path: root/src/recv.rs

use std::collections::HashMap;

use std::sync::Arc;

use log::trace;

use futures::channel::mpsc::{unbounded, UnboundedReceiver, UnboundedSender};
use futures::AsyncReadExt;

use async_trait::async_trait;

use crate::error::*;

use crate::send::*;
use crate::util::Packet;

/// Structure to warn when the sender is dropped before end of stream was reached, like when
/// connection to some remote drops while transmitting data
struct Sender {
	inner: UnboundedSender<Packet>,
	closed: bool,
}

impl Sender {
	fn new(inner: UnboundedSender<Packet>) -> Self {
		Sender {
			inner,
			closed: false,
		}
	}

	fn send(&self, packet: Packet) {
		let _ = self.inner.unbounded_send(packet);
	}

	fn end(&mut self) {
		self.closed = true;
	}
}

impl Drop for Sender {
	fn drop(&mut self) {
		if !self.closed {
			self.send(Err(255));
		}
		self.inner.close_channel();
	}
}

/// The RecvLoop trait, which is implemented both by the client and the server
/// connection objects (ServerConn and ClientConn) adds a method `.recv_loop()`
/// and a prototype of a handler for received messages `.recv_handler()` that
/// must be filled by implementors. `.recv_loop()` receives messages in a loop
/// according to the protocol defined above: chunks of message in progress of being
/// received are stored in a buffer, and when the last chunk of a message is received,
/// the full message is passed to the receive handler.
#[async_trait]
pub(crate) trait RecvLoop: Sync + 'static {
	fn recv_handler(self: &Arc<Self>, id: RequestID, stream: UnboundedReceiver<Packet>);

	async fn recv_loop<R>(self: Arc<Self>, mut read: R) -> Result<(), Error>
	where
		R: AsyncReadExt + Unpin + Send + Sync,
	{
		let mut streams: HashMap<RequestID, Sender> = HashMap::new();
		loop {
			trace!("recv_loop: reading packet");
			let mut header_id = [0u8; RequestID::BITS as usize / 8];
			match read.read_exact(&mut header_id[..]).await {
				Ok(_) => (),
				Err(e) if e.kind() == std::io::ErrorKind::UnexpectedEof => break,
				Err(e) => return Err(e.into()),
			};
			let id = RequestID::from_be_bytes(header_id);
			trace!("recv_loop: got header id: {:04x}", id);

			let mut header_size = [0u8; ChunkLength::BITS as usize / 8];
			read.read_exact(&mut header_size[..]).await?;
			let size = ChunkLength::from_be_bytes(header_size);
			trace!("recv_loop: got header size: {:04x}", size);

			let has_cont = (size & CHUNK_HAS_CONTINUATION) != 0;
			let is_error = (size & ERROR_MARKER) != 0;
			let packet = if is_error {
				Err(size as u8)
			} else {
				let size = size & !CHUNK_HAS_CONTINUATION;
				let mut next_slice = vec![0; size as usize];
				read.read_exact(&mut next_slice[..]).await?;
				trace!("recv_loop: read {} bytes", next_slice.len());
				Ok(next_slice)
			};

			let mut sender = if let Some(send) = streams.remove(&(id)) {
				send
			} else {
				let (send, recv) = unbounded();
				self.recv_handler(id, recv);
				Sender::new(send)
			};

			// if we get an error, the receiving end is disconnected. We still need to
			// reach eos before dropping this sender
			sender.send(packet);

			if has_cont {
				streams.insert(id, sender);
			} else {
				sender.end();
			}
		}
		Ok(())
	}
}