func (p *Presentation) serveTextFile(w http.ResponseWriter, r *http.Request, abspath, relpath, title string) {
	src, err := vfs.ReadFile(p.Corpus.fs, abspath)
	if err != nil {
		log.Printf("ReadFile: %s", err)
		p.ServeError(w, r, relpath, err)
		return
	}

	if r.FormValue("m") == "text" {
		p.ServeText(w, src)
		return
	}

	var buf bytes.Buffer
	buf.WriteString("<pre>")
	FormatText(&buf, src, 1, pathpkg.Ext(abspath) == ".go", r.FormValue("h"), RangeSelection(r.FormValue("s")))
	buf.WriteString("</pre>")
	fmt.Fprintf(&buf, `<p><a href="/%s?m=text">View as plain text</a></p>`, htmlpkg.EscapeString(relpath))

	p.ServePage(w, Page{
		Title:    title + " " + relpath,
		Tabtitle: relpath,
		Body:     buf.Bytes(),
	})
}

// contents reads and returns the content of the named file
// (from the virtual file system, so for example /doc refers to $GOROOT/doc).
func (c *Corpus) contents(name string) string {
	file, err := vfs.ReadFile(c.fs, name)
	if err != nil {
		log.Panic(err)
	}
	return string(file)
}

func (c *Corpus) parseFile(fset *token.FileSet, filename string, mode parser.Mode) (*ast.File, error) {
	src, err := vfs.ReadFile(c.fs, filename)
	if err != nil {
		return nil, err
	}
	return parser.ParseFile(fset, filename, src, mode)
}

// loadCodewalk reads a codewalk from the named XML file.
func loadCodewalk(filename string) (*Codewalk, error) {
	f, err := fs.Open(filename)
	if err != nil {
		return nil, err
	}
	defer f.Close()
	cw := new(Codewalk)
	d := xml.NewDecoder(f)
	d.Entity = xml.HTMLEntity
	err = d.Decode(cw)
	if err != nil {
		return nil, &os.PathError{Op: "parsing", Path: filename, Err: err}
	}

	// Compute file list, evaluate line numbers for addresses.
	m := make(map[string]bool)
	for _, st := range cw.Step {
		i := strings.Index(st.Src, ":")
		if i < 0 {
			i = len(st.Src)
		}
		filename := st.Src[0:i]
		data, err := vfs.ReadFile(fs, filename)
		if err != nil {
			st.Err = err
			continue
		}
		if i < len(st.Src) {
			lo, hi, err := addrToByteRange(st.Src[i+1:], 0, data)
			if err != nil {
				st.Err = err
				continue
			}
			// Expand match to line boundaries.
			for lo > 0 && data[lo-1] != '\n' {
				lo--
			}
			for hi < len(data) && (hi == 0 || data[hi-1] != '\n') {
				hi++
			}
			st.Lo = byteToLine(data, lo)
			st.Hi = byteToLine(data, hi-1)
		}
		st.Data = data
		st.File = filename
		m[filename] = true
	}

	// Make list of files
	cw.File = make([]string, len(m))
	i := 0
	for f := range m {
		cw.File[i] = f
		i++
	}
	sort.Strings(cw.File)

	return cw, nil
}

func (c *Corpus) parseFile(fset *token.FileSet, filename string, mode parser.Mode) (*ast.File, error) {
	src, err := vfs.ReadFile(c.fs, filename)
	if err != nil {
		return nil, err
	}

	// Temporary ad-hoc fix for issue 5247.
	// TODO(gri) Remove this in favor of a better fix, eventually (see issue 7702).
	replaceLinePrefixCommentsWithBlankLine(src)

	return parser.ParseFile(fset, filename, src, mode)
}

func (p *Presentation) ServeHTMLDoc(w http.ResponseWriter, r *http.Request, abspath, relpath string) {
	// get HTML body contents
	src, err := vfs.ReadFile(p.Corpus.fs, abspath)
	if err != nil {
		log.Printf("ReadFile: %s", err)
		p.ServeError(w, r, relpath, err)
		return
	}

	// if it begins with "<!DOCTYPE " assume it is standalone
	// html that doesn't need the template wrapping.
	if bytes.HasPrefix(src, doctype) {
		w.Write(src)
		return
	}

	// if it begins with a JSON blob, read in the metadata.
	meta, src, err := extractMetadata(src)
	if err != nil {
		log.Printf("decoding metadata %s: %v", relpath, err)
	}

	// evaluate as template if indicated
	if meta.Template {
		tmpl, err := template.New("main").Funcs(p.TemplateFuncs()).Parse(string(src))
		if err != nil {
			log.Printf("parsing template %s: %v", relpath, err)
			p.ServeError(w, r, relpath, err)
			return
		}
		var buf bytes.Buffer
		if err := tmpl.Execute(&buf, nil); err != nil {
			log.Printf("executing template %s: %v", relpath, err)
			p.ServeError(w, r, relpath, err)
			return
		}
		src = buf.Bytes()
	}

	// if it's the language spec, add tags to EBNF productions
	if strings.HasSuffix(abspath, "go_spec.html") {
		var buf bytes.Buffer
		Linkify(&buf, src)
		src = buf.Bytes()
	}

	p.ServePage(w, Page{
		Title:    meta.Title,
		Subtitle: meta.Subtitle,
		Body:     src,
	})
}

func (p *Presentation) serveTextFile(w http.ResponseWriter, r *http.Request, abspath, relpath, title string) {
	src, err := vfs.ReadFile(p.Corpus.fs, abspath)
	if err != nil {
		log.Printf("ReadFile: %s", err)
		p.ServeError(w, r, relpath, err)
		return
	}

	if r.FormValue("m") == "text" {
		p.ServeText(w, src)
		return
	}

	h := r.FormValue("h")
	s := RangeSelection(r.FormValue("s"))

	var buf bytes.Buffer
	if pathpkg.Ext(abspath) == ".go" {
		// Find markup links for this file (e.g. "/src/pkg/fmt/print.go").
		data, links := p.Corpus.Analysis.FileInfo(abspath)
		buf.WriteString("<script type='text/javascript'>document.ANALYSIS_DATA = ")
		buf.Write(marshalJSON(data))
		buf.WriteString(";</script>\n")

		// TODO(adonovan): indicate whether analysis is
		// disabled, pending, completed or failed.
		// For now, display help link only if 'completed'.
		if links != nil {
			buf.WriteString("<a href='/lib/godoc/analysis/help.html'>Static analysis features</a><br/>")
		}

		buf.WriteString("<pre>")
		formatGoSource(&buf, src, links, h, s)
		buf.WriteString("</pre>")
	} else {
		buf.WriteString("<pre>")
		FormatText(&buf, src, 1, false, h, s)
		buf.WriteString("</pre>")
	}
	fmt.Fprintf(&buf, `<p><a href="/%s?m=text">View as plain text</a></p>`, htmlpkg.EscapeString(relpath))

	p.ServePage(w, Page{
		Title:    title + " " + relpath,
		Tabtitle: relpath,
		Body:     buf.Bytes(),
	})
}

func (p *Presentation) serveTextFile(w http.ResponseWriter, r *http.Request, abspath, relpath, title string) {
	src, err := vfs.ReadFile(p.Corpus.fs, abspath)
	if err != nil {
		log.Printf("ReadFile: %s", err)
		p.ServeError(w, r, relpath, err)
		return
	}

	if r.FormValue("m") == "text" {
		p.ServeText(w, src)
		return
	}

	h := r.FormValue("h")
	s := RangeSelection(r.FormValue("s"))

	var buf bytes.Buffer
	if pathpkg.Ext(abspath) == ".go" {
		// Find markup links for this file (e.g. "/src/pkg/fmt/print.go").
		fi := p.Corpus.Analysis.FileInfo(abspath)
		buf.WriteString("<script type='text/javascript'>document.ANALYSIS_DATA = ")
		buf.Write(marshalJSON(fi.Data))
		buf.WriteString(";</script>\n")

		if status := p.Corpus.Analysis.Status(); status != "" {
			buf.WriteString("<a href='/lib/godoc/analysis/help.html'>Static analysis features</a> ")
			// TODO(adonovan): show analysis status at per-file granularity.
			fmt.Fprintf(&buf, "<span style='color: grey'>[%s]</span><br/>", htmlpkg.EscapeString(status))
		}

		buf.WriteString("<pre>")
		formatGoSource(&buf, src, fi.Links, h, s)
		buf.WriteString("</pre>")
	} else {
		buf.WriteString("<pre>")
		FormatText(&buf, src, 1, false, h, s)
		buf.WriteString("</pre>")
	}
	fmt.Fprintf(&buf, `<p><a href="/%s?m=text">View as plain text</a></p>`, htmlpkg.EscapeString(relpath))

	p.ServePage(w, Page{
		Title:    title + " " + relpath,
		Tabtitle: relpath,
		Body:     buf.Bytes(),
	})
}

func readTemplate(name string) *template.Template {
	if pres == nil {
		panic("no global Presentation set yet")
	}
	path := "lib/godoc/" + name

	// use underlying file system fs to read the template file
	// (cannot use template ParseFile functions directly)
	data, err := vfs.ReadFile(fs, path)
	if err != nil {
		log.Fatal("readTemplate: ", err)
	}
	// be explicit with errors (for app engine use)
	t, err := template.New(name).Funcs(pres.FuncMap()).Parse(string(data))
	if err != nil {
		log.Fatal("readTemplate: ", err)
	}
	return t
}

// UpdateMetadata scans $GOROOT/doc for HTML files, reads their metadata,
// and updates the DocMetadata map.
func (c *Corpus) updateMetadata() {
	metadata := make(map[string]*Metadata)
	var scan func(string) // scan is recursive
	scan = func(dir string) {
		fis, err := c.fs.ReadDir(dir)
		if err != nil {
			log.Println("updateMetadata:", err)
			return
		}
		for _, fi := range fis {
			name := pathpkg.Join(dir, fi.Name())
			if fi.IsDir() {
				scan(name) // recurse
				continue
			}
			if !strings.HasSuffix(name, ".html") {
				continue
			}
			// Extract metadata from the file.
			b, err := vfs.ReadFile(c.fs, name)
			if err != nil {
				log.Printf("updateMetadata %s: %v", name, err)
				continue
			}
			meta, _, err := extractMetadata(b)
			if err != nil {
				log.Printf("updateMetadata: %s: %v", name, err)
				continue
			}
			// Store relative filesystem path in Metadata.
			meta.filePath = name
			if meta.Path == "" {
				// If no Path, canonical path is actual path.
				meta.Path = meta.filePath
			}
			// Store under both paths.
			metadata[meta.Path] = &meta
			metadata[meta.filePath] = &meta
		}
	}
	scan("/doc")
	c.docMetadata.Set(metadata)
}

// codewalkFileprint serves requests with ?fileprint=f&lo=lo&hi=hi.
// The filename f has already been retrieved and is passed as an argument.
// Lo and hi are the numbers of the first and last line to highlight
// in the response.  This format is used for the middle window pane
// of the codewalk pages.  It is a separate iframe and does not get
// the usual godoc HTML wrapper.
func codewalkFileprint(w http.ResponseWriter, r *http.Request, f string) {
	abspath := f
	data, err := vfs.ReadFile(fs, abspath)
	if err != nil {
		log.Print(err)
		pres.ServeError(w, r, f, err)
		return
	}
	lo, _ := strconv.Atoi(r.FormValue("lo"))
	hi, _ := strconv.Atoi(r.FormValue("hi"))
	if hi < lo {
		hi = lo
	}
	lo = lineToByte(data, lo)
	hi = lineToByte(data, hi+1)

	// Put the mark 4 lines before lo, so that the iframe
	// shows a few lines of context before the highlighted
	// section.
	n := 4
	mark := lo
	for ; mark > 0 && n > 0; mark-- {
		if data[mark-1] == '\n' {
			if n--; n == 0 {
				break
			}
		}
	}

	io.WriteString(w, `<style type="text/css">@import "/doc/codewalk/codewalk.css";</style><pre>`)
	template.HTMLEscape(w, data[0:mark])
	io.WriteString(w, "<a name='mark'></a>")
	template.HTMLEscape(w, data[mark:lo])
	if lo < hi {
		io.WriteString(w, "<div class='codewalkhighlight'>")
		template.HTMLEscape(w, data[lo:hi])
		io.WriteString(w, "</div>")
	}
	template.HTMLEscape(w, data[hi:])
	io.WriteString(w, "</pre>")
}

// getPageInfo returns the PageInfo for a package directory abspath. If the
// parameter genAST is set, an AST containing only the package exports is
// computed (PageInfo.PAst), otherwise package documentation (PageInfo.Doc)
// is extracted from the AST. If there is no corresponding package in the
// directory, PageInfo.PAst and PageInfo.PDoc are nil. If there are no sub-
// directories, PageInfo.Dirs is nil. If an error occurred, PageInfo.Err is
// set to the respective error but the error is not logged.
//
func (h *handlerServer) GetPageInfo(abspath, relpath string, mode PageInfoMode) *PageInfo {
	info := &PageInfo{Dirname: abspath}

	// Restrict to the package files that would be used when building
	// the package on this system.  This makes sure that if there are
	// separate implementations for, say, Windows vs Unix, we don't
	// jumble them all together.
	// Note: Uses current binary's GOOS/GOARCH.
	// To use different pair, such as if we allowed the user to choose,
	// set ctxt.GOOS and ctxt.GOARCH before calling ctxt.ImportDir.
	ctxt := build.Default
	ctxt.IsAbsPath = pathpkg.IsAbs
	ctxt.ReadDir = func(dir string) ([]os.FileInfo, error) {
		return h.c.fs.ReadDir(filepath.ToSlash(dir))
	}
	ctxt.OpenFile = func(name string) (r io.ReadCloser, err error) {
		data, err := vfs.ReadFile(h.c.fs, filepath.ToSlash(name))
		if err != nil {
			return nil, err
		}
		return ioutil.NopCloser(bytes.NewReader(data)), nil
	}

	pkginfo, err := ctxt.ImportDir(abspath, 0)
	// continue if there are no Go source files; we still want the directory info
	if _, nogo := err.(*build.NoGoError); err != nil && !nogo {
		info.Err = err
		return info
	}

	// collect package files
	pkgname := pkginfo.Name
	pkgfiles := append(pkginfo.GoFiles, pkginfo.CgoFiles...)
	if len(pkgfiles) == 0 {
		// Commands written in C have no .go files in the build.
		// Instead, documentation may be found in an ignored file.
		// The file may be ignored via an explicit +build ignore
		// constraint (recommended), or by defining the package
		// documentation (historic).
		pkgname = "main" // assume package main since pkginfo.Name == ""
		pkgfiles = pkginfo.IgnoredGoFiles
	}

	// get package information, if any
	if len(pkgfiles) > 0 {
		// build package AST
		fset := token.NewFileSet()
		files, err := h.c.parseFiles(fset, relpath, abspath, pkgfiles)
		if err != nil {
			info.Err = err
			return info
		}

		// ignore any errors - they are due to unresolved identifiers
		pkg, _ := ast.NewPackage(fset, files, poorMansImporter, nil)

		// extract package documentation
		info.FSet = fset
		if mode&ShowSource == 0 {
			// show extracted documentation
			var m doc.Mode
			if mode&NoFiltering != 0 {
				m |= doc.AllDecls
			}
			if mode&AllMethods != 0 {
				m |= doc.AllMethods
			}
			info.PDoc = doc.New(pkg, pathpkg.Clean(relpath), m) // no trailing '/' in importpath
			if mode&NoTypeAssoc != 0 {
				for _, t := range info.PDoc.Types {
					info.PDoc.Consts = append(info.PDoc.Consts, t.Consts...)
					info.PDoc.Vars = append(info.PDoc.Vars, t.Vars...)
					info.PDoc.Funcs = append(info.PDoc.Funcs, t.Funcs...)
					t.Consts = nil
					t.Vars = nil
					t.Funcs = nil
				}
				// for now we cannot easily sort consts and vars since
				// go/doc.Value doesn't export the order information
				sort.Sort(funcsByName(info.PDoc.Funcs))
			}

			// collect examples
			testfiles := append(pkginfo.TestGoFiles, pkginfo.XTestGoFiles...)
			files, err = h.c.parseFiles(fset, relpath, abspath, testfiles)
			if err != nil {
				log.Println("parsing examples:", err)
			}
			info.Examples = collectExamples(h.c, pkg, files)

			// collect any notes that we want to show
			if info.PDoc.Notes != nil {
//.........这里部分代码省略.........