Add vanilla parity harness and harden server boundaries

internal/network/boundary_test.go

@@ -0,0 +1,67 @@
+package network
+
+import (
+	"log/slog"
+	"math"
+	"testing"
+
+	"regionio/internal/protocol"
+	"regionio/internal/server"
+	"regionio/internal/world"
+)
+
+func TestValidPlayerName(t *testing.T) {
+	for _, name := range []string{"Steve", "player_123", "A"} {
+		if !validPlayerName(name) {
+			t.Errorf("validPlayerName(%q) = false", name)
+		}
+	}
+	for _, name := range []string{"", "seventeen_chars_1", "player-name", "имя"} {
+		if validPlayerName(name) {
+			t.Errorf("validPlayerName(%q) = true", name)
+		}
+	}
+}
+
+func TestPlayerMoveRejectsCoordinatesOutsideWorld(t *testing.T) {
+	cfg := server.DefaultConfig()
+	cfg.WorldDir = ""
+	srv, err := server.NewWithCache(cfg, world.NewCache(-1, func(cx, cz int32) *world.Chunk {
+		return world.GenerateFlat(cx, cz)
+	}))
+	if err != nil {
+		t.Fatal(err)
+	}
+	session, err := srv.RegisterPlayer(server.Profile{Name: "Steve"}, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	h := &handler{srv: srv, session: session, log: slog.Default()}
+	for _, position := range [][3]float64{
+		{maxPlayerXZ + 1, 0, 0},
+		{0, maxPlayerY + 1, 0},
+		{0, 0, -maxPlayerXZ - 1},
+		{math.NaN(), 0, 0},
+	} {
+		if err := h.onPlayerMove(position[0], position[1], position[2], 0, 0, true); err == nil {
+			t.Errorf("accepted position %v", position)
+		}
+	}
+}
+
+func TestKeepAliveRequiresPendingMatchingID(t *testing.T) {
+	h := &handler{log: slog.Default()}
+	w := protocol.NewWriter(8).Int64(42)
+	pkt := protocol.Packet{ID: protocol.PlayKeepAliveServer, Data: w.Bytes()}
+	if err := h.handlePlay(pkt); err == nil {
+		t.Fatal("accepted keep-alive response without a pending challenge")
+	}
+	h.keepAlivePending = true
+	h.keepAliveID = 42
+	if err := h.handlePlay(pkt); err != nil {
+		t.Fatalf("matching response: %v", err)
+	}
+	if h.keepAlivePending {
+		t.Fatal("matching response did not clear pending challenge")
+	}
+}