transfer.sh/server/handlers.go

/*
The MIT License (MIT)

Copyright (c) 2014-2017 DutchCoders [https://github.com/dutchcoders/]
Copyright (c) 2018-2020 Andrea Spacca.
Copyright (c) 2020- Andrea Spacca and Stefan Benten.

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 (
	"archive/tar"
	"archive/zip"
	"bytes"
	"compress/gzip"
	"context"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"html"
	htmlTemplate "html/template"
	"io"
	"mime"
	"net"
	"net/http"
	"net/url"
	"os"
	"path"
	"path/filepath"
	"strconv"
	"strings"
	"sync"
	textTemplate "text/template"
	"time"

	"github.com/ProtonMail/go-crypto/openpgp"
	"github.com/ProtonMail/go-crypto/openpgp/armor"
	"github.com/ProtonMail/go-crypto/openpgp/packet"
	"github.com/ProtonMail/gopenpgp/v2/constants"
	"github.com/dutchcoders/transfer.sh/server/storage"

	web "github.com/dutchcoders/transfer.sh-web"
	"github.com/gorilla/mux"
	"github.com/microcosm-cc/bluemonday"
	blackfriday "github.com/russross/blackfriday/v2"
	qrcode "github.com/skip2/go-qrcode"
	"golang.org/x/net/idna"
)

const getPathPart = "get"

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

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

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

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

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

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

	return templates
}

func attachEncryptionReader(reader io.ReadCloser, password string) (io.ReadCloser, error) {
	if len(password) == 0 {
		return reader, nil
	}

	return encrypt(reader, []byte(password))
}

func attachDecryptionReader(reader io.ReadCloser, password string) (io.ReadCloser, error) {
	if len(password) == 0 {
		return reader, nil
	}

	return decrypt(reader, []byte(password))
}

func decrypt(ciphertext io.ReadCloser, password []byte) (plaintext io.ReadCloser, err error) {
	unarmored, err := armor.Decode(ciphertext)
	if err != nil {
		return
	}

	firstTimeCalled := true
	var prompt = func(keys []openpgp.Key, symmetric bool) ([]byte, error) {
		if firstTimeCalled {
			firstTimeCalled = false
			return password, nil
		}
		// Re-prompt still occurs if SKESK pasrsing fails (i.e. when decrypted cipher algo is invalid).
		// For most (but not all) cases, inputting a wrong passwords is expected to trigger this error.
		return nil, errors.New("gopenpgp: wrong password in symmetric decryption")
	}

	config := &packet.Config{
		DefaultCipher: packet.CipherAES256,
	}

	var emptyKeyRing openpgp.EntityList
	md, err := openpgp.ReadMessage(unarmored.Body, emptyKeyRing, prompt, config)
	if err != nil {
		// Parsing errors when reading the message are most likely caused by incorrect password, but we cannot know for sure
		return
	}

	plaintext = io.NopCloser(md.UnverifiedBody)

	return
}

type encryptWrapperReader struct {
	plaintext         io.Reader
	encrypt           io.WriteCloser
	armored           io.WriteCloser
	buffer            io.ReadWriter
	plaintextReadZero bool
}

func (e *encryptWrapperReader) Read(p []byte) (n int, err error) {
	p2 := make([]byte, len(p))

	n, _ = e.plaintext.Read(p2)
	if n == 0 {
		if !e.plaintextReadZero {
			err = e.encrypt.Close()
			if err != nil {
				return
			}

			err = e.armored.Close()
			if err != nil {
				return
			}

			e.plaintextReadZero = true
		}

		return e.buffer.Read(p)
	}

	return e.buffer.Read(p)
}

func (e *encryptWrapperReader) Close() error {
	return nil
}

func NewEncryptWrapperReader(plaintext io.Reader, armored, encrypt io.WriteCloser, buffer io.ReadWriter) io.ReadCloser {
	return &encryptWrapperReader{
		plaintext: io.TeeReader(plaintext, encrypt),
		encrypt:   encrypt,
		armored:   armored,
		buffer:    buffer,
	}
}

func encrypt(plaintext io.ReadCloser, password []byte) (ciphertext io.ReadCloser, err error) {
	bufferReadWriter := new(bytes.Buffer)
	armored, err := armor.Encode(bufferReadWriter, constants.PGPMessageHeader, nil)
	if err != nil {
		return
	}
	config := &packet.Config{
		DefaultCipher: packet.CipherAES256,
		Time:          time.Now,
	}

	hints := &openpgp.FileHints{
		IsBinary: true,
		FileName: "",
		ModTime:  time.Unix(time.Now().Unix(), 0),
	}

	encryptWriter, err := openpgp.SymmetricallyEncrypt(armored, password, hints, config)
	if err != nil {
		return
	}

	ciphertext = NewEncryptWrapperReader(plaintext, armored, encryptWriter, bufferReadWriter)

	return
}

func healthHandler(w http.ResponseWriter, _ *http.Request) {
	_, _ = w.Write([]byte("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(r.Context(), token, filename, false)

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

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

	var templatePath string
	var content htmlTemplate.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(r.Context(), token, filename, nil); 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 = htmlTemplate.HTML(output)
		} else if strings.HasPrefix(contentType, "text/plain") {
			content = htmlTemplate.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        htmlTemplate.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)

	maxUploadSize := ""
	if s.maxUploadSize > 0 {
		maxUploadSize = formatSize(s.maxUploadSize)
	}

	purgeTime := ""
	if s.purgeDays > 0 {
		purgeTime = s.purgeDays.String()
	}

	data := struct {
		Hostname      string
		WebAddress    string
		EmailContact  string
		GAKey         string
		UserVoiceKey  string
		PurgeTime     string
		MaxUploadSize string
		SampleToken   string
		SampleToken2  string
	}{
		hostname,
		webAddress,
		s.emailContact,
		s.gaKey,
		s.userVoiceKey,
		purgeTime,
		maxUploadSize,
		token(s.randomTokenLength),
		token(s.randomTokenLength),
	}

	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, _ *http.Request) {
	http.Error(w, http.StatusText(404), 404)
}

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

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

	token := token(s.randomTokenLength)

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

	responseBody := ""

	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 {
				s.logger.Printf("%s", err.Error())
				http.Error(w, err.Error(), http.StatusInternalServerError)
				return
			}

			file, err := os.CreateTemp(s.tempPath, "transfer-")
			defer s.cleanTmpFile(file)

			if err != nil {
				s.logger.Printf("%s", err.Error())
				http.Error(w, err.Error(), http.StatusInternalServerError)
				return
			}

			n, err := io.Copy(file, f)
			if err != nil {
				s.logger.Printf("%s", err.Error())
				http.Error(w, err.Error(), http.StatusInternalServerError)
				return
			}

			contentLength := n

			_, err = file.Seek(0, io.SeekStart)
			if err != nil {
				s.logger.Printf("%s", err.Error())
				return
			}

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

			if s.performClamavPrescan {
				status, err := s.performScan(file.Name())
				if err != nil {
					s.logger.Printf("%s", err.Error())
					http.Error(w, "Could not perform prescan", http.StatusInternalServerError)
					return
				}

				if status != clamavScanStatusOK {
					s.logger.Printf("prescan positive: %s", status)
					http.Error(w, "Clamav prescan found a virus", http.StatusPreconditionFailed)
					return
				}
			}

			metadata := metadataForRequest(contentType, contentLength, s.randomTokenLength, r)

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

				return
			} else if err := s.storage.Put(r.Context(), token, fmt.Sprintf("%s.metadata", filename), buffer, "text/json", uint64(buffer.Len())); err != nil {
				s.logger.Printf("%s", err.Error())
				http.Error(w, "Could not save metadata", http.StatusInternalServerError)

				return
			}

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

			reader, err := attachEncryptionReader(file, r.Header.Get("X-Encrypt-Password"))
			if err != nil {
				http.Error(w, "Could not crypt file", http.StatusInternalServerError)
				return
			}

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

			}

			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().Add("X-Url-Delete", resolveURL(r, deleteURL, s.proxyPort))
			responseBody += fmt.Sprintln(getURL(r, s.proxyPort).ResolveReference(relativeURL).String())
		}
	}
	_, err := w.Write([]byte(responseBody))
	if err != nil {
		s.logger.Printf("%s", err.Error())
		http.Error(w, err.Error(), http.StatusInternalServerError)
	}
}

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

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

type metadata struct {
	// ContentType is the original uploading content type
	ContentType string
	// ContentLength is is the original uploading content length
	ContentLength int64
	// 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
	// Encrypted contains if the file was encrypted
	Encrypted bool
	// DecryptedContentType is the original uploading content type
	DecryptedContentType string
}

func metadataForRequest(contentType string, contentLength int64, randomTokenLength int, r *http.Request) metadata {
	metadata := metadata{
		ContentType:   strings.ToLower(contentType),
		ContentLength: contentLength,
		MaxDate:       time.Time{},
		Downloads:     0,
		MaxDownloads:  -1,
		DeletionToken: token(randomTokenLength) + token(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))
	}

	if password := r.Header.Get("X-Encrypt-Password"); password != "" {
		metadata.Encrypted = true
		metadata.ContentType = "text/plain; charset=utf-8"
		metadata.DecryptedContentType = contentType
	} else {
		metadata.Encrypted = false
	}

	return metadata
}

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

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

	contentLength := r.ContentLength

	defer storage.CloseCheck(r.Body)

	reader := r.Body

	if contentLength < 1 || s.performClamavPrescan {
		file, err := os.CreateTemp(s.tempPath, "transfer-")
		defer s.cleanTmpFile(file)
		if err != nil {
			s.logger.Printf("%s", err.Error())
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}

		// queue file to disk, because s3 needs content length
		// and clamav prescan scans a file
		n, err := io.Copy(file, r.Body)
		if err != nil {
			s.logger.Printf("%s", err.Error())
			http.Error(w, err.Error(), http.StatusInternalServerError)

			return
		}

		_, err = file.Seek(0, io.SeekStart)
		if err != nil {
			s.logger.Printf("%s", err.Error())
			http.Error(w, "Cannot reset cache file", http.StatusInternalServerError)

			return
		}

		contentLength = n

		if s.performClamavPrescan {
			status, err := s.performScan(file.Name())
			if err != nil {
				s.logger.Printf("%s", err.Error())
				http.Error(w, "Could not perform prescan", http.StatusInternalServerError)
				return
			}

			if status != clamavScanStatusOK {
				s.logger.Printf("prescan positive: %s", status)
				http.Error(w, "Clamav prescan found a virus", http.StatusPreconditionFailed)
				return
			}
		}

		reader = file
	}

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

	if contentLength == 0 {
		s.logger.Print("Empty content-length")
		http.Error(w, "Could not upload empty file", http.StatusBadRequest)
		return
	}

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

	token := token(s.randomTokenLength)

	metadata := metadataForRequest(contentType, contentLength, s.randomTokenLength, r)

	buffer := &bytes.Buffer{}
	if err := json.NewEncoder(buffer).Encode(metadata); err != nil {
		s.logger.Printf("%s", err.Error())
		http.Error(w, "Could not encode metadata", http.StatusInternalServerError)
		return
	} else if !metadata.MaxDate.IsZero() && time.Now().After(metadata.MaxDate) {
		s.logger.Print("Invalid MaxDate")
		http.Error(w, "Invalid MaxDate, make sure Max-Days is smaller than 290 years", http.StatusBadRequest)
		return
	} else if err := s.storage.Put(r.Context(), token, fmt.Sprintf("%s.metadata", filename), buffer, "text/json", uint64(buffer.Len())); err != nil {
		s.logger.Printf("%s", err.Error())
		http.Error(w, "Could not save metadata", http.StatusInternalServerError)
		return
	}

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

	reader, err := attachEncryptionReader(reader, r.Header.Get("X-Encrypt-Password"))
	if err != nil {
		http.Error(w, "Could not crypt file", http.StatusInternalServerError)
		return
	}

	if err = s.storage.Put(r.Context(), token, filename, reader, contentType, uint64(contentLength)); err != nil {
		s.logger.Printf("Error putting new file: %s", err.Error())
		http.Error(w, "Could not save file", http.StatusInternalServerError)
		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))

	_, _ = w.Write([]byte(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 {
	key = strings.TrimPrefix(key, "/")

	key = strings.TrimPrefix(key, proxyPath)

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

	return key
}

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

	var webAddress string

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

	host, port, err := net.SplitHostPort(r.Host)
	if err != nil {
		host = r.Host
		port = ""
	}

	p := idna.New(idna.ValidateForRegistration())
	var hostFromPunycode string
	hostFromPunycode, err = p.ToUnicode(host)
	if err == nil {
		host = hostFromPunycode
	}

	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 := time.Until(metadata.MaxDate)
		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) {
	key := path.Join(token, filename)

	lock, _ := s.locks.LoadOrStore(key, &sync.Mutex{})

	lock.(*sync.Mutex).Lock()
}

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

	lock, _ := s.locks.LoadOrStore(key, &sync.Mutex{})

	lock.(*sync.Mutex).Unlock()
}

func (s *Server) checkMetadata(ctx context.Context, token, filename string, increaseDownload bool) (metadata, error) {
	s.lock(token, filename)
	defer s.unlock(token, filename)

	var metadata metadata

	r, _, err := s.storage.Get(ctx, token, fmt.Sprintf("%s.metadata", filename), nil)
	defer storage.CloseCheck(r)

	if err != nil {
		return metadata, err
	}

	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(ctx, 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(ctx context.Context, deletionToken, token, filename string) error {
	s.lock(token, filename)
	defer s.unlock(token, filename)

	var metadata metadata

	r, _, err := s.storage.Get(ctx, token, fmt.Sprintf("%s.metadata", filename), nil)
	defer storage.CloseCheck(r)

	if s.storage.IsNotExist(err) {
		return errors.New("metadata doesn't exist")
	} else if err != nil {
		return err
	}

	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 {
			<-ticker.C
			err := s.storage.Purge(context.TODO(), s.purgeDays)
			if err != nil {
				s.logger.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(r.Context(), deletionToken, token, filename); err != nil {
		s.logger.Printf("Error metadata: %s", err.Error())
		http.Error(w, http.StatusText(http.StatusNotFound), http.StatusNotFound)
		return
	}

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

	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(r.Context(), token, filename, true); err != nil {
			s.logger.Printf("Error metadata: %s", err.Error())
			continue
		}

		reader, _, err := s.storage.Get(r.Context(), token, filename, nil)
		defer storage.CloseCheck(reader)

		if err != nil {
			if s.storage.IsNotExist(err) {
				http.Error(w, "File not found", 404)
				return
			}

			s.logger.Printf("%s", err.Error())
			http.Error(w, "Could not retrieve file.", http.StatusInternalServerError)
			return
		}

		header := &zip.FileHeader{
			Name:   strings.Split(key, "/")[1],
			Method: zip.Store,

			Modified: time.Now().UTC(),
		}

		fw, err := zw.CreateHeader(header)

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

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

	if err := zw.Close(); err != nil {
		s.logger.Printf("%s", err.Error())
		http.Error(w, "Internal server error.", http.StatusInternalServerError)
		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")
	commonHeader(w, tarfilename)

	gw := gzip.NewWriter(w)
	defer storage.CloseCheck(gw)

	zw := tar.NewWriter(gw)
	defer storage.CloseCheck(zw)

	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(r.Context(), token, filename, true); err != nil {
			s.logger.Printf("Error metadata: %s", err.Error())
			continue
		}

		reader, contentLength, err := s.storage.Get(r.Context(), token, filename, nil)
		defer storage.CloseCheck(reader)

		if err != nil {
			if s.storage.IsNotExist(err) {
				http.Error(w, "File not found", 404)
				return
			}

			s.logger.Printf("%s", err.Error())
			http.Error(w, "Could not retrieve file.", http.StatusInternalServerError)
			return
		}

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

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

		if _, err = io.Copy(zw, reader); err != nil {
			s.logger.Printf("%s", err.Error())
			http.Error(w, "Internal server error.", http.StatusInternalServerError)
			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")
	commonHeader(w, tarfilename)

	zw := tar.NewWriter(w)
	defer storage.CloseCheck(zw)

	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(r.Context(), token, filename, true); err != nil {
			s.logger.Printf("Error metadata: %s", err.Error())
			continue
		}

		reader, contentLength, err := s.storage.Get(r.Context(), token, filename, nil)
		defer storage.CloseCheck(reader)

		if err != nil {
			if s.storage.IsNotExist(err) {
				http.Error(w, "File not found", 404)
				return
			}

			s.logger.Printf("%s", err.Error())
			http.Error(w, "Could not retrieve file.", http.StatusInternalServerError)
			return
		}

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

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

		if _, err = io.Copy(zw, reader); err != nil {
			s.logger.Printf("%s", err.Error())
			http.Error(w, "Internal server error.", http.StatusInternalServerError)
			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(r.Context(), token, filename, false)

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

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

	if s.storage.IsRangeSupported() {
		w.Header().Set("Accept-Ranges", "bytes")
	}
}

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(r.Context(), token, filename, true)

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

	var rng *storage.Range
	if r.Header.Get("Range") != "" {
		rng = storage.ParseRange(r.Header.Get("Range"))
	}

	contentType := metadata.ContentType
	reader, contentLength, err := s.storage.Get(r.Context(), token, filename, rng)
	defer storage.CloseCheck(reader)

	if s.storage.IsNotExist(err) {
		http.Error(w, http.StatusText(http.StatusNotFound), http.StatusNotFound)
		return
	} else if err != nil {
		s.logger.Printf("%s", err.Error())
		http.Error(w, "Could not retrieve file.", http.StatusInternalServerError)
		return
	}
	if rng != nil {
		cr := rng.ContentRange()
		if cr != "" {
			w.Header().Set("Accept-Ranges", "bytes")
			w.Header().Set("Content-Range", cr)
			if rng.Limit > 0 {
				reader = io.NopCloser(io.LimitReader(reader, int64(rng.Limit)))
			}
		}
	}

	var disposition string
	if action == "inline" {
		disposition = "inline"
		/*
			metadata.ContentType is unable to determine the type of the content,
			So add text/plain in this case to fix XSS related issues/
		*/
		if strings.TrimSpace(contentType) == "" {
			contentType = "text/plain"
		}
	} else {
		disposition = "attachment"
	}

	remainingDownloads, remainingDays := metadata.remainingLimitHeaderValues()

	w.Header().Set("Content-Disposition", fmt.Sprintf(`%s; filename="%s"`, disposition, filename))
	w.Header().Set("Connection", "keep-alive")
	w.Header().Set("Cache-Control", "no-store")
	w.Header().Set("X-Remaining-Downloads", remainingDownloads)
	w.Header().Set("X-Remaining-Days", remainingDays)

	if rng != nil && rng.ContentRange() != "" {
		w.WriteHeader(http.StatusPartialContent)
	}

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

	password := r.Header.Get("X-Decrypt-Password")
	decryptionReader, err := attachDecryptionReader(reader, password)
	if err != nil {
		http.Error(w, "Could not decrypt file", http.StatusInternalServerError)
		return
	}

	if metadata.Encrypted && len(password) > 0 {
		contentType = metadata.DecryptedContentType
		contentLength = uint64(metadata.ContentLength)
	}

	w.Header().Set("Content-Type", contentType)
	w.Header().Set("Content-Length", strconv.FormatUint(contentLength, 10))

	if _, err = io.Copy(w, decryptionReader); err != nil {
		s.logger.Printf("%s", err.Error())
		http.Error(w, "Error occurred copying to output stream", http.StatusInternalServerError)
		return
	}
}

func commonHeader(w http.ResponseWriter, filename string) {
	w.Header().Set("Content-Disposition", fmt.Sprintf("attachment; filename=\"%s\"", filename))
	w.Header().Set("Connection", "close")
	w.Header().Set("Cache-Control", "no-store")
}

// RedirectHandler handles redirect
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.TLS != nil {
		} else {
			u := getURL(r, s.proxyPort)
			u.Scheme = "https"
			if len(s.proxyPort) == 0 && len(s.TLSListenerString) > 0 {
				_, port, err := net.SplitHostPort(s.TLSListenerString)
				if err != nil || port == "443" {
					port = ""
				}

				if len(port) > 0 {
					u.Host = net.JoinHostPort(u.Hostname(), port)
				} else {
					u.Host = u.Hostname()
				}
			}

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

		h.ServeHTTP(w, r)
	}
}

// LoveHandler 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")
		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)
		}
	}
}

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 {
			http.Error(w, "Not authorized", http.StatusUnauthorized)
			return
		}

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

		h.ServeHTTP(w, r)
	}
}