archive/zip: make Reader implement fs.FS

Now a zip.Reader (an open zip file) can be passed to code
that accepts a file system, such as (soon) template parsing.

For #41190.

Change-Id: If51b12e39db3ccc27f643c2453d3300a38035360
Reviewed-on: https://go-review.googlesource.com/c/go/+/243937
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

src/archive/zip/reader.go

@@ -11,7 +11,12 @@ import (
 	"hash"
 	"hash/crc32"
 	"io"
+	"io/fs"
 	"os"
+	"path"
+	"sort"
+	"strings"
+	"sync"
 	"time"
 )
 
@@ -21,18 +26,28 @@ var (
 	ErrChecksum  = errors.New("zip: checksum error")
 )
 
+// A Reader serves content from a ZIP archive.
 type Reader struct {
 	r             io.ReaderAt
 	File          []*File
 	Comment       string
 	decompressors map[uint16]Decompressor
+
+	// fileList is a list of files sorted by ename,
+	// for use by the Open method.
+	fileListOnce sync.Once
+	fileList     []fileListEntry
 }
 
+// A ReadCloser is a Reader that must be closed when no longer needed.
 type ReadCloser struct {
 	f *os.File
 	Reader
 }
 
+// A File is a single file in a ZIP archive.
+// The file information is in the embedded FileHeader.
+// The file content can be accessed by calling Open.
 type File struct {
 	FileHeader
 	zip          *Reader
@@ -187,6 +202,10 @@ type checksumReader struct {
 	err   error     // sticky error
 }
 
+func (r *checksumReader) Stat() (fs.FileInfo, error) {
+	return headerFileInfo{&r.f.FileHeader}, nil
+}
+
 func (r *checksumReader) Read(b []byte) (n int, err error) {
 	if r.err != nil {
 		return 0, r.err
@@ -607,3 +626,173 @@ func (b *readBuf) sub(n int) readBuf {
 	*b = (*b)[n:]
 	return b2
 }
+
+// A fileListEntry is a File and its ename.
+// If file == nil, the fileListEntry describes a directory, without metadata.
+type fileListEntry struct {
+	name string
+	file *File // nil for directories
+}
+
+type fileInfoDirEntry interface {
+	fs.FileInfo
+	fs.DirEntry
+}
+
+func (e *fileListEntry) stat() fileInfoDirEntry {
+	if e.file != nil {
+		return headerFileInfo{&e.file.FileHeader}
+	}
+	return e
+}
+
+// Only used for directories.
+func (f *fileListEntry) Name() string       { _, elem, _ := split(f.name); return elem }
+func (f *fileListEntry) Size() int64        { return 0 }
+func (f *fileListEntry) ModTime() time.Time { return time.Time{} }
+func (f *fileListEntry) Mode() fs.FileMode  { return fs.ModeDir | 0555 }
+func (f *fileListEntry) Type() fs.FileMode  { return fs.ModeDir }
+func (f *fileListEntry) IsDir() bool        { return true }
+func (f *fileListEntry) Sys() interface{}   { return nil }
+
+func (f *fileListEntry) Info() (fs.FileInfo, error) { return f, nil }
+
+// toValidName coerces name to be a valid name for fs.FS.Open.
+func toValidName(name string) string {
+	name = strings.ReplaceAll(name, `\`, `/`)
+	p := path.Clean(name)
+	if strings.HasPrefix(p, "/") {
+		p = p[len("/"):]
+	}
+	for strings.HasPrefix(name, "../") {
+		p = p[len("../"):]
+	}
+	return p
+}
+
+func (r *Reader) initFileList() {
+	r.fileListOnce.Do(func() {
+		dirs := make(map[string]bool)
+		for _, file := range r.File {
+			name := toValidName(file.Name)
+			for dir := path.Dir(name); dir != "."; dir = path.Dir(dir) {
+				dirs[dir] = true
+			}
+			r.fileList = append(r.fileList, fileListEntry{name, file})
+		}
+		for dir := range dirs {
+			r.fileList = append(r.fileList, fileListEntry{dir + "/", nil})
+		}
+
+		sort.Slice(r.fileList, func(i, j int) bool { return fileEntryLess(r.fileList[i].name, r.fileList[j].name) })
+	})
+}
+
+func fileEntryLess(x, y string) bool {
+	xdir, xelem, _ := split(x)
+	ydir, yelem, _ := split(y)
+	return xdir < ydir || xdir == ydir && xelem < yelem
+}
+
+// Open opens the named file in the ZIP archive,
+// using the semantics of io.FS.Open:
+// paths are always slash separated, with no
+// leading / or ../ elements.
+func (r *Reader) Open(name string) (fs.File, error) {
+	r.initFileList()
+
+	e := r.openLookup(name)
+	if e == nil || !fs.ValidPath(name) {
+		return nil, &fs.PathError{Op: "open", Path: name, Err: fs.ErrNotExist}
+	}
+	if e.file == nil || strings.HasSuffix(e.file.Name, "/") {
+		return &openDir{e, r.openReadDir(name), 0}, nil
+	}
+	rc, err := e.file.Open()
+	if err != nil {
+		return nil, err
+	}
+	return rc.(fs.File), nil
+}
+
+func split(name string) (dir, elem string, isDir bool) {
+	if name[len(name)-1] == '/' {
+		isDir = true
+		name = name[:len(name)-1]
+	}
+	i := len(name) - 1
+	for i >= 0 && name[i] != '/' {
+		i--
+	}
+	if i < 0 {
+		return ".", name, isDir
+	}
+	return name[:i], name[i+1:], isDir
+}
+
+var dotFile = &fileListEntry{name: "./"}
+
+func (r *Reader) openLookup(name string) *fileListEntry {
+	if name == "." {
+		return dotFile
+	}
+
+	dir, elem, _ := split(name)
+	files := r.fileList
+	i := sort.Search(len(files), func(i int) bool {
+		idir, ielem, _ := split(files[i].name)
+		return idir > dir || idir == dir && ielem >= elem
+	})
+	if i < len(files) {
+		fname := files[i].name
+		if fname == name || len(fname) == len(name)+1 && fname[len(name)] == '/' && fname[:len(name)] == name {
+			return &files[i]
+		}
+	}
+	return nil
+}
+
+func (r *Reader) openReadDir(dir string) []fileListEntry {
+	files := r.fileList
+	i := sort.Search(len(files), func(i int) bool {
+		idir, _, _ := split(files[i].name)
+		return idir >= dir
+	})
+	j := sort.Search(len(files), func(j int) bool {
+		jdir, _, _ := split(files[j].name)
+		return jdir > dir
+	})
+	return files[i:j]
+}
+
+type openDir struct {
+	e      *fileListEntry
+	files  []fileListEntry
+	offset int
+}
+
+func (d *openDir) Close() error               { return nil }
+func (d *openDir) Stat() (fs.FileInfo, error) { return d.e.stat(), nil }
+
+func (d *openDir) Read([]byte) (int, error) {
+	return 0, &fs.PathError{Op: "read", Path: d.e.name, Err: errors.New("is a directory")}
+}
+
+func (d *openDir) ReadDir(count int) ([]fs.DirEntry, error) {
+	n := len(d.files) - d.offset
+	if count > 0 && n > count {
+		n = count
+	}
+	if n == 0 {
+		if count <= 0 {
+			return nil, nil
+		}
+		return nil, io.EOF
+	}
+	list := make([]fs.DirEntry, n)
+	for i := range list {
+		list[i] = d.files[d.offset+i].stat()
+	}
+	d.offset += n
+	return list, nil
+}

src/archive/zip/reader_test.go

@@ -17,6 +17,7 @@ import (
 	"regexp"
 	"strings"
 	"testing"
+	"testing/fstest"
 	"time"
 )
 
@@ -1071,3 +1072,13 @@ func TestIssue12449(t *testing.T) {
 		t.Errorf("Error reading the archive: %v", err)
 	}
 }
+
+func TestFS(t *testing.T) {
+	z, err := OpenReader("testdata/unix.zip")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := fstest.TestFS(z, "hello", "dir/bar", "dir/empty", "readonly"); err != nil {
+		t.Fatal(err)
+	}
+}

src/archive/zip/struct.go

@@ -162,8 +162,11 @@ func (fi headerFileInfo) ModTime() time.Time {
 	return fi.fh.Modified.UTC()
 }
 func (fi headerFileInfo) Mode() fs.FileMode { return fi.fh.Mode() }
+func (fi headerFileInfo) Type() fs.FileMode { return fi.fh.Mode().Type() }
 func (fi headerFileInfo) Sys() interface{}  { return fi.fh }
 
+func (fi headerFileInfo) Info() (fs.FileInfo, error) { return fi, nil }
+
 // FileInfoHeader creates a partially-populated FileHeader from an
 // fs.FileInfo.
 // Because fs.FileInfo's Name method returns only the base name of