Moving to glide

vendor/github.com/mattermost/rsc/appfs/server/app.go

@@ -0,0 +1,982 @@
+// Copyright 2012 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package server implements an appfs server backed by the 
+// App Engine datastore.
+package server
+
+import (
+	"bytes"
+	"crypto/sha1"
+	"encoding/base64"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"path"
+	"strconv"
+	"strings"
+	"time"
+
+	"appengine"
+	"appengine/datastore"
+	"appengine/memcache"
+	"appengine/user"
+
+	"github.com/mattermost/rsc/appfs/fs"
+	"github.com/mattermost/rsc/appfs/proto"
+)
+
+const pwFile = "/.password"
+var chatty = false
+
+func init() {
+	handle(proto.ReadURL, (*request).read)
+	handle(proto.WriteURL, (*request).write)
+	handle(proto.StatURL, (*request).stat)
+	handle(proto.MkfsURL, (*request).mkfs)
+	handle(proto.CreateURL, (*request).create)
+	handle(proto.RemoveURL, (*request).remove)
+}
+
+type request struct {
+	w     http.ResponseWriter
+	req   *http.Request
+	c     appengine.Context
+	name  string
+	mname string
+	key   *datastore.Key
+}
+
+func auth(r *request) bool {
+	hdr := r.req.Header.Get("Authorization")
+	if !strings.HasPrefix(hdr, "Basic ") {
+		return false
+	}
+	data, err := base64.StdEncoding.DecodeString(hdr[6:])
+	if err != nil {
+		return false
+	}
+	i := bytes.IndexByte(data, ':')
+	if i < 0 {
+		return false
+	}
+	user, passwd := string(data[:i]), string(data[i+1:])
+	
+	_, data, err = read(r.c, pwFile)
+	if err != nil {
+		r.c.Errorf("reading %s: %v", pwFile, err)
+		if _, err := mkfs(r.c); err != nil {
+			r.c.Errorf("creating fs: %v", err)
+		}
+		_, data, err = read(r.c, pwFile)
+		if err != nil {
+			r.c.Errorf("reading %s again: %v", pwFile, err)
+			return false
+		}
+	}
+
+	lines := strings.Split(string(data), "\n")
+	for _, line := range lines {
+		if strings.HasPrefix(line, "#") {
+			continue
+		}
+		f := strings.Fields(line)
+		if len(f) < 3 {
+			continue
+		}
+		if f[0] == user {
+			return hash(f[1]+passwd) == f[2]
+		}
+	}
+	return false
+}
+
+func hash(s string) string {
+	h := sha1.New()
+	h.Write([]byte(s))
+	return fmt.Sprintf("%x", h.Sum(nil))
+}
+
+func handle(prefix string, f func(*request)) {
+	http.HandleFunc(prefix, func(w http.ResponseWriter, req *http.Request) {
+		c := appengine.NewContext(req)
+		r := &request{
+			w:   w,
+			req: req,
+			c:   c,
+		}
+
+		if strings.HasSuffix(prefix, "/") {
+			r.name, r.mname, r.key = mangle(c, req.URL.Path[len(prefix)-1:])
+		} else {
+			req.URL.Path = "/"
+		}
+		defer func() {
+			if err := recover(); err != nil {
+				w.WriteHeader(http.StatusConflict)
+				fmt.Fprintf(w, "%s\n", err)
+			}
+		}()
+
+		if !auth(r) {
+			w.Header().Set("WWW-Authenticate", "Basic realm=\"appfs\"")
+			http.Error(w, "Need auth", http.StatusUnauthorized)
+			return
+		}
+
+		f(r)
+	})
+}
+
+func mangle(c appengine.Context, name string) (string, string, *datastore.Key) {
+	name = path.Clean("/" + name)
+	n := strings.Count(name, "/")
+	if name == "/" {
+		n = 0
+	}
+	mname := fmt.Sprintf("%d%s", n, name)
+	root := datastore.NewKey(c, "RootKey", "v2:", 0, nil)
+	key := datastore.NewKey(c, "FileInfo", mname, 0, root)
+	return name, mname, key
+}
+
+type FileInfo struct {
+	Path    string // mangled path
+	Name    string
+	Qid     int64 // assigned unique id number
+	Seq     int64 // modification sequence number in file tree
+	ModTime time.Time
+	Size    int64
+	IsDir   bool
+}
+
+type FileData struct {
+	Data []byte
+}
+
+func stat(c appengine.Context, name string) (*FileInfo, error) {
+	var fi FileInfo
+	name, _, key := mangle(c, name)
+	c.Infof("DATASTORE Stat %q", name)
+	err := datastore.Get(c, key, &fi)
+	if err != nil {
+		return nil, err
+	}
+	return &fi, nil
+}
+
+func (r *request) saveStat(fi *FileInfo) {
+	jfi, err := json.Marshal(&fi)
+	if err != nil {
+		panic(err)
+	}
+	r.w.Header().Set("X-Appfs-Stat", string(jfi))
+}
+
+func (r *request) tx(f func(c appengine.Context) error) {
+	err := datastore.RunInTransaction(r.c, f, &datastore.TransactionOptions{XG: true})
+	if err != nil {
+		panic(err)
+	}
+}
+
+func (r *request) stat() {
+	var fi *FileInfo
+	r.tx(func(c appengine.Context) error {
+		fi1, err := stat(c, r.name)
+		if err != nil {
+			return err
+		}
+		fi = fi1
+		return nil
+	})
+
+	jfi, err := json.Marshal(&fi)
+	if err != nil {
+		panic(err)
+	}
+	r.w.Write(jfi)
+}
+
+func read(c appengine.Context, name string) (fi *FileInfo, data []byte, err error) {
+	name, _, _ = mangle(c, name)
+	fi1, err := stat(c, name)
+	if err != nil {
+		return nil, nil, err
+	}
+	if fi1.IsDir {
+		dt, err := readdir(c, name)
+		if err != nil {
+			return nil, nil, err
+		}
+		fi = fi1
+		data = dt
+		return fi, data, nil
+	}
+
+	root := datastore.NewKey(c, "RootKey", "v2:", 0, nil)
+	dkey := datastore.NewKey(c, "FileData", "", fi1.Qid, root)
+	var fd FileData
+	c.Infof("DATASTORE Read %q", name)
+	if err := datastore.Get(c, dkey, &fd); err != nil {
+		return nil, nil, err
+	}
+	fi = fi1
+	data = fd.Data
+	return fi, data, nil
+}
+
+func (r *request) read() {
+	var (
+		fi *FileInfo
+		data []byte
+	)
+	r.tx(func(c appengine.Context) error {
+		var err error
+		fi, data, err = read(r.c, r.name)
+		return err
+	})
+	r.saveStat(fi)
+	r.w.Write(data)
+}
+
+func readdir(c appengine.Context, name string) ([]byte, error) {
+	name, _, _ = mangle(c, name)
+	var buf bytes.Buffer
+
+	n := strings.Count(name, "/")
+	if name == "/" {
+		name = ""
+		n = 0
+	}
+	root := datastore.NewKey(c, "RootKey", "v2:", 0, nil)
+	first := fmt.Sprintf("%d%s/", n+1, name)
+	limit := fmt.Sprintf("%d%s0", n+1, name)
+	c.Infof("DATASTORE ReadDir %q", name)
+	q := datastore.NewQuery("FileInfo").
+		Filter("Path >=", first).
+		Filter("Path <", limit).
+		Ancestor(root)
+	enc := json.NewEncoder(&buf)
+	it := q.Run(c)
+	var fi FileInfo
+	var pfi proto.FileInfo
+	for {
+		fi = FileInfo{}
+		_, err := it.Next(&fi)
+		if err != nil {
+			if err == datastore.Done {
+				break
+			}
+			return nil, err
+		}
+		pfi = proto.FileInfo{
+			Name:    fi.Name,
+			ModTime: fi.ModTime,
+			Size:    fi.Size,
+			IsDir:   fi.IsDir,
+		}
+		if err := enc.Encode(&pfi); err != nil {
+			return nil, err
+		}
+	}
+
+	return buf.Bytes(), nil
+}
+
+func readdirRaw(c appengine.Context, name string) ([]proto.FileInfo, error) {
+	name, _, _ = mangle(c, name)
+	n := strings.Count(name, "/")
+	if name == "/" {
+		name = ""
+		n = 0
+	}
+	root := datastore.NewKey(c, "RootKey", "v2:", 0, nil)
+	first := fmt.Sprintf("%d%s/", n+1, name)
+	limit := fmt.Sprintf("%d%s0", n+1, name)
+	c.Infof("DATASTORE ReadDir %q", name)
+	q := datastore.NewQuery("FileInfo").
+		Filter("Path >=", first).
+		Filter("Path <", limit).
+		Ancestor(root)
+	it := q.Run(c)
+	var fi FileInfo
+	var pfi proto.FileInfo
+	var out []proto.FileInfo
+	for {
+		fi = FileInfo{}
+		_, err := it.Next(&fi)
+		if err != nil {
+			if err == datastore.Done {
+				break
+			}
+			return nil, err
+		}
+		pfi = proto.FileInfo{
+			Name:    fi.Name,
+			ModTime: fi.ModTime,
+			Size:    fi.Size,
+			IsDir:   fi.IsDir,
+		}
+		out = append(out, pfi)
+	}
+println("READDIR", name, len(out))
+	return out, nil
+}
+
+
+var initPasswd = `# Password file
+# This file controls access to the server.
+# The format is lines of space-separated fields:
+#	user salt pwhash
+# The pwhash is the SHA1 of the salt string concatenated with the password.
+
+# user=dummy password=dummy (replace with your own entries)
+dummy 12345 faa863c7d3d41893f80165c704b714d5e31bdd3b
+`
+
+func (r *request) mkfs() {
+	var fi *FileInfo
+	r.tx(func(c appengine.Context) error {
+		var err error
+		fi, err = mkfs(c)
+		return err
+	})
+	r.saveStat(fi)
+}
+
+func mkfs(c appengine.Context) (fi *FileInfo, err error) {
+	fi1, err := stat(c, "/")
+	if err == nil {
+		return fi1, nil
+	}
+
+	// Root needs to be created.
+	// Probably root key does too.
+	root := datastore.NewKey(c, "RootKey", "v2:", 0, nil)
+	_, err = datastore.Put(c, root, &struct{}{})
+	if err != nil {
+		return nil, fmt.Errorf("mkfs put root: %s", err)
+	}
+
+	// Entry for /.
+	_, mpath, key := mangle(c, "/")
+	fi3 := FileInfo{
+		Path:    mpath,
+		Name:    "/",
+		Seq:     2,  // 2, not 1, because we're going to write password file with #2
+		Qid:     1,
+		ModTime: time.Now(),
+		Size:    0,
+		IsDir:   true,
+	}
+	_, err = datastore.Put(c, key, &fi3)
+	if err != nil {
+		return nil, fmt.Errorf("mkfs put /: %s", err)
+	}
+
+	/*
+	 * Would like to use this code but App Engine apparently
+	 * does not let Get observe the effect of a Put in the same
+	 * transaction.  What planet does that make sense on?
+	 * Instead, we have to execute just the datastore writes that this
+	 * sequence would.
+	 *
+	_, err = create(c, pwFile, false)
+	if err != nil {
+		return nil, fmt.Errorf("mkfs create .password: %s", err)
+	}
+	_, err = write(c, pwFile, []byte(initPasswd))
+	if err != nil {
+		return nil, fmt.Errorf("mkfs write .password: %s", err)
+	}
+	 *
+	 */
+
+	{
+		name, mname, key := mangle(c, pwFile)
+
+		// Create data object.
+		dataKey := int64(2)
+		root := datastore.NewKey(c, "RootKey", "v2:", 0, nil)
+		dkey := datastore.NewKey(c, "FileData", "", dataKey, root)
+		_, err := datastore.Put(c, dkey, &FileData{[]byte(initPasswd)})
+		if err != nil {
+			return nil, err
+		}
+	
+		// Create new directory entry.
+		_, elem := path.Split(name)
+		fi1 = &FileInfo{
+			Path:    mname,
+			Name:    elem,
+			Qid:     2,
+			Seq:     2,
+			ModTime: time.Now(),
+			Size:    int64(len(initPasswd)),
+			IsDir: false,
+		}
+		if _, err := datastore.Put(c, key, fi1); err != nil {
+			return nil, err
+		}
+	}
+
+	return &fi3, nil
+}
+
+func (r *request) write() {
+	data, err := ioutil.ReadAll(r.req.Body)
+	if err != nil {
+		panic(err)
+	}
+
+	var fi *FileInfo
+	var seq int64
+	r.tx(func(c appengine.Context) error {
+		var err error
+		fi, seq, err = write(r.c, r.name, data)
+		return err
+	})
+	updateCacheTime(r.c, seq)
+	r.saveStat(fi)
+}
+
+func write(c appengine.Context, name string, data []byte) (*FileInfo, int64, error) {
+	name, _, key := mangle(c, name)
+
+	// Check that file exists and is not a directory.
+	fi1, err := stat(c, name)
+	if err != nil {
+		return nil, 0, err
+	}
+	if fi1.IsDir {
+		return nil, 0, fmt.Errorf("cannot write to directory")
+	}
+
+	// Fetch and increment root sequence number.
+	rfi, err := stat(c, "/")
+	if err != nil {
+		return nil, 0, err
+	}
+	rfi.Seq++
+
+	// Write data.
+	root := datastore.NewKey(c, "RootKey", "v2:", 0, nil)
+	dkey := datastore.NewKey(c, "FileData", "", fi1.Qid, root)
+	fd := &FileData{data}
+	if _, err := datastore.Put(c, dkey, fd); err != nil {
+		return nil, 0, err
+	}
+
+	// Update directory entry.
+	fi1.Seq = rfi.Seq
+	fi1.Size = int64(len(data))
+	fi1.ModTime = time.Now()
+	if _, err := datastore.Put(c, key, fi1); err != nil {
+		return nil, 0, err
+	}
+
+	// Update sequence numbers all the way to the root.
+	if err := updateSeq(c, name, rfi.Seq, 1); err != nil {
+		return nil, 0, err
+	}
+
+	return fi1, rfi.Seq, nil
+}
+
+func updateSeq(c appengine.Context, name string, seq int64, skip int) error {
+	p := path.Clean(name)
+	for i := 0; ; i++ {
+		if i >= skip {
+			_, _, key := mangle(c, p)
+			var fi FileInfo
+			if err := datastore.Get(c, key, &fi); err != nil {
+				return err
+			}
+			fi.Seq = seq
+			if _, err := datastore.Put(c, key, &fi); err != nil {
+				return err
+			}
+		}
+		if p == "/" {
+			break
+		}
+		p, _ = path.Split(p)
+		p = path.Clean(p)
+	}
+	return nil
+}
+
+func (r *request) remove() {
+	panic("remove not implemented")
+}
+
+func (r *request) create() {
+	var fi *FileInfo
+	var seq int64
+	isDir := r.req.FormValue("dir") == "1"
+	r.tx(func(c appengine.Context) error {
+		var err error
+		fi, seq, err = create(r.c, r.name, isDir, nil)
+		return err
+	})
+	updateCacheTime(r.c, seq)
+	r.saveStat(fi)
+}
+
+func create(c appengine.Context, name string, isDir bool, data []byte) (*FileInfo, int64, error) {
+	name, mname, key := mangle(c, name)
+
+	// File must not exist.
+	fi1, err := stat(c, name)
+	if err == nil {
+		return nil, 0, fmt.Errorf("file already exists")
+	}
+	if err != datastore.ErrNoSuchEntity {
+		return nil, 0, err
+	}
+
+	// Parent must exist and be a directory.
+	p, _ := path.Split(name)
+	fi2, err := stat(c, p)
+	if err != nil {
+		if err == datastore.ErrNoSuchEntity {
+			return nil, 0, fmt.Errorf("parent directory %q does not exist", p)
+		}
+		return nil, 0, err
+	}
+	if !fi2.IsDir {
+		return nil, 0, fmt.Errorf("parent %q is not a directory", p)
+	}
+
+	// Fetch and increment root sequence number.
+	rfi, err := stat(c, "/")
+	if err != nil {
+		return nil, 0, err
+	}
+	rfi.Seq++
+
+	var dataKey int64
+	// Create data object.
+	if !isDir {
+		dataKey = rfi.Seq
+		root := datastore.NewKey(c, "RootKey", "v2:", 0, nil)
+		dkey := datastore.NewKey(c, "FileData", "", dataKey, root)
+		_, err := datastore.Put(c, dkey, &FileData{data})
+		if err != nil {
+			return nil, 0, err
+		}
+	}
+
+	// Create new directory entry.
+	_, elem := path.Split(name)
+	fi1 = &FileInfo{
+		Path:    mname,
+		Name:    elem,
+		Qid:     rfi.Seq,
+		Seq:     rfi.Seq,
+		ModTime: time.Now(),
+		Size:    int64(len(data)),
+		IsDir:   isDir,
+	}
+	if _, err := datastore.Put(c, key, fi1); err != nil {
+		return nil, 0, err
+	}
+
+	// Update sequence numbers all the way to root,
+	// but skip entry we just wrote.
+	if err := updateSeq(c, name, rfi.Seq, 1); err != nil {
+		return nil, 0, err
+	}
+
+	return fi1, rfi.Seq, nil
+}
+
+// Implementation of fs.AppEngine.
+
+func init() {
+	fs.Register(ae{})
+}
+
+type ae struct{}
+
+func tx(c interface{}, f func(c appengine.Context) error) error {
+	return datastore.RunInTransaction(c.(appengine.Context), f, &datastore.TransactionOptions{XG: true})
+}
+
+func (ae) NewContext(req *http.Request) interface{} {
+	return appengine.NewContext(req)
+}
+
+func (ae) User(ctxt interface{}) string {
+	c := ctxt.(appengine.Context)
+	u := user.Current(c)
+	if u == nil {
+		return "?"
+	}
+	return u.String()
+}
+
+type cacheKey struct {
+	t int64
+	name string
+}
+
+func (ae) CacheRead(ctxt interface{}, name, path string) (key interface{}, data []byte, found bool) {
+	c := ctxt.(appengine.Context)
+	t, data, _, err := cacheRead(c, "cache", name, path)
+	return &cacheKey{t, name}, data, err == nil
+}
+
+func (ae) CacheWrite(ctxt, key interface{}, data []byte) {
+	c := ctxt.(appengine.Context)
+	k := key.(*cacheKey)
+	cacheWrite(c, k.t, "cache", k.name, data)
+}
+
+func (ae ae) Read(ctxt interface{}, name string) (data []byte, pfi *proto.FileInfo, err error) {
+	c := ctxt.(appengine.Context)
+	name = path.Clean("/"+name)
+	if chatty {
+		c.Infof("AE Read %s", name)
+	}
+	_, data, pfi, err = cacheRead(c, "data", name, name)
+	if err != nil {
+		err = fmt.Errorf("Read %q: %v", name, err)
+	}
+	return
+}
+
+func (ae) Write(ctxt interface{}, path string, data []byte) error {
+	var seq int64
+	err := tx(ctxt, func(c appengine.Context) error {
+		_, err := stat(c, path)
+		if err != nil {
+			_, seq, err = create(c, path, false, data)
+		} else {
+			_, seq, err = write(c, path, data)
+		}
+		return err
+	})
+	if seq != 0 {
+		updateCacheTime(ctxt.(appengine.Context), seq)
+	}
+	if err != nil {
+		err = fmt.Errorf("Write %q: %v", path, err)
+	}
+	return err
+}
+
+func (ae) Remove(ctxt interface{}, path string) error {
+	return fmt.Errorf("remove not implemented")
+}
+
+func (ae) Mkdir(ctxt interface{}, path string) error {
+	var seq int64
+	err := tx(ctxt, func(c appengine.Context) error {
+		var err error
+		_, seq, err = create(c, path, true, nil)
+		return err
+	})
+	if seq != 0 {
+		updateCacheTime(ctxt.(appengine.Context), seq)
+	}
+	if err != nil {
+		err = fmt.Errorf("Mkdir %q: %v", path, err)
+	}
+	return err
+}
+
+func (ae) Criticalf(ctxt interface{}, format string, args ...interface{}) {
+	ctxt.(appengine.Context).Criticalf(format, args...)
+}
+
+type readDirCacheEntry struct {
+	Dir []proto.FileInfo
+	Error string
+}
+
+func (ae) ReadDir(ctxt interface{}, name string) (dir []proto.FileInfo, err error) {	
+	c := ctxt.(appengine.Context)
+	name = path.Clean("/"+name)
+	t, data, _, err := cacheRead(c, "dir", name, name)
+	if err == nil {
+		var e readDirCacheEntry
+		if err := json.Unmarshal(data, &e); err == nil {
+			if chatty {
+				c.Infof("cached ReadDir %q", name)
+			}
+			if e.Error != "" {
+				return nil, errors.New(e.Error)
+			}
+			return e.Dir, nil
+		}
+		c.Criticalf("unmarshal cached dir %q: %v", name)
+	}
+	err = tx(ctxt, func(c appengine.Context) error {
+		var err error
+		dir, err = readdirRaw(c, name)
+		return err
+	})
+	var e readDirCacheEntry
+	e.Dir = dir
+	if err != nil {
+		err = fmt.Errorf("ReadDir %q: %v", name, err)
+		e.Error = err.Error()
+	}
+	if data, err := json.Marshal(&e); err != nil {
+		c.Criticalf("json marshal cached dir: %v", err)
+	} else {
+		c.Criticalf("caching dir %q@%d %d bytes", name, t, len(data))
+		cacheWrite(c, t, "dir", name, data)
+	}
+	return
+}
+
+// Caching of file system data.
+//
+// The cache stores entries under keys of the form time,space,name,
+// where time is the time at which the entry is valid for, space is a name
+// space identifier, and name is an arbitrary name.
+//
+// A key of the form t,mtime,path maps to an integer value giving the
+// modification time of the named path at root time t.
+// The special key 0,mtime,/ is an integer giving the current time at the root.
+//
+// A key of the form t,data,path maps to the content of path at time t.
+//
+// Thus, a read from path should first obtain the root time,
+// then obtain the modification time for the path at that root time
+// then obtain the data for that path.
+//	t1 = get(0,mtime,/)
+//	t2 = get(t1,mtime,path)
+//	data = get(t2,data,path)
+//
+// The API allows clients to cache their own data too, with expiry tied to
+// the modification time of a particular path (file or directory).  To look
+// up one of those, we use:
+//	t1 = get(0,mtime,/)
+//	t2 = get(t1,mtime,path)
+//	data = get(t2,clientdata,name)
+//
+// To store data in the cache, the t1, t2 should be determined before reading
+// from datastore.  Then the data should be saved under t2.  This ensures
+// that if a datastore update happens after the read but before the cache write,
+// we'll be writing to an entry that will no longer be used (t2).
+
+const rootMemcacheKey = "0,mtime,/"
+
+func updateCacheTime(c appengine.Context, seq int64) {
+	const key = rootMemcacheKey
+	bseq := []byte(strconv.FormatInt(seq, 10))
+	for tries := 0; tries < 10; tries++ {
+		item, err := memcache.Get(c, key)
+		if err != nil {
+			c.Infof("memcache.Get %q: %v", key, err)
+			err = memcache.Add(c, &memcache.Item{Key: key, Value: bseq})
+			if err == nil {
+				c.Infof("memcache.Add %q %q ok", key, bseq)
+				return
+			}
+			c.Infof("memcache.Add %q %q: %v", key, bseq, err)
+		}
+		v, err := strconv.ParseInt(string(item.Value), 10, 64)
+		if err != nil {
+			c.Criticalf("memcache.Get %q = %q (%v)", key, item.Value, err)
+			return
+		}
+		if v >= seq {
+			return
+		}
+		item.Value = bseq
+		err = memcache.CompareAndSwap(c, item)
+		if err == nil {
+			c.Infof("memcache.CAS %q %d->%d ok", key, v, seq)
+			return
+		}
+		c.Infof("memcache.CAS %q %d->%d: %v", key, v, seq, err)
+	}
+	c.Criticalf("repeatedly failed to update root key")
+}
+
+func cacheTime(c appengine.Context) (t int64, err error) {
+	const key = rootMemcacheKey
+	item, err := memcache.Get(c, key)
+	if err == nil {
+		v, err := strconv.ParseInt(string(item.Value), 10, 64)
+		if err == nil {
+			if chatty {
+				c.Infof("cacheTime %q = %v", key, v)
+			}
+			return v, nil
+		}
+		c.Criticalf("memcache.Get %q = %q (%v) - deleting", key, item.Value, err)
+		memcache.Delete(c, key)
+	}
+	fi, err := stat(c, "/")
+	if err != nil {
+		c.Criticalf("stat /: %v", err)
+		return 0, err
+	}
+	updateCacheTime(c, fi.Seq)
+	return fi.Seq, nil
+}
+
+func cachePathTime(c appengine.Context, path string) (t int64, err error) {
+	t, err = cacheTime(c)
+	if err != nil {
+		return 0, err
+	}
+	
+	key := fmt.Sprintf("%d,mtime,%s", t, path)
+	item, err := memcache.Get(c, key)
+	if err == nil {
+		v, err := strconv.ParseInt(string(item.Value), 10, 64)
+		if err == nil {
+			if chatty {
+				c.Infof("cachePathTime %q = %v", key, v)
+			}
+			return v, nil
+		}
+		c.Criticalf("memcache.Get %q = %q (%v) - deleting", key, item.Value, err)
+		memcache.Delete(c, key)
+	}
+
+	var seq int64
+	if fi, err := stat(c, path); err == nil {
+		seq = fi.Seq
+	}
+
+	c.Infof("cachePathTime save %q = %v", key, seq)
+	item = &memcache.Item{Key: key, Value: []byte(strconv.FormatInt(seq, 10))}
+	if err := memcache.Set(c, item); err != nil {
+		c.Criticalf("memcache.Set %q %q: %v", key, item.Value, err)
+	}
+	return seq, nil
+}
+
+type statCacheEntry struct {
+	FileInfo *proto.FileInfo
+	Error string
+}
+
+func cacheRead(c appengine.Context, kind, name, path string) (mtime int64, data []byte, pfi *proto.FileInfo, err error) {
+	for tries := 0; tries < 10; tries++ {
+		t, err := cachePathTime(c, path)
+		if err != nil {
+			return 0, nil, nil, err
+		}
+	
+		key := fmt.Sprintf("%d,%s,%s", t, kind, name)
+		item, err := memcache.Get(c, key)
+		var data []byte
+		if item != nil {
+			data = item.Value
+		}
+		if err != nil {
+			c.Infof("memcache miss %q %v", key, err)
+		} else if chatty {
+			c.Infof("memcache hit %q (%d bytes)", key, len(data))
+		}
+		if kind != "data" {
+			// Not a file; whatever memcache says is all we have.
+			return t, data, nil, err
+		}
+
+		// Load stat from cache (includes negative entry).
+		statkey := fmt.Sprintf("%d,stat,%s", t, name)
+		var st statCacheEntry
+		_, err = memcache.JSON.Get(c, statkey, &st)
+		if err == nil {
+			if st.Error != "" {
+				if chatty {
+					c.Infof("memcache hit stat error %q %q", statkey, st.Error)
+				}
+				err = errors.New(st.Error)
+			} else {
+				if chatty {
+					c.Infof("memcache hit stat %q", statkey)
+				}
+			}
+			if err != nil || data != nil {
+				return t, data, st.FileInfo, err
+			}
+		}
+		
+		// Need stat, or maybe stat+data.
+		var fi *FileInfo
+		if data != nil {
+			c.Infof("stat %q", name)
+			fi, err = stat(c, name)
+			if err == nil && fi.Seq != t {
+				c.Criticalf("loaded %s but found stat %d", key, fi.Seq)
+				continue
+			}
+		} else {
+			c.Infof("read %q", name)
+			fi, data, err = read(c, name)
+			if err == nil && fi.Seq != t {
+				c.Infof("loaded %s but found read %d", key, fi.Seq)
+				t = fi.Seq
+				key = fmt.Sprintf("%d,data,%s", t, name)
+				statkey = fmt.Sprintf("%d,stat,%s", t, name)
+			}
+
+			// Save data to memcache.
+			if err == nil {
+				if true || chatty {
+					c.Infof("save data in memcache %q", key)
+				}
+				item := &memcache.Item{Key: key, Value: data}
+				if err := memcache.Set(c, item); err != nil {
+					c.Criticalf("failed to cache %s: %v", key, err)
+				}
+			}
+		}
+		
+		// Cache stat, including error.
+		st = statCacheEntry{}
+		if fi != nil {
+			st.FileInfo = &proto.FileInfo{
+				Name:    fi.Name,
+				ModTime: fi.ModTime,
+				Size:    fi.Size,
+				IsDir:   fi.IsDir,
+			}
+		}
+		if err != nil {
+			st.Error = err.Error()
+			// If this is a deadline exceeded, do not cache.
+			if strings.Contains(st.Error, "Canceled") || strings.Contains(st.Error, "Deadline") {
+				return t, data, st.FileInfo, err
+			}
+		}
+		if chatty {
+			c.Infof("save stat in memcache %q", statkey)
+		}
+		if err := memcache.JSON.Set(c, &memcache.Item{Key: statkey, Object: &st}); err != nil {
+			c.Criticalf("failed to cache %s: %v", statkey, err)
+		}
+
+		// Done!
+		return t, data, st.FileInfo, err
+	}
+	
+	c.Criticalf("failed repeatedly in cacheRead")
+	return 0, nil, nil, errors.New("cacheRead loop failed")
+}
+
+func cacheWrite(c appengine.Context, t int64, kind, name string, data []byte) error {
+	mkey := fmt.Sprintf("%d,%s,%s", t, kind, name)
+	if true || chatty {
+		c.Infof("cacheWrite %s %d bytes", mkey, len(data))
+	}
+	err := memcache.Set(c, &memcache.Item{Key: mkey, Value: data})
+	if err != nil {
+		c.Criticalf("cacheWrite memcache.Set %q: %v", mkey, err)
+	}
+	return err
+}