daemon: Preserve prefixes on config reload

copystructure cannot reflect the unexported fields in netip.Prefix and replaces configured default address pools with zero values during a daemon reload. Register an immutable-value copier, matching the existing netip.Addr handling, and cover it with a regression test.

Signed-off-by: Erick Shaffer <324667592+erishaffdev@users.noreply.github.com>

daemon/reload.go

@@ -17,16 +17,19 @@ import (
 )
 
 func init() {
-	// Register a custom copier for netip.Addr. The copystructure library uses
-	// reflection which cannot access unexported fields in netip.Addr, resulting
-	// in zero-value copies. Since netip.Addr is an immutable value type, we can
-	// safely return it as-is.
+	// Register custom copiers for netip values. The copystructure library uses
+	// reflection which cannot access unexported fields in these types, resulting
+	// in zero-value copies. Since netip values are immutable, we can safely return
+	// them as-is.
 	//
 	// Note: copystructure is archived (https://github.com/mitchellh/copystructure)
 	// and won't receive upstream fixes for this limitation.
 	copystructure.Copiers[reflect.TypeFor[netip.Addr]()] = func(v any) (any, error) {
 		return v.(netip.Addr), nil
 	}
+	copystructure.Copiers[reflect.TypeFor[netip.Prefix]()] = func(v any) (any, error) {
+		return v.(netip.Prefix), nil
+	}
 }
 
 // reloadTxn is used to defer side effects of a config reload.

daemon/reload_test.go

@@ -35,6 +35,15 @@ func TestCopystructureNetipAddr(t *testing.T) {
 	assert.Check(t, is.DeepEqual(copied.([]netip.Addr), original, cmpopts.EquateComparable(netip.Addr{})))
 }
 
+func TestCopystructureNetipPrefix(t *testing.T) {
+	// Verify that our custom copier for netip.Prefix works correctly.
+	// Without it, copystructure.Copy produces zero-value (invalid) prefixes.
+	original := []netip.Prefix{netip.MustParsePrefix("172.30.0.0/16")}
+	copied, err := copystructure.Copy(original)
+	assert.NilError(t, err)
+	assert.Check(t, is.DeepEqual(copied.([]netip.Prefix), original, cmpopts.EquateComparable(netip.Prefix{})))
+}
+
 func newDaemonForReloadT(t *testing.T, cfg *config.Config) *Daemon {
 	t.Helper()
 	daemon := &Daemon{