outbound_session: replace downgrade_host() with `rejected` vector

downgrade_host() is costly (reads through many vectors) and redundant
because it repeats the behavior that should be handled by the greylist
refinery.

what we need is a way to avoid instantly reconnecting to hosts that we
have just failed to connect to.

this commit introduces a simple fix- we write to a vector called
`rejected` and avoid trying to reconnect to its entries once a
connection has failed.

however, this is not ideal as it means we will never connect to that
host- see TODO.

src/net/p2p.rs

@@ -228,9 +228,7 @@ impl P2p {
 
     /// Check whether we're connected to a given address
     pub async fn exists(&self, addr: &Url) -> bool {
-        //self.channels.lock().await.contains_key(addr)
-        //true
-        false
+        self.channels.lock().await.contains_key(addr)
     }
 
     /// Add a channel to the set of connected channels

src/net/session/outbound_session.rs

@@ -229,7 +229,6 @@ impl Slot {
         // * address is already pending a connection
         let addr = hosts.check_address_with_lock(self.p2p(), addrs).await;
         return addr
-        //return None
     }
 
     // We first try to make connections to the addresses on our anchor list. We then find some
@@ -238,6 +237,7 @@ impl Slot {
     async fn run(self: Arc<Self>) {
         let hosts = self.p2p().hosts();
         let slot_count = self.p2p().settings().outbound_connections;
+        let mut rejected = vec![];
 
         loop {
             // Activate the slot
@@ -262,6 +262,7 @@ impl Slot {
                 self.session().wakeup_peer_discovery();
                 // Wait to be woken up by peer discovery
                 self.wakeup_self.wait().await;
+
                 continue
             }
 
@@ -279,11 +280,10 @@ impl Slot {
                 self.session().wakeup_peer_discovery();
                 // Wait to be woken up by peer discovery
                 self.wakeup_self.wait().await;
+
                 continue
             };
 
-            debug!(target: "deadlock", "Got addrs: {}, slot {} node {}", addr.0, self.slot, self.p2p().settings().node_id);
-
             let host = addr.0;
             let slot = self.slot;
 
@@ -298,6 +298,10 @@ impl Slot {
                 addr: host.clone(),
             });
 
+            if rejected.contains(&host) {
+                continue
+            }
+
             let (addr, channel) = match self.try_connect(host.clone()).await {
                 Ok(connect_info) => connect_info,
                 Err(err) => {
@@ -307,20 +311,18 @@ impl Slot {
                         slot, err, self.p2p().settings().node_id
                     );
 
-                    debug!(
-                        target: "deadlock",
-                        "connection failed: {}, slot {} node {}, channel {}",
-                        err, slot, self.p2p().settings().node_id, host.clone()
-                    );
-
                     dnetev!(self, OutboundSlotDisconnected, {
                         slot,
                         err: err.to_string()
                     });
 
-                    self.channel_id.store(0, Ordering::Relaxed);
+                    // Add to the rejected list to avoid immediately reconnecting.
+                    // TODO: Once it's been added to this list it will never be connected to
+                    // in the lifespan of Outbound Session. Refactor this so that it gets put
+                    // in a temporary quarantine and is freed up to try again later.
+                    rejected.push(host.clone());
 
-                    sleep(1).await;
+                    self.channel_id.store(0, Ordering::Relaxed);
                     continue
                 }
             };
@@ -337,6 +339,8 @@ impl Slot {
                 channel_id: channel.info.id
             });
 
+            // At this point we've managed to connect.
+
             let stop_sub = channel.subscribe_stop().await.expect("Channel should not be stopped");
             // Setup new channel
             if let Err(err) = self.setup_channel(host.clone(), channel.clone()).await {
@@ -387,10 +391,6 @@ impl Slot {
                     self.slot, addr, e
                 );
 
-                //// At this point we've failed to connect.
-                //// If the host is in the anchorlist or whitelist, downgrade it to greylist.
-                //self.p2p().hosts().downgrade_host(&addr).await?;
-
                 // Remove connection from pending
                 self.p2p().remove_pending(&addr).await;