Add FifoIO to expose fifos directly to client

This allows clients an easier way to interact with the fifos for a
container without having to use the built in copyIO functions when
opening fifos.

It's nothing that clients could not have already coded but since we use
this type of functionality in the tests it makes sense to add an
implementation here.

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

io_unix.go

@@ -88,3 +88,85 @@ func copyIO(fifos *FIFOSet, ioset *ioSet, tty bool) (_ *wgCloser, err error) {
 		cancel: cancel,
 	}, nil
 }
+
+// NewDirectIO returns an IO implementation that exposes the pipes directly
+func NewDirectIO(ctx context.Context, terminal bool) (*DirectIO, error) {
+	set, err := NewFifos("")
+	if err != nil {
+		return nil, err
+	}
+	f := &DirectIO{
+		set:      set,
+		terminal: terminal,
+	}
+	defer func() {
+		if err != nil {
+			f.Delete()
+		}
+	}()
+	if f.Stdin, err = fifo.OpenFifo(ctx, set.In, syscall.O_WRONLY|syscall.O_CREAT|syscall.O_NONBLOCK, 0700); err != nil {
+		return nil, err
+	}
+	if f.Stdout, err = fifo.OpenFifo(ctx, set.Out, syscall.O_RDONLY|syscall.O_CREAT|syscall.O_NONBLOCK, 0700); err != nil {
+		f.Stdin.Close()
+		return nil, err
+	}
+	if f.Stderr, err = fifo.OpenFifo(ctx, set.Err, syscall.O_RDONLY|syscall.O_CREAT|syscall.O_NONBLOCK, 0700); err != nil {
+		f.Stdin.Close()
+		f.Stdout.Close()
+		return nil, err
+	}
+	return f, nil
+}
+
+type DirectIO struct {
+	Stdin  io.WriteCloser
+	Stdout io.ReadCloser
+	Stderr io.ReadCloser
+
+	set      *FIFOSet
+	terminal bool
+}
+
+func (f *DirectIO) IOCreate(id string) (IO, error) {
+	return f, nil
+}
+
+func (f *DirectIO) IOAttach(set *FIFOSet) (IO, error) {
+	return f, nil
+}
+
+func (f *DirectIO) Config() IOConfig {
+	return IOConfig{
+		Terminal: f.terminal,
+		Stdin:    f.set.In,
+		Stdout:   f.set.Out,
+		Stderr:   f.set.Err,
+	}
+}
+
+func (f *DirectIO) Cancel() {
+	// nothing to cancel as all operations are handled externally
+}
+
+func (f *DirectIO) Wait() {
+	// nothing to wait on as all operations are handled externally
+}
+
+func (f *DirectIO) Close() error {
+	err := f.Stdin.Close()
+	if err2 := f.Stdout.Close(); err == nil {
+		err = err2
+	}
+	if err2 := f.Stderr.Close(); err == nil {
+		err = err2
+	}
+	return err
+}
+
+func (f *DirectIO) Delete() error {
+	if f.set.Dir == "" {
+		return nil
+	}
+	return os.RemoveAll(f.set.Dir)
+}