Add a timeout to the `PeerServer` event loop.

I think this code could be cleaned up significantly (e.g., removing the
other use of select!) but that's potentially a larger change than this
PR.

zebra-network/src/constants.rs

@@ -5,6 +5,9 @@ use std::time::Duration;
 // XXX should these constants be split into protocol also?
 use crate::protocol::types::*;
 
+/// The timeout for requests made to a remote peer.
+pub const REQUEST_TIMEOUT: Duration = Duration::from_secs(10);
+
 /// We expect to receive a message from a live peer at least once in this time duration.
 /// XXX this needs to be synchronized with the ping transmission times.
 pub const LIVE_PEER_DURATION: Duration = Duration::from_secs(12);

zebra-network/src/peer/connector.rs

@@ -164,6 +164,7 @@ where
                 client_rx: rx,
                 error_slot: slot,
                 peer_tx,
+                request_timer: None,
             };
 
             let hooked_peer_rx = peer_rx

zebra-network/src/peer/server.rs

@@ -3,12 +3,17 @@ use std::sync::{Arc, Mutex};
 use failure::Error;
 use futures::{
     channel::{mpsc, oneshot},
+    future::{self, Either},
     stream::Stream,
 };
-use tokio::prelude::*;
+use tokio::{
+    prelude::*,
+    timer::{delay_for, Delay},
+};
 use tower::Service;
 
 use crate::{
+    constants,
     protocol::{
         internal::{Request, Response},
         message::Message,
@@ -43,6 +48,10 @@ pub(super) enum ServerState {
 /// The "server" duplex half of a peer connection.
 pub struct PeerServer<S, Tx> {
     pub(super) state: ServerState,
+    /// A timeout for a client request. This is stored separately from
+    /// ServerState so that we can move the future out of it independently of
+    /// other state handling.
+    pub(super) request_timer: Option<Delay>,
     pub(super) svc: S,
     pub(super) client_rx: mpsc::Receiver<ClientRequest>,
     /// A slot shared between the PeerServer and PeerClient for storing an error.
@@ -123,25 +132,49 @@ where
                     }
                 },
                 // We're awaiting a response to a client request,
-                // so only listen to peer messages, not further requests.
+                // so wait on either a peer message, or on a request timeout.
                 ServerState::AwaitingResponse { .. } => {
-                    let msg = peer_rx_fut.await;
-                    peer_rx_fut = peer_rx.next().fuse();
-                    match msg {
-                        // The peer channel has closed -- no more messages.
-                        // However, we still need to flush pending client requests.
-                        None => self.fail_with(format_err!("peer closed connection").into()),
-                        // We got a peer message but it was malformed.
-                        //Some(Err(e)) => self.fail_with(e.into()),
-                        // XXX remove this when we parse all message types
-                        Some(Err(e)) => {
-                            error!(%e);
+                    let timer: Delay = self
+                        .request_timer
+                        .take()
+                        .expect("timeout must be set while awaiting response");
+                    match future::select(peer_rx_fut, timer).await {
+                        Either::Left((msg, timer)) => {
+                            // The timer didn't resolve, put it back.
+                            self.request_timer = Some(timer);
+                            // XXX this can maybe be cleaned up.
+                            peer_rx_fut = peer_rx.next().fuse();
+                            match msg {
+                                // The peer channel has closed -- no more messages.
+                                // However, we still need to flush pending client requests.
+                                None => {
+                                    self.fail_with(format_err!("peer closed connection").into())
+                                }
+                                // We got a peer message but it was malformed.
+                                //Some(Err(e)) => self.fail_with(e.into()),
+                                // XXX remove this when we parse all message types
+                                Some(Err(e)) => {
+                                    error!(%e);
+                                }
+                                // We got a peer message and it was well-formed.
+                                Some(Ok(msg)) => match self.handle_message_as_response(msg) {
+                                    None => continue,
+                                    Some(msg) => self.handle_message_as_request(msg).await,
+                                },
+                            }
+                        }
+                        Either::Right(((), prev_peer_rx_fut)) => {
+                            // XXX cleanup
+                            peer_rx_fut = prev_peer_rx_fut;
+                            trace!("client request timed out");
+                            let old_state =
+                                std::mem::replace(&mut self.state, ServerState::AwaitingRequest);
+                            if let ServerState::AwaitingResponse(_, tx) = old_state {
+                                let _ = tx.send(Err(format_err!("request timed out").into()));
+                            } else {
+                                panic!("unreachable");
+                            }
                         }
-                        // We got a peer message and it was well-formed.
-                        Some(Ok(msg)) => match self.handle_message_as_response(msg) {
-                            None => continue,
-                            Some(msg) => self.handle_message_as_request(msg).await,
-                        },
                     }
                 }
                 // We've failed, but we need to flush all pending client
@@ -229,7 +262,10 @@ where
                     AwaitingRequest
                 }),
         } {
-            Ok(new_state) => self.state = new_state,
+            Ok(new_state) => {
+                self.state = new_state;
+                self.request_timer = Some(delay_for(constants::REQUEST_TIMEOUT));
+            }
             Err(e) => self.fail_with(e),
         }
     }