server: disable DNS boostrap for SigNet nodes (#5564)

* server: disable DNS boostrap for SigNet nodes

In this commit, we fix a bug that would cause nodes attempting to run
using the signet chain, to waste CPU as they attempted to boostrap to a
non-existent DNS seed. We fix this by ignoring the DNS boostrapper is
signet is active. Along the way, we refactor the conditional sightly to
be more readable, and easily extensible.

* server: extract bootstrap logic into new function w/ unit test

* docs/release-notes: update release notes for signet DNS fix

docs/release-notes/release-notes-0.14.0.md

@@ -106,6 +106,12 @@ you.
 * [Update MC store in blocks](https://github.com/lightningnetwork/lnd/pull/5515)
   to make payment throughput better when using etcd.
 
+## Bug Fixes
+
+A bug has been fixed that would cause `lnd` to [try to bootstrap using the
+currnet DNS seeds when in SigNet
+mode](https://github.com/lightningnetwork/lnd/pull/5564).
+
 # Contributors (Alphabetical Order)
 * ErikEk
 * Martin Habovstiak

server.go

@@ -1788,10 +1788,7 @@ func (s *server) Start() error {
 		// configure the set of active bootstrappers, and launch a
 		// dedicated goroutine to maintain a set of persistent
 		// connections.
-		if !s.cfg.NoNetBootstrap &&
-			!(s.cfg.Bitcoin.SimNet || s.cfg.Litecoin.SimNet) &&
-			!(s.cfg.Bitcoin.RegTest || s.cfg.Litecoin.RegTest) {
-
+		if shouldPeerBootstrap(s.cfg) {
 			bootstrappers, err := initNetworkBootstrappers(s)
 			if err != nil {
 				startErr = err
@@ -3963,3 +3960,15 @@ func newSweepPkScriptGen(
 		return txscript.PayToAddrScript(sweepAddr)
 	}
 }
+
+// shouldPeerBootstrap returns true if we should attempt to perform peer
+// boostrapping to actively seek our peers using the set of active network
+// bootsrappers.
+func shouldPeerBootstrap(cfg *Config) bool {
+	isSimnet := (cfg.Bitcoin.SimNet || cfg.Litecoin.SimNet)
+	isSignet := (cfg.Bitcoin.SigNet || cfg.Litecoin.SigNet)
+	isRegtest := (cfg.Bitcoin.RegTest || cfg.Litecoin.RegTest)
+	isDevNetwork := isSimnet || isSignet || isRegtest
+
+	return !cfg.NoNetBootstrap && !isDevNetwork
+}

server_test.go

@@ -17,6 +17,8 @@ import (
 	"os"
 	"testing"
 	"time"
+
+	"github.com/lightningnetwork/lnd/lncfg"
 )
 
 func TestParseHexColor(t *testing.T) {
@@ -203,3 +205,84 @@ func genExpiredCertPair(t *testing.T, certDirPath string) ([]byte, []byte) {
 
 	return certDerBytes, keyBytes
 }
+
+// TestShouldPeerBootstrap tests that we properly skip network bootstrap for
+// the developer networks, and also if bootstrapping is explicitly disabled.
+func TestShouldPeerBootstrap(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		cfg            *Config
+		shouldBoostrap bool
+	}{
+		// Simnet active, no bootstrap.
+		{
+			cfg: &Config{
+				Bitcoin: &lncfg.Chain{
+					SimNet: true,
+				},
+				Litecoin: &lncfg.Chain{},
+			},
+		},
+
+		// Regtest active, no bootstrap.
+		{
+			cfg: &Config{
+				Bitcoin: &lncfg.Chain{
+					RegTest: true,
+				},
+				Litecoin: &lncfg.Chain{},
+			},
+		},
+
+		// Signet active, no bootstrap.
+		{
+			cfg: &Config{
+				Bitcoin: &lncfg.Chain{
+					SigNet: true,
+				},
+				Litecoin: &lncfg.Chain{},
+			},
+		},
+
+		// Mainnet active, but boostrap disabled, no boostrap.
+		{
+			cfg: &Config{
+				Bitcoin: &lncfg.Chain{
+					MainNet: true,
+				},
+				Litecoin:       &lncfg.Chain{},
+				NoNetBootstrap: true,
+			},
+		},
+
+		// Mainnet active, should boostrap.
+		{
+			cfg: &Config{
+				Bitcoin: &lncfg.Chain{
+					MainNet: true,
+				},
+				Litecoin: &lncfg.Chain{},
+			},
+			shouldBoostrap: true,
+		},
+
+		// Testnet active, should boostrap.
+		{
+			cfg: &Config{
+				Bitcoin: &lncfg.Chain{
+					TestNet3: true,
+				},
+				Litecoin: &lncfg.Chain{},
+			},
+			shouldBoostrap: true,
+		},
+	}
+	for i, testCase := range testCases {
+		bootstrapped := shouldPeerBootstrap(testCase.cfg)
+		if bootstrapped != testCase.shouldBoostrap {
+			t.Fatalf("#%v: expected bootstrap=%v, got bootstrap=%v",
+				i, testCase.shouldBoostrap, bootstrapped)
+		}
+	}
+}