Accept changes to compression treshold on the fly.

Vanilla allows this for some reason, and there has been one case where Velocity's strict behavior has caused a bug. Fix this.

proxy/src/main/java/com/velocitypowered/proxy/connection/MinecraftConnection.java

@@ -382,17 +382,26 @@ public class MinecraftConnection extends ChannelInboundHandlerAdapter {
     if (threshold == -1) {
       channel.pipeline().remove(COMPRESSION_DECODER);
       channel.pipeline().remove(COMPRESSION_ENCODER);
-      return;
-    }
-
+    } else {
+      MinecraftCompressDecoder decoder = (MinecraftCompressDecoder) channel.pipeline()
+          .get(COMPRESSION_DECODER);
+      MinecraftCompressEncoder encoder = (MinecraftCompressEncoder) channel.pipeline()
+          .get(COMPRESSION_ENCODER);
+      if (decoder != null && encoder != null) {
+        decoder.setThreshold(threshold);
+        encoder.setThreshold(threshold);
+      } else {
         int level = server.getConfiguration().getCompressionLevel();
         VelocityCompressor compressor = Natives.compress.get().create(level);
-    MinecraftCompressEncoder encoder = new MinecraftCompressEncoder(threshold, compressor);
-    MinecraftCompressDecoder decoder = new MinecraftCompressDecoder(threshold, compressor);
+
+        encoder = new MinecraftCompressEncoder(threshold, compressor);
+        decoder = new MinecraftCompressDecoder(threshold, compressor);
 
         channel.pipeline().addBefore(MINECRAFT_DECODER, COMPRESSION_DECODER, decoder);
         channel.pipeline().addBefore(MINECRAFT_ENCODER, COMPRESSION_ENCODER, encoder);
       }
+    }
+  }
 
   /**
    * Enables encryption on the connection.

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

@@ -20,7 +20,7 @@ public class MinecraftCompressDecoder extends MessageToMessageDecoder<ByteBuf> {
       Boolean.getBoolean("velocity.increased-compression-cap")
           ? HARD_MAXIMUM_UNCOMPRESSED_SIZE : VANILLA_MAXIMUM_UNCOMPRESSED_SIZE;
 
-  private final int threshold;
+  private int threshold;
   private final VelocityCompressor compressor;
 
   public MinecraftCompressDecoder(int threshold, VelocityCompressor compressor) {
@@ -60,4 +60,8 @@ public class MinecraftCompressDecoder extends MessageToMessageDecoder<ByteBuf> {
   public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
     compressor.close();
   }
+
+  public void setThreshold(int threshold) {
+    this.threshold = threshold;
+  }
 }

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

@@ -9,7 +9,7 @@ import io.netty.handler.codec.MessageToByteEncoder;
 
 public class MinecraftCompressEncoder extends MessageToByteEncoder<ByteBuf> {
 
-  private final int threshold;
+  private int threshold;
   private final VelocityCompressor compressor;
 
   public MinecraftCompressEncoder(int threshold, VelocityCompressor compressor) {
@@ -54,4 +54,8 @@ public class MinecraftCompressEncoder extends MessageToByteEncoder<ByteBuf> {
   public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
     compressor.close();
   }
+
+  public void setThreshold(int threshold) {
+    this.threshold = threshold;
+  }
 }