netsync: allow sync with non localhost peers

netsync/manager.go

@@ -6,7 +6,6 @@ package netsync
 
 import (
 	"math/rand"
-	"net"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -364,19 +363,12 @@ func (sm *SyncManager) isSyncCandidate(peer *peerpkg.Peer) bool {
 	// Typically a peer is not a candidate for sync if it's not a full node,
 	// however regression test is special in that the regression tool is
 	// not a full node and still needs to be considered a sync candidate.
-	if sm.chainParams == &chaincfg.RegressionNetParams {
-		// The peer is not a candidate if it's not coming from localhost
-		// or the hostname can't be determined for some reason.
-		host, _, err := net.SplitHostPort(peer.Addr())
-		if err != nil {
-			return false
-		}
-
-		if host != "127.0.0.1" && host != "localhost" {
-			return false
-		}
-
-		// Candidate if all checks passed.
+	switch sm.chainParams.Name {
+	case chaincfg.RegressionNetParams.Name, chaincfg.SimNetParams.Name:
+		// In regtest/simnet mode, any peer is a valid sync candidate
+		// regardless of its address or service flags. This allows
+		// syncing from peers on non-localhost networks such as Docker
+		// bridge networks.
 		return true
 	}
 
@@ -715,7 +707,7 @@ func (sm *SyncManager) handleBlockMsg(bmsg *blockMsg) {
 		// the peer or ignore the block when we're in regression test
 		// mode in this case so the chain code is actually fed the
 		// duplicate blocks.
-		if sm.chainParams != &chaincfg.RegressionNetParams {
+		if sm.chainParams.Name != chaincfg.RegressionNetParams.Name {
 			log.Warnf("Got unrequested block %v from %s -- "+
 				"disconnecting", blockHash, peer.Addr())
 			peer.Disconnect()

netsync/manager_test.go

@@ -1213,3 +1213,52 @@ func TestStartSyncChainCurrent(t *testing.T) {
 	require.False(t, sm.ibdMode,
 		"ibdMode should not be activated when chain is already current")
 }
+
+// TestIsSyncCandidateRegtest verifies that isSyncCandidate accepts any peer
+// on regtest regardless of address, including non-localhost Docker bridge
+// addresses.
+func TestIsSyncCandidateRegtest(t *testing.T) {
+	t.Parallel()
+
+	params := chaincfg.RegressionNetParams
+	sm, tearDown := makeMockSyncManager(t, &params)
+	defer tearDown()
+
+	tests := []struct {
+		name string
+		addr string
+		want bool
+	}{
+		{
+			name: "localhost",
+			addr: "127.0.0.1:18444",
+			want: true,
+		},
+		{
+			name: "docker bridge ip",
+			addr: "172.18.0.2:18444",
+			want: true,
+		},
+		{
+			name: "remote ip",
+			addr: "93.184.216.34:18444",
+			want: true,
+		},
+		{
+			name: "ipv6 loopback",
+			addr: "[::1]:18444",
+			want: true,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			p := peer.NewInboundPeer(&peer.Config{
+				ChainParams: sm.chainParams,
+			})
+
+			got := sm.isSyncCandidate(p)
+			require.Equal(t, tc.want, got)
+		})
+	}
+}