Add basic bootnode (#735)

* Add basic bootnode

* Add comment

* fix logging

tools/bootnode/BUILD.bazel

@@ -0,0 +1,23 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["bootnode.go"],
+    importpath = "github.com/prysmaticlabs/prysm/tools/bootnode",
+    visibility = ["//visibility:private"],
+    deps = [
+        "@com_github_ipfs_go_datastore//:go_default_library",
+        "@com_github_ipfs_go_datastore//sync:go_default_library",
+        "@com_github_ipfs_go_log//:go_default_library",
+        "@com_github_libp2p_go_libp2p//:go_default_library",
+        "@com_github_libp2p_go_libp2p_crypto//:go_default_library",
+        "@com_github_libp2p_go_libp2p_kad_dht//:go_default_library",
+        "@com_github_multiformats_go_multiaddr//:go_default_library",
+    ],
+)
+
+go_binary(
+    name = "bootnode",
+    embed = [":go_default_library"],
+    visibility = ["//visibility:public"],
+)

tools/bootnode/bootnode.go

@@ -0,0 +1,81 @@
+/**
+ * Bootnode
+ *
+ * A simple peer Kademlia distributed hash table (DHT) service for peer
+ * discovery. The purpose of this service is to provide a starting point for
+ * newly connected services to find other peers outside of their network.
+ *
+ * Usage: Run bootnode --help for flag options.
+ */
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+
+	ds "github.com/ipfs/go-datastore"
+	dsync "github.com/ipfs/go-datastore/sync"
+	logging "github.com/ipfs/go-log"
+	libp2p "github.com/libp2p/go-libp2p"
+	crypto "github.com/libp2p/go-libp2p-crypto"
+	kaddht "github.com/libp2p/go-libp2p-kad-dht"
+	ma "github.com/multiformats/go-multiaddr"
+)
+
+var (
+	debug      = flag.Bool("debug", false, "Enable debug logging")
+	privateKey = flag.String("private", "", "Private key to use for peer ID")
+	port       = flag.Int("port", 4000, "Port to listen for connections")
+
+	log = logging.Logger("prysm-bootnode")
+)
+
+func main() {
+	flag.Parse()
+	if *debug {
+		logging.SetDebugLogging()
+	}
+
+	listen, err := ma.NewMultiaddr(fmt.Sprintf("/ip4/0.0.0.0/tcp/%d", *port))
+	if err != nil {
+		log.Fatalf("Failed to construct new multiaddress. %v", err)
+	}
+
+	opts := []libp2p.Option{
+		libp2p.ListenAddrs(listen),
+	}
+	opts = addPrivateKeyOpt(opts)
+
+	host, err := libp2p.New(context.Background(), opts...)
+	if err != nil {
+		log.Fatalf("Failed to create new host. %v", err)
+	}
+
+	dstore := dsync.MutexWrap(ds.NewMapDatastore())
+	dht := kaddht.NewDHT(context.Background(), host, dstore)
+	if err := dht.Bootstrap(context.Background()); err != nil {
+		log.Fatalf("Failed to bootstrap DHT. %v", err)
+	}
+
+	fmt.Printf("Running bootnode: /ip4/0.0.0.0/tcp/%d/p2p/%s\n", *port, host.ID().Pretty())
+
+	select {}
+}
+
+func addPrivateKeyOpt(opts []libp2p.Option) []libp2p.Option {
+	if *privateKey != "" {
+		b, err := crypto.ConfigDecodeKey(*privateKey)
+		if err != nil {
+			panic(err)
+		}
+		pk, err := crypto.UnmarshalPrivateKey(b)
+		if err != nil {
+			panic(err)
+		}
+		opts = append(opts, libp2p.Identity(pk))
+	} else {
+		log.Warning("No private key was provided. Using default/random private key")
+	}
+	return opts
+}