src/{syscall, os}: add File.Stat, with smoke test

This is dgryski's File.Stat from #2371,
plus the windows bits,
plus a smoke test more or less from upstream,
rebased on FileHandle.SysHandle from #2469.

Author: dgryski

src/os/file.go

@@ -161,11 +161,6 @@ func (f *File) Seek(offset int64, whence int) (ret int64, err error) {
 	return 0, &PathError{"seek", f.name, ErrNotImplemented}
 }
 
-// Stat is a stub, not yet implemented
-func (f *File) Stat() (FileInfo, error) {
-	return nil, &PathError{"stat", f.name, ErrNotImplemented}
-}
-
 func (f *File) SyscallConn() (syscall.RawConn, error) {
 	return nil, ErrNotImplemented
 }

src/os/os_anyos_test.go

@@ -1,3 +1,4 @@
+//go:build windows || darwin || (linux && !baremetal)
 // +build windows darwin linux,!baremetal
 
 package os_test
@@ -7,6 +8,7 @@ import (
 	"path/filepath"
 	"runtime"
 	"strconv"
+	"strings"
 	"testing"
 	"time"
 )
@@ -21,7 +23,7 @@ func randomName() string {
 func TestMkdir(t *testing.T) {
 	dir := "TestMkdir" + randomName()
 	Remove(dir)
-	err := Mkdir(dir, 0755)
+	err := Mkdir(dir, 0o755)
 	defer Remove(dir)
 	if err != nil {
 		t.Errorf("Mkdir(%s, 0755) returned %v", dir, err)
@@ -47,8 +49,42 @@ func TestStatBadDir(t *testing.T) {
 	}
 }
 
+func equal(name1, name2 string) (r bool) {
+	switch runtime.GOOS {
+	case "windows":
+		r = strings.ToLower(name1) == strings.ToLower(name2)
+	default:
+		r = name1 == name2
+	}
+	return
+}
+
+func TestFstat(t *testing.T) {
+	sfname := "TestFstat"
+	path := TempDir() + "/" + sfname
+	payload := writeFile(t, path, O_CREATE|O_TRUNC|O_RDWR, "Hello")
+	defer Remove(path)
+
+	file, err1 := Open(path)
+	if err1 != nil {
+		t.Fatal("open failed:", err1)
+	}
+	defer file.Close()
+	dir, err2 := file.Stat()
+	if err2 != nil {
+		t.Fatal("fstat failed:", err2)
+	}
+	if !equal(sfname, dir.Name()) {
+		t.Error("name should be ", sfname, "; is", dir.Name())
+	}
+	filesize := len(payload)
+	if dir.Size() != int64(filesize) {
+		t.Error("size should be", filesize, "; is", dir.Size())
+	}
+}
+
 func writeFile(t *testing.T, fname string, flag int, text string) string {
-	f, err := OpenFile(fname, flag, 0666)
+	f, err := OpenFile(fname, flag, 0o666)
 	if err != nil {
 		t.Fatalf("Open: %v", err)
 	}

src/os/stat_other.go

@@ -1,4 +1,5 @@
-//  +build baremetal wasm,!wasi
+//go:build baremetal || (wasm && !wasi)
+// +build baremetal wasm,!wasi
 
 // Copyright 2016 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
@@ -11,6 +12,11 @@ func (f *File) Sync() error {
 	return ErrNotImplemented
 }
 
+// Stat is a stub, not yet implemented
+func (f *File) Stat() (FileInfo, error) {
+	return nil, ErrNotImplemented
+}
+
 // statNolog stats a file with no test logging.
 func statNolog(name string) (FileInfo, error) {
 	return nil, &PathError{Op: "stat", Path: name, Err: ErrNotImplemented}

src/os/stat_unix.go

@@ -1,3 +1,4 @@
+//go:build darwin || (linux && !baremetal)
 // +build darwin linux,!baremetal
 
 // Copyright 2016 The Go Authors. All rights reserved.
@@ -15,6 +16,20 @@ func (f *File) Sync() error {
 	return ErrNotImplemented
 }
 
+// Stat returns the FileInfo structure describing file.
+// If there is an error, it will be of type *PathError.
+func (f *File) Stat() (FileInfo, error) {
+	var fs fileStat
+	err := ignoringEINTR(func() error {
+		return syscall.Fstat(int(f.handle.(unixFileHandle)), &fs.sys)
+	})
+	if err != nil {
+		return nil, &PathError{Op: "fstat", Path: f.name, Err: err}
+	}
+	fillFileStatFromSys(&fs, f.name)
+	return &fs, nil
+}
+
 // statNolog stats a file with no test logging.
 func statNolog(name string) (FileInfo, error) {
 	var fs fileStat

src/os/stat_windows.go

@@ -15,6 +15,34 @@ func (f *File) Sync() error {
 	return ErrNotImplemented
 }
 
+// Stat returns the FileInfo structure describing file.
+// If there is an error, it will be of type *PathError.
+func (file *File) Stat() (FileInfo, error) {
+	if file == nil {
+		return nil, ErrInvalid
+	}
+
+	if isWindowsNulName(file.name) {
+		return &devNullStat, nil
+	}
+
+	ft, err := syscall.GetFileType(syscallFd(file.SysHandle()))
+	if err != nil {
+		return nil, &PathError{Op: "GetFileType", Path: file.name, Err: err}
+	}
+	switch ft {
+	case syscall.FILE_TYPE_PIPE, syscall.FILE_TYPE_CHAR:
+		return &fileStat{name: basename(file.name), filetype: ft}, nil
+	}
+
+	fs, err := newFileStatFromGetFileInformationByHandle(file.name, syscallFd(file.SysHandle()))
+	if err != nil {
+		return nil, err
+	}
+	fs.filetype = ft
+	return fs, err
+}
+
 // stat implements both Stat and Lstat of a file.
 func stat(funcname, name string, createFileAttrs uint32) (FileInfo, error) {
 	if len(name) == 0 {

src/syscall/syscall_libc_darwin.go

@@ -1,3 +1,4 @@
+//go:build darwin
 // +build darwin
 
 package syscall
@@ -172,6 +173,15 @@ func Stat(path string, p *Stat_t) (err error) {
 	return
 }
 
+func Fstat(fd int, p *Stat_t) (err error) {
+	n := libc_fstat(int32(fd), unsafe.Pointer(p))
+
+	if n < 0 {
+		err = getErrno()
+	}
+	return
+}
+
 func Lstat(path string, p *Stat_t) (err error) {
 	data := cstring(path)
 	n := libc_lstat(&data[0], unsafe.Pointer(p))
@@ -188,6 +198,10 @@ func Lstat(path string, p *Stat_t) (err error) {
 //export stat$INODE64
 func libc_stat(pathname *byte, ptr unsafe.Pointer) int32
 
+// int fstat(int fd, struct stat * buf);
+//export fstat$INODE64
+func libc_fstat(fd int32, ptr unsafe.Pointer) int32
+
 // int lstat(const char *path, struct stat * buf);
 //export lstat$INODE64
 func libc_lstat(pathname *byte, ptr unsafe.Pointer) int32

src/syscall/syscall_libc_wasi.go

@@ -1,3 +1,4 @@
+//go:build wasi
 // +build wasi
 
 package syscall
@@ -212,6 +213,15 @@ func Stat(path string, p *Stat_t) (err error) {
 	return
 }
 
+func Fstat(fd int, p *Stat_t) (err error) {
+	n := libc_fstat(int32(fd), unsafe.Pointer(p))
+
+	if n < 0 {
+		err = getErrno()
+	}
+	return
+}
+
 func Lstat(path string, p *Stat_t) (err error) {
 	data := cstring(path)
 	n := libc_lstat(&data[0], unsafe.Pointer(p))
@@ -225,6 +235,10 @@ func Lstat(path string, p *Stat_t) (err error) {
 //export stat
 func libc_stat(pathname *byte, ptr unsafe.Pointer) int32
 
+// int fstat(fd int, struct stat * buf);
+//export fstat
+func libc_fstat(fd int32, ptr unsafe.Pointer) int32
+
 // int lstat(const char *path, struct stat * buf);
 //export lstat
 func libc_lstat(pathname *byte, ptr unsafe.Pointer) int32