rpc rewrite: control RPCs using gRPC + separate RPC for data transfer

transport/ssh: update go-netssh to new version
    => supports CloseWrite and Deadlines
    => build: require Go 1.11 (netssh requires it)

util/bytecounter/bytecounter_streamcopier.go

@@ -0,0 +1,71 @@
+package bytecounter
+
+import (
+	"io"
+	"sync/atomic"
+
+	"github.com/zrepl/zrepl/zfs"
+)
+
+// StreamCopier wraps a zfs.StreamCopier, reimplemening
+// its interface and counting the bytes written to during copying.
+type StreamCopier interface {
+	zfs.StreamCopier
+	Count() int64
+}
+
+// NewStreamCopier wraps sc into a StreamCopier.
+// If sc is io.Reader, it is guaranteed that the returned StreamCopier
+// implements that interface, too.
+func NewStreamCopier(sc zfs.StreamCopier) StreamCopier {
+	bsc := &streamCopier{sc, 0}
+	if scr, ok := sc.(io.Reader); ok {
+		return streamCopierAndReader{bsc, scr}
+	} else {
+		return bsc
+	}
+}
+
+type streamCopier struct {
+	sc    zfs.StreamCopier
+	count int64
+}
+
+// proxy writer used by streamCopier
+type streamCopierWriter struct {
+	parent *streamCopier
+	w      io.Writer
+}
+
+func (w streamCopierWriter) Write(p []byte) (n int, err error) {
+	n, err = w.w.Write(p)
+	atomic.AddInt64(&w.parent.count, int64(n))
+	return
+}
+
+func (s *streamCopier) Count() int64 {
+	return atomic.LoadInt64(&s.count)
+}
+
+var _ zfs.StreamCopier = &streamCopier{}
+
+func (s streamCopier) Close() error {
+	return s.sc.Close()
+}
+
+func (s *streamCopier) WriteStreamTo(w io.Writer) zfs.StreamCopierError {
+	ww := streamCopierWriter{s, w}
+	return s.sc.WriteStreamTo(ww)
+}
+
+// a streamCopier whose underlying sc is an io.Reader
+type streamCopierAndReader struct {
+	*streamCopier
+	asReader io.Reader
+}
+
+func (scr streamCopierAndReader) Read(p []byte) (int, error) {
+	n, err := scr.asReader.Read(p)
+	atomic.AddInt64(&scr.streamCopier.count, int64(n))
+	return n, err
+}