Fixed disconnecting players in the middle of a backend server reconfiguration (#1669)

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

@@ -257,7 +257,13 @@ public class ConfigSessionHandler implements MinecraftSessionHandler {
   @Override
   public boolean handle(DisconnectPacket packet) {
     serverConn.disconnect();
-    resultFuture.complete(ConnectionRequestResults.forDisconnect(packet, serverConn.getServer()));
+    // If the player receives a DisconnectPacket without a connection to a server in progress,
+    // it means that the backend server has kicked the player during reconfiguration
+    if (serverConn.getPlayer().getConnectionInFlight() != null) {
+      resultFuture.complete(ConnectionRequestResults.forDisconnect(packet, serverConn.getServer()));
+    } else {
+      serverConn.getPlayer().handleConnectionException(serverConn.getServer(), packet, true);
+    }
     return true;
   }
 

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

@@ -165,7 +165,7 @@ public class LoginSessionHandler implements MinecraftSessionHandler {
       }
       if (player.getConnection().getActiveSessionHandler() instanceof ClientPlaySessionHandler clientPlaySessionHandler) {
         smc.setAutoReading(false);
-        clientPlaySessionHandler.doSwitch().thenAcceptAsync((unused) -> smc.setAutoReading(true), smc.eventLoop());
+        clientPlaySessionHandler.doSwitch().thenRunAsync(() -> smc.setAutoReading(true), smc.eventLoop());
       } else {
         // Initial login - the player is already in configuration state.
         server.getEventManager().fireAndForget(new PlayerEnteredConfigurationEvent(player, serverConn));

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

@@ -817,9 +817,7 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player,
         createConnectionRequest(res.getServer(), previousConnection).connect()
             .whenCompleteAsync((status, throwable) -> {
               if (throwable != null) {
-                handleConnectionException(
+                handleConnectionException(res.getServer(), throwable, true);
-                    status != null ? status.getAttemptedConnection() : res.getServer(), throwable,
-                    true);
                 return;
               }
 
@@ -1497,7 +1495,16 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player,
           VelocityServerConnection con =
               new VelocityServerConnection(vrs, previousServer, ConnectedPlayer.this, server);
           connectionInFlight = con;
-          return con.connect().whenCompleteAsync((result, exception) -> this.resetIfInFlightIs(con),
+
+          return con.connect().whenCompleteAsync((result, exception) -> {
+            if (result != null && !result.isSuccessful() && !result.isSafe()) {
+              handleConnectionException(result.getAttemptedConnection(),
+                  // The only way for the reason to be null is if the result is safe
+                  DisconnectPacket.create(result.getReasonComponent().orElseThrow(),
+                      getProtocolVersion(), connection.getState()), false);
+            }
+            this.resetIfInFlightIs(con);
+          },
               connection.eventLoop());
         }, connection.eventLoop());
       });
@@ -1511,22 +1518,14 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player,
 
     @Override
     public CompletableFuture<Result> connect() {
-      return this.internalConnect().whenCompleteAsync((status, throwable) -> {
+      return this.internalConnect().thenApply(x -> x);
-        if (status != null && !status.isSuccessful()) {
-          if (!status.isSafe()) {
-            handleConnectionException(status.getAttemptedConnection(), throwable, false);
-          }
-        }
-      }, connection.eventLoop()).thenApply(x -> x);
     }
 
     @Override
     public CompletableFuture<Boolean> connectWithIndication() {
       return internalConnect().whenCompleteAsync((status, throwable) -> {
         if (throwable != null) {
-          // TODO: The exception handling from this is not very good. Find a better way.
+          handleConnectionException(toConnect, throwable, true);
-          handleConnectionException(status != null ? status.getAttemptedConnection() : toConnect,
-              throwable, true);
           return;
         }