gcache 0.0.1

A cache group to accurate remote data access
Documentation 
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use std::io;
use std::marker::Unpin;

use byteorder::{BigEndian, ByteOrder};
use bytes::Bytes;
use tokio::io::{AsyncRead, AsyncReadExt, AsyncWrite, AsyncWriteExt};
use Operation::*;

#[derive(Debug, PartialEq, Eq)]
pub enum Operation {
    Ping,
    Read { key: Bytes, offset: u64, limit: u64 },
    Evict(Bytes),
}

impl Operation {
    pub async fn decode<R: AsyncRead + Unpin>(reader: &mut R) -> Result<Self, io::Error> {
        let opcode = reader.read_u8().await?;
        match opcode {
            1 => Ok(Ping),
            2 => {
                let key_length = reader.read_u16().await? as usize;
                let mut key = vec![0; key_length + 16];
                reader.read_exact(&mut key).await?;
                let offset = BigEndian::read_u64(&key[key_length..]);
                let limit = BigEndian::read_u64(&key[key_length + 8..]);
                key.truncate(key_length);
                Ok(Read {
                    key: key.into(),
                    offset,
                    limit,
                })
            }
            3 => {
                let key_length = reader.read_u16().await? as usize;
                let mut key = vec![0; key_length];
                reader.read_exact(&mut key).await?;
                Ok(Evict(key.into()))
            }
            _ => Err(io::Error::new(
                io::ErrorKind::Other,
                format!("unknown opcode({})", opcode),
            )),
        }
    }

    pub async fn encode<W: AsyncWrite + Unpin>(&self, writer: &mut W) -> Result<(), io::Error> {
        writer.write_u8(self.opcode()).await?;
        match self {
            Ping => Ok(()),
            Read { key, offset, limit } => {
                writer.write_u16(key.len() as u16).await?;
                writer.write_all(&key).await?;
                writer.write_u64(*offset).await?;
                writer.write_u64(*limit).await
            }
            Evict(key) => {
                writer.write_u16(key.len() as u16).await?;
                writer.write_all(&key).await
            }
        }
    }

    fn size(&self) -> usize {
        match self {
            Ping => 1,
            Read { key, offset, limit } => 2 + key.len() + 16,
            Evict(key) => 2 + key.len(),
        }
    }

    fn opcode(&self) -> u8 {
        match self {
            Ping => 1,
            Read {
                key: _,
                offset: _,
                limit: _,
            } => 2,
            Evict(_) => 3,
        }
    }
}

#[cfg(test)]
mod tests {
    use std::io;

    use super::Operation;

    #[tokio::test]
    async fn test_operation() -> Result<(), io::Error> {
        for o in [
            Operation::Ping,
            Operation::Read {
                key: "aaa".into(),
                offset: 0,
                limit: 0,
            },
            Operation::Read {
                key: "bbb".into(),
                offset: 1 << 10,
                limit: 1 << 10,
            },
            Operation::Evict("ccc".into()),
        ] {
            let mut buffer = Vec::new();
            o.encode(&mut buffer).await?;
            let mut s = &buffer[..];
            let op = Operation::decode(&mut s).await?;
            assert_eq!(op, o);
        }
        Ok(())
    }
}