Revert "Minor changes to support go 1.17"

This reverts commit 2d224ae049.

src/os/file_go_116.go

@@ -0,0 +1,113 @@
+// +build go1.16
+
+package os
+
+import (
+	"io"
+	"io/fs"
+)
+
+type (
+	DirEntry = fs.DirEntry
+	FileMode = fs.FileMode
+	FileInfo = fs.FileInfo
+)
+
+func (f *File) ReadDir(n int) ([]DirEntry, error) {
+	return nil, &PathError{"ReadDir", f.name, ErrNotImplemented}
+}
+
+func ReadDir(name string) ([]DirEntry, error) {
+	return nil, &PathError{"ReadDir", name, ErrNotImplemented}
+}
+
+// The followings are copied from Go 1.16 official implementation:
+// https://github.com/golang/go/blob/go1.16/src/os/file.go
+
+// ReadFile reads the named file and returns the contents.
+// A successful call returns err == nil, not err == EOF.
+// Because ReadFile reads the whole file, it does not treat an EOF from Read
+// as an error to be reported.
+func ReadFile(name string) ([]byte, error) {
+	f, err := Open(name)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+
+	var size int
+	if info, err := f.Stat(); err == nil {
+		size64 := info.Size()
+		if int64(int(size64)) == size64 {
+			size = int(size64)
+		}
+	}
+	size++ // one byte for final read at EOF
+
+	// If a file claims a small size, read at least 512 bytes.
+	// In particular, files in Linux's /proc claim size 0 but
+	// then do not work right if read in small pieces,
+	// so an initial read of 1 byte would not work correctly.
+	if size < 512 {
+		size = 512
+	}
+
+	data := make([]byte, 0, size)
+	for {
+		if len(data) >= cap(data) {
+			d := append(data[:cap(data)], 0)
+			data = d[:len(data)]
+		}
+		n, err := f.Read(data[len(data):cap(data)])
+		data = data[:len(data)+n]
+		if err != nil {
+			if err == io.EOF {
+				err = nil
+			}
+			return data, err
+		}
+	}
+}
+
+// WriteFile writes data to the named file, creating it if necessary.
+// If the file does not exist, WriteFile creates it with permissions perm (before umask);
+// otherwise WriteFile truncates it before writing, without changing permissions.
+func WriteFile(name string, data []byte, perm FileMode) error {
+	f, err := OpenFile(name, O_WRONLY|O_CREATE|O_TRUNC, perm)
+	if err != nil {
+		return err
+	}
+	_, err = f.Write(data)
+	if err1 := f.Close(); err1 != nil && err == nil {
+		err = err1
+	}
+	return err
+}
+
+// The defined file mode bits are the most significant bits of the FileMode.
+// The nine least-significant bits are the standard Unix rwxrwxrwx permissions.
+// The values of these bits should be considered part of the public API and
+// may be used in wire protocols or disk representations: they must not be
+// changed, although new bits might be added.
+const (
+	// The single letters are the abbreviations
+	// used by the String method's formatting.
+	ModeDir        = fs.ModeDir        // d: is a directory
+	ModeAppend     = fs.ModeAppend     // a: append-only
+	ModeExclusive  = fs.ModeExclusive  // l: exclusive use
+	ModeTemporary  = fs.ModeTemporary  // T: temporary file; Plan 9 only
+	ModeSymlink    = fs.ModeSymlink    // L: symbolic link
+	ModeDevice     = fs.ModeDevice     // D: device file
+	ModeNamedPipe  = fs.ModeNamedPipe  // p: named pipe (FIFO)
+	ModeSocket     = fs.ModeSocket     // S: Unix domain socket
+	ModeSetuid     = fs.ModeSetuid     // u: setuid
+	ModeSetgid     = fs.ModeSetgid     // g: setgid
+	ModeCharDevice = fs.ModeCharDevice // c: Unix character device, when ModeDevice is set
+	ModeSticky     = fs.ModeSticky     // t: sticky
+	ModeIrregular  = fs.ModeIrregular  // ?: non-regular file; nothing else is known about this file
+
+	// Mask for the type bits. For regular files, none will be set.
+	ModeType = fs.ModeType
+
+	ModePerm = fs.ModePerm // Unix permission bits, 0o777
+)