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[SOLVED][1.12.2] Send custom CPacketChatMessage to server?


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Hello again everyone. Thanks for stopping by!


For reasons which I have explained over in this thread, I am creating a mod which extends the maximum amount of characters a player can type and send in chat for the client side only. That thread got closed for being about Forge for 1.8.9, so I have now ported my code to 1.12.2. Which means yes, this code is completely useless in 1.12, but hopefully the knowledge I gain from it will help me fix my 1.8.9 mod, as the code I am working with has not changed much between the versions.


With that said, here's what I've done with Forge 1.12.2-


1) Created a custom class, LongGuiChat, extending GuiChat, which is displayed to the player whenever I catch (and cancel) a GuiOpenEvent associated with a GuiChat.


2) Overridden LongGuiChat's sendChatMessage(String, boolean) method, as by default it converts the text to a CPacketChatMessage packet and then sends it off to be sent to the server. In CPacketChatMessage's constructor it truncates the String given to it down to 256 characters, and there is no public method to modify the String outside of this, so I had to override sendChatMessage to get around using that class. I would like to note that I could also subscribe to ClientChatEvent for the same effect here.


3) Created another custom class, LongCPacketChatMessage, which extends CPacketChatMessage and changes nothing. No, seriously, I didn't change anything, I just super call the constructor. In the final code this will have the maximum character limit raised, but that is not relevant right now.


So what is the effect of this? Well, in singleplayer, the game works like normal. The game skips over the problematic code and there are no issues. When connected to a multiplayer server, however, things don't go so well.


I can connect to a server, open chat, and type in it just fine. When I press Enter, though, I am kicked from the server, given this error message in-game:

Internal Exception: io.netty.handler.codec.EncoderException: java.lang.RuntimeException: ConnectionProtocol unknown: net.kalman98.longerchat.LongCPacketChatMessage@3bd493fc


...and a stack trace in the logs. The trace leads to net.minecraft.network.NettyPacketEncoder.encode:

protected void encode(ChannelHandlerContext p_encode_1_, Packet<?> p_encode_2_, ByteBuf p_encode_3_) throws IOException, Exception
    EnumConnectionState enumconnectionstate = (EnumConnectionState)p_encode_1_.channel().attr(NetworkManager.PROTOCOL_ATTRIBUTE_KEY).get();

    if (enumconnectionstate == null)
        throw new RuntimeException("ConnectionProtocol unknown: " + p_encode_2_.toString());


...with that if statement resolving to true and the RuntimeException being thrown. The trace up to this point is just several classes passing the packet back and forth over and over again. For reference, the EncoderException is thrown in io.netty.handler.codec.MessageToByteEncoder.write(ChannelHandlerContext, Object, ChannelPromise), which is what calls the encode method shown above.


I get these errors when I send my own LongCPacketChatMessage, which, as I said, extends CPacketChatMessage and has no code changes. The errors do not occur when I'm using my custom code but the original CPacketChatMessage instead of my LongCPacketChatMessage. I'm not sure how to write my own version of NettyPacketEncoder.encode to accomplish my purposes, and really, I don't think that would be a great idea. By the way, the ByteBuf argument comes from io.netty.handler.codec.MessageToByteEncoder.write(ChannelHandlerContext, Object, ChannelPromise), and the ChannelHandlerContext comes from io.netty.channel.DefaultChannelPipeline.writeAndflush(Object).


Any insight, suggestions, opinions, and advice you can give would be appreciated. I'm not even sure what I'm trying to do is actually possible at this point. I make no claims to being incredibly knowledgeable about Java, and I'm sure I've made some mistakes in the process of creating this mod. I would be grateful if you could point out anything I've done incorrectly. And again, sorry about all the text.


Thanks in advance for your time!

Edited by Kalman98
Marking as solved.
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I am marking this thread as solved. A friend of mine saw the thread and told me to use reflection. I have heard of this magical "reflection" in many places on the Internet, and I have always veered away from its mysterious workings. However, he gave me a sample of code, and it works perfectly! I am now researching how reflection works for the future.


Thanks to anyone who took the time to read my silly, uneducated threads! ?


Edit: Oh, fine, I can mention how it was fixed. The solution was to not use my custom packet class, and instead to use the original CPacketChatMessage class. Reflection allowed us to access the private String variable in the class, and from there we were able to set it to any length of String we wanted to! The following is code for the useless 1.12.2 version of the mod. I simply changed the class name to adapt this to 1.8.


// code courtesy of @ParkerMc! Thanks a ton!
try {
    // Needs to only be done once
    Field f = CPacketChatMessage.class.getDeclaredFields()[0]; // Get all the fields of the class including the private one(s). As it is the only field you need index 0
    f.setAccessible(true); // Set the field to accessible so you can change it

    // Create the packet
    CPacketChatMessage packet = new CPacketChatMessage();
    // Set it
    f.set(packet, "some text");
} catch (SecurityException | IllegalArgumentException | IllegalAccessException e) {


Edited by Kalman98
Added solution code.
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Forge has always had inbuilt Reflection util code. Look at ReflectionHelper and ObfuscationReflectionHelper (only in the latest forge version) as you are in 1.8.9. You may have to copy some classes/methods to your own util classes. Just please, change the Reflection code you have right now - it’s unreadable. Also don’t just catch a mod-breaking exception and do nothing with it

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14 minutes ago, Cadiboo said:

Forge has always had inbuilt Reflection util code. Look at ReflectionHelper and ObfuscationReflectionHelper (only in the latest forge version) as you are in 1.8.9. You may have to copy some classes/methods to your own util classes. Just please, change the Reflection code you have right now - it’s unreadable. Also don’t just catch a mod-breaking exception and do nothing with it

Thank you very much! I am a bit busy at the moment, but I will look into the ReflectionHelper as soon as I am able to. Thank you again for pointing out the issue with the exceptions... I've never really heard of those particular exceptions before now and kind of glazed over them. I'll be sure to pay more attention to exception handling in the future. I'll post my updated solution code on this thread once it's finished.


Thanks again, I appreciate the tips!

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The code has now been ported to use ReflectionHelper. Thanks @Cardiboo! Here is the new solution (note that I wrote the code for 1.8.9, I believe it is the same or very similar on current versions):

		Field c01MessageField = ReflectionHelper.findField(C01PacketChatMessage.class, "message", "field_149440_a");
		C01PacketChatMessage packet = new C01PacketChatMessage();
        try {
        	c01MessageField.set(packet, msg);
        } catch (IllegalAccessException e) {
        	MyModClass.logger.error("Error setting message length, sticking with 100.", e);
        	packet = new C01PacketChatMessage(msg);



If more examples are needed for any future help-seekers, my full (1.8.9) source code is here: https://gitlab.com/Kalman98/256chat


I am sorry to have devolved this thread back to 1.8. The code really is very close to the modern stuff, at least. ?

Edited by Kalman98
Removed things I accidentally left in the code sample.
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