vendor: add buildkit

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

vendor/github.com/moby/buildkit/session/sshforward/copy.go

@@ -0,0 +1,61 @@
+package sshforward
+
+import (
+	io "io"
+
+	context "golang.org/x/net/context"
+	"golang.org/x/sync/errgroup"
+	"google.golang.org/grpc"
+)
+
+func Copy(ctx context.Context, conn io.ReadWriteCloser, stream grpc.Stream) error {
+	g, ctx := errgroup.WithContext(ctx)
+
+	g.Go(func() (retErr error) {
+		p := &BytesMessage{}
+		for {
+			if err := stream.RecvMsg(p); err != nil {
+				if err == io.EOF {
+					return nil
+				}
+				conn.Close()
+				return err
+			}
+			select {
+			case <-ctx.Done():
+				conn.Close()
+				return ctx.Err()
+			default:
+			}
+			if _, err := conn.Write(p.Data); err != nil {
+				conn.Close()
+				return err
+			}
+			p.Data = p.Data[:0]
+		}
+	})
+
+	g.Go(func() (retErr error) {
+		for {
+			buf := make([]byte, 32*1024)
+			n, err := conn.Read(buf)
+			switch {
+			case err == io.EOF:
+				return nil
+			case err != nil:
+				return err
+			}
+			select {
+			case <-ctx.Done():
+				return ctx.Err()
+			default:
+			}
+			p := &BytesMessage{Data: buf[:n]}
+			if err := stream.SendMsg(p); err != nil {
+				return err
+			}
+		}
+	})
+
+	return g.Wait()
+}