Both protocols are designed for server information transmission and share a
similar structure, differing only in minor details. They are implemented as
nested sub-protocols within the Steam A2S_RULES protocol. The keys encode
chunk metadata (current index and total count), while the values store the
actual chunks.
Server details are transmitted through the A2S_RULES protocol in messages
formatted as described below. Before transmission, the message undergoes the
following processing:
- Escape sequence replacement: All bytes unsuitable for reliable
transmission through Steam servers are replaced according to the table:
{0x01, 0x01}→0x01{0x01, 0x02}→0x00{0x01, 0x03}→0xFF
- Chunking: The message is split into
124-byte fragments and placed intoA2S_RULESkey-value pairs.
If the entire message exceeds 1400 bytes (the maximum size of a single UDP
packet in the Steam API), some data must be truncated. However, in practice,
a buffer of up to 8192 bytes is often sufficient, allowing servers to
respond with all data in a single packet.
Background information: https://community.bistudio.com/wiki/Arma_3:_ServerBrowserProtocol3
