files_web_viewer/internal/handler/handler.go

package handler

import (
	"fmt"
	"html/template"
	"io/ioutil"
	"net/http"
	"net/url"
	"os"
	"path"
	"sort"
	"strings"
)

func renderError(w http.ResponseWriter, msg string, code int) {
	http.Error(w, msg, 404)
}

func byteCountBinary(b int64) string {
	const unit = 1024
	if b < unit {
		return fmt.Sprintf("%d B", b)
	}
	div, exp := int64(unit), 0
	for n := b / unit; n >= unit; n /= unit {
		div *= unit
		exp++
	}
	return fmt.Sprintf("%.1f %ciB", float64(b)/float64(div), "KMGTPE"[exp])
}

var htmlReplacer = strings.NewReplacer(
	"&", "&amp;",
	"<", "&lt;",
	">", "&gt;",
	// "&#34;" is shorter than "&quot;".
	`"`, "&#34;",
	// "&#39;" is shorter than "&apos;" and apos was not in HTML until HTML5.
	"'", "&#39;",
)

func localRedirect(w http.ResponseWriter, r *http.Request, newPath string) {
	if q := r.URL.RawQuery; q != "" {
		newPath += "?" + q
	}
	w.Header().Set("Location", newPath)
	w.WriteHeader(http.StatusMovedPermanently)
}

func toHTTPError(err error) (msg string, httpStatus int) {
	switch {
	case os.IsNotExist(err):
		return "404 page not found", http.StatusNotFound
	case os.IsPermission(err):
		return "403 Forbidden", http.StatusForbidden
	default:
		return "500 Internal Server Error", http.StatusInternalServerError
	}
}

func serveFile(w http.ResponseWriter, r *http.Request, fs http.FileSystem, filePath string) {
	f, err := fs.Open(filePath)
	if err != nil {
		msg, code := toHTTPError(err)
		renderError(w, msg, code)
		return
	}
	defer f.Close()

	d, err := f.Stat()
	if err != nil {
		msg, code := toHTTPError(err)
		renderError(w, msg, code)
		return
	}

	// redirect if the directory name doesn't end in a slash
	if d.IsDir() {
		url := r.URL.Path
		if url[len(url)-1] != '/' {
			localRedirect(w, r, path.Base(url)+"/")
			return
		}
	}

	// Still a directory? (we didn't find an index.html file)
	if d.IsDir() {
		dirList(w, r, f, fs, filePath)
		return
	}

	// serveContent will check modification time
	// sizeFunc := func() (int64, error) { return d.Size(), nil }
	http.ServeContent(w, r, d.Name(), d.ModTime(), f)
}

func dirList(w http.ResponseWriter, r *http.Request, f http.File, fs http.FileSystem, filePath string) {
	dirs, err := f.Readdir(-1)
	if err != nil {
		renderError(w, "Error reading directory", http.StatusInternalServerError)
		return
	}
	sort.Slice(dirs, func(i, j int) bool {
		if dirs[j].IsDir() && !dirs[i].IsDir() {
			return true
		}
		return dirs[i].Name() < dirs[j].Name()
	})

	w.Header().Set("Content-Type", "text/html; charset=utf-8")

	t, err := template.New("main.html").ParseFiles("static/main.html")
	if err != nil {
		fmt.Printf(err.Error())
		return
	}

	data := &Data{
		Title:  filePath,
		IsRoot: filePath == "/",
		Files:  make([]*File, 0, len(dirs)),
	}

	for _, d := range dirs {
		fileName := d.Name()
		icon := "file"
		size := byteCountBinary(d.Size())

		if d.IsDir() {
			fileName += "/"
			icon = "folder"
			size = "-"
		}

		if !d.IsDir() && strings.HasPrefix(strings.ToLower(fileName), "readme.") {
			data.Readme = loadReadmeFile(fs, filePath+"/"+fileName)
		}

		url := url.URL{Path: fileName}

		data.Files = append(data.Files, &File{
			Icon: icon,
			URL:  url.String(),
			Name: htmlReplacer.Replace(fileName),
			Size: size,
			Date: d.ModTime().Format("02.01.2006 15:04:05"),
		})

	}

	err = t.Execute(w, data)
	if err != nil {
		fmt.Printf(err.Error())
	}

}

func loadReadmeFile(fs http.FileSystem, fileName string) string {
	f, err := fs.Open(fileName)
	if err != nil {
		return ""
	}

	defer f.Close()

	data, err := ioutil.ReadAll(f)

	return string(data)
}

type fileHandler struct {
	rootPath string
}

func NewHandler(rootPath string) http.Handler {
	return &fileHandler{
		rootPath: rootPath,
	}
}

func (fh *fileHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	upath := r.URL.Path

	if !strings.HasPrefix(upath, "/") {
		upath = "/" + upath
		r.URL.Path = upath
	}

	serveFile(w, r, http.Dir(fh.rootPath), path.Clean(upath))
}