Add support for Mindustry (#178)

* buffer: Add UTF8LengthPrefixed string decoder

* games: Use expression for default port

This allows us to refer to constants for the default ports if we want to
(literals will still work).

* games: Add support for mindustry

crates/lib/src/games/mindustry/protocol.rs

@@ -0,0 +1,58 @@
+use std::net::SocketAddr;
+
+use crate::{
+    buffer::{self, Buffer},
+    socket::{Socket, UdpSocket},
+    utils,
+    GDResult,
+    TimeoutSettings,
+};
+
+use super::types::ServerData;
+
+/// Mindustry max datagram packet size.
+pub const MAX_BUFFER_SIZE: usize = 500;
+
+/// Send a ping packet.
+///
+/// [Reference](https://github.com/Anuken/Mindustry/blob/a2e5fbdedb2fc1c8d3c157bf344d10ad6d321442/core/src/mindustry/net/ArcNetProvider.java#L248)
+pub fn send_ping(socket: &mut UdpSocket) -> GDResult<()> { socket.send(&[-2i8 as u8, 1i8 as u8]) }
+
+/// Parse server data.
+///
+/// [Reference](https://github.com/Anuken/Mindustry/blob/a2e5fbdedb2fc1c8d3c157bf344d10ad6d321442/core/src/mindustry/net/NetworkIO.java#L122-L135)
+pub fn parse_server_data<B: byteorder::ByteOrder, D: buffer::StringDecoder>(
+    buffer: &mut Buffer<B>,
+) -> GDResult<ServerData> {
+    Ok(ServerData {
+        host: buffer.read_string::<D>(None)?,
+        map: buffer.read_string::<D>(None)?,
+        players: buffer.read()?,
+        wave: buffer.read()?,
+        version: buffer.read()?,
+        version_type: buffer.read_string::<D>(None)?,
+        gamemode: buffer.read::<u8>()?.try_into()?,
+        player_limit: buffer.read()?,
+        description: buffer.read_string::<D>(None)?,
+        mode_name: buffer.read_string::<D>(None).ok(),
+    })
+}
+
+/// Query a Mindustry server (without retries).
+pub fn query(address: &SocketAddr, timeout_settings: &Option<TimeoutSettings>) -> GDResult<ServerData> {
+    let mut socket = UdpSocket::new(address, timeout_settings)?;
+
+    send_ping(&mut socket)?;
+
+    let socket_data = socket.receive(Some(MAX_BUFFER_SIZE))?;
+    let mut buffer = Buffer::new(&socket_data);
+
+    parse_server_data::<byteorder::BigEndian, buffer::Utf8LengthPrefixedDecoder>(&mut buffer)
+}
+
+/// Query a Mindustry server.
+pub fn query_with_retries(address: &SocketAddr, timeout_settings: &Option<TimeoutSettings>) -> GDResult<ServerData> {
+    let retries = TimeoutSettings::get_retries_or_default(timeout_settings);
+
+    utils::retry_on_timeout(retries, || query(address, timeout_settings))
+}