Don't connect to private or loopback addresses

This probably doesn't matter but it is pointless to try to connect to
those.

service/app/downloader.go

@@ -338,6 +338,11 @@ func (m *DatabaseRelaySource) GetRelays(ctx context.Context) ([]domain.RelayAddr
 				Message("address is invalid")
 			continue
 		}
+
+		if address.IsLoopbackOrPrivate() {
+			continue
+		}
+
 		result = append(result, address)
 	}
 

service/domain/relay_address.go

@@ -1,6 +1,8 @@
 package domain
 
 import (
+	"net"
+	"net/url"
 	"strings"
 
 	"github.com/boreq/errors"
@@ -32,6 +34,15 @@ func NewRelayAddressFromMaybeAddress(maybe MaybeRelayAddress) (RelayAddress, err
 	return NewRelayAddress(maybe.String())
 }
 
+func (r RelayAddress) IsLoopbackOrPrivate() bool {
+	u, err := url.Parse(r.s)
+	if err != nil {
+		return false
+	}
+	ip := net.ParseIP(u.Host)
+	return ip.IsLoopback() || ip.IsPrivate()
+}
+
 func (r RelayAddress) String() string {
 	return r.s
 }

service/domain/relay_address_test.go

@@ -51,3 +51,34 @@ func TestRelayAddress(t *testing.T) {
 		})
 	}
 }
+
+func TestRelayAddress_IsLocal(t *testing.T) {
+	testCases := []struct {
+		Input  string
+		Result bool
+	}{
+		{
+			Input:  "ws://127.0.0.1",
+			Result: true,
+		},
+		{
+			Input:  "ws://192.168.0.10",
+			Result: true,
+		},
+		{
+			Input:  "ws://1.2.3.4",
+			Result: false,
+		},
+		{
+			Input:  "ws://example.com",
+			Result: false,
+		},
+	}
+
+	for _, testCase := range testCases {
+		t.Run(testCase.Input, func(t *testing.T) {
+			address := MustNewRelayAddress(testCase.Input)
+			require.Equal(t, testCase.Result, address.IsLoopbackOrPrivate())
+		})
+	}
+}