chore: integrate multiplayer code (wip)

server/protocol/Cargo.toml

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+[package]
+name = "protocol"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+serde = { version = "1.0.228", features = ["derive"] }

server/protocol/src/lib.rs

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+//! The ids for messages that we use. They will be used consistent across the server and the client.
+//! Also contains the protocol structure for joining a game.
+
+use serde::{Deserialize, Serialize};
+
+/// The buffer sizes for the channels for intra VPS communication.
+pub const CHANNEL_BUFFER_SIZE: usize = 256;
+
+// Client -> Server.
+
+/// The message to announce a new client (Client->Server) followed by u16 client id.
+pub const NEW_CLIENT: u8 = 0;
+/// The message size for a new client (Header + Client Id) (u8 + u16)
+pub const NEW_CLIENT_MSG_SIZE: usize = 3;
+
+/// A client disconnects from the game. (Client->Server) and removes him from the room. followed by u16 client id.
+pub const CLIENT_DISCONNECTS: u8 = 1;
+/// The disconnect client message size (Header + Client Id) (u8 + u16)
+pub const CLIENT_DISCONNECT_MSG_SIZE: usize = 3;
+
+/// Client -> Server RPC followed by u16 Clientid, followed by payload from postcard or other coding.  (Client->Server)
+pub const SERVER_RPC: u8 = 2;
+
+/// The disconnection message that is used for disconnecting without any arguments, that gets passed through the web socket layer.
+pub const CLIENT_DISCONNECTS_SELF: u8 = 3;
+
+// Server -> Client
+
+/// The server disconnects from the game and the room gets closed.
+pub const SERVER_DISCONNECTS: u8 = 0;
+/// The disconnection message is just the byte itself.
+pub const SERVER_DISCONNECT_MSG_SIZE: usize = 1;
+
+/// A client gets kicked, meant for the situation, when no more clients should get accepted. followed by u16 client id. The receiving tokio task has to act on its own. (Server -> Client)
+pub const CLIENT_GETS_KICKED: u8 = 1;
+
+/// Delta update. Followed by payload for every delta update. May carry several delta messages in one pass.
+pub const DELTA_UPDATE: u8 = 2;
+
+/// Flagging a full update. Followed by payload for full update.
+pub const FULL_UPDATE: u8 = 3;
+
+/// The message to reset the game. This is also followed by a full update. Difference is, that every client will get the full update.
+pub const RESET: u8 = 4;
+
+/// The error message we add.
+pub const SERVER_ERROR: u8 = 5;
+
+/// The response message for the handshake.
+pub const HAND_SHAKE_RESPONSE: u8 = 6;
+
+// Sizes of entries.
+/// For the handshake we respond with player id (u16), rule variation (u16), and reconnect token (u64).
+pub const HAND_SHAKE_RESPONSE_SIZE: usize = 13;
+
+/// The size of a new client. (u16)
+pub const CLIENT_ID_SIZE: usize = 2;
+
+/// The join request. This struct is used on the server and on the client.
+#[derive(Deserialize, Serialize)]
+pub struct JoinRequest {
+    /// Which game do we want to join.
+    pub game_id: String,
+    /// Which room do we want to join.
+    pub room_id: String,
+    /// The rule variation that is applied, this gets only interpreted if a room gets constructed.
+    pub rule_variation: u16,
+    /// Do we want to create a room and act as a server?
+    pub create_room: bool,
+    /// Reconnect token from a previous session. `None` = fresh join/create, `Some` = reconnect.
+    pub reconnect_token: Option<u64>,
+}