flatland-protocol 0.1.0

Flatland3 wire protocol types and codecs
Documentation 
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use serde::{de::DeserializeOwned, Serialize};

use crate::Envelope;

#[derive(Debug, thiserror::Error)]
pub enum CodecError {
    #[error("postcard encode failed: {0}")]
    PostcardEncode(postcard::Error),
    #[error("postcard decode failed: {0}")]
    PostcardDecode(postcard::Error),
    #[error("bincode encode failed: {0}")]
    BincodeEncode(bincode::Error),
    #[error("bincode decode failed: {0}")]
    BincodeDecode(bincode::Error),
}

pub trait Codec {
    fn encode<T: Serialize>(&self, value: &T) -> Result<Vec<u8>, CodecError>;
    fn decode<T: DeserializeOwned>(&self, bytes: &[u8]) -> Result<T, CodecError>;
}

/// Default on-wire codec for game traffic (compact, serde-native).
#[derive(Debug, Clone, Copy, Default)]
pub struct PostcardCodec;

impl Codec for PostcardCodec {
    fn encode<T: Serialize>(&self, value: &T) -> Result<Vec<u8>, CodecError> {
        postcard::to_allocvec(value).map_err(CodecError::PostcardEncode)
    }

    fn decode<T: DeserializeOwned>(&self, bytes: &[u8]) -> Result<T, CodecError> {
        postcard::from_bytes(bytes).map_err(CodecError::PostcardDecode)
    }
}

/// Alternative codec used in benchmarks and for comparison.
#[derive(Debug, Clone, Copy, Default)]
pub struct BincodeCodec;

impl Codec for BincodeCodec {
    fn encode<T: Serialize>(&self, value: &T) -> Result<Vec<u8>, CodecError> {
        bincode::serialize(value).map_err(CodecError::BincodeEncode)
    }

    fn decode<T: DeserializeOwned>(&self, bytes: &[u8]) -> Result<T, CodecError> {
        bincode::deserialize(bytes).map_err(CodecError::BincodeDecode)
    }
}

pub fn encode_envelope<T: Serialize>(codec: &impl Codec, payload: T) -> Result<Vec<u8>, CodecError> {
    codec.encode(&Envelope::new(payload))
}

pub fn decode_envelope<T: DeserializeOwned>(
    codec: &impl Codec,
    bytes: &[u8],
) -> Result<Envelope<T>, CodecError> {
    codec.decode(bytes)
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::types::{EntityState, TickDelta, Transform, WorldCoord};

    fn sample_tick_delta() -> TickDelta {
        TickDelta {
            tick: 42,
            entities: (0..15)
                .map(|i| EntityState {
                    id: i + 1,
                    transform: Transform {
                        position: WorldCoord::surface(i as f32, i as f32 * 0.5),
                        yaw: 1.25,
                        velocity: crate::types::Velocity2D { vx: 0.5, vy: -0.2 },
                    },
                })
                .collect(),
        }
    }

    #[test]
    fn postcard_roundtrip_tick_delta() {
        let codec = PostcardCodec;
        let original = Envelope::new(sample_tick_delta());
        let bytes = codec.encode(&original).expect("encode");
        let decoded: Envelope<TickDelta> = codec.decode(&bytes).expect("decode");
        assert_eq!(original, decoded);
    }

    #[test]
    fn bincode_roundtrip_tick_delta() {
        let codec = BincodeCodec;
        let original = Envelope::new(sample_tick_delta());
        let bytes = codec.encode(&original).expect("encode");
        let decoded: Envelope<TickDelta> = codec.decode(&bytes).expect("decode");
        assert_eq!(original, decoded);
    }
}