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)

rpc/rpc_mux.go

@@ -0,0 +1,57 @@
+package rpc
+
+import (
+	"context"
+	"time"
+
+	"github.com/zrepl/zrepl/transport"
+	"github.com/zrepl/zrepl/rpc/transportmux"
+	"github.com/zrepl/zrepl/util/envconst"
+)
+
+type demuxedListener struct {
+	control, data transport.AuthenticatedListener
+}
+
+const (
+	transportmuxLabelControl string = "zrepl_control"
+	transportmuxLabelData    string = "zrepl_data"
+)
+
+func demux(serveCtx context.Context, listener transport.AuthenticatedListener) demuxedListener {
+	listeners, err := transportmux.Demux(
+		serveCtx, listener,
+		[]string{transportmuxLabelControl, transportmuxLabelData},
+		envconst.Duration("ZREPL_TRANSPORT_DEMUX_TIMEOUT", 10*time.Second),
+	)
+	if err != nil {
+		// transportmux API guarantees that the returned error can only be due
+		// to invalid API usage (i.e. labels too long)
+		panic(err)
+	}
+	return demuxedListener{
+		control: listeners[transportmuxLabelControl],
+		data:    listeners[transportmuxLabelData],
+	}
+}
+
+type muxedConnecter struct {
+	control, data transport.Connecter
+}
+
+func mux(rawConnecter transport.Connecter) muxedConnecter {
+	muxedConnecters, err := transportmux.MuxConnecter(
+		rawConnecter,
+		[]string{transportmuxLabelControl, transportmuxLabelData},
+		envconst.Duration("ZREPL_TRANSPORT_MUX_TIMEOUT", 10*time.Second),
+	)
+	if err != nil {
+		// transportmux API guarantees that the returned error can only be due
+		// to invalid API usage (i.e. labels too long)
+		panic(err)
+	}
+	return muxedConnecter{
+		control: muxedConnecters[transportmuxLabelControl],
+		data:    muxedConnecters[transportmuxLabelData],
+	}
+}