Add relay node tool (#825)

* Add relay node

* gosec

* add docker image config

* gazelle

* punctuation

tools/relaynode/BUILD.bazel

@@ -0,0 +1,52 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library")
+load("@io_bazel_rules_docker//go:image.bzl", "go_image")
+load("@io_bazel_rules_docker//container:container.bzl", "container_push")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["relaynode.go"],
+    importpath = "github.com/prysmaticlabs/prysm/tools/relaynode",
+    visibility = ["//visibility:private"],
+    deps = [
+        "@com_github_ipfs_go_log//:go_default_library",
+        "@com_github_libp2p_go_libp2p//:go_default_library",
+        "@com_github_libp2p_go_libp2p_circuit//:go_default_library",
+        "@com_github_libp2p_go_libp2p_crypto//:go_default_library",
+        "@com_github_multiformats_go_multiaddr//:go_default_library",
+    ],
+)
+
+go_image(
+    name = "image",
+    srcs = ["relaynode.go"],
+    importpath = "github.com/prysmaticlabs/prysm/tools/relaynode",
+    visibility = ["//visibility:private"],
+    static = "on",
+    tags = ["manual"],
+    goarch = "amd64",
+    goos = "linux",
+    deps = [
+        "@com_github_ipfs_go_log//:go_default_library",
+        "@com_github_libp2p_go_libp2p//:go_default_library",
+        "@com_github_libp2p_go_libp2p_circuit//:go_default_library",
+        "@com_github_libp2p_go_libp2p_crypto//:go_default_library",
+        "@com_github_multiformats_go_multiaddr//:go_default_library",
+    ],
+)
+
+container_push(
+    name = "push_image",
+    format = "Docker",
+    image = ":image",
+    registry = "gcr.io",
+    repository = "prysmaticlabs/prysm/relaynode",
+    tag = "latest",
+    tags = ["manual"],
+    visibility = ["//visibility:private"],
+)
+
+go_binary(
+    name = "relaynode",
+    embed = [":go_default_library"],
+    visibility = ["//visibility:public"],
+)

tools/relaynode/relaynode.go

@@ -0,0 +1,77 @@
+/**
+ * Relay node
+ *
+ * A simple libp2p relay node peers to connect inbound traffic behind a NAT or
+ * other network restriction.
+ *
+ * Usage: Run relaynode --help for flag options.
+ */
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+
+	logging "github.com/ipfs/go-log"
+	libp2p "github.com/libp2p/go-libp2p"
+	circuit "github.com/libp2p/go-libp2p-circuit"
+	crypto "github.com/libp2p/go-libp2p-crypto"
+	multiaddr "github.com/multiformats/go-multiaddr"
+)
+
+var (
+	privateKey = flag.String("private", "", "Private key to use for peer ID")
+	port       = flag.Int("port", 4000, "Port to listen for connections")
+	debug      = flag.Bool("debug", false, "Enable debug logging")
+
+	log = logging.Logger("prysm-relaynode")
+)
+
+func main() {
+	flag.Parse()
+
+	if *debug {
+		logging.SetDebugLogging()
+	}
+
+	ctx := context.Background()
+	log.Start(ctx, "main")
+	defer log.Finish(ctx)
+
+	srcMAddr, err := multiaddr.NewMultiaddr(fmt.Sprintf("/ip4/0.0.0.0/tcp/%d", *port))
+	if err != nil {
+		log.Fatalf("Unable to construct multiaddr %v", err)
+	}
+
+	opts := []libp2p.Option{
+		libp2p.EnableRelay(circuit.OptHop),
+		libp2p.ListenAddrs(srcMAddr),
+	}
+
+	if *privateKey != "" {
+		b, err := crypto.ConfigDecodeKey(*privateKey)
+		if err != nil {
+			log.Fatalf("Failed to decode private key %v", err)
+		}
+		pk, err := crypto.UnmarshalPrivateKey(b)
+		if err != nil {
+			log.Fatalf("Failed to unmarshal private key %v", err)
+		}
+		opts = append(opts, libp2p.Identity(pk))
+	} else {
+		log.Warning("No private key provided. Using random key.")
+	}
+
+	h, err := libp2p.New(
+		ctx,
+		opts...,
+	)
+	if err != nil {
+		log.Fatalf("Failed to create host %v", err)
+	}
+
+	fmt.Printf("Relay available: /ip4/0.0.0.0/tcp/%v/p2p/%s\n", *port, h.ID().Pretty())
+
+	select {}
+}