---
title: "Packet 57: MapSyncChunk"
description: "Carries one bounded chunk of the active VXL map stream."
canonical: "https://aosplay.net/protocol-168/packets/57"
markdown: "https://aosplay.net/docs/protocol-168/packets/57.md"
last_updated: "2026-07-16"
protocol: "Ace of Spades Battle Builder 168"
packet_id_decimal: "57"
packet_id_hex: "0x39"
direction: "S→C"
family: "Map sync"
implementation_status: "Sent"
evidence: "Live-verified"
wire_size: "4 + N bytes"
---

# Packet 57: MapSyncChunk

> Carries one bounded chunk of the active VXL map stream.

- **Decimal ID:** 57
- **Hex ID:** 0x39
- **Direction:** S→C
- **Family:** Map sync
- **Status:** Sent
- **Evidence:** Live-verified
- **Wire size:** 4 + N bytes

## Exact wire layout

The application packet ID is the first byte. The remaining rows are in decode order. Byte sizes exclude ENet headers, wrapper prefixes, LZF chunk framing, and compression effects.

| # | Field | Encoding | Bytes | Purpose | Condition |
| ---: | --- | --- | ---: | --- | --- |
| 0 | `packet_id` | u8 | 1 | Always 57 (0x39). | — |
| 1 | `percent_complete` | u8 | 1 | percent complete value. | — |
| 2 | `data_size` | u16 LE | 2 | N: raw payload length. | — |
| 3 | `data` | raw bytes | N | VXL stream bytes. | — |

## Encoding conventions

- `LE` means least-significant byte first.
- `fixed16` is two-byte sign-magnitude at 1/64 precision.
- `orientation16` uses the measured 1/8192 orientation mapping.
- NUL strings consume their encoded byte length plus one `00` terminator.
- Counted arrays repeat immediately in the documented order.

## Related resources

- [HTML packet page](https://aosplay.net/protocol-168/packets/57)
- [Complete packet catalog](https://aosplay.net/protocol-168/packets)
- [Packet catalog in Markdown](https://aosplay.net/docs/protocol-168/packets.md)
- [Protocol 168 guide](https://aosplay.net/protocol-168)