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/grpcclientidentity/example/main.go

@@ -0,0 +1,107 @@
+// This package demonstrates how the grpcclientidentity package can be used
+// to set up a gRPC greeter service.
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"os"
+	"time"
+
+	"github.com/zrepl/zrepl/config"
+	"github.com/zrepl/zrepl/logger"
+	"github.com/zrepl/zrepl/rpc/grpcclientidentity/example/pdu"
+	"github.com/zrepl/zrepl/rpc/grpcclientidentity/grpchelper"
+	"github.com/zrepl/zrepl/transport/tcp"
+)
+
+var args struct {
+	mode string
+}
+
+var log = logger.NewStderrDebugLogger()
+
+func main() {
+	flag.StringVar(&args.mode, "mode", "", "client|server")
+	flag.Parse()
+
+	switch args.mode {
+	case "client":
+		client()
+	case "server":
+		server()
+	default:
+		log.Printf("unknown mode %q")
+		os.Exit(1)
+	}
+}
+
+func onErr(err error, format string, args ...interface{}) {
+	log.WithError(err).Error(fmt.Sprintf("%s: %s", fmt.Sprintf(format, args...), err))
+	os.Exit(1)
+}
+
+func client() {
+	cn, err := tcp.TCPConnecterFromConfig(&config.TCPConnect{
+		ConnectCommon: config.ConnectCommon{
+			Type: "tcp",
+		},
+		Address:     "127.0.0.1:8080",
+		DialTimeout: 10 * time.Second,
+	})
+	if err != nil {
+		onErr(err, "build connecter error")
+	}
+
+	clientConn := grpchelper.ClientConn(cn, log)
+	defer clientConn.Close()
+
+	// normal usage from here on
+
+	client := pdu.NewGreeterClient(clientConn)
+	resp, err := client.Greet(context.Background(), &pdu.GreetRequest{Name: "somethingimadeup"})
+	if err != nil {
+		onErr(err, "RPC error")
+	}
+
+	fmt.Printf("got response:\n\t%s\n", resp.GetMsg())
+}
+
+const clientIdentityKey = "clientIdentity"
+
+func server() {
+	authListenerFactory, err := tcp.TCPListenerFactoryFromConfig(nil, &config.TCPServe{
+		ServeCommon: config.ServeCommon{
+			Type: "tcp",
+		},
+		Listen: "127.0.0.1:8080",
+		Clients: map[string]string{
+			"127.0.0.1": "localclient",
+			"::1":       "localclient",
+		},
+	})
+	if err != nil {
+		onErr(err, "cannot build listener factory")
+	}
+
+	log := logger.NewStderrDebugLogger()
+
+	srv, serve, err := grpchelper.NewServer(authListenerFactory, clientIdentityKey, log)
+	svc := &greeter{"hello "}
+	pdu.RegisterGreeterServer(srv, svc)
+
+	if err := serve(); err != nil {
+		onErr(err, "error serving")
+	}
+}
+
+type greeter struct {
+	prepend string
+}
+
+func (g *greeter) Greet(ctx context.Context, r *pdu.GreetRequest) (*pdu.GreetResponse, error) {
+	ci, _ := ctx.Value(clientIdentityKey).(string)
+	log.WithField("clientIdentity", ci).Info("Greet() request") // show that we got the client identity
+	return &pdu.GreetResponse{Msg: fmt.Sprintf("%s%s (clientIdentity=%q)", g.prepend, r.GetName(), ci)}, nil
+}