sgrpc: Init gRPC over SCION/QUIC example (#236)

* sgrpc: Init gRPC over SCION/QUIC example

* README: add gRPC over SCION/QUIC example

* revision

* linters

Co-authored-by: Jordi Subirà Nieto <[email protected]>

Author: fstreun

README.md

@@ -101,6 +101,8 @@ The directory _examples contains examples for the usage of the SCION libraries.
   Example for the use of QUIC over SCION.
 * [_examples/hellodrkey](_examples/hellodrkey/README.md):
   Example for the the use of DRKey.
+* [_examples/sgrpc](_examples/sgrpc/README.md):
+  Example for using gRPC over SCION/QUIC with the PAN library.
 * [_examples/shttp](_examples/shttp/README.md):
   Examples for using HTTP over SCION/QUIC, examples for servers, proxies, and clients.
 

_examples/go.mod

@@ -3,6 +3,7 @@ module examples
 go 1.16
 
 require (
+	github.com/golang/protobuf v1.5.2
 	github.com/gorilla/handlers v1.5.1
 	github.com/lucas-clemente/quic-go v0.23.0
 	github.com/netsec-ethz/scion-apps v0.5.1-0.20220504120040-79211109ed3f

_examples/sgrpc/README.md

@@ -0,0 +1,46 @@
+# Example for gRPC over SCION/QUIC
+
+This directory contains a small example program that shows how gRPC can be used over SCION/QUIC with the PAN library.
+The example consists of an echo server and a client that sends a message to the service.
+
+## Running
+
+The example requires a running SCION endhost stack, i.e. a running SCION dispatcher and SCION daemon. Please refer to '[Running](../../README.md#Running)' in this repository's main README and the [SCIONLab tutorials](https://docs.scionlab.org) to get started.
+See '[Environment](../../README.md#Environment)' on how to set the dispatcher and sciond environment variables when e.g. running multiple local ASes.
+
+To test the server and client, run the SCION tiny test topology.
+
+Open a shell and run the server in the AS `1-ff00:0:111`:
+```bash
+# Server in 1-ff00:0:111
+SCION_DAEMON_ADDRESS="127.0.0.20:30255" \
+go run server/main.go --server-address 127.0.0.1:5000
+```
+
+Open a shell and run the client in the AS `1-ff00:0:112` and send a message to the server:
+```bash
+# Client in 1-ff00:0:112
+SCION_DAEMON_ADDRESS="127.0.0.28:30255" \
+go run client/main.go --server-address "1-ff00:0:111,127.0.0.1:5000" --message "gRPC over SCION/QUIC"
+```
+
+## Protobuf
+Tutorial: https://grpc.io/docs/languages/go/basics/
+
+Requirements:
+```bash
+go install google.golang.org/grpc/cmd/protoc-gen-go-grpc@latest
+```
+
+The compiler plugin protoc-gen-go will be installed in $GOBIN, defaulting to $GOPATH/bin. It must be in your $PATH for the protocol compiler protoc to find it.
+```bash
+export GO_PATH=~/go
+export PATH=$PATH:/$GO_PATH/bin
+```
+
+The generation of the gRPC client and server interface is performed as follows:
+```bash
+protoc --go_out=. --go_opt=paths=source_relative \
+  --go-grpc_out=. --go-grpc_opt=paths=source_relative \
+  proto/*.proto
+```

_examples/sgrpc/client/main.go

@@ -0,0 +1,75 @@
+package main
+
+import (
+	"context"
+	"crypto/tls"
+	"flag"
+	"fmt"
+	"log"
+	"net"
+	"time"
+
+	"github.com/lucas-clemente/quic-go"
+	"github.com/netsec-ethz/scion-apps/pkg/pan"
+	"github.com/netsec-ethz/scion-apps/pkg/quicutil"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/credentials/insecure"
+	"inet.af/netaddr"
+
+	pb "examples/sgrpc/proto"
+)
+
+var (
+	Message    = flag.String("message", "", "Message to send to the gRPC echo server")
+	ServerAddr = flag.String("server-addr", "1-ff00:0:111,127.0.0.1:5000", "Address of the echo server")
+)
+
+func NewPanQuicDialer(tlsCfg *tls.Config) func(context.Context, string) (net.Conn, error) {
+	dialer := func(ctx context.Context, addr string) (net.Conn, error) {
+		panAddr, err := pan.ResolveUDPAddr(ctx, addr)
+		if err != nil {
+			return nil, err
+		}
+
+		clientQuicConfig := &quic.Config{KeepAlive: true}
+		session, err := pan.DialQUIC(ctx, netaddr.IPPort{}, panAddr, nil, nil, "", tlsCfg, clientQuicConfig)
+		if err != nil {
+			return nil, fmt.Errorf("did not dial: %w", err)
+		}
+		return quicutil.NewSingleStream(session)
+	}
+
+	return dialer
+}
+
+func main() {
+	flag.Parse()
+
+	tlsCfg := &tls.Config{
+		InsecureSkipVerify: true,
+		NextProtos:         []string{"echo_service"},
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+
+	grpcDial, err := grpc.DialContext(ctx, *ServerAddr,
+		grpc.WithContextDialer(NewPanQuicDialer(tlsCfg)),
+		grpc.WithTransportCredentials(insecure.NewCredentials()),
+	)
+	if err != nil {
+		log.Fatalf("failed to dial gRPC: %v", err)
+	}
+
+	c := pb.NewEchoServiceClient(grpcDial)
+
+	req := &pb.EchoRequest{
+		Msg: *Message,
+	}
+	resp, err := c.Echo(ctx, req)
+	if err != nil {
+		log.Fatalf("gRPC did not connect: %v", err)
+	}
+
+	fmt.Println(resp.Msg)
+}

_examples/sgrpc/proto/echo.pb.go

@@ -0,0 +1,17 @@
+syntax = "proto3";
+
+package proto.echo;
+
+option go_package = "examples/sgrpc/proto";
+
+service EchoService{
+    rpc Echo(EchoRequest) returns (EchoResponse) {}
+}
+
+message EchoRequest{
+    string msg = 1;
+}
+
+message EchoResponse{
+  string msg = 1;
+}