Simple static file and cgi server in go

cgiserver.go

package main

import (
	"bytes"
	"flag"
	"fmt"
	"io/ioutil"
	"net/http"
	"net/http/cgi"
	"os"
	"path"
	"path/filepath"
	"sort"
	"strings"
	"text/template"
	"time"
)

var (
	port                      int
	autoindex                 bool
	cgiURL, cgiDir, htdocsDir string
	staticTmpl                *template.Template
)

type CGIHandler struct {
	http.Handler
	cgiURL, cgiDir, htdocsDir, wd string
}

type fileStats []os.FileInfo

type fileList struct {
	CurDir string
	Stats  fileStats
}

func (h *CGIHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	rPath := filepath.Clean(filepath.FromSlash(r.URL.Path))

	if len(rPath) > 0 && os.IsPathSeparator(rPath[len(rPath)-1]) {
		rPath = rPath[:len(rPath)-1]
	}

	var isCGI bool
	var scriptPath string
	if strings.HasPrefix(path.Clean(r.URL.Path), h.cgiURL) {
		isCGI = true
	}

	if isCGI {
		scriptPath = r.URL.Path[len(h.cgiURL):]
		if i := strings.Index(scriptPath, "/"); i > -1 {
			scriptPath = scriptPath[:i]
			rPath = rPath[len(h.cgiURL):]
			rPath = rPath[:strings.Index(rPath, "/")]

			rPath = filepath.Join(h.cgiDir, rPath)
		} else {
			rPath = filepath.Join(h.cgiDir, rPath[len(h.cgiURL):])
		}
		scriptPath = path.Join(h.cgiURL, scriptPath)
	} else {
		rPath = filepath.Join(h.htdocsDir, rPath)
	}

	st, err := os.Stat(rPath)
	if err != nil {
		http.NotFound(w, r)
		fmt.Fprintf(os.Stderr, "Error stat-ing '%s': %v\n", rPath, err)
		return

	}

	if isCGI {
		var cgih cgi.Handler

		cgih = cgi.Handler{
			Path: rPath,
			Root: scriptPath,
			Env:  []string{"DOCUMENT_ROOT=" + h.htdocsDir},
		}

		cgih.ServeHTTP(w, r)
	} else {
		if st.IsDir() {
			iPath := filepath.Join(rPath, "index.html")
			st, err = os.Stat(iPath)
			if err != nil {
				if autoindex {
					if !strings.HasSuffix(r.URL.Path, "/") {
						http.Redirect(w, r, r.URL.Path+"/", http.StatusFound)
						return
					}

					stats, err := ioutil.ReadDir(rPath)
					if err == nil {
						sort.Sort(fileStats(stats))
						fileList := &fileList{CurDir: path.Base(rPath), Stats: stats}
						var buf bytes.Buffer

						if err := staticTmpl.Execute(&buf, fileList); err != nil {
							http.NotFound(w, r)
							fmt.Fprintf(os.Stderr, "Error executing template: %v\n", err)
							return
						}

						if _, err := buf.WriteTo(w); err != nil {
							http.NotFound(w, r)
							fmt.Fprintf(os.Stderr, "Error writing buffer: %v\n", err)
							return
						}
					} else {
						http.NotFound(w, r)
						fmt.Fprintf(os.Stderr, "Error reading '%s': %v\n", iPath, err)
					}
				} else {
					http.NotFound(w, r)
				}
				return
			}
		}

		if !strings.HasPrefix(rPath, h.htdocsDir) {
			http.NotFound(w, r)
			return
		}

		http.ServeFile(w, r, rPath)
	}
}

func (fs fileStats) Len() int           { return len(fs) }
func (fs fileStats) Swap(i, j int)      { fs[i], fs[j] = fs[j], fs[i] }
func (fs fileStats) Less(i, j int) bool { return fs[i].Name() < fs[j].Name() }

func main() {
	wd, err := os.Getwd()
	if err != nil {
		fmt.Fprintf(os.Stderr, "Error getting current working dir: %v\n", err)
		os.Exit(0)
	}

	cgiURL = path.Clean(cgiURL)
	if len(cgiURL) == 0 {
		fmt.Fprintf(os.Stderr, "No cgi url given\n")
		os.Exit(0)
	}

	if cgiURL[0] != '/' {
		cgiURL = "/" + cgiURL
	}

	if !strings.HasSuffix(cgiURL, "/") {
		cgiURL = cgiURL + "/"
	}

	h := &CGIHandler{
		cgiURL:    cgiURL,
		cgiDir:    filepath.Join(wd, cgiDir),
		htdocsDir: filepath.Join(wd, htdocsDir),
		wd:        wd,
	}

	http.ListenAndServe(fmt.Sprintf(":%d", port), h)
}

func init() {
	flag.IntVar(&port, "port", 8080, "port")
	flag.BoolVar(&autoindex, "autoindex", true, "generate a directory index")
	flag.StringVar(&cgiURL, "cgi-url", "/cgi-bin", "cgi url")
	flag.StringVar(&cgiDir, "cgi-dir", "cgi-bin", "cgi directory")
	flag.StringVar(&htdocsDir, "htdocs-dir", "htdocs", "htdocs directory")
	flag.Parse()

	if autoindex {
		staticTmpl = template.Must(template.New("autoindex").Funcs(template.FuncMap{
			"formatdate": func(t time.Time) string {
				return t.Format(dateFormat)
			},
		}).Parse(fileListTemplate))
	}
}

const (
	dateFormat       = "Jan 2, 2006 at 3:04pm (MST)"
	fileListTemplate = `
<!doctype html>
<html>
	<head>
		<title>{{ .CurDir }}</title>
	</head>
	<body>
		<table>
			<tbody>
				<tr>
					<td><a href="../">../</a></td>
					<td colspan="2"></td>
				</tr>
				{{ range .Stats }}
					<tr>
						<td>
							{{ if .IsDir }}
								<a href="{{ .Name }}/">{{ .Name }}/</a>
							{{ else }}
								<a href="{{ .Name }}">{{ .Name }}</a>
							{{ end }}
						</td>
						<td>
							{{ .ModTime | formatdate }}
						</td>
						<td>
							{{ .Size }}
						</td>
					</tr>
				{{ end }}
	</body>
</html>
`
)