godoc: support for reading/writing (splitted) index files.

This CL implements a new godoc feature to save the search
index on disk. Use -write_index to create the search
index file named with -index_files. Use -index_files to
provide a glob pattern specifying index file(s) when
starting godoc; in this case the run-time indexer is not
run.

Known issues:
- saving/restoring full text index is not yet supported
- the list of flags and overall usage logic could use a
  cleanup

R=rsc, dsymonds
CC=golang-dev
https://golang.org/cl/4974045

6 files changed, 170 insertions, 35 deletions

diff --git a/src/cmd/godoc/appconfig.go b/src/cmd/godoc/appconfig.go
index 9cbe7a4434..1f420fc6cf 100644
--- a/src/cmd/godoc/appconfig.go
+++ b/src/cmd/godoc/appconfig.go
@@ -11,9 +11,18 @@ package main
 const (
 	// zipFilename is the name of the .zip file
 	// containing the file system served by godoc.
-	zipFilename = "go.zip"
+	zipFilename = "godoc.zip"
 
 	// zipGoroot is the path of the goroot directory
 	// in the .zip file.
-	zipGoroot = "/home/username/go"
+	zipGoroot = "/home/user/go"
+
+	// indexFilenames is a glob pattern specifying
+	// files containing the search index served by
+	// godoc. The files are concatenated in sorted
+	// order (by filename).
+	// app-engine limit: file sizes must be <= 10MB;
+	// use "split -b8m indexfile index.split." to get
+	// smaller files.
+	indexFilenames = "index.split.*"
 )
diff --git a/src/cmd/godoc/appinit.go b/src/cmd/godoc/appinit.go
index 20e0fdc30a..96f8d5e2ac 100644
--- a/src/cmd/godoc/appinit.go
+++ b/src/cmd/godoc/appinit.go
@@ -23,11 +23,12 @@
 //		strings		// never version of the strings package
 //		...		//
 //	app.yaml		// app engine control file
-//	go.zip			// zip file containing the file system to serve
+//	godoc.zip		// .zip file containing the file system to serve
 //	godoc			// contains godoc sources
 //		appinit.go	// this file instead of godoc/main.go
 //		appconfig.go	// godoc for app engine configuration
 //		...		//
+//	index.split.*		// index file(s) containing the search index to serve
 //
 // To run app the engine emulator locally:
 //
@@ -43,6 +44,7 @@ import (
 	"http"
 	"log"
 	"os"
+	"path"
 )
 
 func serveError(w http.ResponseWriter, r *http.Request, relpath string, err os.Error) {
@@ -53,7 +55,16 @@ func serveError(w http.ResponseWriter, r *http.Request, relpath string, err os.E
 
 func init() {
 	log.Println("initializing godoc ...")
+	log.Printf(".zip file   = %s", zipFilename)
+	log.Printf(".zip GOROOT = %s", zipGoroot)
+	log.Printf("index files = %s", indexFilenames)
+
+	// initialize flags for app engine
 	*goroot = path.Join("/", zipGoroot) // fsHttp paths are relative to '/'
+	*indexEnabled = true
+	*indexFiles = indexFilenames
+	*maxResults = 0      // save space for now
+	*indexThrottle = 0.3 // in case *indexFiles is empty (and thus the indexer is run)
 
 	// read .zip file and set up file systems
 	const zipfile = zipFilename
@@ -65,8 +76,8 @@ func init() {
 	fsHttp = NewHttpZipFS(rc, *goroot)
 
 	// initialize http handlers
-	initHandlers()
 	readTemplates()
+	initHandlers()
 	registerPublicHandlers(http.DefaultServeMux)
 
 	// initialize default directory tree with corresponding timestamp.
@@ -75,12 +86,12 @@ func init() {
 	// initialize directory trees for user-defined file systems (-path flag).
 	initDirTrees()
 
-	// create search index
-	// TODO(gri) Disabled for now as it takes too long. Find a solution for this.
-	/*
-		*indexEnabled = true
-		go indexer()
-	*/
+	// initialize search index
+	if *indexEnabled {
+		if err := initIndex(); err != nil {
+			log.Fatalf("error initializing index: %s", err)
+		}
+	}
 
 	log.Println("godoc initialization complete")
 }
diff --git a/src/cmd/godoc/doc.go b/src/cmd/godoc/doc.go
index 57073ffb1f..813527d280 100644
--- a/src/cmd/godoc/doc.go
+++ b/src/cmd/godoc/doc.go
@@ -50,11 +50,17 @@ The flags are:
 	-index
 		enable identifier and full text search index
 		(no search box is shown if -index is not set)
+	-index_files=""
+		glob pattern specifying index files; if not empty,
+		the index is read from these files in sorted order
 	-index_throttle=0.75
 		index throttle value; a value of 0 means no time is allocated
 		to the indexer (the indexer will never finish), a value of 1.0
 		means that index creation is running at full throttle (other
 		goroutines may get no time while the index is built)
+	-write_index=false
+		write index to a file; the file name must be specified with
+		-index_files
 	-maxresults=10000
 		maximum number of full text search results shown
 		(no full text index is built if maxresults <= 0)
diff --git a/src/cmd/godoc/godoc.go b/src/cmd/godoc/godoc.go
index 9554d47b77..c172235168 100644
--- a/src/cmd/godoc/godoc.go
+++ b/src/cmd/godoc/godoc.go
@@ -63,7 +63,9 @@ var (
 	templateDir    = flag.String("templates", "", "directory containing alternate template files")
 
 	// search index
-	indexEnabled  = flag.Bool("index", false, "enable search index")
+	indexEnabled = flag.Bool("index", false, "enable search index")
+	indexFiles   = flag.String("index_files", "", "glob pattern specifying index files;"+
+		"if not empty, the index is read from these files in sorted order")
 	maxResults    = flag.Int("maxresults", 10000, "maximum number of full text search results shown")
 	indexThrottle = flag.Float64("index_throttle", 0.75, "index throttle value; 0.0 = no time allocated, 1.0 = full throttle")
 
@@ -1062,10 +1064,12 @@ func lookup(query string) (result SearchResult) {
 	// is the result accurate?
 	if *indexEnabled {
 		if _, ts := fsModified.get(); timestamp < ts {
-			// The index is older than the latest file system change
-			// under godoc's observation. Indexing may be in progress
-			// or start shortly (see indexer()).
-			result.Alert = "Indexing in progress: result may be inaccurate"
+			// The index is older than the latest file system change under godoc's observation.
+			if *indexFiles != "" {
+				result.Alert = "Index not automatically updated: result may be inaccurate"
+			} else {
+				result.Alert = "Indexing in progress: result may be inaccurate"
+			}
 		}
 	} else {
 		result.Alert = "Search index disabled: no results available"
@@ -1141,26 +1145,30 @@ func fsDirnames() <-chan string {
 	return c
 }
 
+func updateIndex() {
+	if *verbose {
+		log.Printf("updating index...")
+	}
+	start := time.Nanoseconds()
+	index := NewIndex(fsDirnames(), *maxResults > 0, *indexThrottle)
+	stop := time.Nanoseconds()
+	searchIndex.set(index)
+	if *verbose {
+		secs := float64((stop-start)/1e6) / 1e3
+		stats := index.Stats()
+		log.Printf("index updated (%gs, %d bytes of source, %d files, %d lines, %d unique words, %d spots)",
+			secs, stats.Bytes, stats.Files, stats.Lines, stats.Words, stats.Spots)
+	}
+	log.Printf("before GC: bytes = %d footprint = %d", runtime.MemStats.HeapAlloc, runtime.MemStats.Sys)
+	runtime.GC()
+	log.Printf("after  GC: bytes = %d footprint = %d", runtime.MemStats.HeapAlloc, runtime.MemStats.Sys)
+}
+
 func indexer() {
 	for {
 		if !indexUpToDate() {
 			// index possibly out of date - make a new one
-			if *verbose {
-				log.Printf("updating index...")
-			}
-			start := time.Nanoseconds()
-			index := NewIndex(fsDirnames(), *maxResults > 0, *indexThrottle)
-			stop := time.Nanoseconds()
-			searchIndex.set(index)
-			if *verbose {
-				secs := float64((stop-start)/1e6) / 1e3
-				stats := index.Stats()
-				log.Printf("index updated (%gs, %d bytes of source, %d files, %d lines, %d unique words, %d spots)",
-					secs, stats.Bytes, stats.Files, stats.Lines, stats.Words, stats.Spots)
-			}
-			log.Printf("before GC: bytes = %d footprint = %d", runtime.MemStats.HeapAlloc, runtime.MemStats.Sys)
-			runtime.GC()
-			log.Printf("after  GC: bytes = %d footprint = %d", runtime.MemStats.HeapAlloc, runtime.MemStats.Sys)
+			updateIndex()
 		}
 		var delay int64 = 60 * 1e9 // by default, try every 60s
 		if *testDir != "" {
@@ -1170,3 +1178,33 @@ func indexer() {
 		time.Sleep(delay)
 	}
 }
+
+func initIndex() os.Error {
+	if *indexFiles == "" {
+		// run periodic indexer
+		go indexer()
+		return nil
+	}
+
+	// get search index from files
+	matches, err := filepath.Glob(*indexFiles)
+	if err != nil {
+		return err
+	}
+	sort.Strings(matches) // make sure files are in the right order
+	files := make([]io.Reader, 0, len(matches))
+	for _, filename := range matches {
+		f, err := os.Open(filename)
+		if err != nil {
+			return err
+		}
+		defer f.Close()
+		files = append(files, f)
+	}
+	x := new(Index)
+	if err := x.Read(io.MultiReader(files...)); err != nil {
+		return err
+	}
+	searchIndex.set(x)
+	return nil
+}
diff --git a/src/cmd/godoc/index.go b/src/cmd/godoc/index.go
index f33ca05730..8bf1a9eb38 100644
--- a/src/cmd/godoc/index.go
+++ b/src/cmd/godoc/index.go
@@ -43,7 +43,9 @@ import (
 	"go/parser"
 	"go/token"
 	"go/scanner"
+	"gob"
 	"index/suffixarray"
+	"io"
 	"os"
 	"path/filepath"
 	"regexp"
@@ -804,6 +806,37 @@ func NewIndex(dirnames <-chan string, fulltextIndex bool, throttle float64) *Ind
 	return &Index{x.fset, suffixes, words, alts, x.snippets, x.stats}
 }
 
+type FileIndex struct {
+	Words    map[string]*LookupResult
+	Alts     map[string]*AltWords
+	Snippets []*Snippet
+}
+
+// Write writes the index x to w.
+func (x *Index) Write(w io.Writer) os.Error {
+	if x.suffixes != nil {
+		panic("no support for writing full text index yet")
+	}
+	fx := FileIndex{
+		x.words,
+		x.alts,
+		x.snippets,
+	}
+	return gob.NewEncoder(w).Encode(fx)
+}
+
+// Read reads the index from r into x; x must not be nil.
+func (x *Index) Read(r io.Reader) os.Error {
+	var fx FileIndex
+	if err := gob.NewDecoder(r).Decode(&fx); err != nil {
+		return err
+	}
+	x.words = fx.Words
+	x.alts = fx.Alts
+	x.snippets = fx.Snippets
+	return nil
+}
+
 // Stats() returns index statistics.
 func (x *Index) Stats() Statistics {
 	return x.stats
diff --git a/src/cmd/godoc/main.go b/src/cmd/godoc/main.go
index 48bfa2477e..20eff6dd3a 100644
--- a/src/cmd/godoc/main.go
+++ b/src/cmd/godoc/main.go
@@ -54,6 +54,9 @@ var (
 	// (with e.g.: zip -r go.zip $GOROOT -i \*.go -i \*.html -i \*.css -i \*.js -i \*.txt -i \*.c -i \*.h -i \*.s -i \*.png -i \*.jpg -i \*.sh -i favicon.ico)
 	zipfile = flag.String("zip", "", "zip file providing the file system to serve; disabled if empty")
 
+	// file-based index
+	writeIndex = flag.Bool("write_index", false, "write index to a file; the file name must be specified with -index_files")
+
 	// periodic sync
 	syncCmd   = flag.String("sync", "", "sync command; disabled if empty")
 	syncMin   = flag.Int("sync_minutes", 0, "sync interval in minutes; disabled if <= 0")
@@ -221,8 +224,8 @@ func main() {
 	flag.Usage = usage
 	flag.Parse()
 
-	// Check usage: either server and no args, or command line and args
-	if (*httpAddr != "") != (flag.NArg() == 0) {
+	// Check usage: either server and no args, command line and args, or index creation mode
+	if (*httpAddr != "") != (flag.NArg() == 0) && !*writeIndex {
 		usage()
 	}
 
@@ -253,6 +256,39 @@ func main() {
 	readTemplates()
 	initHandlers()
 
+	if (*indexEnabled || *writeIndex) && *indexFiles != "" && *maxResults > 0 {
+		log.Println("warning: no support for full-text index yet (setting -maxresults to 0)")
+		*maxResults = 0
+	}
+
+	if *writeIndex {
+		if *indexFiles == "" {
+			log.Fatal("no index files specified")
+		}
+
+		log.Println("initialize file systems")
+		*verbose = true // want to see what happens
+		initFSTree()
+		initDirTrees()
+
+		*indexThrottle = 1
+		updateIndex()
+
+		log.Println("writing index file", *indexFiles)
+		f, err := os.Create(*indexFiles)
+		if err != nil {
+			log.Fatal(err)
+		}
+		index, _ := searchIndex.get()
+		err = index.(*Index).Write(f)
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		log.Println("done")
+		return
+	}
+
 	if *httpAddr != "" {
 		// HTTP server mode.
 		var handler http.Handler = http.DefaultServeMux
@@ -304,9 +340,11 @@ func main() {
 			}()
 		}
 
-		// Start indexing goroutine.
+		// Initialize search index.
 		if *indexEnabled {
-			go indexer()
+			if err := initIndex(); err != nil {
+				log.Fatalf("error initializing index: %s", err)
+			}
 		}
 
 		// Start http server.