Handle exceptions relating to CompletableFuture operations

Solves #374

proxy/src/main/java/com/velocitypowered/proxy/VelocityServer.java

@@ -425,8 +425,11 @@ public class VelocityServer implements ProxyServer, ForwardingAudience {
                   .toArray((IntFunction<CompletableFuture<Void>[]>) CompletableFuture[]::new));
 
           playersTeardownFuture.get(10, TimeUnit.SECONDS);
-        } catch (TimeoutException | ExecutionException e) {
+        } catch (TimeoutException e) {
           timedOut = true;
+        } catch (ExecutionException e) {
+          timedOut = true;
+          logger.error("Exception while tearing down player connections", e);
         }
 
         eventManager.fireShutdownEvent();

proxy/src/main/java/com/velocitypowered/proxy/connection/backend/BackendPlaySessionHandler.java

@@ -149,7 +149,11 @@ public class BackendPlaySessionHandler implements MinecraftSessionHandler {
                 Unpooled.wrappedBuffer(copy));
             playerConnection.write(copied);
           }
-        }, playerConnection.eventLoop());
+        }, playerConnection.eventLoop())
+        .exceptionally((ex) -> {
+          logger.error("Exception while handling plugin message {}", packet, ex);
+          return null;
+        });
     return true;
   }
 
@@ -186,7 +190,11 @@ public class BackendPlaySessionHandler implements MinecraftSessionHandler {
 
     server.getEventManager().fire(
         new PlayerAvailableCommandsEvent(serverConn.getPlayer(), rootNode))
-        .thenAcceptAsync(event -> playerConnection.write(commands), playerConnection.eventLoop());
+        .thenAcceptAsync(event -> playerConnection.write(commands), playerConnection.eventLoop())
+        .exceptionally((ex) -> {
+          logger.error("Exception while handling available commands for {}", playerConnection, ex);
+          return null;
+        });
     return true;
   }
 

proxy/src/main/java/com/velocitypowered/proxy/connection/client/ClientPlaySessionHandler.java

@@ -157,7 +157,11 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
                 smc.write(packet);
               }
             }
-          }, smc.eventLoop());
+          }, smc.eventLoop())
+          .exceptionally((ex) -> {
+            logger.error("Exception while handling player chat for {}", player, ex);
+            return null;
+          });
     }
     return true;
   }
@@ -225,7 +229,12 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
                       Unpooled.wrappedBuffer(copy));
                   backendConn.write(message);
                 }
-              }, backendConn.eventLoop());
+              }, backendConn.eventLoop())
+                  .exceptionally((ex) -> {
+                    logger.error("Exception while handling plugin message packet for {}",
+                        player, ex);
+                    return null;
+                  });
             }
           }
         }
@@ -423,7 +432,12 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
             resp.getOffers().addAll(offers);
             player.getConnection().write(resp);
           }
-        }, player.getConnection().eventLoop());
+        }, player.getConnection().eventLoop())
+        .exceptionally((ex) -> {
+          logger.error("Exception while handling command tab completion for player {} executing {}",
+              player, command, ex);
+          return null;
+        });
     return true; // Sorry, handler; we're just gonna have to lie to you here.
   }
 
@@ -475,7 +489,13 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
                 player.getUsername(),
                 command, e);
           }
-        }, player.getConnection().eventLoop());
+        }, player.getConnection().eventLoop())
+        .exceptionally((ex) -> {
+          logger.error(
+              "Exception while finishing command tab completion, with request {} and response {}",
+              request, response, ex);
+          return null;
+        });
   }
 
   private void finishRegularTabComplete(TabCompleteRequest request, TabCompleteResponse response) {
@@ -490,7 +510,13 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
             response.getOffers().add(new Offer(s));
           }
           player.getConnection().write(response);
-        }, player.getConnection().eventLoop());
+        }, player.getConnection().eventLoop())
+        .exceptionally((ex) -> {
+          logger.error(
+              "Exception while finishing regular tab completion, with request {} and response{}",
+              request, response, ex);
+          return null;
+        });
   }
 
   private CompletableFuture<Void> processCommandExecuteResult(String originalCommand,

proxy/src/main/java/com/velocitypowered/proxy/connection/client/ConnectedPlayer.java

@@ -757,7 +757,13 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player {
     }
 
     DisconnectEvent event = new DisconnectEvent(this, status);
-    server.getEventManager().fire(event).thenRun(() -> this.teardownFuture.complete(null));
+    server.getEventManager().fire(event).whenComplete((val, ex) -> {
+      if (ex == null) {
+        this.teardownFuture.complete(null);
+      } else {
+        this.teardownFuture.completeExceptionally(ex);
+      }
+    });
   }
 
   public CompletableFuture<Void> getTeardownFuture() {

proxy/src/main/java/com/velocitypowered/proxy/connection/client/LoginSessionHandler.java

@@ -183,7 +183,11 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
           } else {
             initializePlayer(GameProfile.forOfflinePlayer(login.getUsername()), false);
           }
-        }, mcConnection.eventLoop());
+        }, mcConnection.eventLoop())
+        .exceptionally((ex) -> {
+          logger.error("Exception in pre-login stage", ex);
+          return null;
+        });
   }
 
   private EncryptionRequest generateEncryptionRequest() {
@@ -202,6 +206,7 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
         server.getConfiguration().getPlayerInfoForwardingMode());
     GameProfileRequestEvent profileRequestEvent = new GameProfileRequestEvent(inbound, profile,
         onlineMode);
+    final GameProfile finalProfile = profile;
 
     server.getEventManager().fire(profileRequestEvent).thenCompose(profileEvent -> {
       if (mcConnection.isClosed()) {
@@ -229,6 +234,9 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
               completeLoginProtocolPhaseAndInitialize(player);
             }
           }, mcConnection.eventLoop());
+    }).exceptionally((ex) -> {
+      logger.error("Exception during connection of {}", finalProfile, ex);
+      return null;
     });  
   }
 
@@ -274,7 +282,11 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
             server.getEventManager().fire(new PostLoginEvent(player))
                 .thenRun(() -> connectToInitialServer(player));
           }
-        }, mcConnection.eventLoop());
+        }, mcConnection.eventLoop())
+        .exceptionally((ex) -> {
+          logger.error("Exception while completing login initialisation phase for {}", player, ex);
+          return null;
+        });
   }
 
   private void connectToInitialServer(ConnectedPlayer player) {
@@ -291,7 +303,11 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
             return;
           }
           player.createConnectionRequest(toTry.get()).fireAndForget();
-        }, mcConnection.eventLoop());
+        }, mcConnection.eventLoop())
+        .exceptionally((ex) -> {
+          logger.error("Exception while connecting {} to initial server", player, ex);
+          return null;
+        });
   }
 
   @Override

proxy/src/main/java/com/velocitypowered/proxy/connection/client/StatusSessionHandler.java

@@ -163,7 +163,11 @@ public class StatusSessionHandler implements MinecraftSessionHandler {
         .thenCompose(ping -> server.getEventManager().fire(new ProxyPingEvent(inbound, ping)))
         .thenAcceptAsync(event -> connection.closeWith(
             LegacyDisconnect.fromServerPing(event.getPing(), packet.getVersion())),
-            connection.eventLoop());
+            connection.eventLoop())
+        .exceptionally((ex) -> {
+          logger.error("Exception while handling legacy ping {}", packet, ex);
+          return null;
+        });
     return true;
   }
 
@@ -189,7 +193,11 @@ public class StatusSessionHandler implements MinecraftSessionHandler {
                   .toJson(event.getPing(), json);
               connection.write(new StatusResponse(json));
             },
-            connection.eventLoop());
+            connection.eventLoop())
+        .exceptionally((ex) -> {
+          logger.error("Exception while handling status request {}", packet, ex);
+          return null;
+        });
     return true;
   }
 

proxy/src/main/java/com/velocitypowered/proxy/plugin/VelocityEventManager.java

@@ -115,12 +115,10 @@ public class VelocityEventManager implements EventManager {
       return CompletableFuture.completedFuture(event);
     }
 
-    CompletableFuture<E> eventFuture = new CompletableFuture<>();
+    return CompletableFuture.supplyAsync(() -> {
-    service.execute(() -> {
       fireEvent(event);
-      eventFuture.complete(event);
+      return event;
-    });
+    }, service);
-    return eventFuture;
   }
 
   @Override

proxy/src/main/java/com/velocitypowered/proxy/protocol/netty/GS4QueryHandler.java

@@ -29,6 +29,7 @@ import java.util.Optional;
 import java.util.concurrent.TimeUnit;
 import java.util.stream.Collectors;
 import net.kyori.adventure.text.serializer.plain.PlainComponentSerializer;
+import org.apache.logging.log4j.LogManager;
 
 public class GS4QueryHandler extends SimpleChannelInboundHandler<DatagramPacket> {
 
@@ -162,7 +163,12 @@ public class GS4QueryHandler extends SimpleChannelInboundHandler<DatagramPacket>
               // Send the response
               DatagramPacket responsePacket = new DatagramPacket(queryResponse, msg.sender());
               ctx.writeAndFlush(responsePacket, ctx.voidPromise());
-            }, ctx.channel().eventLoop());
+            }, ctx.channel().eventLoop())
+            .exceptionally((ex) -> {
+              LogManager.getLogger(getClass()).error(
+                  "Exception while writing GS4 response for query from {}", senderAddress, ex);
+              return null;
+            });
         break;
       }
       default: