Printf("%s", err.Error())
			http.Error(w, "Internal server error.", 500)
			return
		}
	}

	if err := zw.Close(); err != nil {
		log.Printf("%s", err.Error())
		http.Error(w, "Internal server error.", 500)
		return
	}
}

func (s *Server) tarGzHandler(w http.ResponseWriter, r *http.Request) {
	vars := mux.Vars(r)

	files := vars["files"]

	tarfilename := fmt.Sprintf("transfersh-%d.tar.gz", uint16(time.Now().UnixNano()))

	w.Header().Set("Content-Type", "application/x-gzip")
	w.Header().Set("Content-Disposition", fmt.Sprintf("attachment; filename=\"%s\"", tarfilename))
	w.Header().Set("Connection", "close")

	os := gzip.NewWriter(w)
	defer os.Close()

	zw := tar.NewWriter(os)
	defer zw.Close()

	for _, key := range strings.Split(files, ",") {
		key = resolveKey(key, s.proxyPath)

		token := strings.Split(key, "/")[0]
		filename := sanitize(strings.Split(key, "/")[1])

		if _, err := s.CheckMetadata(token, filename, true); err != nil {
			log.Printf("Error metadata: %s", err.Error())
			continue
		}

		reader, contentLength, err := s.storage.Get(token, filename)
		if err != nil {
			if s.storage.IsNotExist(err) {
				http.Error(w, "File not found", 404)
				return
			} else {
				log.Printf("%s", err.Error())
				http.Error(w, "Could not retrieve file.", 500)
				return
			}
		}

		defer reader.Close()

		header := &tar.Header{
			Name: strings.Split(key, "/")[1],
			Size: int64(contentLength),
		}

		err = zw.WriteHeader(header)
		if err != nil {
			log.Printf("%s", err.Error())
			http.Error(w, "Internal server error.", 500)
			return
		}

		if _, err = io.Copy(zw, reader); err != nil {
			log.Printf("%s", err.Error())
			http.Error(w, "Internal server error.", 500)
			return
		}
	}
}

func (s *Server) tarHandler(w http.ResponseWriter, r *http.Request) {
	vars := mux.Vars(r)

	files := vars["files"]

	tarfilename := fmt.Sprintf("transfersh-%d.tar", uint16(time.Now().UnixNano()))

	w.Header().Set("Content-Type", "application/x-tar")
	w.Header().Set("Content-Disposition", fmt.Sprintf("attachment; filename=\"%s\"", tarfilename))
	w.Header().Set("Connection", "close")

	zw := tar.NewWriter(w)
	defer zw.Close()

	for _, key := range strings.Split(files, ",") {
		key = resolveKey(key, s.proxyPath)

		token := strings.Split(key, "/")[0]
		filename := strings.Split(key, "/")[1]

		if _, err := s.CheckMetadata(token, filename, true); err != nil {
			log.Printf("Error metadata: %s", err.Error())
			continue
		}

		reader, contentLength, err := s.storage.Get(token, filename)
		if err != nil {
			if s.storage.IsNotExist(err) {
				http.Error(w, "File not found", 404)
				return
			} else {
				log.Printf("%s", err.Error())
				http.Error(w, "Could not retrieve file.", 500)
				return
			}
		}

		defer reader.Close()

		header := &tar.Header{
			Name: strings.Split(key, "/")[1],
			Size: int64(contentLength),
		}

		err = zw.WriteHeader(header)
		if err != nil {
			log.Printf("%s", err.Error())
			http.Error(w, "Internal server error.", 500)
			return
		}

		if _, err = io.Copy(zw, reader); err != nil {
			log.Printf("%s", err.Error())
			http.Error(w, "Internal server error.", 500)
			return
		}
	}
}

func (s *Server) headHandler(w http.ResponseWriter, r *http.Request) {
	vars := mux.Vars(r)

	token := vars["token"]
	filename := vars["filename"]

	metadata, err := s.CheckMetadata(token, filename, false)

	if err != nil {
		log.Printf("Error metadata: %s", err.Error())
		http.Error(w, http.StatusText(http.StatusNotFound), http.StatusNotFound)
		return
	}

	contentType := metadata.ContentType
	contentLength, err := s.storage.Head(token, filename)
	if s.storage.IsNotExist(err) {
		http.Error(w, http.StatusText(http.StatusNotFound), http.StatusNotFound)
		return
	} else if err != nil {
		log.Printf("%s", err.Error())
		http.Error(w, "Could not retrieve file.", 500)
		return
	}

	remainingDownloads, remainingDays := metadata.remainingLimitHeaderValues()

	w.Header().Set("Content-Type", contentType)
	w.Header().Set("Content-Length", strconv.FormatUint(contentLength, 10))
	w.Header().Set("Connection", "close")
	w.Header().Set("X-Remaining-Downloads", remainingDownloads)
	w.Header().Set("X-Remaining-Days", remainingDays)
}

func (s *Server) getHandler(w http.ResponseWriter, r *http.Request) {
	vars := mux.Vars(r)

	action := vars["action"]
	token := vars["token"]
	filename := vars["filename"]

	metadata, err := s.CheckMetadata(token, filename, true)

	if err != nil {
		log.Printf("Error metadata: %s", err.Error())
		http.Error(w, http.StatusText(http.StatusNotFound), http.StatusNotFound)
		return
	}

	contentType := metadata.ContentType
	reader, contentLength, err := s.storage.Get(token, filename)
	if s.storage.IsNotExist(err) {
		http.Error(w, http.StatusText(http.StatusNotFound), http.StatusNotFound)
		return
	} else if err != nil {
		log.Printf("%s", err.Error())
		http.Error(w, "Could not retrieve file.", 500)
		return
	}

	defer reader.Close()

	var disposition string

	if action == "inline" {
		disposition = "inline"
	} else {
		disposition = "attachment"
	}

	remainingDownloads, remainingDays := metadata.remainingLimitHeaderValues()

	w.Header().Set("Content-Type", contentType)
	w.Header().Set("Content-Length", strconv.FormatUint(contentLength, 10))
	w.Header().Set("Content-Disposition", fmt.Sprintf("%s; filename=\"%s\"", disposition, filename))
	w.Header().Set("Connection", "keep-alive")
	w.Header().Set("X-Remaining-Downloads", remainingDownloads)
	w.Header().Set("X-Remaining-Days", remainingDays)

	if disposition == "inline" && strings.Contains(contentType, "html") {
		reader = ioutil.NopCloser(bluemonday.UGCPolicy().SanitizeReader(reader))
	}

	if w.Header().Get("Range") == "" {
		if _, err = io.Copy(w, reader); err != nil {
			log.Printf("%s", err.Error())
			http.Error(w, "Error occurred copying to output stream", 500)
			return
		}

		return
	}

	file, err := ioutil.TempFile(s.tempPath, "range-")
	if err != nil {
		log.Printf("%s", err.Error())
		http.Error(w, "Error occurred copying to output stream", 500)
		return
	}

	defer cleanTmpFile(file)

	tee := io.TeeReader(reader, file)
	for {
		b := make([]byte, _5M)
		_, err = tee.Read(b)
		if err == io.EOF {
			break
		}

		if err != nil {
			log.Printf("%s", err.Error())
			http.Error(w, "Error occurred copying to output stream", 500)
			return
		}
	}

	http.ServeContent(w, r, filename, time.Now(), file)
}

func (s *Server) RedirectHandler(h http.Handler) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if !s.forceHTTPs {
			// we don't want to enforce https
		} else if r.URL.Path == "/health.html" {
			// health check url won't redirect
		} else if strings.HasSuffix(ipAddrFromRemoteAddr(r.Host), ".onion") {
			// .onion addresses cannot get a valid certificate, so don't redirect
		} else if r.Header.Get("X-Forwarded-Proto") == "https" {
		} else if r.URL.Scheme == "https" {
		} else {
			u := getURL(r, s.proxyPort)
			u.Scheme = "https"

			http.Redirect(w, r, u.String(), http.StatusPermanentRedirect)
			return
		}

		h.ServeHTTP(w, r)
	}
}

// Create a log handler for every request it receives.
func LoveHandler(h http.Handler) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("x-made-with", "<3 by DutchCoders")
		w.Header().Set("x-served-by", "Proudly served by DutchCoders")
		w.Header().Set("Server", "Transfer.sh HTTP Server 1.0")
		h.ServeHTTP(w, r)
	}
}

func IPFilterHandler(h http.Handler, ipFilterOptions *IPFilterOptions) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if ipFilterOptions == nil {
			h.ServeHTTP(w, r)
		} else {
			WrapIPFilter(h, *ipFilterOptions).ServeHTTP(w, r)
		}
		return
	}
}

func (s *Server) BasicAuthHandler(h http.Handler) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if s.AuthUser == "" || s.AuthPass == "" {
			h.ServeHTTP(w, r)
			return
		}

		w.Header().Set("WWW-Authenticate", "Basic realm=\"Restricted\"")

		username, password, authOK := r.BasicAuth()
		if authOK == false {
			http.Error(w, "Not authorized", 401)
			return
		}

		if username != s.AuthUser || password != s.AuthPass {
			http.Error(w, "Not authorized", 401)
			return
		}

		h.ServeHTTP(w, r)
	}
}


Fixed version (ground truth):
/*
The MIT License (MIT)

Copyright (c) 2014-2017 DutchCoders [https://github.com/dutchcoders/]

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/

package server

import (
	// _ "transfer.sh/app/handlers"
	// _ "transfer.sh/app/utils"

	"archive/tar"
	"archive/zip"
	"bytes"
	"compress/gzip"
	"encoding/json"
	"errors"
	"fmt"
	blackfriday "github.com/russross/blackfriday/v2"
	"html"
	html_template "html/template"
	"io"
	"io/ioutil"
	"log"
	"mime"
	"net/http"
	"net/url"
	"os"
	"path"
	"path/filepath"
	"strconv"
	"strings"
	"sync"
	text_template "text/template"
	"time"

	"net"

	"encoding/base64"
	web "github.com/dutchcoders/transfer.sh-web"
	"github.com/gorilla/mux"
	"github.com/microcosm-cc/bluemonday"
	"github.com/skip2/go-qrcode"
)

const getPathPart = "get"

var (
	htmlTemplates = initHTMLTemplates()
	textTemplates = initTextTemplates()
)

func stripPrefix(path string) string {
	return strings.Replace(path, web.Prefix+"/", "", -1)
}

func initTextTemplates() *text_template.Template {
	templateMap := text_template.FuncMap{"format": formatNumber}

	// Templates with functions available to them
	var templates = text_template.New("").Funcs(templateMap)
	return templates
}

func initHTMLTemplates() *html_template.Template {
	templateMap := html_template.FuncMap{"format": formatNumber}

	// Templates with functions available to them
	var templates = html_template.New("").Funcs(templateMap)

	return templates
}

func healthHandler(w http.ResponseWriter, r *http.Request) {
	fmt.Fprintf(w, "Approaching Neutral Zone, all systems normal and functioning.")
}

func canContainsXSS(contentType string) bool {
	switch {
	case strings.Contains(contentType, "cache-manifest"):
		fallthrough
	case strings.Contains(contentType, "html"):
		fallthrough
	case strings.Contains(contentType, "rdf"):
		fallthrough
	case strings.Contains(contentType, "vtt"):
		fallthrough
	case strings.Contains(contentType, "xml"):
		fallthrough
	case strings.Contains(contentType, "xsl"):
		return true
	case strings.Contains(contentType, "x-mixed-replace"):
		return true
	}

	return false
}

/* The preview handler will show a preview of the content for browsers (accept type text/html), and referer is not transfer.sh */
func (s *Server) previewHandler(w http.ResponseWriter, r *http.Request) {
	vars := mux.Vars(r)

	token := vars["token"]
	filename := vars["filename"]

	metadata, err := s.CheckMetadata(token, filename, false)

	if err != nil {
		log.Printf("Error metadata: %s", err.Error())
		http.Error(w, http.StatusText(http.StatusNotFound), http.StatusNotFound)
		return
	}

	contentType := metadata.ContentType
	contentLength, err := s.storage.Head(token, filename)
	if err != nil {
		http.Error(w, http.StatusText(404), 404)
		return
	}

	var templatePath string
	var content html_template.HTML

	switch {
	case strings.HasPrefix(contentType, "image/"):
		templatePath = "download.image.html"
	case strings.HasPrefix(contentType, "video/"):
		templatePath = "download.video.html"
	case strings.HasPrefix(contentType, "audio/"):
		templatePath = "download.audio.html"
	case strings.HasPrefix(contentType, "text/"):
		templatePath = "download.markdown.html"

		var reader io.ReadCloser
		if reader, _, err = s.storage.Get(token, filename); err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}

		var data []byte
		data = make([]byte, _5M)
		if _, err = reader.Read(data); err != io.EOF && err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}

		if strings.HasPrefix(contentType, "text/x-markdown") || strings.HasPrefix(contentType, "text/markdown") {
			unsafe := blackfriday.Run(data)
			output := bluemonday.UGCPolicy().SanitizeBytes(unsafe)
			content = html_template.HTML(output)
		} else if strings.HasPrefix(contentType, "text/plain") {
			content = html_template.HTML(fmt.Sprintf("<pre>%s</pre>", html.EscapeString(string(data))))
		} else {
			templatePath = "download.sandbox.html"
		}

	default:
		templatePath = "download.html"
	}

	relativeURL, _ := url.Parse(path.Join(s.proxyPath, token, filename))
	resolvedURL := resolveURL(r, relativeURL, s.proxyPort)
	relativeURLGet, _ := url.Parse(path.Join(s.proxyPath, getPathPart, token, filename))
	resolvedURLGet := resolveURL(r, relativeURLGet, s.proxyPort)
	var png []byte
	png, err = qrcode.Encode(resolvedURL, qrcode.High, 150)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	qrCode := base64.StdEncoding.EncodeToString(png)

	hostname := getURL(r, s.proxyPort).Host
	webAddress := resolveWebAddress(r, s.proxyPath, s.proxyPort)

	data := struct {
		ContentType    string
		Content        html_template.HTML
		Filename       string
		Url            string
		UrlGet         string
		UrlRandomToken string
		Hostname       string
		WebAddress     string
		ContentLength  uint64
		GAKey          string
		UserVoiceKey   string
		QRCode         string
	}{
		contentType,
		content,
		filename,
		resolvedURL,
		resolvedURLGet,
		token,
		hostname,
		webAddress,
		contentLength,
		s.gaKey,
		s.userVoiceKey,
		qrCode,
	}

	if err := htmlTemplates.ExecuteTemplate(w, templatePath, data); err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

}

// this handler will output html or text, depending on the
// support of the client (Accept header).

func (s *Server) viewHandler(w http.ResponseWriter, r *http.Request) {
	// vars := mux.Vars(r)

	hostname := getURL(r, s.proxyPort).Host
	webAddress := resolveWebAddress(r, s.proxyPath, s.proxyPort)

	data := struct {
		Hostname     string
		WebAddress   string
		GAKey        string
		UserVoiceKey string
	}{
		hostname,
		webAddress,
		s.gaKey,
		s.userVoiceKey,
	}

	if acceptsHTML(r.Header) {
		if err := htmlTemplates.ExecuteTemplate(w, "index.html", data); err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}
	} else {
		if err := textTemplates.ExecuteTemplate(w, "index.txt", data); err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}
	}
}

func (s *Server) notFoundHandler(w http.ResponseWriter, r *http.Request) {
	http.Error(w, http.StatusText(404), 404)
}

func sanitize(fileName string) string {
	return path.Clean(path.Base(fileName))
}

func (s *Server) postHandler(w http.ResponseWriter, r *http.Request) {
	if err := r.ParseMultipartForm(_24K); nil != err {
		log.Printf("%s", err.Error())
		http.Error(w, "Error occurred copying to output stream", 500)
		return
	}

	token := Encode(INIT_SEED, s.randomTokenLength)

	w.Header().Set("Content-Type", "text/plain")

	for _, fheaders := range r.MultipartForm.File {
		for _, fheader := range fheaders {
			filename := sanitize(fheader.Filename)
			contentType := mime.TypeByExtension(filepath.Ext(fheader.Filename))

			var f io.Reader
			var err error

			if f, err = fheader.Open(); err != nil {
				log.Printf("%s", err.Error())
				http.Error(w, err.Error(), 500)
				return
			}

			var b bytes.Buffer

			n, err := io.CopyN(&b, f, _24K+1)
			if err != nil && err != io.EOF {
				log.Printf("%s", err.Error())
				http.Error(w, err.Error(), 500)
				return
			}

			var file *os.File
			var reader io.Reader

			if n > _24K {
				file, err = ioutil.TempFile(s.tempPath, "transfer-")
				if err != nil {
					log.Fatal(err)
				}

				n, err = io.Copy(file, io.MultiReader(&b, f))
				if err != nil {
					cleanTmpFile(file)

					log.Printf("%s", err.Error())
					http.Error(w, err.Error(), 500)
					return
				}

				reader, err = os.Open(file.Name())
			} else {
				reader = bytes.NewReader(b.Bytes())
			}

			contentLength := n

			if s.maxUploadSize > 0 && contentLength > s.maxUploadSize {
				log.Print("Entity too large")
				http.Error(w, http.StatusText(http.StatusRequestEntityTooLarge), http.StatusRequestEntityTooLarge)
				return
			}

			metadata := MetadataForRequest(contentType, s.randomTokenLength, r)

			buffer := &bytes.Buffer{}
			if err := json.NewEncoder(buffer).Encode(metadata); err != nil {
				log.Printf("%s", err.Error())
				http.Error(w, errors.New("Could not encode metadata").Error(), 500)

				cleanTmpFile(file)
				return
			} else if err := s.storage.Put(token, fmt.Sprintf("%s.metadata", filename), buffer, "text/json", uint64(buffer.Len())); err != nil {
				log.Printf("%s", err.Error())
				http.Error(w, errors.New("Could not save metadata").Error(), 500)

				cleanTmpFile(file)
				return
			}

			log.Printf("Uploading %s %s %d %s", token, filename, contentLength, contentType)

			if err = s.storage.Put(token, filename, reader, contentType, uint64(contentLength)); err != nil {
				log.Printf("Backend storage error: %s", err.Error())
				http.Error(w, err.Error(), 500)
				return

			}

			filename = url.PathEscape(filename)
			relativeURL, _ := url.Parse(path.Join(s.proxyPath, token, filename))
			fmt.Fprintln(w, getURL(r, s.proxyPort).ResolveReference(relativeURL).String())

			cleanTmpFile(file)
		}
	}
}

func cleanTmpFile(f *os.File) {
	if f != nil {
		err := f.Close()
		if err != nil {
			log.Printf("Error closing tmpfile: %s (%s)", err, f.Name())
		}

		err = os.Remove(f.Name())
		if err != nil {
			log.Printf("Error removing tmpfile: %s (%s)", err, f.Name())
		}
	}
}

type Metadata struct {
	// ContentType is the original uploading content type
	ContentType string
	// Secret as knowledge to delete file
	// Secret string
	// Downloads is the actual number of downloads
	Downloads int
	// MaxDownloads contains the maximum numbers of downloads
	MaxDownloads int
	// MaxDate contains the max age of the file
	MaxDate time.Time
	// DeletionToken contains the token to match against for deletion
	DeletionToken string
}

func MetadataForRequest(contentType string, randomTokenLength int64, r *http.Request) Metadata {
	metadata := Metadata{
		ContentType:   strings.ToLower(contentType),
		MaxDate:       time.Time{},
		Downloads:     0,
		MaxDownloads:  -1,
		DeletionToken: Encode(INIT_SEED, randomTokenLength) + Encode(INIT_SEED, randomTokenLength),
	}

	if v := r.Header.Get("Max-Downloads"); v == "" {
	} else if v, err := strconv.Atoi(v); err != nil {
	} else {
		metadata.MaxDownloads = v
	}

	if v := r.Header.Get("Max-Days"); v == "" {
	} else if v, err := strconv.Atoi(v); err != nil {
	} else {
		metadata.MaxDate = time.Now().Add(time.Hour * 24 * time.Duration(v))
	}

	return metadata
}

func (s *Server) putHandler(w http.ResponseWriter, r *http.Request) {
	vars := mux.Vars(r)

	filename := sanitize(vars["filename"])

	contentLength := r.ContentLength

	var reader io.Reader

	reader = r.Body

	defer r.Body.Close()

	if contentLength == -1 {
		// queue file to disk, because s3 needs content length
		var err error
		var f io.Reader

		f = reader

		var b bytes.Buffer

		n, err := io.CopyN(&b, f, _24K+1)
		if err != nil && err != io.EOF {
			log.Printf("Error putting new file: %s", err.Error())
			http.Error(w, err.Error(), 500)
			return
		}

		var file *os.File

		if n > _24K {
			file, err = ioutil.TempFile(s.tempPath, "transfer-")
			if err != nil {
				log.Printf("%s", err.Error())
				http.Error(w, err.Error(), 500)
				return
			}

			defer cleanTmpFile(file)

			n, err = io.Copy(file, io.MultiReader(&b, f))
			if err != nil {
				log.Printf("%s", err.Error())
				http.Error(w, err.Error(), 500)
				return
			}

			reader, err = os.Open(file.Name())
		} else {
			reader = bytes.NewReader(b.Bytes())
		}

		contentLength = n
	}

	if s.maxUploadSize > 0 && contentLength > s.maxUploadSize {
		log.Print("Entity too large")
		http.Error(w, http.StatusText(http.StatusRequestEntityTooLarge), http.StatusRequestEntityTooLarge)
		return
	}

	if contentLength == 0 {
		log.Print("Empty content-length")
		http.Error(w, errors.New("Could not upload empty file").Error(), 400)
		return
	}

	contentType := mime.TypeByExtension(filepath.Ext(vars["filename"]))

	token := Encode(INIT_SEED, s.randomTokenLength)

	metadata := MetadataForRequest(contentType, s.randomTokenLength, r)

	buffer := &bytes.Buffer{}
	if err := json.NewEncoder(buffer).Encode(metadata); err != nil {
		log.Printf("%s", err.Error())
		http.Error(w, errors.New("Could not encode metadata").Error(), 500)
		return
	} else if err := s.storage.Put(token, fmt.Sprintf("%s.metadata", filename), buffer, "text/json", uint64(buffer.Len())); err != nil {
		log.Printf("%s", err.Error())
		http.Error(w, errors.New("Could not save metadata").Error(), 500)
		return
	}

	log.Printf("Uploading %s %s %d %s", token, filename, contentLength, contentType)

	var err error

	if err = s.storage.Put(token, filename, reader, contentType, uint64(contentLength)); err != nil {
		log.Printf("Error putting new file: %s", err.Error())
		http.Error(w, errors.New("Could not save file").Error(), 500)
		return
	}

	// w.Statuscode = 200

	w.Header().Set("Content-Type", "text/plain")

	filename = url.PathEscape(filename)
	relativeURL, _ := url.Parse(path.Join(s.proxyPath, token, filename))
	deleteURL, _ := url.Parse(path.Join(s.proxyPath, token, filename, metadata.DeletionToken))

	w.Header().Set("X-Url-Delete", resolveURL(r, deleteURL, s.proxyPort))

	fmt.Fprint(w, resolveURL(r, relativeURL, s.proxyPort))
}

func resolveURL(r *http.Request, u *url.URL, proxyPort string) string {
	r.URL.Path = ""

	return getURL(r, proxyPort).ResolveReference(u).String()
}

func resolveKey(key, proxyPath string) string {
	if strings.HasPrefix(key, "/") {
		key = key[1:]
	}

	if strings.HasPrefix(key, proxyPath) {
		key = key[len(proxyPath):]
	}

	key = strings.Replace(key, "\\", "/", -1)

	return key
}

func resolveWebAddress(r *http.Request, proxyPath string, proxyPort string) string {
	url := getURL(r, proxyPort)

	var webAddress string

	if len(proxyPath) == 0 {
		webAddress = fmt.Sprintf("%s://%s/",
			url.ResolveReference(url).Scheme,
			url.ResolveReference(url).Host)
	} else {
		webAddress = fmt.Sprintf("%s://%s/%s",
			url.ResolveReference(url).Scheme,
			url.ResolveReference(url).Host,
			proxyPath)
	}

	return webAddress
}

// Similar to the logic found here:
// https://github.com/golang/go/blob/release-branch.go1.14/src/net/http/clone.go#L22-L33
func cloneURL(u *url.URL) *url.URL {
	c := &url.URL{}
	*c = *u

	if u.User != nil {
		c.User = &url.Userinfo{}
		*c.User = *u.User
	}

	return c
}

func getURL(r *http.Request, proxyPort string) *url.URL {
	u := cloneURL(r.URL)

	if r.TLS != nil {
		u.Scheme = "https"
	} else if proto := r.Header.Get("X-Forwarded-Proto"); proto != "" {
		u.Scheme = proto
	} else {
		u.Scheme = "http"
	}

	if u.Host == "" {
		host, port, err := net.SplitHostPort(r.Host)
		if err != nil {
			host = r.Host
			port = ""
		}
		if len(proxyPort) != 0 {
			port = proxyPort
		}
		if len(port) == 0 {
			u.Host = host
		} else {
			if port == "80" && u.Scheme == "http" {
				u.Host = host
			} else if port == "443" && u.Scheme == "https" {
				u.Host = host
			} else {
				u.Host = net.JoinHostPort(host, port)
			}
		}
	}

	return u
}

func (metadata Metadata) remainingLimitHeaderValues() (remainingDownloads, remainingDays string) {
	if metadata.MaxDate.IsZero() {
		remainingDays = "n/a"
	} else {
		timeDifference := metadata.MaxDate.Sub(time.Now())
		remainingDays = strconv.Itoa(int(timeDifference.Hours()/24) + 1)
	}

	if metadata.MaxDownloads == -1 {
		remainingDownloads = "n/a"
	} else {
		remainingDownloads = strconv.Itoa(metadata.MaxDownloads - metadata.Downloads)
	}

	return remainingDownloads, remainingDays
}

func (s *Server) Lock(token, filename string) error {
	key := path.Join(token, filename)

	if _, ok := s.locks[key]; !ok {
		s.locks[key] = &sync.Mutex{}
	}

	s.locks[key].Lock()

	return nil
}

func (s *Server) Unlock(token, filename string) error {
	key := path.Join(token, filename)
	s.locks[key].Unlock()

	return nil
}

func (s *Server) CheckMetadata(token, filename string, increaseDownload bool) (Metadata, error) {
	s.Lock(token, filename)
	defer s.Unlock(token, filename)

	var metadata Metadata

	r, _, err := s.storage.Get(token, fmt.Sprintf("%s.metadata", filename))
	if err != nil {
		return metadata, err
	}

	defer r.Close()

	if err := json.NewDecoder(r).Decode(&metadata); err != nil {
		return metadata, err
	} else if metadata.MaxDownloads != -1 && metadata.Downloads >= metadata.MaxDownloads {
		return metadata, errors.New("MaxDownloads expired.")
	} else if !metadata.MaxDate.IsZero() && time.Now().After(metadata.MaxDate) {
		return metadata, errors.New("MaxDate expired.")
	} else if metadata.MaxDownloads != -1 && increaseDownload {
		// todo(nl5887): mutex?

		// update number of downloads
		metadata.Downloads++

		buffer := &bytes.Buffer{}
		if err := json.NewEncoder(buffer).Encode(metadata); err != nil {
			return metadata, errors.New("Could not encode metadata")
		} else if err := s.storage.Put(token, fmt.Sprintf("%s.metadata", filename), buffer, "text/json", uint64(buffer.Len())); err != nil {
			return metadata, errors.New("Could not save metadata")
		}
	}

	return metadata, nil
}

func (s *Server) CheckDeletionToken(deletionToken, token, filename string) error {
	s.Lock(token, filename)
	defer s.Unlock(token, filename)

	var metadata Metadata

	r, _, err := s.storage.Get(token, fmt.Sprintf("%s.metadata", filename))
	if s.storage.IsNotExist(err) {
		return errors.New("Metadata doesn't exist")
	} else if err != nil {
		return err
	}

	defer r.Close()

	if err := json.NewDecoder(r).Decode(&metadata); err != nil {
		return err
	} else if metadata.DeletionToken != deletionToken {
		return errors.New("Deletion token doesn't match.")
	}

	return nil
}

func (s *Server) purgeHandler() {
	ticker := time.NewTicker(s.purgeInterval)
	go func() {
		for {
			select {
			case <-ticker.C:
				err := s.storage.Purge(s.purgeDays)
				log.Printf("error cleaning up expired files: %v", err)
			}
		}
	}()
}

func (s *Server) deleteHandler(w http.ResponseWriter, r *http.Request) {
	vars := mux.Vars(r)

	token := vars["token"]
	filename := vars["filename"]
	deletionToken := vars["deletionToken"]

	if err := s.CheckDeletionToken(deletionToken, token, filename); err != nil {
		log.Printf("Error metadata: %s", err.Error())
		http.Error(w, http.StatusText(http.StatusNotFound), http.StatusNotFound)
		return
	}

	err := s.storage.Delete(token, filename)
	if s.storage.IsNotExist(err) {
		http.Error(w, http.StatusText(http.StatusNotFound), http.StatusNotFound)
		return
	} else if err != nil {
		log.Printf("%s", err.Error())
		http.Error(w, "Could not delete file.", 500)
		return
	}
}

func (s *Server) zipHandler(w http.ResponseWriter, r *http.Request) {
	vars := mux.Vars(r)

	files := vars["files"]

	zipfilename := fmt.Sprintf("transfersh-%d.zip", uint16(time.Now().UnixNano()))

	w.Header().Set("Content-Type", "application/zip")
	w.Header().Set("Content-Disposition", fmt.Sprintf("attachment; filename=\"%s\"", zipfilename))
	w.Header().Set("Connection", "close")

	zw := zip.NewWriter(w)

	for _, key := range strings.Split(files, ",") {
		key = resolveKey(key, s.proxyPath)

		token := strings.Split(key, "/")[0]
		filename := sanitize(strings.Split(key, "/")[1])

		if _, err := s.CheckMetadata(token, filename, true); err != nil {
			log.Printf("Error metadata: %s", err.Error())
			continue
		}

		reader, _, err := s.storage.Get(token, filename)

		if err != nil {
			if s.storage.IsNotExist(err) {
				http.Error(w, "File not found", 404)
				return
			} else {
				log.Printf("%s", err.Error())
				http.Error(w, "Could not retrieve file.", 500)
				return
			}
		}

		defer reader.Close()

		header := &zip.FileHeader{
			Name:         strings.Split(key, "/")[1],
			Method:       zip.Store,
			ModifiedTime: uint16(time.Now().UnixNano()),
			ModifiedDate: uint16(time.Now().UnixNano()),
		}

		fw, err := zw.CreateHeader(header)

		if err != nil {
			log.Printf("%s", err.Error())
			http.Error(w, "Internal server error.", 500)
			return
		}

		if _, err = io.Copy(fw, reader); err != nil {
			log.Printf("%s", err.Error())
			http.Error(w, "Internal server error.", 500)
			return
		}
	}

	if err := zw.Close(); err != nil {
		log.Printf("%s", err.Error())
		http.Error(w, "Internal server error.", 500)
		return
	}
}

func (s *Server) tarGzHandler(w http.ResponseWriter, r *http.Request) {
	vars := mux.Vars(r)

	files := vars["files"]

	tarfilename := fmt.Sprintf("transfersh-%d.tar.gz", uint16(time.Now().UnixNano()))

	w.Header().Set("Content-Type", "application/x-gzip")
	w.Header().Set("Content-Disposition", fmt.Sprintf("attachment; filename=\"%s\"", tarfilename))
	w.Header().Set("Connection", "close")

	os := gzip.NewWriter(w)
	defer os.Close()

	zw := tar.NewWriter(os)
	defer zw.Close()

	for _, key := range strings.Split(files, ",") {
		key = resolveKey(key, s.proxyPath)

		token := strings.Split(key, "/")[0]
		filename := sanitize(strings.Split(key, "/")[1])

		if _, err := s.CheckMetadata(token, filename, true); err != nil {
			log.Printf("Error metadata: %s", err.Error())
			continue
		}

		reader, contentLength, err := s.storage.Get(token, filename)
		if err != nil {
			if s.storage.IsNotExist(err) {
				http.Error(w, "File not found", 404)
				return
			} else {
				log.Printf("%s", err.Error())
				http.Error(w, "Could not retrieve file.", 500)
				return
			}
		}

		defer reader.Close()

		header := &tar.Header{
			Name: strings.Split(key, "/")[1],
			Size: int64(contentLength),
		}

		err = zw.WriteHeader(header)
		if err != nil {
			log.Printf("%s", err.Error())
			http.Error(w, "Internal server error.", 500)
			return
		}

		if _, err = io.Copy(zw, reader); err != nil {
			log.Printf("%s", err.Error())
			http.Error(w, "Internal server error.", 500)
			return
		}
	}
}

func (s *Server) tarHandler(w http.ResponseWriter, r *http.Request) {
	vars := mux.Vars(r)

	files := vars["files"]

	tarfilename := fmt.Sprintf("transfersh-%d.tar", uint16(time.Now().UnixNano()))

	w.Header().Set("Content-Type", "application/x-tar")
	w.Header().Set("Content-Disposition", fmt.Sprintf("attachment; filename=\"%s\"", tarfilename))
	w.Header().Set("Connection", "close")

	zw := tar.NewWriter(w)
	defer zw.Close()

	for _, key := range strings.Split(files, ",") {
		key = resolveKey(key, s.proxyPath)

		token := strings.Split(key, "/")[0]
		filename := strings.Split(key, "/")[1]

		if _, err := s.CheckMetadata(token, filename, true); err != nil {
			log.Printf("Error metadata: %s", err.Error())
			continue
		}

		reader, contentLength, err := s.storage.Get(token, filename)
		if err != nil {
			if s.storage.IsNotExist(err) {
				http.Error(w, "File not found", 404)
				return
			} else {
				log.Printf("%s", err.Error())
				http.Error(w, "Could not retrieve file.", 500)
				return
			}
		}

		defer reader.Close()

		header := &tar.Header{
			Name: strings.Split(key, "/")[1],
			Size: int64(contentLength),
		}

		err = zw.WriteHeader(header)
		if err != nil {
			log.Printf("%s", err.Error())
			http.Error(w, "Internal server error.", 500)
			return
		}

		if _, err = io.Copy(zw, reader); err != nil {
			log.Printf("%s", err.Error())
			http.Error(w, "Internal server error.", 500)
			return
		}
	}
}

func (s *Server) headHandler(w http.ResponseWriter, r *http.Request) {
	vars := mux.Vars(r)

	token := vars["token"]
	filename := vars["filename"]

	metadata, err := s.CheckMetadata(token, filename, false)

	if err != nil {
		log.Printf("Error metadata: %s", err.Error())
		http.Error(w, http.StatusText(http.StatusNotFound), http.StatusNotFound)
		return
	}

	contentType := metadata.ContentType
	contentLength, err := s.storage.Head(token, filename)
	if s.storage.IsNotExist(err) {
		http.Error(w, http.StatusText(http.StatusNotFound), http.StatusNotFound)
		return
	} else if err != nil {
		log.Printf("%s", err.Error())
		http.Error(w, "Could not retrieve file.", 500)
		return
	}

	remainingDownloads, remainingDays := metadata.remainingLimitHeaderValues()

	w.Header().Set("Content-Type", contentType)
	w.Header().Set("Content-Length", strconv.FormatUint(contentLength, 10))
	w.Header().Set("Connection", "close")
	w.Header().Set("X-Remaining-Downloads", remainingDownloads)
	w.Header().Set("X-Remaining-Days", remainingDays)
}

func (s *Server) getHandler(w http.ResponseWriter, r *http.Request) {
	vars := mux.Vars(r)

	action := vars["action"]
	token := vars["token"]
	filename := vars["filename"]

	metadata, err := s.CheckMetadata(token, filename, true)

	if err != nil {
		log.Printf("Error metadata: %s", err.Error())
		http.Error(w, http.StatusText(http.StatusNotFound), http.StatusNotFound)
		return
	}

	contentType := metadata.ContentType
	reader, contentLength, err := s.storage.Get(token, filename)
	if s.storage.IsNotExist(err) {
		http.Error(w, http.StatusText(http.StatusNotFound), http.StatusNotFound)
		return
	} else if err != nil {
		log.Printf("%s", err.Error())
		http.Error(w, "Could not retrieve file.", 500)
		return
	}

	defer reader.Close()

	var disposition string

	if action == "inline" {
		disposition = "inline"
	} else {
		disposition = "attachment"
	}

	remainingDownloads, remainingDays := metadata.remainingLimitHeaderValues()

	w.Header().Set("Content-Type", contentType)
	w.Header().Set("Content-Length", strconv.FormatUint(contentLength, 10))
	w.Header().Set("Content-Disposition", fmt.Sprintf("%s; filename=\"%s\"", disposition, filename))
	w.Header().Set("Connection", "keep-alive")
	w.Header().Set("X-Remaining-Downloads", remainingDownloads)
	w.Header().Set("X-Remaining-Days", remainingDays)

	if disposition == "inline" && canContainsXSS(contentType) {
		reader = ioutil.NopCloser(bluemonday.UGCPolicy().SanitizeReader(reader))
	}

	if w.Header().Get("Range") == "" {
		if _, err = io.Copy(w, reader); err != nil {
			log.Printf("%s", err.Error())
			http.Error(w, "Error occurred copying to output stream", 500)
			return
		}

		return
	}

	file, err := ioutil.TempFile(s.tempPath, "range-")
	if err != nil {
		log.Printf("%s", err.Error())
		http.Error(w, "Error occurred copying to output stream", 500)
		return
	}

	defer cleanTmpFile(file)

	tee := io.TeeReader(reader, file)
	for {
		b := make([]byte, _5M)
		_, err = tee.Read(b)
		if err == io.EOF {
			break
		}

		if err != nil {
			log.Printf("%s", err.Error())
			http.Error(w, "Error occurred copying to output stream", 500)
			return
		}
	}

	http.ServeContent(w, r, filename, time.Now(), file)
}

func (s *Server) RedirectHandler(h http.Handler) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if !s.forceHTTPs {
			// we don't want to enforce https
		} else if r.URL.Path == "/health.html" {
			// health check url won't redirect
		} else if strings.HasSuffix(ipAddrFromRemoteAddr(r.Host), ".onion") {
			// .onion addresses cannot get a valid certificate, so don't redirect
		} else if r.Header.Get("X-Forwarded-Proto") == "https" {
		} else if r.URL.Scheme == "https" {
		} else {
			u := getURL(r, s.proxyPort)
			u.Scheme = "https"

			http.Redirect(w, r, u.String(), http.StatusPermanentRedirect)
			return
		}

		h.ServeHTTP(w, r)
	}
}

// Create a log handler for every request it receives.
func LoveHandler(h http.Handler) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("x-made-with", "<3 by DutchCoders")
		w.Header().Set("x-served-by", "Proudly served by DutchCoders")
		w.Header().Set("Server", "Transfer.sh HTTP Server 1.0")
		h.ServeHTTP(w, r)
	}
}

func IPFilterHandler(h http.Handler, ipFilterOptions *IPFilterOptions) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if ipFilterOptions == nil {
			h.ServeHTTP(w, r)
		} else {
			WrapIPFilter(h, *ipFilterOptions).ServeHTTP(w, r)
		}
		return
	}
}

func (s *Server) BasicAuthHandler(h http.Handler) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if s.AuthUser == "" || s.AuthPass == "" {
			h.ServeHTTP(w, r)
			return
		}

		w.Header().Set("WWW-Authenticate", "Basic realm=\"Restricted\"")

		username, password, authOK := r.BasicAuth()
		if authOK == false {
			http.Error(w, "Not authorized", 401)
			return
		}

		if username != s.AuthUser || password != s.AuthPass {
			http.Error(w, "Not authorized", 401)
			return
		}

		h.ServeHTTP(w, r)
	}
}