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use crate::{connect::PacketFlow, mc_buf::Readable, packets::ProtocolPacket};
use async_compression::tokio::bufread::ZlibDecoder;
use tokio::io::{AsyncRead, AsyncReadExt};
async fn frame_splitter<R>(stream: &mut R) -> Result<Vec<u8>, String>
where
R: AsyncRead + std::marker::Unpin + std::marker::Send,
{
// Packet Length
let length_result = stream.read_varint().await;
match length_result {
Ok(length) => {
let mut buf = vec![0; length as usize];
stream
.read_exact(&mut buf)
.await
.map_err(|e| e.to_string())?;
Ok(buf)
}
Err(_) => Err("length wider than 21-bit".to_string()),
}
}
async fn packet_decoder<P: ProtocolPacket, R>(
stream: &mut R,
flow: &PacketFlow,
) -> Result<P, String>
where
R: AsyncRead + std::marker::Unpin + std::marker::Send,
{
// Packet ID
let packet_id = stream.read_varint().await?;
Ok(P::read(packet_id.try_into().unwrap(), flow, stream).await?)
}
// this is always true in multiplayer, false in singleplayer
static VALIDATE_DECOMPRESSED: bool = true;
pub static MAXIMUM_UNCOMPRESSED_LENGTH: u32 = 8388608;
async fn compression_decoder<R>(
stream: &mut R,
compression_threshold: u32,
) -> Result<Vec<u8>, String>
where
R: AsyncRead + std::marker::Unpin + std::marker::Send,
{
// Data Length
let n: u32 = stream.read_varint().await?.try_into().unwrap();
if n == 0 {
// no data size, no compression
let mut buf = vec![];
stream
.read_to_end(&mut buf)
.await
.map_err(|e| e.to_string())?;
return Ok(buf);
}
if VALIDATE_DECOMPRESSED {
if n < compression_threshold {
return Err(format!(
"Badly compressed packet - size of {} is below server threshold of {}",
n, compression_threshold
));
}
if n > MAXIMUM_UNCOMPRESSED_LENGTH {
return Err(format!(
"Badly compressed packet - size of {} is larger than protocol maximum of {}",
n, MAXIMUM_UNCOMPRESSED_LENGTH
));
}
}
let mut buf = vec![];
stream
.read_to_end(&mut buf)
.await
.map_err(|e| e.to_string())?;
let mut decoded_buf = vec![];
let mut decoder = ZlibDecoder::new(buf.as_slice());
decoder
.read_to_end(&mut decoded_buf)
.await
.map_err(|e| e.to_string())?;
Ok(decoded_buf)
}
pub async fn read_packet<P: ProtocolPacket, R>(
flow: &PacketFlow,
stream: &mut R,
compression_threshold: Option<u32>,
) -> Result<P, String>
where
R: AsyncRead + std::marker::Unpin + std::marker::Send,
{
let mut buf = frame_splitter(stream).await?;
if let Some(compression_threshold) = compression_threshold {
buf = compression_decoder(&mut buf.as_slice(), compression_threshold).await?;
}
let packet = packet_decoder(&mut buf.as_slice(), flow).await?;
Ok(packet)
}
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