Merge pull request #4744 from guggero/dns-seed-config

discovery: allow DNS seeds to be overwritten

lncfg/chain.go

@@ -26,6 +26,7 @@ type Chain struct {
 	BaseFee             lnwire.MilliSatoshi `long:"basefee" description:"The base fee in millisatoshi we will charge for forwarding payments on our channels"`
 	FeeRate             lnwire.MilliSatoshi `long:"feerate" description:"The fee rate used when forwarding payments on our channels. The total fee charged is basefee + (amount * feerate / 1000000), where amount is the forwarded amount."`
 	TimeLockDelta       uint32              `long:"timelockdelta" description:"The CLTV delta we will subtract from a forwarded HTLC's timelock value"`
+	DNSSeeds            []string            `long:"dnsseed" description:"The seed DNS server(s) to use for initial peer discovery. Must be specified as a '<primary_dns>[,<soa_primary_dns>]' tuple where the SOA address is needed for DNS resolution through Tor but is optional for clearnet users. Multiple tuples can be specified, will overwrite the default seed servers."`
 }
 
 // Validate performs validation on our chain config.

sample-lnd.conf

@@ -417,6 +417,21 @@ bitcoin.node=btcd
 ; The CLTV delta we will subtract from a forwarded HTLC's timelock value.
 ; bitcoin.timelockdelta=40
 
+; The seed DNS server(s) to use for initial peer discovery. Must be specified as
+; a '<primary_dns>[,<soa_primary_dns>]' tuple where the SOA address is needed
+; for DNS resolution through Tor but is optional for clearnet users. Multiple
+; tuples can be specified, will overwrite the default seed servers.
+; The default seed servers are:
+;  mainnet:
+;    bitcoin.dnsseed=nodes.lightning.directory,soa.nodes.lightning.directory
+;    bitcoin.dnsseed=lseed.bitcoinstats.com
+;  testnet:
+;    bitcoin.dnsseed=test.nodes.lightning.directory,soa.nodes.lightning.directory
+;
+; Example for custom DNS servers:
+; bitcoin.dnsseed=seed1.test.lightning
+; bitcoin.dnsseed=seed2.test.lightning,soa.seed2.test.lightning
+
 ; Used to help identify ourselves to other bitcoin peers (default: neutrino).
 ; neutrino.useragentname=neutrino
 
@@ -589,6 +604,18 @@ litecoin.node=ltcd
 ; The CLTV delta we will subtract from a forwarded HTLC's timelock value.
 ; litecoin.timelockdelta=576
 
+; The seed DNS server(s) to use for initial peer discovery. Must be specified as
+; a '<primary_dns>[,<soa_primary_dns>]' tuple where the SOA address is needed
+; for DNS resolution through Tor but is optional for clearnet users. Multiple
+; tuples can be specified, will overwrite the default seed servers.
+; The default seed servers are:
+;  mainnet:
+;    litecoin.dnsseed=ltc.nodes.lightning.directory,soa.nodes.lightning.directory
+;
+; Example for custom DNS servers:
+; litecoin.dnsseed=seed1.test-ltc.lightning
+; litecoin.dnsseed=seed2.test-ltc.lightning,soa.seed2.test-ltc.lightning
+
 [Ltcd]
 
 ; The base directory that contains the node's data, logs, configuration file,

server.go

@@ -13,6 +13,7 @@ import (
 	"path/filepath"
 	"regexp"
 	"strconv"
+	"strings"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -1536,6 +1537,57 @@ func (s *server) Start() error {
 			return
 		}
 
+		// setSeedList is a helper function that turns multiple DNS seed
+		// server tuples from the command line or config file into the
+		// data structure we need and does a basic formal sanity check
+		// in the process.
+		setSeedList := func(tuples []string, genesisHash chainhash.Hash) {
+			if len(tuples) == 0 {
+				return
+			}
+
+			result := make([][2]string, len(tuples))
+			for idx, tuple := range tuples {
+				tuple = strings.TrimSpace(tuple)
+				if len(tuple) == 0 {
+					return
+				}
+
+				servers := strings.Split(tuple, ",")
+				if len(servers) > 2 || len(servers) == 0 {
+					srvrLog.Warnf("Ignoring invalid DNS "+
+						"seed tuple: %v", servers)
+					return
+				}
+
+				copy(result[idx][:], servers)
+			}
+
+			chainreg.ChainDNSSeeds[genesisHash] = result
+		}
+
+		// Let users overwrite the DNS seed nodes. We only allow them
+		// for bitcoin mainnet/testnet and litecoin mainnet, all other
+		// combinations will just be ignored.
+		if s.cfg.Bitcoin.Active && s.cfg.Bitcoin.MainNet {
+			setSeedList(
+				s.cfg.Bitcoin.DNSSeeds,
+				chainreg.BitcoinMainnetGenesis,
+			)
+		}
+		if s.cfg.Bitcoin.Active && s.cfg.Bitcoin.TestNet3 {
+			setSeedList(
+				s.cfg.Bitcoin.DNSSeeds,
+				chainreg.BitcoinTestnetGenesis,
+			)
+		}
+		if s.cfg.Litecoin.Active && s.cfg.Litecoin.MainNet {
+			setSeedList(
+				s.cfg.Litecoin.DNSSeeds,
+				chainreg.LitecoinMainnetGenesis,
+			)
+		}
+
 		// If network bootstrapping hasn't been disabled, then we'll
 		// configure the set of active bootstrappers, and launch a
 		// dedicated goroutine to maintain a set of persistent