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x/tools/godoc/vfs: adds NewNameSpace() and emptyVFS for better behavior

The existing implementation of NameSpace implicitly assumes that a
FileSystem with a directory at the top will be mounted at the root
mount point "/" of the NameSpace. If this is not the case, then
Stat("/") will fail even if ReadDir("/") succeedes. This is unexpected
behavior which breaks directory traversal routines (eg. http.FileServer).

This CL adds an unexported implementation of FileSystem called emptyVFS
that emulates an empty directory and adds a NewNameSpace() function that
binds emptyVFS to "/" so that unexpected behavior does not arise even if
the use does not mount anything explicitly at "/".

Latest patch set causes the FileInfo of the empty top level emulated
directory to return "/" for Name() and Zero Time for ModTime() and
removes the related struct state fields being used in the previous
implementation.

Fixes golang/go#14190

Change-Id: Idce2fc3c9b81206847a33840d76b660059d53d18
Reviewed-on: https://go-review.googlesource.com/19445
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
This commit is contained in:
Hariharan Srinath 2016-02-15 07:44:09 +05:30 committed by Brad Fitzpatrick
parent 6e94e8a89f
commit 936084890a
3 changed files with 147 additions and 0 deletions

85
godoc/vfs/emptyvfs.go Normal file
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@ -0,0 +1,85 @@
// Copyright 2016 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
import (
"fmt"
"os"
"time"
)
// NewNameSpace returns a NameSpace pre-initialized with an empty
// emulated directory mounted on the root mount point "/". This
// allows directory traversal routines to work properly even if
// a folder is not explicitly mounted at root by the user.
func NewNameSpace() NameSpace {
ns := NameSpace{}
ns.Bind("/", &emptyVFS{}, "/", BindReplace)
return ns
}
// type emptyVFS emulates a FileSystem consisting of an empty directory
type emptyVFS struct{}
// Open implements Opener. Since emptyVFS is an empty directory, all
// attempts to open a file should returns errors.
func (e *emptyVFS) Open(path string) (ReadSeekCloser, error) {
if path == "/" {
return nil, fmt.Errorf("open: / is a directory")
}
return nil, os.ErrNotExist
}
// Stat returns os.FileInfo for an empty directory if the path is
// is root "/" or error. os.FileInfo is implemented by emptyVFS
func (e *emptyVFS) Stat(path string) (os.FileInfo, error) {
if path == "/" {
return e, nil
}
return nil, os.ErrNotExist
}
func (e *emptyVFS) Lstat(path string) (os.FileInfo, error) {
return e.Stat(path)
}
// ReadDir returns an empty os.FileInfo slice for "/", else error.
func (e *emptyVFS) ReadDir(path string) ([]os.FileInfo, error) {
if path == "/" {
return []os.FileInfo{}, nil
}
return nil, os.ErrNotExist
}
func (e *emptyVFS) String() string {
return "emptyVFS(/)"
}
// These functions below implement os.FileInfo for the single
// empty emulated directory.
func (e *emptyVFS) Name() string {
return "/"
}
func (e *emptyVFS) Size() int64 {
return 0
}
func (e *emptyVFS) Mode() os.FileMode {
return os.ModeDir | os.ModePerm
}
func (e *emptyVFS) ModTime() time.Time {
return time.Time{}
}
func (e *emptyVFS) IsDir() bool {
return true
}
func (e *emptyVFS) Sys() interface{} {
return nil
}

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@ -0,0 +1,57 @@
// Copyright 2016 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_test
import (
"golang.org/x/tools/godoc/vfs"
"golang.org/x/tools/godoc/vfs/mapfs"
"testing"
"time"
)
func TestNewNameSpace(t *testing.T) {
// We will mount this filesystem under /fs1
mount := mapfs.New(map[string]string{"fs1file": "abcdefgh"})
// Existing process. This should give error on Stat("/")
t1 := vfs.NameSpace{}
t1.Bind("/fs1", mount, "/", vfs.BindReplace)
// using NewNameSpace. This should work fine.
t2 := vfs.NewNameSpace()
t2.Bind("/fs1", mount, "/", vfs.BindReplace)
testcases := map[string][]bool{
"/": []bool{false, true},
"/fs1": []bool{true, true},
"/fs1/fs1file": []bool{true, true},
}
fss := []vfs.FileSystem{t1, t2}
for j, fs := range fss {
for k, v := range testcases {
_, err := fs.Stat(k)
result := err == nil
if result != v[j] {
t.Errorf("fs: %d, testcase: %s, want: %v, got: %v, err: %s", j, k, v[j], result, err)
}
}
}
fi, err := t2.Stat("/")
if err != nil {
t.Fatal(err)
}
if fi.Name() != "/" {
t.Errorf("t2.Name() : want:%s got:%s", "/", fi.Name())
}
if !fi.ModTime().IsZero() {
t.Errorf("t2.Modime() : want:%v got:%v", time.Time{}, fi.ModTime())
}
}

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@ -53,6 +53,11 @@ const debugNS = false
// operate on a path beginning with old, replace that prefix (old) with new // operate on a path beginning with old, replace that prefix (old) with new
// and then pass that path to the FileSystem implementation fs. // and then pass that path to the FileSystem implementation fs.
// //
// If you do not explicitly mount a FileSystem at the root mountpoint "/" of the
// NameSpace like above, Stat("/") will return a "not found" error which could
// break typical directory traversal routines. In such cases, use NewNameSpace()
// to get a NameSpace pre-initialized with an emulated empty directory at root.
//
// Given this name space, a ReadDir of /src/pkg/code will check each prefix // Given this name space, a ReadDir of /src/pkg/code will check each prefix
// of the path for a mount point (first /src/pkg/code, then /src/pkg, then /src, // of the path for a mount point (first /src/pkg/code, then /src/pkg, then /src,
// then /), stopping when it finds one. For the above example, /src/pkg/code // then /), stopping when it finds one. For the above example, /src/pkg/code