flatland_protocol/
frame.rs

1//! Length-prefixed postcard frames for TCP transport.
2//!
3//! Wire layout: `[magic:4][len:4 LE][postcard envelope]`
4//! Magic prevents interpreting payload bytes as a length after stream slip.
5
6use std::marker::Unpin;
7
8use crate::codec::Codec;
9use crate::{ClientMessage, Envelope, PostcardCodec, ServerMessage, PROTOCOL_VERSION};
10use tokio::io::{AsyncRead, AsyncReadExt, AsyncWrite, AsyncWriteExt};
11
12const MAX_FRAME_BYTES: usize = 1_048_576;
13/// Frame sentinel — must not appear as a misaligned length prefix.
14pub const FRAME_MAGIC: [u8; 4] = *b"FL3\x01";
15
16#[derive(Debug, thiserror::Error)]
17pub enum FrameError {
18    #[error("frame too large: {0} bytes")]
19    TooLarge(usize),
20    #[error("frame magic mismatch: expected FL3\\x01, got {got:?} (TCP frame read was interrupted — file a bug)")]
21    BadMagic { got: [u8; 4] },
22    #[error("io error: {0}")]
23    Io(#[from] std::io::Error),
24    #[error("codec error: {0}")]
25    Codec(#[from] crate::codec::CodecError),
26    #[error("protocol version mismatch: expected {PROTOCOL_VERSION}, got {0}")]
27    VersionMismatch(u16),
28}
29
30pub async fn write_client_message<W>(
31    writer: &mut W,
32    message: &ClientMessage,
33) -> Result<(), FrameError>
34where
35    W: AsyncWrite + Unpin + Send,
36{
37    write_payload(writer, &Envelope::new(message.clone())).await
38}
39
40pub async fn read_client_message<R>(reader: &mut R) -> Result<ClientMessage, FrameError>
41where
42    R: AsyncRead + Unpin + Send,
43{
44    let envelope: Envelope<ClientMessage> = read_payload(reader).await?;
45    Ok(envelope.payload)
46}
47
48pub async fn write_server_message<W>(
49    writer: &mut W,
50    message: &ServerMessage,
51) -> Result<(), FrameError>
52where
53    W: AsyncWrite + Unpin + Send,
54{
55    write_payload(writer, &Envelope::new(message.clone())).await
56}
57
58pub async fn read_server_message<R>(reader: &mut R) -> Result<ServerMessage, FrameError>
59where
60    R: AsyncRead + Unpin + Send,
61{
62    let envelope: Envelope<ServerMessage> = read_payload(reader).await?;
63    Ok(envelope.payload)
64}
65
66async fn write_payload<W, T>(writer: &mut W, envelope: &Envelope<T>) -> Result<(), FrameError>
67where
68    W: AsyncWrite + Unpin + Send,
69    T: serde::Serialize,
70{
71    let codec = PostcardCodec;
72    let bytes = codec.encode(envelope)?;
73    if bytes.len() > MAX_FRAME_BYTES {
74        return Err(FrameError::TooLarge(bytes.len()));
75    }
76    let len = u32::try_from(bytes.len()).map_err(|_| FrameError::TooLarge(bytes.len()))?;
77    writer.write_all(&FRAME_MAGIC).await?;
78    writer.write_u32_le(len).await?;
79    writer.write_all(&bytes).await?;
80    writer.flush().await?;
81    Ok(())
82}
83
84async fn read_payload<R, T>(reader: &mut R) -> Result<Envelope<T>, FrameError>
85where
86    R: AsyncRead + Unpin + Send,
87    T: serde::de::DeserializeOwned,
88{
89    let mut magic = [0_u8; 4];
90    reader.read_exact(&mut magic).await?;
91    if magic != FRAME_MAGIC {
92        return Err(FrameError::BadMagic { got: magic });
93    }
94    let len = reader.read_u32_le().await? as usize;
95    if len > MAX_FRAME_BYTES {
96        return Err(FrameError::TooLarge(len));
97    }
98    let mut buf = vec![0_u8; len];
99    reader.read_exact(&mut buf).await?;
100    let codec = PostcardCodec;
101    let envelope: Envelope<T> = codec.decode(&buf)?;
102    if envelope.protocol_version != PROTOCOL_VERSION {
103        return Err(FrameError::VersionMismatch(envelope.protocol_version));
104    }
105    Ok(envelope)
106}
107
108#[cfg(test)]
109mod tests {
110    use super::*;
111    use crate::types::EntityState;
112    use crate::{AuthCredential, ClientMessage, Hello, PROTOCOL_VERSION};
113    use uuid::Uuid;
114
115    #[tokio::test]
116    async fn roundtrip_client_message() {
117        let msg = ClientMessage::Hello(Hello {
118            client_name: "test".into(),
119            protocol_version: PROTOCOL_VERSION,
120            auth: Default::default(),
121            character_id: None,
122        });
123        let mut buf = Vec::new();
124        write_client_message(&mut buf, &msg).await.unwrap();
125        let parsed = read_client_message(&mut buf.as_slice()).await.unwrap();
126        assert_eq!(msg, parsed);
127    }
128
129    #[tokio::test]
130    async fn roundtrip_full_world_tick() {
131        use crate::types::{
132            PlayerSkills, PlayerVitals, PrimaryAttributes, ResourceNodeState, ResourceNodeView,
133            ServerMessage, TickDelta, Transform, Velocity2D, WorldClock, WorldCoord,
134        };
135
136        let delta = TickDelta {
137            tick: 42,
138            entities: vec![EntityState {
139                id: 1,
140                label: "Traveler".into(),
141                transform: Transform {
142                    position: WorldCoord::surface(128.0, 128.0),
143                    yaw: 0.0,
144                    velocity: Velocity2D { vx: 0.0, vy: 0.0 },
145                },
146                vitals: Some(PlayerVitals::default()),
147                attributes: Some(PrimaryAttributes::default()),
148                skills: Some(PlayerSkills::default()),
149                inside_building: None,
150                tile_id: None,
151                paperdoll_ref: None,
152                presentation_state: None,
153                sprite_mode: None,
154                progression_xp: None,
155            }],
156            resource_nodes: vec![ResourceNodeView {
157                id: "spawn-oak-1".into(),
158                label: "Oak tree".into(),
159                x: 126.0,
160                y: 134.0,
161                z: 0.0,
162                item_template: "oak_log".into(),
163                state: ResourceNodeState::Available,
164                blocking: true,
165                blocking_radius_m: 0.8,
166                tile_id: None,
167                paperdoll_ref: None,
168                yaw: 0.0,
169                pitch: 0.0,
170                roll: 0.0,
171                draw_scale: 1.0,
172                sprite_mode: None,
173                presentation_state: None,
174            }],
175            buildings: Vec::new(),
176            doors: Vec::new(),
177            npcs: Vec::new(),
178            inventory: Vec::new(),
179            blueprints: Vec::new(),
180            world_clock: WorldClock::default(),
181            ground_drops: Vec::new(),
182            placed_containers: Vec::new(),
183            combat: None,
184            interior_map: None,
185            quest_log: Vec::new(),
186            hired_workers: Vec::new(),
187            interactables: Vec::new(),
188            ledger: None,
189            career: None,
190            combat_fx: Vec::new(),
191        };
192        let msg = ServerMessage::Tick(delta);
193        let mut buf = Vec::new();
194        write_server_message(&mut buf, &msg).await.unwrap();
195        let parsed = read_server_message(&mut buf.as_slice()).await.unwrap();
196        assert_eq!(msg, parsed);
197    }
198
199    #[tokio::test]
200    async fn roundtrip_session_auth_hello() {
201        let msg = ClientMessage::Hello(Hello {
202            client_name: "traveler".into(),
203            protocol_version: PROTOCOL_VERSION,
204            auth: AuthCredential::Session {
205                token: "flat_sess_test".into(),
206            },
207            character_id: Some(Uuid::parse_str("019f399e-2b4e-7001-87a2-2e99c005e79d").unwrap()),
208        });
209        let mut buf = Vec::new();
210        write_client_message(&mut buf, &msg).await.unwrap();
211        let parsed = read_client_message(&mut buf.as_slice()).await.unwrap();
212        assert_eq!(msg, parsed);
213    }
214
215    #[tokio::test]
216    async fn rejects_garbage_without_length_desync() {
217        let mut buf = b"GET /health HTTP/1.1\r\n".as_slice();
218        let err = read_client_message(&mut buf).await.unwrap_err();
219        assert!(matches!(err, FrameError::BadMagic { .. }));
220    }
221
222    #[tokio::test]
223    async fn multiplexed_frames_stay_aligned() {
224        use crate::types::{TickDelta, Transform, WorldClock, WorldCoord};
225        use crate::{Intent, ServerMessage};
226
227        let (mut client_io, mut server_io) = tokio::io::duplex(64 * 1024);
228
229        for seq in 1..=200u32 {
230            write_client_message(
231                &mut client_io,
232                &ClientMessage::Intent(Intent::Stop { entity_id: 1, seq }),
233            )
234            .await
235            .unwrap();
236            write_server_message(
237                &mut server_io,
238                &ServerMessage::Tick(TickDelta {
239                    tick: seq as u64,
240                    entities: vec![EntityState {
241                        id: 1,
242                        label: "p".into(),
243                        transform: Transform {
244                            position: WorldCoord::surface(128.0, 128.0),
245                            yaw: 0.0,
246                            velocity: crate::types::Velocity2D { vx: 0.0, vy: 0.0 },
247                        },
248                        vitals: None,
249                        attributes: None,
250                        skills: None,
251                        inside_building: None,
252                        tile_id: None,
253                        paperdoll_ref: None,
254                        presentation_state: None,
255                        sprite_mode: None,
256                        progression_xp: None,
257                    }],
258                    resource_nodes: vec![],
259                    buildings: vec![],
260                    doors: vec![],
261                    npcs: vec![],
262                    inventory: vec![],
263                    blueprints: vec![],
264                    world_clock: WorldClock::default(),
265                    ground_drops: vec![],
266                    placed_containers: vec![],
267                    combat: None,
268                    interior_map: None,
269                    quest_log: vec![],
270                    hired_workers: Vec::new(),
271                    interactables: vec![],
272                    ledger: None,
273                    career: None,
274                    combat_fx: Vec::new(),
275                }),
276            )
277            .await
278            .unwrap();
279        }
280
281        for seq in 1..=200u32 {
282            let intent = read_client_message(&mut server_io).await.unwrap();
283            assert_eq!(
284                intent,
285                ClientMessage::Intent(Intent::Stop { entity_id: 1, seq })
286            );
287            let ServerMessage::Tick(delta) = read_server_message(&mut client_io).await.unwrap()
288            else {
289                panic!("expected tick");
290            };
291            assert_eq!(delta.tick, seq as u64);
292        }
293    }
294}
flatland_protocol/frame.rs

flatland_protocol/
frame.rs
