os/File: add stubs for os.File Deadlines (#4465)

os/File: add stubs for os.File Deadlines
* add os.SetDeadline, os.SetReadDeadline, os.SetWriteDeadline stubs for
posix files.
* deadline: add tests

Signed-off-by: leongross <leon.gross@9elements.com>

src/os/file.go

@@ -257,12 +257,29 @@ func (f *File) SyscallConn() (conn syscall.RawConn, err error) {
 	return
 }
 
+// SetDeadline sets the read and write deadlines for a File.
+// Calls to SetDeadline for files that do not support deadlines will return ErrNoDeadline
+// This stub always returns ErrNoDeadline.
+// A zero value for t means I/O operations will not time out.
+func (f *File) SetDeadline(t time.Time) error {
+	if f.handle == nil {
+		return ErrClosed
+	}
+	return f.setDeadline(t)
+}
+
 // SetReadDeadline sets the deadline for future Read calls and any
 // currently-blocked Read call.
 func (f *File) SetReadDeadline(t time.Time) error {
 	return f.setReadDeadline(t)
 }
 
+// SetWriteDeadline sets the deadline for any future Write calls and any
+// currently-blocked Write call.
+func (f *File) SetWriteDeadline(t time.Time) error {
+	return f.setWriteDeadline(t)
+}
+
 // fd is an internal interface that is used to try a type assertion in order to
 // call the Fd() method of the underlying file handle if it is implemented.
 type fd interface {