Relay more exceptions (#446)

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

@@ -86,7 +86,7 @@ public class TransitionSessionHandler implements MinecraftSessionHandler {
     server.getEventManager()
         .fire(new ServerConnectedEvent(player, serverConn.getServer(),
             existingConnection != null ? existingConnection.getServer() : null))
-        .whenCompleteAsync((x, error) -> {
+        .thenRunAsync(() -> {
           // Make sure we can still transition (player might have disconnected here).
           if (!serverConn.isActive()) {
             // Connection is obsolete.

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

@@ -1000,8 +1000,10 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player {
                   VelocityServerConnection con = new VelocityServerConnection(vrs,
                       ConnectedPlayer.this, server);
                   connectionInFlight = con;
-                  return con.connect().whenCompleteAsync((result, throwable) ->
-                      this.resetIfInFlightIs(con), connection.eventLoop());
+                  return con.connect().thenApplyAsync((result) -> {
+                    this.resetIfInFlightIs(con);
+                    return result;
+                  }, connection.eventLoop());
                 }, connection.eventLoop());
           });
     }
@@ -1019,8 +1021,12 @@ public class ConnectedPlayer implements MinecraftConnectionAssociation, Player {
             if (status != null && !status.isSuccessful()) {
               if (!status.isSafe()) {
                 handleConnectionException(status.getAttemptedConnection(), throwable, false);
+                return;
               }
             }
+            if (throwable != null) {
+              logger.error("Exception during connect; status = {}", status, throwable);
+            }
           }, connection.eventLoop())
           .thenApply(x -> x);
     }

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

@@ -134,7 +134,7 @@ public class GS4QueryHandler extends SimpleChannelInboundHandler<DatagramPacket>
         // Call event and write response
         server.getEventManager()
             .fire(new ProxyQueryEvent(isBasic ? BASIC : FULL, senderAddress, response))
-            .whenCompleteAsync((event, exc) -> {
+            .thenAcceptAsync((event) -> {
               // Packet header
               ByteBuf queryResponse = ctx.alloc().buffer();
               queryResponse.writeByte(QUERY_TYPE_STAT);