Don't panic at startup when duplicate peers are configured

Fixes #1077

src/core/options.go

@@ -13,7 +13,15 @@ func (c *Core) _applyOption(opt SetupOption) (err error) {
 		if err != nil {
 			return fmt.Errorf("unable to parse peering URI: %w", err)
 		}
-		return c.links.add(u, v.SourceInterface, linkTypePersistent)
+		err = c.links.add(u, v.SourceInterface, linkTypePersistent)
+		switch err {
+		case ErrLinkAlreadyConfigured:
+			// Don't return this error, otherwise we'll panic at startup
+			// if there are multiple of the same peer configured
+			return nil
+		default:
+			return err
+		}
 	case ListenAddress:
 		c.config._listeners[v] = struct{}{}
 	case NodeInfo:

src/core/options_test.go

@@ -0,0 +1,22 @@
+package core
+
+import (
+	"testing"
+
+	"github.com/yggdrasil-network/yggdrasil-go/src/config"
+)
+
+func TestDuplicatePeer(t *testing.T) {
+	cfg := config.GenerateConfig()
+	c, err := New(cfg.Certificate, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Add the same peer multiple times. This should not return an error.
+	for i := 0; i < 5; i++ {
+		if err := c._applyOption(Peer{"tcp://1.2.3.4:4321", ""}); err != nil {
+			t.Fatalf("Adding peer failed on iteration %d", i)
+		}
+	}
+}