zipstatic.go

package main

import (
	"archive/zip"
	"bytes"
	"crypto/sha1"
	"encoding/hex"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"net/http"
	"os"
	"time"
)

type zipHandler struct {
	ts   time.Time
	data map[string][]byte
}

func (z *zipHandler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
	data, ok := z.data[req.URL.Path]
	if !ok {
		http.Error(w, "Not found", 404)
		return
	}

	http.ServeContent(w, req, req.URL.Path, z.ts, bytes.NewReader([]byte(data)))
}

var httpTimeFormats = []string{
	http.TimeFormat,
	time.RFC850,
	time.ANSIC,
}

// Stolen from go ~1.1
func parseHTTPTime(text string) (t time.Time, err error) {
	for _, layout := range httpTimeFormats {
		t, err = time.Parse(layout, text)
		if err == nil {
			return
		}
	}
	return
}

func updateStatic(path, cachePath string) (time.Time, error) {
	lastTs := time.Now()

	res, err := http.Get(path)
	if err != nil {
		return lastTs, err
	}
	defer res.Body.Close()
	if res.StatusCode != 200 {
		return lastTs, fmt.Errorf("HTTP error getting %v: %v", path, res.Status)
	}

	ftmp := cachePath + ".tmp"
	os.Remove(ftmp)
	defer os.Remove(ftmp)
	f, err := os.OpenFile(ftmp, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0666)
	if err != nil {
		return lastTs, err
	}
	defer f.Close()

	hash := sha1.New()
	_, err = io.Copy(f, io.TeeReader(res.Body, hash))
	if err != nil {
		return lastTs, err
	}
	h := `"` + hex.EncodeToString(hash.Sum(nil)) + `"`
	et := res.Header.Get("Etag")
	if et != "" && h != et {
		err := fmt.Errorf("invalid download: etag=%v, computed=%v",
			res.Header.Get("Etag"), h)
		return lastTs, err
	}

	t, parseErr := parseHTTPTime(res.Header.Get("Last-Modified"))
	if parseErr == nil {
		lastTs = t
	}

	os.Remove(cachePath)
	os.Rename(f.Name(), cachePath)

	return lastTs, nil
}

func zipStatic(path, cachePath string) (*zipHandler, error) {
	log.Printf("loading static content from: %v", path)
	lastTs, err := updateStatic(path, cachePath)
	if err != nil {
		st, e2 := os.Stat(cachePath)
		if e2 == nil {
			log.Printf("Error loading static data (%v). Proceeding with local copy",
				err)
			err = nil
			lastTs = st.ModTime()
		} else {
			err = fmt.Errorf("Both remote (%v) and local (%v) static content "+
				"is unavailable.", err, e2)
		}
	}

	if err != nil {
		return nil, err
	}

	zf, zerr := zipStaticServe(cachePath, lastTs)
	if zerr != nil {
		// If we couldn't serve from cache, errors from http take precendence.
		if err != nil {
			return nil, err
		}
		return nil, zerr
	}

	log.Printf("Static init complete")
	return zf, nil
}

func zipStaticServe(fn string, lastTs time.Time) (*zipHandler, error) {
	zr, err := zip.OpenReader(fn)
	if err != nil {
		return nil, err
	}
	defer zr.Close()

	zf := &zipHandler{
		ts:   lastTs,
		data: map[string][]byte{},
	}

	for _, f := range zr.File {
		rc, err := f.Open()
		if err != nil {
			return nil, err
		}

		d, err := ioutil.ReadAll(rc)
		if err != nil {
			return nil, err
		}
		rc.Close()

		zf.data[f.Name] = d
	}

	return zf, nil
}

type lastResortHandler struct{}

func (h *lastResortHandler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
	w.Header().Set("Content-Type", "text/html")
	w.Write([]byte(lastResortText))
}

const lastResortText = `<html>
<head><title>cbgb missing UI</title></head>

<body>
  <h1>cbgb is missing its UI</h1>

  <p>
    cbgb was not given a usable UI and could not fetch one from the
    internet.  The REST API will continue to work, but no admin UI
    will be available to you until you fix whatever got you here.
  </p>

  <p>
    For more info, check your logs and stuff.
  </p>
</body> </html>`