Pumpkin/pumpkin-protocol/src/bedrock/packet_decoder.rs

use std::{
    io::Cursor,
    pin::Pin,
    task::{Context, Poll},
};

use async_compression::tokio::bufread::DeflateDecoder;
use tokio::io::{AsyncRead, BufReader, ReadBuf};

use crate::{
    Aes128Cfb8Dec, CompressionThreshold, PacketDecodeError, RawPacket, StreamDecryptor,
    codec::var_uint::VarUInt,
    ser::{NetworkReadExt, ReadingError},
};

pub enum DecryptionReader<R: AsyncRead + Unpin> {
    Decrypt(Box<StreamDecryptor<R>>),
    None(R),
}

impl<R: AsyncRead + Unpin> DecryptionReader<R> {
    #[must_use]
    pub fn upgrade(self, cipher: Aes128Cfb8Dec) -> Self {
        match self {
            Self::None(stream) => Self::Decrypt(Box::new(StreamDecryptor::new(cipher, stream))),
            Self::Decrypt(_) => self,
        }
    }
}

impl<R: AsyncRead + Unpin> AsyncRead for DecryptionReader<R> {
    #[inline]
    fn poll_read(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &mut ReadBuf<'_>,
    ) -> Poll<std::io::Result<()>> {
        match self.get_mut() {
            Self::Decrypt(reader) => {
                let reader = Pin::new(reader);
                reader.poll_read(cx, buf)
            }
            Self::None(reader) => {
                let reader = Pin::new(reader);
                reader.poll_read(cx, buf)
            }
        }
    }
}

/// Decoder: Client -> Server
/// Supports `ZLib` decoding/decompression
/// Supports Aes128 Encryption
pub struct UDPNetworkDecoder {
    compression: Option<CompressionThreshold>,
}

impl Default for UDPNetworkDecoder {
    fn default() -> Self {
        Self::new()
    }
}

use thiserror::Error;

#[derive(Debug, Error)]
#[error("Encryption already enabled")]
pub struct EncryptionAlreadyEnabledError;

impl UDPNetworkDecoder {
    #[must_use]
    pub const fn new() -> Self {
        Self { compression: None }
    }

    pub const fn set_compression(&mut self, threshold: CompressionThreshold) {
        self.compression = Some(threshold);
    }

    /// NOTE: Encryption can only be set; a minecraft stream cannot go back to being unencrypted
    pub const fn set_encryption(
        &mut self,
        _key: &[u8; 16],
    ) -> Result<(), EncryptionAlreadyEnabledError> {
        Ok(())
    }

    pub async fn get_packet_payload(
        &mut self,
        full_packet: Vec<u8>,
    ) -> Result<Vec<u8>, PacketDecodeError> {
        if full_packet.is_empty() {
            return Err(PacketDecodeError::MalformedLength("Empty packet".into()));
        }

        // If the first byte isn't 0xfe, it's likely a RakNet control packet or encrypted.
        // Ensure your RakNet implementation is providing ONLY the payload here.
        if full_packet[0] != 0xfe {
            return Err(PacketDecodeError::MalformedLength(format!(
                "Missing 0xfe header (found 0x{:02x})",
                full_packet[0]
            )));
        }

        // If compression is NOT enabled yet, the payload starts at index 1.
        if self.compression.is_none() {
            return Ok(full_packet[1..].to_vec());
        }

        // If compression IS enabled, Bedrock expects a compression method byte at index 1.
        let compression_method = full_packet[1];
        let data_start = 2;

        match compression_method {
            0x00 => {
                use tokio::io::AsyncReadExt;
                let compressed_payload = &full_packet[data_start..];
                let mut decoder = DeflateDecoder::new(BufReader::new(compressed_payload));
                let mut decompressed = Vec::new();
                decoder
                    .read_to_end(&mut decompressed)
                    .await
                    .map_err(|e| PacketDecodeError::FailedDecompression(e.to_string()))?;
                Ok(decompressed)
            }
            0xff => {
                // None (Compression enabled but this specific packet is raw)
                Ok(full_packet[data_start..].to_vec())
            }
            _ => Err(PacketDecodeError::FailedDecompression(format!(
                "Unsupported compression method: 0x{compression_method:02x}"
            ))),
        }
    }

    pub fn get_game_packet(
        &mut self,
        decompressed_reader: &mut Cursor<Vec<u8>>,
    ) -> Result<RawPacket, PacketDecodeError> {
        let packet_len = VarUInt::decode(decompressed_reader).map_err(|err| match err {
            ReadingError::CleanEOF(_) => PacketDecodeError::ConnectionClosed,
            err => PacketDecodeError::MalformedLength(err.to_string()),
        })?;

        let var_header = VarUInt::decode(decompressed_reader)?;
        let header = var_header.0 & 0x3FFF;
        let gamepacket_id = (header & 0x3FF) as u16;

        let header_size = var_header.written_size();
        let payload_len = packet_len.0 as usize - header_size;

        let payload = decompressed_reader
            .read_boxed_slice(payload_len)
            .map_err(|err| PacketDecodeError::FailedDecompression(err.to_string()))?;

        Ok(RawPacket {
            id: i32::from(gamepacket_id),
            payload: payload.into(),
        })
    }
}