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os: add File.ReadDir method and DirEntry type

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ReadDir provides a portable, efficient way to read a directory
and discover the type of directory entries.
This enables a more efficient file system walk, yet to be added.

See #41467 for the proposal review for the API.

Fixes #41467.

Change-Id: I461a526793ae46df48821aa448b04f1705546739
Reviewed-on: https://go-review.googlesource.com/c/go/+/261540
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
This commit is contained in:
Russ Cox 2020-10-09 11:49:59 -04:00
parent 8fe372c7b3
commit a4ede9f9a6
20 changed files with 784 additions and 110 deletions
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66
src/os/file_unix.go
View file

@ -9,7 +9,6 @@ package os
import (
"internal/poll"
"internal/syscall/unix"
"io"
"runtime"
"syscall"
)
@ -353,33 +352,6 @@ func Symlink(oldname, newname string) error {
return nil
}
func (f *File) readdir(n int) (fi []FileInfo, err error) {
dirname := f.name
if dirname == "" {
dirname = "."
}
names, err := f.Readdirnames(n)
fi = make([]FileInfo, 0, len(names))
for _, filename := range names {
fip, lerr := lstat(dirname + "/" + filename)
if IsNotExist(lerr) {
// File disappeared between readdir + stat.
// Just treat it as if it didn't exist.
continue
}
if lerr != nil {
return fi, lerr
}
fi = append(fi, fip)
}
if len(fi) == 0 && err == nil && n > 0 {
// Per File.Readdir, the slice must be non-empty or err
// must be non-nil if n > 0.
err = io.EOF
}
return fi, err
}
// Readlink returns the destination of the named symbolic link.
// If there is an error, it will be of type *PathError.
func Readlink(name string) (string, error) {
@ -407,3 +379,41 @@ func Readlink(name string) (string, error) {
}
}
}
type unixDirent struct {
parent string
name string
typ FileMode
info FileInfo
}
func (d *unixDirent) Name() string { return d.name }
func (d *unixDirent) IsDir() bool { return d.typ.IsDir() }
func (d *unixDirent) Type() FileMode { return d.typ }
func (d *unixDirent) Info() (FileInfo, error) {
if d.info != nil {
return d.info, nil
}
return lstat(d.parent + "/" + d.name)
}
func newUnixDirent(parent, name string, typ FileMode) (DirEntry, error) {
ude := &unixDirent{
parent: parent,
name: name,
typ: typ,
}
if typ != ^FileMode(0) && !testingForceReadDirLstat {
return ude, nil
}
info, err := lstat(parent + "/" + name)
if err != nil {
return nil, err
}
ude.typ = info.Mode().Type()
ude.info = info
return ude, nil
}