diff --git a/cmd/godoc/filesystem.go b/cmd/godoc/filesystem.go
index 0309d7cabe..6679380180 100644
--- a/cmd/godoc/filesystem.go
+++ b/cmd/godoc/filesystem.go
@@ -19,6 +19,8 @@ import (
 	"sort"
 	"strings"
 	"time"
+
+	"code.google.com/p/go.tools/godoc/vfs"
 )
 
 // fs is the file system that godoc reads from and serves.
@@ -51,19 +53,13 @@ const debugNS = false
 // The FileSystem interface specifies the methods godoc is using
 // to access the file system for which it serves documentation.
 type FileSystem interface {
-	Open(path string) (readSeekCloser, error)
+	Open(path string) (vfs.ReadSeekCloser, error)
 	Lstat(path string) (os.FileInfo, error)
 	Stat(path string) (os.FileInfo, error)
 	ReadDir(path string) ([]os.FileInfo, error)
 	String() string
 }
 
-type readSeekCloser interface {
-	io.Reader
-	io.Seeker
-	io.Closer
-}
-
 // ReadFile reads the file named by path from fs and returns the contents.
 func ReadFile(fs FileSystem, path string) ([]byte, error) {
 	rc, err := fs.Open(path)
@@ -97,7 +93,7 @@ func (root osFS) resolve(path string) string {
 	return filepath.Join(string(root), path)
 }
 
-func (root osFS) Open(path string) (readSeekCloser, error) {
+func (root osFS) Open(path string) (vfs.ReadSeekCloser, error) {
 	f, err := os.Open(root.resolve(path))
 	if err != nil {
 		return nil, err
@@ -319,7 +315,7 @@ func (ns nameSpace) resolve(path string) []mountedFS {
 }
 
 // Open implements the FileSystem Open method.
-func (ns nameSpace) Open(path string) (readSeekCloser, error) {
+func (ns nameSpace) Open(path string) (vfs.ReadSeekCloser, error) {
 	var err error
 	for _, m := range ns.resolve(path) {
 		if debugNS {
@@ -552,7 +548,7 @@ func (h *httpDir) Readdir(count int) ([]os.FileInfo, error) {
 // httpFile implements http.File for a file (not directory) in a FileSystem.
 type httpFile struct {
 	fs FileSystem
-	readSeekCloser
+	vfs.ReadSeekCloser
 	name string
 }
 
diff --git a/cmd/godoc/godoc.go b/cmd/godoc/godoc.go
index 79d485b93d..84c8fa8f1b 100644
--- a/cmd/godoc/godoc.go
+++ b/cmd/godoc/godoc.go
@@ -32,26 +32,13 @@ import (
 	"time"
 	"unicode"
 	"unicode/utf8"
+
+	"code.google.com/p/go.tools/godoc/util"
 )
 
 // ----------------------------------------------------------------------------
 // Globals
 
-type delayTime struct {
-	RWValue
-}
-
-func (dt *delayTime) backoff(max time.Duration) {
-	dt.mutex.Lock()
-	v := dt.value.(time.Duration) * 2
-	if v > max {
-		v = max
-	}
-	dt.value = v
-	// don't change dt.timestamp - calling backoff indicates an error condition
-	dt.mutex.Unlock()
-}
-
 var (
 	verbose = flag.Bool("v", false, "verbose mode")
 
@@ -76,9 +63,9 @@ var (
 	indexThrottle = flag.Float64("index_throttle", 0.75, "index throttle value; 0.0 = no time allocated, 1.0 = full throttle")
 
 	// file system information
-	fsTree      RWValue // *Directory tree of packages, updated with each sync (but sync code is removed now)
-	fsModified  RWValue // timestamp of last call to invalidateIndex
-	docMetadata RWValue // mapping from paths to *Metadata
+	fsTree      util.RWValue // *Directory tree of packages, updated with each sync (but sync code is removed now)
+	fsModified  util.RWValue // timestamp of last call to invalidateIndex
+	docMetadata util.RWValue // mapping from paths to *Metadata
 
 	// http handlers
 	fileServer http.Handler // default file server
@@ -112,7 +99,7 @@ func initFSTree() {
 		log.Println("Warning: FSTree is nil")
 		return
 	}
-	fsTree.set(dir)
+	fsTree.Set(dir)
 	invalidateIndex()
 }
 
@@ -250,7 +237,7 @@ func infoKind_htmlFunc(info SpotInfo) string {
 func infoLineFunc(info SpotInfo) int {
 	line := info.Lori()
 	if info.IsIndex() {
-		index, _ := searchIndex.get()
+		index, _ := searchIndex.Get()
 		if index != nil {
 			line = index.(*Index).Snippet(line).Line
 		} else {
@@ -266,7 +253,7 @@ func infoLineFunc(info SpotInfo) int {
 
 func infoSnippet_htmlFunc(info SpotInfo) string {
 	if info.IsIndex() {
-		index, _ := searchIndex.get()
+		index, _ := searchIndex.Get()
 		// Snippet.Text was HTML-escaped when it was generated
 		return index.(*Index).Snippet(info.Lori()).Text
 	}
@@ -838,7 +825,7 @@ func serveFile(w http.ResponseWriter, r *http.Request) {
 		if redirect(w, r) {
 			return
 		}
-		if index := pathpkg.Join(abspath, "index.html"); isTextFile(index) {
+		if index := pathpkg.Join(abspath, "index.html"); util.IsTextFile(fs, index) {
 			serveHTMLDoc(w, r, index, index)
 			return
 		}
@@ -846,7 +833,7 @@ func serveFile(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if isTextFile(abspath) {
+	if util.IsTextFile(fs, abspath) {
 		if redirectFile(w, r) {
 			return
 		}
@@ -1168,7 +1155,7 @@ func (h *docServer) getPageInfo(abspath, relpath string, mode PageInfoMode) *Pag
 	// get directory information, if any
 	var dir *Directory
 	var timestamp time.Time
-	if tree, ts := fsTree.get(); tree != nil && tree.(*Directory) != nil {
+	if tree, ts := fsTree.Get(); tree != nil && tree.(*Directory) != nil {
 		// directory tree is present; lookup respective directory
 		// (may still fail if the file system was updated and the
 		// new directory tree has not yet been computed)
@@ -1256,7 +1243,7 @@ func (h *docServer) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 // ----------------------------------------------------------------------------
 // Search
 
-var searchIndex RWValue
+var searchIndex util.RWValue
 
 type SearchResult struct {
 	Query string
@@ -1276,7 +1263,7 @@ type SearchResult struct {
 func lookup(query string) (result SearchResult) {
 	result.Query = query
 
-	index, timestamp := searchIndex.get()
+	index, timestamp := searchIndex.Get()
 	if index != nil {
 		index := index.(*Index)
 
@@ -1311,7 +1298,7 @@ func lookup(query string) (result SearchResult) {
 
 	// is the result accurate?
 	if *indexEnabled {
-		if _, ts := fsModified.get(); timestamp.Before(ts) {
+		if _, ts := fsModified.Get(); timestamp.Before(ts) {
 			// The index is older than the latest file system change under godoc's observation.
 			result.Alert = "Indexing in progress: result may be inaccurate"
 		}
@@ -1422,7 +1409,7 @@ func updateMetadata() {
 		}
 	}
 	scan("/doc")
-	docMetadata.set(metadata)
+	docMetadata.Set(metadata)
 }
 
 // Send a value on this channel to trigger a metadata refresh.
@@ -1455,7 +1442,7 @@ func refreshMetadataLoop() {
 // exists.
 //
 func metadataFor(relpath string) *Metadata {
-	if m, _ := docMetadata.get(); m != nil {
+	if m, _ := docMetadata.Get(); m != nil {
 		meta := m.(map[string]*Metadata)
 		// If metadata for this relpath exists, return it.
 		if p := meta[relpath]; p != nil {
@@ -1479,7 +1466,7 @@ func metadataFor(relpath string) *Metadata {
 // under godoc's observation change so that the indexer is kicked on.
 //
 func invalidateIndex() {
-	fsModified.set(nil)
+	fsModified.Set(nil)
 	refreshMetadata()
 }
 
@@ -1487,16 +1474,16 @@ func invalidateIndex() {
 // than any of the file systems under godoc's observation.
 //
 func indexUpToDate() bool {
-	_, fsTime := fsModified.get()
-	_, siTime := searchIndex.get()
+	_, fsTime := fsModified.Get()
+	_, siTime := searchIndex.Get()
 	return !fsTime.After(siTime)
 }
 
 // feedDirnames feeds the directory names of all directories
 // under the file system given by root to channel c.
 //
-func feedDirnames(root *RWValue, c chan<- string) {
-	if dir, _ := root.get(); dir != nil {
+func feedDirnames(root *util.RWValue, c chan<- string) {
+	if dir, _ := root.Get(); dir != nil {
 		for d := range dir.(*Directory).iter(false) {
 			c <- d.Path
 		}
@@ -1536,7 +1523,7 @@ func readIndex(filenames string) error {
 	if err := x.Read(io.MultiReader(files...)); err != nil {
 		return err
 	}
-	searchIndex.set(x)
+	searchIndex.Set(x)
 	return nil
 }
 
@@ -1547,7 +1534,7 @@ func updateIndex() {
 	start := time.Now()
 	index := NewIndex(fsDirnames(), *maxResults > 0, *indexThrottle)
 	stop := time.Now()
-	searchIndex.set(index)
+	searchIndex.Set(index)
 	if *verbose {
 		secs := stop.Sub(start).Seconds()
 		stats := index.Stats()
diff --git a/cmd/godoc/index.go b/cmd/godoc/index.go
index d1292d5053..c3cfe69adf 100644
--- a/cmd/godoc/index.go
+++ b/cmd/godoc/index.go
@@ -54,6 +54,8 @@ import (
 	"strings"
 	"time"
 	"unicode"
+
+	"code.google.com/p/go.tools/godoc/util"
 )
 
 // ----------------------------------------------------------------------------
@@ -634,7 +636,7 @@ func (x *Indexer) addFile(filename string, goFile bool) (file *token.File, ast *
 			return
 		}
 
-		if isText(src) {
+		if util.IsText(src) {
 			// only add the file to the file set (for the full text index)
 			file = x.fset.AddFile(filename, x.fset.Base(), len(src))
 			file.SetLinesForContent(src)
diff --git a/cmd/godoc/main.go b/cmd/godoc/main.go
index 81e739d20c..0d1546b11f 100644
--- a/cmd/godoc/main.go
+++ b/cmd/godoc/main.go
@@ -212,7 +212,7 @@ func main() {
 		if err != nil {
 			log.Fatal(err)
 		}
-		index, _ := searchIndex.get()
+		index, _ := searchIndex.Get()
 		err = index.(*Index).Write(f)
 		if err != nil {
 			log.Fatal(err)
diff --git a/cmd/godoc/zip.go b/cmd/godoc/zip.go
index 620eb4f3cc..899f6914d6 100644
--- a/cmd/godoc/zip.go
+++ b/cmd/godoc/zip.go
@@ -27,6 +27,8 @@ import (
 	"sort"
 	"strings"
 	"time"
+
+	"code.google.com/p/go.tools/godoc/vfs"
 )
 
 // zipFI is the zip-file based implementation of FileInfo
@@ -107,7 +109,7 @@ func (fs *zipFS) stat(abspath string) (int, zipFI, error) {
 	return i, zipFI{name, file}, nil
 }
 
-func (fs *zipFS) Open(abspath string) (readSeekCloser, error) {
+func (fs *zipFS) Open(abspath string) (vfs.ReadSeekCloser, error) {
 	_, fi, err := fs.stat(zipPath(abspath))
 	if err != nil {
 		return nil, err
diff --git a/cmd/godoc/utils.go b/godoc/util/util.go
similarity index 73%
rename from cmd/godoc/utils.go
rename to godoc/util/util.go
index 0cdb7ff7af..b3eac39a46 100644
--- a/cmd/godoc/utils.go
+++ b/godoc/util/util.go
@@ -1,44 +1,44 @@
-// Copyright 2010 The Go Authors. All rights reserved.
+// Copyright 2013 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.
 
-// This file contains support functionality for godoc.
-
-package main
+// Package util contains utility types and functions for godoc.
+package util
 
 import (
+	"io"
 	pathpkg "path"
 	"sync"
 	"time"
 	"unicode/utf8"
+
+	"code.google.com/p/go.tools/godoc/vfs"
 )
 
 // An RWValue wraps a value and permits mutually exclusive
 // access to it and records the time the value was last set.
-//
 type RWValue struct {
 	mutex     sync.RWMutex
 	value     interface{}
 	timestamp time.Time // time of last set()
 }
 
-func (v *RWValue) set(value interface{}) {
+func (v *RWValue) Set(value interface{}) {
 	v.mutex.Lock()
 	v.value = value
 	v.timestamp = time.Now()
 	v.mutex.Unlock()
 }
 
-func (v *RWValue) get() (interface{}, time.Time) {
+func (v *RWValue) Get() (interface{}, time.Time) {
 	v.mutex.RLock()
 	defer v.mutex.RUnlock()
 	return v.value, v.timestamp
 }
 
-// isText returns true if a significant prefix of s looks like correct UTF-8;
+// IsText returns whether a significant prefix of s looks like correct UTF-8;
 // that is, if it is likely that s is human-readable text.
-//
-func isText(s []byte) bool {
+func IsText(s []byte) bool {
 	const max = 1024 // at least utf8.UTFMax
 	if len(s) > max {
 		s = s[0:max]
@@ -62,12 +62,16 @@ var textExt = map[string]bool{
 	".js":  false, // must be served raw
 }
 
-// isTextFile returns true if the file has a known extension indicating
+// FileSystem is a minimal virtual filesystem.
+type FileSystem interface {
+	Open(name string) (io.ReadCloser, error)
+}
+
+// IsTextFile returns whether the file has a known extension indicating
 // a text file, or if a significant chunk of the specified file looks like
 // correct UTF-8; that is, if it is likely that the file contains human-
 // readable text.
-//
-func isTextFile(filename string) bool {
+func IsTextFile(fs vfs.Opener, filename string) bool {
 	// if the extension is known, use it for decision making
 	if isText, found := textExt[pathpkg.Ext(filename)]; found {
 		return isText
@@ -87,5 +91,5 @@ func isTextFile(filename string) bool {
 		return false
 	}
 
-	return isText(buf[0:n])
+	return IsText(buf[0:n])
 }
diff --git a/godoc/vfs/vfs.go b/godoc/vfs/vfs.go
new file mode 100644
index 0000000000..55ba231bf3
--- /dev/null
+++ b/godoc/vfs/vfs.go
@@ -0,0 +1,23 @@
+// Copyright 2013 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 vfs defines virtual filesystem types.
+package vfs
+
+import (
+	"io"
+)
+
+// Opener is a minimal virtual filesystem that can only open
+// regular files.
+type Opener interface {
+	Open(name string) (ReadSeekCloser, error)
+}
+
+// A ReadSeekCloser can Read, Seek, and Close.
+type ReadSeekCloser interface {
+	io.Reader
+	io.Seeker
+	io.Closer
+}