fix: Find IPv6 addresses properly

internal/peer/peers.go

@@ -72,20 +72,7 @@ func getIdentifierFromInterface(logger logger.Logger, cfg config.Config) (string
 				Logf("IdentifierInterfaceName set but couldn't list addresses")
 			return "", err
 		}
-		var ipStr string
-		for _, addr := range addrs {
-			// ParseIP doesn't know what to do with the suffix
-			ip := net.ParseIP(strings.Split(addr.String(), "/")[0])
-			ipv6 := cfg.GetUseIPV6Identifier()
-			if ipv6 && ip.To16() != nil {
-				ipStr = fmt.Sprintf("[%s]", ip.String())
-				break
-			}
-			if !ipv6 && ip.To4() != nil {
-				ipStr = ip.String()
-				break
-			}
-		}
+		ipStr := selectIPFromAddrs(addrs, cfg.GetUseIPV6Identifier())
 		if ipStr == "" {
 			err = errors.New("could not find a valid IP to use from interface")
 			logger.Error().WithField("interface", ifc.Name).
@@ -99,3 +86,19 @@ func getIdentifierFromInterface(logger logger.Logger, cfg config.Config) (string
 
 	return myIdentifier, nil
 }
+
+// selectIPFromAddrs selects an IP address from a list of network addresses.
+// If useIPV6 is true, it returns the first IPv6 address wrapped in brackets.
+// If useIPV6 is false, it returns the first IPv4 address.
+func selectIPFromAddrs(addrs []net.Addr, useIPV6 bool) string {
+	for _, addr := range addrs {
+		ip := net.ParseIP(strings.Split(addr.String(), "/")[0])
+		if useIPV6 && ip.To4() == nil {
+			return fmt.Sprintf("[%s]", ip.String())
+		}
+		if !useIPV6 && ip.To4() != nil {
+			return ip.String()
+		}
+	}
+	return ""
+}

internal/peer/peers_test.go

@@ -3,6 +3,7 @@ package peer
 import (
 	"errors"
 	"fmt"
+	"net"
 	"os"
 	"strings"
 	"testing"
@@ -115,3 +116,80 @@ func TestPeerShutdown(t *testing.T) {
 		return len(peers) == 1
 	}, 5*time.Second, 200*time.Millisecond)
 }
+
+// mockAddr implements net.Addr for testing
+type mockAddr struct {
+	addr string
+}
+
+func (m mockAddr) Network() string { return "ip" }
+func (m mockAddr) String() string  { return m.addr }
+
+func TestSelectIPFromAddrs(t *testing.T) {
+	tests := []struct {
+		name     string
+		addrs    []net.Addr
+		useIPV6  bool
+		expected string
+	}{
+		{
+			name: "IPv4 only, useIPV6=false, should return IPv4",
+			addrs: []net.Addr{
+				mockAddr{"100.122.159.209/18"},
+			},
+			useIPV6:  false,
+			expected: "100.122.159.209",
+		},
+		{
+			name: "IPv4 only, useIPV6=true, should return empty (no IPv6 available)",
+			addrs: []net.Addr{
+				mockAddr{"100.122.159.209/18"},
+			},
+			useIPV6:  true,
+			expected: "",
+		},
+		{
+			name: "IPv6 only, useIPV6=true, should return bracketed IPv6",
+			addrs: []net.Addr{
+				mockAddr{"2600:1f18:2772:d500:a772:1d0e:8ef5:93de/128"},
+			},
+			useIPV6:  true,
+			expected: "[2600:1f18:2772:d500:a772:1d0e:8ef5:93de]",
+		},
+		{
+			name: "IPv6 only, useIPV6=false, should return empty (no IPv4 available)",
+			addrs: []net.Addr{
+				mockAddr{"2600:1f18:2772:d500:a772:1d0e:8ef5:93de/128"},
+			},
+			useIPV6:  false,
+			expected: "",
+		},
+		{
+			name: "Mixed IPv4 and IPv6, useIPV6=false, should return IPv4",
+			addrs: []net.Addr{
+				mockAddr{"100.122.159.209/18"},
+				mockAddr{"2600:1f18:2772:d500:a772:1d0e:8ef5:93de/128"},
+				mockAddr{"fe80::514d:14e3:9e02:b884/64"},
+			},
+			useIPV6:  false,
+			expected: "100.122.159.209",
+		},
+		{
+			name: "Mixed IPv4 and IPv6, useIPV6=true, should return bracketed IPv6 (not bracketed IPv4)",
+			addrs: []net.Addr{
+				mockAddr{"100.122.159.209/18"},
+				mockAddr{"2600:1f18:2772:d500:a772:1d0e:8ef5:93de/128"},
+				mockAddr{"fe80::514d:14e3:9e02:b884/64"},
+			},
+			useIPV6:  true,
+			expected: "[2600:1f18:2772:d500:a772:1d0e:8ef5:93de]",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := selectIPFromAddrs(tt.addrs, tt.useIPV6)
+			assert.Equal(t, tt.expected, result)
+		})
+	}
+}