Revert "Clean up ClientPlaySessionHandler#handle(PluginMessage)"

This reverts commit ac4359ad21.

Suspected to be causing problems with Fabric and Forge

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

@@ -170,45 +170,59 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
   public boolean handle(PluginMessage packet) {
     VelocityServerConnection serverConn = player.getConnectedServer();
     MinecraftConnection backendConn = serverConn != null ? serverConn.getConnection() : null;
-    if (serverConn == null || backendConn == null) {
-      return true;
-    }
-
-    if (backendConn.getState() != StateRegistry.PLAY) {
-      logger.warn("A plugin message was received while the backend server was not "
-          + "ready. Channel: {}. Packet discarded.", packet.getChannel());
-      return true;
-    }
-
-    if (this.tryHandleVanillaPluginMessageChannel(packet, backendConn)) {
-      return true;
-    }
-
-    if (serverConn.getPhase() == BackendConnectionPhases.IN_TRANSITION) {
-      // We must bypass the currently-connected server when forwarding Forge packets.
-      VelocityServerConnection inFlight = player.getConnectionInFlight();
-      if (inFlight != null) {
-        if (player.getPhase().handle(player, packet, inFlight)) {
+    if (serverConn != null && backendConn != null) {
+      if (backendConn.getState() != StateRegistry.PLAY) {
+        logger.warn("A plugin message was received while the backend server was not "
+            + "ready. Channel: {}. Packet discarded.", packet.getChannel());
+      } else if (PluginMessageUtil.isRegister(packet)) {
+        player.getKnownChannels().addAll(PluginMessageUtil.getChannels(packet));
+        backendConn.write(packet.retain());
+      } else if (PluginMessageUtil.isUnregister(packet)) {
+        player.getKnownChannels().removeAll(PluginMessageUtil.getChannels(packet));
+        backendConn.write(packet.retain());
+      } else if (PluginMessageUtil.isMcBrand(packet)) {
+        backendConn.write(PluginMessageUtil
+            .rewriteMinecraftBrand(packet, server.getVersion(), player.getProtocolVersion()));
+      } else {
+        if (serverConn.getPhase() == BackendConnectionPhases.IN_TRANSITION) {
+          // We must bypass the currently-connected server when forwarding Forge packets.
+          VelocityServerConnection inFlight = player.getConnectionInFlight();
+          if (inFlight != null) {
+            player.getPhase().handle(player, packet, inFlight);
+          }
           return true;
         }
+
+        if (!player.getPhase().handle(player, packet, serverConn)) {
+          if (!player.getPhase().consideredComplete() || !serverConn.getPhase()
+              .consideredComplete()) {
+            // The client is trying to send messages too early. This is primarily caused by mods,
+            // but further aggravated by Velocity. To work around these issues, we will queue any
+            // non-FML handshake messages to be sent once the FML handshake has completed or the
+            // JoinGame packet has been received by the proxy, whichever comes first.
+            //
+            // We also need to make sure to retain these packets so they can be flushed
+            // appropriately.
+            loginPluginMessages.add(packet.retain());
+          } else {
+            ChannelIdentifier id = server.getChannelRegistrar().getFromId(packet.getChannel());
+            if (id == null) {
+              backendConn.write(packet.retain());
+            } else {
+              byte[] copy = ByteBufUtil.getBytes(packet.content());
+              PluginMessageEvent event = new PluginMessageEvent(player, serverConn, id,
+                  ByteBufUtil.getBytes(packet.content()));
+              server.getEventManager().fire(event).thenAcceptAsync(pme -> {
+                PluginMessage message = new PluginMessage(packet.getChannel(),
+                    Unpooled.wrappedBuffer(copy));
+                backendConn.write(message);
+              }, backendConn.eventLoop());
+            }
+          }
+        }
       }
-    } else if (!this.tryHandleForgeMessage(packet, serverConn)) {
-      return true;
     }
 
-    ChannelIdentifier id = server.getChannelRegistrar().getFromId(packet.getChannel());
-    if (id == null) {
-      backendConn.write(packet.retain());
-    } else {
-      byte[] copy = ByteBufUtil.getBytes(packet.content());
-      PluginMessageEvent event = new PluginMessageEvent(player, serverConn, id,
-          ByteBufUtil.getBytes(packet.content()));
-      server.getEventManager().fire(event).thenAcceptAsync(pme -> {
-        PluginMessage message = new PluginMessage(packet.getChannel(),
-            Unpooled.wrappedBuffer(copy));
-        backendConn.write(message);
-      }, backendConn.eventLoop());
-    }
     return true;
   }
 
@@ -279,44 +293,6 @@ public class ClientPlaySessionHandler implements MinecraftSessionHandler {
     }
   }
 
-  private boolean tryHandleVanillaPluginMessageChannel(PluginMessage packet,
-      MinecraftConnection backendConn) {
-    if (PluginMessageUtil.isRegister(packet)) {
-      player.getKnownChannels().addAll(PluginMessageUtil.getChannels(packet));
-      backendConn.write(packet.retain());
-      return true;
-    } else if (PluginMessageUtil.isUnregister(packet)) {
-      player.getKnownChannels().removeAll(PluginMessageUtil.getChannels(packet));
-      backendConn.write(packet.retain());
-      return true;
-    } else if (PluginMessageUtil.isMcBrand(packet)) {
-      backendConn.write(PluginMessageUtil.rewriteMinecraftBrand(packet, server.getVersion(),
-          player.getProtocolVersion()));
-      return true;
-    }
-    return false;
-  }
-
-  private boolean tryHandleForgeMessage(PluginMessage packet, VelocityServerConnection serverConn) {
-    if (player.getPhase().handle(player, packet, serverConn)) {
-      return true;
-    }
-
-    if (!player.getPhase().consideredComplete() || !serverConn.getPhase().consideredComplete()) {
-      // The client is trying to send messages too early. This is primarily caused by mods,
-      // but further aggravated by Velocity. To work around these issues, we will queue any
-      // non-FML handshake messages to be sent once the FML handshake has completed or the
-      // JoinGame packet has been received by the proxy, whichever comes first.
-      //
-      // We also need to make sure to retain these packets so they can be flushed
-      // appropriately.
-      loginPluginMessages.add(packet.retain());
-      return true;
-    } else {
-      return false;
-    }
-  }
-
   /**
    * Handles the {@code JoinGame} packet. This function is responsible for handling the client-side
    * switching servers in Velocity.