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mod client;
#[cfg(test)]
mod tests;
use std::io;
use std::marker::PhantomData;
use std::ops::Deref;
use std::sync::atomic::{AtomicU64, Ordering};
use std::sync::Arc;
use tokio::io::{AsyncBufReadExt, AsyncReadExt as _, AsyncWriteExt as _};
use tokio::net;
use tokio::sync::{self, mpsc};
use crate::event::Event;
use crate::protocol::ProtocolMessage;
use crate::request::{Request, ReverseRequest};
use crate::response::Response;
pub use async_trait::async_trait;
pub use client::*;
pub use serde_json::Value;
pub use tokio::sync::mpsc::Sender;
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct ReactorReverseRequest {
/// Id to be received in `response`.
///
/// If `None`, the reactor will pick the next available `seq`.
pub id: Option<u64>,
/// Reverse request to be sent to the client.
pub request: ReverseRequest,
}
impl From<ReverseRequest> for ReactorReverseRequest {
fn from(request: ReverseRequest) -> Self {
Self { id: None, request }
}
}
#[async_trait]
pub trait Backend {
/// Initialize a new instance of a backend.
///
/// The provided mpsc senders will be listened by the reactor and forwarded to the client
///
/// If an id is provided via `Option<u64>`, it will be the id of the response. Otherwise, the
/// reactor will pick the next available id.
async fn init(events: Sender<Event>, requests: Sender<ReactorReverseRequest>) -> Self;
/// A request was sent by the client. It should be replied as response.
///
/// This is infallible because any error that might have happened should be described as a
/// valid response with success set to `false`.
///
/// Ideally, a backend will always produce a response out of a request. However, this is an
/// implementation decision so we require `Option` instead. If `None` is passed, the reactor
/// will not submit a response to the incoming request - this need to be used carefully because
/// the client might end up in a dangling state for the protocol asks to always provide a
/// response.
async fn request(&mut self, request: Request) -> Option<Response>;
/// The client replied to a reverse request
async fn response(&mut self, id: u64, response: Response);
}
pub struct Reactor<B> {
capacity: usize,
provider: PhantomData<B>,
}
impl<B> Reactor<B>
where
B: Backend + Send,
{
pub const fn new() -> Self {
Self {
capacity: 100,
provider: PhantomData,
}
}
pub fn with_capacity(&mut self, capacity: usize) -> &mut Self {
self.capacity = capacity;
self
}
pub async fn bind<S>(&mut self, socket: S) -> io::Result<ReactorListener<B>>
where
S: net::ToSocketAddrs,
{
let listener = net::TcpListener::bind(socket).await?;
Ok(ReactorListener {
capacity: self.capacity,
listener,
provider: PhantomData,
})
}
}
pub struct ReactorListener<B> {
capacity: usize,
listener: net::TcpListener,
provider: PhantomData<B>,
}
impl<B> Deref for ReactorListener<B> {
type Target = net::TcpListener;
fn deref(&self) -> &Self::Target {
&self.listener
}
}
impl<B> ReactorListener<B>
where
B: Backend + Send,
{
pub async fn listen(self) -> io::Result<()> {
let socket = self
.local_addr()
.map_err(|e| io::Error::new(io::ErrorKind::Other, e))?;
tracing::info!("listening on {}", socket);
let Self {
capacity, listener, ..
} = self;
loop {
match listener.accept().await {
Ok((stream, addr)) => {
tracing::trace!("incoming connection from {}", addr);
// this service is not particularly expected to be target of adversarial
// clients. this way, we can simplify the implementation with a naive approach
// to spawn threads for every socket.
//
// this is easily attacked by malicious clients because they can send huge
// amounts of connections and it would quickly exhaust the reactor. if this
// becomes a concern, we can alternatively use some server implementation that
// treats such cases for us - as example, actix-server. it will distribute the
// incoming requests around a given number of workers
let (events_tx, events_rx) = mpsc::channel::<Event>(capacity);
let (requests_tx, requests_rx) =
mpsc::channel::<ReactorReverseRequest>(capacity);
let (mut events, mut requests) = (events_rx, requests_rx);
// overflowing a seq in a DAP usage is not really feasible since the limit of
// u64 is far beyond any normal usage. so we don't really need to put some
// special guard here to check for overflows and we can just benefit from
// atomic performance and security
let seq_event = Arc::new(AtomicU64::new(1));
let seq_request = Arc::clone(&seq_event);
let seq_reverse = Arc::clone(&seq_event);
let (inbound, outbound) = stream.into_split();
let outbound = sync::RwLock::new(outbound);
let outbound_event = Arc::new(outbound);
let outbound_request = Arc::clone(&outbound_event);
let outbound_reverse = Arc::clone(&outbound_event);
// thread to handle outbound events generated by the backend
tokio::spawn(async move {
let outbound = outbound_event;
let seq = seq_event;
while let Some(ev) = events.recv().await {
let seq = seq.fetch_add(1, Ordering::SeqCst);
let ev = ev.into_protocol(seq);
let ev = ProtocolMessage::from(ev);
let ev = ev.into_adapter_message();
tracing::debug!("outbound {:?}", ev);
if let Err(e) = outbound.write().await.write_all(ev.as_bytes()).await {
tracing::error!("error sending event: {}", e);
}
}
});
// thread to handle reverse requests from the backend to the client
tokio::spawn(async move {
let seq = seq_reverse;
let outbound = outbound_reverse;
while let Some(re) = requests.recv().await {
let seq = re.id.unwrap_or_else(|| seq.fetch_add(1, Ordering::SeqCst));
let request = re.request.into_protocol(seq);
let request = ProtocolMessage::from(request);
let request = request.into_adapter_message();
if let Err(e) =
outbound.write().await.write_all(request.as_bytes()).await
{
tracing::error!("error sending reverse request: {}", e);
}
}
});
// thread to handle inbound requests to be processed by the backend
tokio::spawn(async move {
let mut backend = B::init(events_tx, requests_tx).await;
let seq = seq_request;
let mut buffer = tokio::io::BufReader::new(inbound);
let outbound = outbound_request;
loop {
let len;
let mut consumed = 0;
// attempt to fetch content-length
{
let mut lines = (&mut buffer).lines();
loop {
let line = match lines.next_line().await {
Ok(Some(l)) => l.to_ascii_lowercase(),
Ok(None) => return,
Err(_e) => return,
};
consumed += line.len() + 1;
let value = match line.trim_end_matches('\r').split_once(": ") {
Some((key, value)) if key == "content-length" => value,
_ => continue,
};
len = match value.parse::<usize>() {
Ok(n) => n,
Err(e) => {
tracing::warn!("invalid content-lenght: {}", e);
continue;
}
};
break;
}
// skip while line not empty
loop {
let line = match lines.next_line().await {
Ok(Some(l)) => l,
_ => return,
};
consumed += line.len() + 1;
if line.trim_end_matches('\r').is_empty() {
break;
}
}
}
let mut content = vec![0u8; len];
if let Err(e) = buffer.read_exact(&mut content).await {
tracing::warn!("couldn't read message len: {}", e);
continue;
}
buffer.consume(len + consumed);
let message = match ProtocolMessage::try_from_json_bytes(content) {
Ok(m) => m,
Err(e) => {
tracing::warn!("invalid message: {}", e);
continue;
}
};
tracing::debug!("received message {:?}", message);
let request = match message {
ProtocolMessage::Request(re) => re,
ProtocolMessage::Response(re) => {
let id = re.request_seq;
let response = match Response::try_from(&re) {
Ok(re) => re,
Err(e) => {
tracing::debug!(
"error parsing a response from the client: {}",
e
);
continue;
}
};
backend.response(id, response).await;
continue;
}
ProtocolMessage::Event(ev) => {
tracing::debug!(
"received unexpected event from client: {:?}",
ev
);
continue;
}
};
let request_seq = request.seq;
let request = match Request::try_from(&request) {
Ok(re) => re,
Err(e) => {
tracing::warn!("received invalid request from client: {}", e);
continue;
}
};
let response = match backend.request(request).await {
Some(re) => re,
None => {
tracing::debug!("request didn't produce a response");
continue;
}
};
let seq = seq.fetch_add(1, Ordering::SeqCst);
let response = response.into_protocol(seq, request_seq);
let response =
ProtocolMessage::Response(response).into_adapter_message();
tracing::debug!("outbound {:?}", response);
if let Err(e) =
outbound.write().await.write_all(response.as_bytes()).await
{
tracing::error!("error sending response: {}", e);
}
}
});
}
Err(e) => tracing::error!("error accepting socket: {}", e),
}
}
}
}