From a1e3c2d47cf55fecdbbd066f5d18ec5122490f30 Mon Sep 17 00:00:00 2001
From: Tim Myers <timmyers09@gmail.com>
Date: Wed, 22 Jan 2020 15:07:22 -0700
Subject: [PATCH] Add --p2p-host-dns flag to specify p2p external DNS (#4608)

Co-authored-by: Raul Jordan <raul@prysmaticlabs.com>
---
 beacon-chain/main.go        |  1 +
 beacon-chain/node/node.go   |  1 +
 beacon-chain/p2p/config.go  |  1 +
 beacon-chain/p2p/options.go | 11 +++++++++++
 beacon-chain/p2p/service.go | 21 ++++++++++++++++++++-
 beacon-chain/usage.go       |  1 +
 shared/cmd/flags.go         |  6 ++++++
 7 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/beacon-chain/main.go b/beacon-chain/main.go
index 21d3c0db60b..2395efb5a89 100644
--- a/beacon-chain/main.go
+++ b/beacon-chain/main.go
@@ -51,6 +51,7 @@ var appFlags = []cli.Flag{
 	cmd.P2PUDPPort,
 	cmd.P2PTCPPort,
 	cmd.P2PHost,
+	cmd.P2PHostDNS,
 	cmd.P2PMaxPeers,
 	cmd.P2PPrivKey,
 	cmd.P2PWhitelist,
diff --git a/beacon-chain/node/node.go b/beacon-chain/node/node.go
index 995bfce2554..b5c86cf60fc 100644
--- a/beacon-chain/node/node.go
+++ b/beacon-chain/node/node.go
@@ -269,6 +269,7 @@ func (b *BeaconNode) registerP2P(ctx *cli.Context) error {
 		RelayNodeAddr:     ctx.GlobalString(cmd.RelayNode.Name),
 		DataDir:           ctx.GlobalString(cmd.DataDirFlag.Name),
 		HostAddress:       ctx.GlobalString(cmd.P2PHost.Name),
+		HostDNS:           ctx.GlobalString(cmd.P2PHostDNS.Name),
 		PrivateKey:        ctx.GlobalString(cmd.P2PPrivKey.Name),
 		TCPPort:           ctx.GlobalUint(cmd.P2PTCPPort.Name),
 		UDPPort:           ctx.GlobalUint(cmd.P2PUDPPort.Name),
diff --git a/beacon-chain/p2p/config.go b/beacon-chain/p2p/config.go
index c89ff3ad705..d3a1d10f4a3 100644
--- a/beacon-chain/p2p/config.go
+++ b/beacon-chain/p2p/config.go
@@ -10,6 +10,7 @@ type Config struct {
 	Discv5BootStrapAddr   []string
 	RelayNodeAddr         string
 	HostAddress           string
+	HostDNS               string
 	PrivateKey            string
 	DataDir               string
 	TCPPort               uint
diff --git a/beacon-chain/p2p/options.go b/beacon-chain/p2p/options.go
index 524216fcbfa..c2d7040a592 100644
--- a/beacon-chain/p2p/options.go
+++ b/beacon-chain/p2p/options.go
@@ -45,6 +45,17 @@ func buildOptions(cfg *Config, ip net.IP, priKey *ecdsa.PrivateKey) []libp2p.Opt
 			return addrs
 		}))
 	}
+	if cfg.HostDNS != "" {
+		options = append(options, libp2p.AddrsFactory(func(addrs []multiaddr.Multiaddr) []multiaddr.Multiaddr {
+			external, err := multiaddr.NewMultiaddr(fmt.Sprintf("/dns4/%s/tcp/%d", cfg.HostDNS, cfg.TCPPort))
+			if err != nil {
+				log.WithError(err).Error("Unable to create external multiaddress")
+			} else {
+				addrs = append(addrs, external)
+			}
+			return addrs
+		}))
+	}
 	return options
 }
 
diff --git a/beacon-chain/p2p/service.go b/beacon-chain/p2p/service.go
index 05ee0d4ff3c..91039acb3b4 100644
--- a/beacon-chain/p2p/service.go
+++ b/beacon-chain/p2p/service.go
@@ -217,7 +217,15 @@ func (s *Service) Start() {
 
 	p2pHostAddress := s.cfg.HostAddress
 	p2pTCPPort := s.cfg.TCPPort
-	logExternalIP4Addr(s.host.ID(), p2pHostAddress, p2pTCPPort)
+
+	if p2pHostAddress != "" {
+		logExternalIP4Addr(s.host.ID(), p2pHostAddress, p2pTCPPort)
+	}
+
+	p2pHostDNS := s.cfg.HostDNS
+	if p2pHostDNS != "" {
+		logExternalDNSAddr(s.host.ID(), p2pHostDNS, p2pTCPPort)
+	}
 }
 
 // Stop the p2p service and terminate all peer connections.
@@ -380,3 +388,14 @@ func logExternalIP4Addr(id peer.ID, addr string, port uint) {
 		).Info("Node started external p2p server")
 	}
 }
+
+func logExternalDNSAddr(id peer.ID, addr string, port uint) {
+	if addr != "" {
+		p := strconv.FormatUint(uint64(port), 10)
+
+		log.WithField(
+			"multiAddr",
+			"/dns4/"+addr+"/tcp/"+p+"/p2p/"+id.String(),
+		).Info("Node started external p2p server")
+	}
+}
diff --git a/beacon-chain/usage.go b/beacon-chain/usage.go
index 151048a500f..2313cbc1064 100644
--- a/beacon-chain/usage.go
+++ b/beacon-chain/usage.go
@@ -95,6 +95,7 @@ var appHelpFlagGroups = []flagGroup{
 		Name: "p2p",
 		Flags: []cli.Flag{
 			cmd.P2PHost,
+			cmd.P2PHostDNS,
 			cmd.P2PMaxPeers,
 			cmd.P2PPrivKey,
 			cmd.P2PWhitelist,
diff --git a/shared/cmd/flags.go b/shared/cmd/flags.go
index 23a2c18f7ef..b4263e2e45e 100644
--- a/shared/cmd/flags.go
+++ b/shared/cmd/flags.go
@@ -94,6 +94,12 @@ var (
 		Usage: "The IP address advertised by libp2p. This may be used to advertise an external IP.",
 		Value: "",
 	}
+	// P2PHostDNS defines the host DNS to be used by libp2p.
+	P2PHostDNS = cli.StringFlag{
+		Name:  "p2p-host-dns",
+		Usage: "The DNS address advertised by libp2p. This may be used to advertise an external DNS.",
+		Value: "",
+	}
 	// P2PPrivKey defines a flag to specify the location of the private key file for libp2p.
 	P2PPrivKey = cli.StringFlag{
 		Name:  "p2p-priv-key",