rework size estimation & dry sends

- use control connection (gRPC)
- use uint64 everywhere => fixes https://github.com/zrepl/zrepl/issues/463
- [BREAK] bump protocol version

closes https://github.com/zrepl/zrepl/pull/518
fixes https://github.com/zrepl/zrepl/issues/463

rpc/dataconn/dataconn_client.go

@@ -114,12 +114,6 @@ func (c *Client) ReqSend(ctx context.Context, req *pdu.SendReq) (*pdu.SendRes, i
 	if err != nil {
 		return nil, nil, err
 	}
-	putWireOnReturn := true
-	defer func() {
-		if putWireOnReturn {
-			c.putWire(conn)
-		}
-	}()
 
 	if err := c.send(ctx, conn, EndpointSend, req, nil); err != nil {
 		return nil, nil, err
@@ -131,14 +125,10 @@ func (c *Client) ReqSend(ctx context.Context, req *pdu.SendReq) (*pdu.SendRes, i
 	}
 
 	var stream io.ReadCloser
-	if !req.DryRun {
-		putWireOnReturn = false
-		stream, err = conn.ReadStream(ZFSStream, true) // no shadow
-		if err != nil {
-			return nil, nil, err
-		}
+	stream, err = conn.ReadStream(ZFSStream, true) // no shadow
+	if err != nil {
+		return nil, nil, err
 	}
-
 	return &res, stream, nil
 }
 

rpc/rpc_client.go

@@ -108,6 +108,13 @@ func (c *Client) Receive(ctx context.Context, req *pdu.ReceiveReq, stream io.Rea
 	return c.dataClient.ReqRecv(ctx, req, stream)
 }
 
+func (c *Client) SendDry(ctx context.Context, in *pdu.SendReq) (*pdu.SendRes, error) {
+	ctx, endSpan := trace.WithSpan(ctx, "rpc.client.SendDry")
+	defer endSpan()
+
+	return c.controlClient.SendDry(ctx, in)
+}
+
 func (c *Client) ListFilesystems(ctx context.Context, in *pdu.ListFilesystemReq) (*pdu.ListFilesystemRes, error) {
 	ctx, endSpan := trace.WithSpan(ctx, "rpc.client.ListFilesystems")
 	defer endSpan()

rpc/versionhandshake/versionhandshake.go

@@ -152,7 +152,7 @@ func (m *HandshakeMessage) DecodeReader(r io.Reader, maxLen int) error {
 
 func DoHandshakeCurrentVersion(conn net.Conn, deadline time.Time) *HandshakeError {
 	// current protocol version is hardcoded here
-	return DoHandshakeVersion(conn, deadline, 5)
+	return DoHandshakeVersion(conn, deadline, 6)
 }
 
 const HandshakeMessageMaxLen = 16 * 4096