Fix off-by-one error for keepalive timer (#543)

Author: EpicEric

russh/src/client/mod.rs

@@ -1115,13 +1115,13 @@ impl Session {
                     reading.set(start_reading(stream_read, buffer, opening_cipher));
                 }
                 () = &mut keepalive_timer => {
+                    self.common.alive_timeouts = self.common.alive_timeouts.saturating_add(1);
                     if self.common.config.keepalive_max != 0 && self.common.alive_timeouts > self.common.config.keepalive_max {
                         debug!("Timeout, server not responding to keepalives");
                         return Err(crate::Error::KeepaliveTimeout.into());
                     }
-                    self.common.alive_timeouts = self.common.alive_timeouts.saturating_add(1);
-                    self.send_keepalive(true)?;
                     sent_keepalive = true;
+                    self.send_keepalive(true)?;
                 }
                 () = &mut inactivity_timer => {
                     debug!("timeout");

russh/src/server/session.rs

@@ -543,11 +543,11 @@ impl Session {
                     reading.set(start_reading(stream_read, buffer, opening_cipher));
                 }
                 () = &mut keepalive_timer => {
+                    self.common.alive_timeouts = self.common.alive_timeouts.saturating_add(1);
                     if self.common.config.keepalive_max != 0 && self.common.alive_timeouts > self.common.config.keepalive_max {
                         debug!("Timeout, client not responding to keepalives");
                         return Err(crate::Error::KeepaliveTimeout.into());
                     }
-                    self.common.alive_timeouts = self.common.alive_timeouts.saturating_add(1);
                     sent_keepalive = true;
                     self.keepalive_request()?;
                 }