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fix: bounded MPSC channel in relay to prevent unbounded memory growth #27

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Merged
cptrodgers merged 1 commit into from
Mar 30, 2026
Merged

fix: bounded MPSC channel in relay to prevent unbounded memory growth #27

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43 changes: 29 additions & 14 deletions src/relay/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -69,7 +69,7 @@ pub struct SubdomainPick {
// ── Relay server ────────────────────────────────────────────────────────

type PendingRequests = Arc<RwLock<HashMap<String, oneshot::Sender<TunnelResponse>>>>;
type TunnelSender = tokio::sync::mpsc::UnboundedSender<String>;
type TunnelSender = tokio::sync::mpsc::Sender<String>;

struct TunnelConnection {
sender: TunnelSender,
Expand Down Expand Up @@ -327,7 +327,7 @@ async fn handle_tunnel_ws(socket: WebSocket, state: Arc<RelayState>) {
}

// Create channel for sending requests to this tunnel client
let (tx, mut rx) = tokio::sync::mpsc::unbounded_channel::<String>();
let (tx, mut rx) = tokio::sync::mpsc::channel::<String>(64);
let pending: PendingRequests = Arc::new(RwLock::new(HashMap::new()));

let conn = Arc::new(TunnelConnection {
Expand Down Expand Up @@ -483,19 +483,34 @@ async fn handle_tunnel_request(
let (resp_tx, resp_rx) = oneshot::channel();
conn.pending.write().await.insert(req_id.clone(), resp_tx);

// Send request to tunnel client
// Send request to tunnel client (bounded channel — immediate backpressure)
let msg = serde_json::to_string(&tunnel_req).unwrap();
if conn.sender.send(msg).is_err() {
conn.pending.write().await.remove(&req_id);
relay_log(
&subdomain,
method.as_str(),
&path_str,
502,
0,
std::time::Duration::ZERO,
);
return (StatusCode::BAD_GATEWAY, "tunnel disconnected").into_response();
match conn.sender.try_send(msg) {
Ok(()) => {}
Err(tokio::sync::mpsc::error::TrySendError::Full(_)) => {
conn.pending.write().await.remove(&req_id);
relay_log(
&subdomain,
method.as_str(),
&path_str,
503,
0,
std::time::Duration::ZERO,
);
return (StatusCode::SERVICE_UNAVAILABLE, "tunnel overloaded").into_response();
}
Err(tokio::sync::mpsc::error::TrySendError::Closed(_)) => {
conn.pending.write().await.remove(&req_id);
relay_log(
&subdomain,
method.as_str(),
&path_str,
502,
0,
std::time::Duration::ZERO,
);
return (StatusCode::BAD_GATEWAY, "tunnel disconnected").into_response();
}
}

// Wait for response with timeout
Expand Down
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