Fix default spawn packet layout

internal/network/play.go

@@ -72,9 +72,13 @@ func (h *handler) sendChunkCacheCenter(cx, cz int32) error {
 }
 
 func (h *handler) sendDefaultSpawnPosition() error {
-	w := protocol.NewWriter(12)
+	// 26.1.2 wraps the spawn in LevelData.RespawnData: GlobalPos followed by
+	// yaw and pitch. GlobalPos starts with the dimension resource key.
+	w := protocol.NewWriter(40)
+	w.String("minecraft:overworld")
 	w.Position(8, 100, 8)
 	w.Float32(0.0)
+	w.Float32(0.0)
 	return h.conn.SendWriter(protocol.PlayDefaultSpawnPos, w)
 }
 

internal/network/play_spawn_test.go

@@ -0,0 +1,40 @@
+package network
+
+import (
+	"testing"
+
+	"regionio/internal/protocol"
+)
+
+func TestSendDefaultSpawnPositionLayout(t *testing.T) {
+	recorder := &recordingConn{}
+	h := &handler{conn: NewConn(recorder)}
+
+	if err := h.sendDefaultSpawnPosition(); err != nil {
+		t.Fatal(err)
+	}
+	packets := recorder.take(t)
+	if len(packets) != 1 {
+		t.Fatalf("packet count = %d, want 1", len(packets))
+	}
+	if packets[0].ID != protocol.PlayDefaultSpawnPos {
+		t.Fatalf("packet ID = %#x, want %#x", packets[0].ID, protocol.PlayDefaultSpawnPos)
+	}
+
+	r := protocol.NewReader(packets[0].Data)
+	if dimension, err := r.String(); err != nil || dimension != "minecraft:overworld" {
+		t.Fatalf("dimension = %q, %v; want minecraft:overworld", dimension, err)
+	}
+	if x, y, z, err := r.Position(); err != nil || x != 8 || y != 100 || z != 8 {
+		t.Fatalf("position = (%d, %d, %d), %v; want (8, 100, 8)", x, y, z, err)
+	}
+	if yaw, err := r.Float32(); err != nil || yaw != 0 {
+		t.Fatalf("yaw = %v, %v; want 0", yaw, err)
+	}
+	if pitch, err := r.Float32(); err != nil || pitch != 0 {
+		t.Fatalf("pitch = %v, %v; want 0", pitch, err)
+	}
+	if remaining := r.Remaining(); remaining != 0 {
+		t.Fatalf("remaining bytes = %d, want 0", remaining)
+	}
+}