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[1.16.4] SimplImpl sends packet to client instead server


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I implementing screen, where user may select option and server should be notified about it. Simple case. I found tutorial and implemented this feature uses SimpleImp. Maybe I missed something - packet from server sends to client successfully, but when I tries to use sendToServer client get message instead server.


My network class

public class ModNetworking {

    private static final String PROTOCOL_VERSION = "1.0";
    private static SimpleChannel INSTANCE;
    private static int ID = 0;

    public static int nextId () { return ID++; }

    public static void registerMessages() {
        INSTANCE = NetworkRegistry.newSimpleChannel(new ResourceLocation(ArtOfFood.MOD_ID, "mod_channel"),
                () -> PROTOCOL_VERSION,

        INSTANCE.messageBuilder(SSetConceptResultSlotPacket.class, nextId())

        INSTANCE.messageBuilder(CUpdateConceptPacket.class, nextId())

    public static void sendToClient(Object packet, ServerPlayerEntity player) {
        INSTANCE.sendTo(packet, player.connection.netManager, NetworkDirection.PLAY_TO_CLIENT);

    public static void sendToServer(Object packet) {


Problem packet is CUpdateConceptPacket:

public class CUpdateConceptPacket {

    private String conceptId;

    public CUpdateConceptPacket(String conceptId) {
        this.conceptId = conceptId;

    public void processPacket(Supplier<NetworkEvent.Context> ctx) {
        PlayerEntity playerEntity = Minecraft.getInstance().player;
        if (playerEntity.openContainer instanceof IUpdateConceptPacketHandler) {
            IUpdateConceptPacketHandler handler = (IUpdateConceptPacketHandler) playerEntity.openContainer;

    public CUpdateConceptPacket(PacketBuffer buf) {

    public void readPacketData(PacketBuffer buf) {
        this.conceptId = buf.readString();

    public void writePacketData(PacketBuffer buf) {

    public String getConceptId() {
        return this.conceptId;


Minimalistic handler:

public interface IUpdateConceptPacketHandler {

    void handleConceptUpdate(String conceptId);


This is how I call it:

public void setConcept(MBConcept concept) {
    this.concept = concept;
    CUpdateConceptPacket packet = new CUpdateConceptPacket(concept.conceptId);


And get client call (see screen, at debug value of playerEntity is ClientPlayerEntity)

P.S. Can't find spoiler for hiding code listings. Is it available here? And ofcouse I tried to investigate Vanila examples few times but didn't get results.


Edited by S-Spirit
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7 hours ago, diesieben07 said:
  • Do not use OnlyIn.
  • Minecraft#player is always the client player. By accessing it on a packet thats sent to the server, you are reaching across logical sides, which will just crash on dedicated servers and cause strange behavior in single player.

Thank you very much! You was right - problem was related to code Minecraft.getInstance().player. I Have read page about networking few times and missed this example of common beginners mistakes...

But how I should get opened container at server side? I added list of listeners into ModNetworking 

private static final NonNullList<WeakReference<Object>> serverListeners = NonNullList.create();

public static void addServerListener(Object obj) {
	serverListeners.add(new WeakReference(obj));

public static void removeServerListener(Object obj) {

public static <T> Stream<T> listeners(Class<T> listenerClass) {
    serverListeners.removeIf(r -> r.get() == null);
    return serverListeners.stream()
            .filter(r -> listenerClass.isAssignableFrom(r.get().getClass()))
            .map(r -> ((T) r.get()));


At packet processing ModNetworking provides listeners of necessary type:

public void processPacket(Supplier<NetworkEvent.Context> ctx) {
    Stream<IUpdateConceptPacketHandler> listeners = ModNetworking.listeners(IUpdateConceptPacketHandler.class);
    listeners.forEach( l -> l.handleConceptUpdate(conceptId));


My container add itself like a listener in constructor and remove at the finalize(). This solution works, but is it brilliant idea or ugly implementation of something, which platform already may provide to me?


P.S. Why you notify me to not use @OnlyIn? As I understood, it should be written everywhere, in case when method should be called only from client. Is it wrong vision?

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Who told you to use OnlyIn everywhere?

This is my Forum Signature, I am currently attempting to transform it into a small guide for fixing easier issues using spoiler blocks to keep things tidy.


As the most common issue I feel I should put this outside the main bulk:

The only official source for Forge is https://files.minecraftforge.net, and the only site I trust for getting mods is CurseForge.

If you use any site other than these, please take a look at the StopModReposts project and install their browser extension, I would also advise running a virus scan.


For players asking for assistance with Forge please expand the spoiler below and read the appropriate section(s) in its/their entirety.


Logs (Most issues require logs to diagnose):


Please post logs using one of the following sites (Thank you Lumber Wizard for the list):

https://gist.github.com/100MB Requires member (Free)

https://pastebin.com/: 512KB as guest, 10MB as Pro ($$$)

https://hastebin.com/: 400KB

Do NOT use sites like Mediafire, Dropbox, OneDrive, Google Drive, or a site that has a countdown before offering downloads.


What to provide:

...for Crashes and Runtime issues:

Minecraft 1.14.4 and newer:

Post debug.log

Older versions:

Please update...


...for Installer Issues:

Post your installer log, found in the same place you ran the installer

This log will be called either installer.log or named the same as the installer but with .log on the end

Note for Windows users:

Windows hides file extensions by default so the installer may appear without the .jar extension then when the .log is added the log will appear with the .jar extension


Where to get it:

Mojang Launcher: When using the Mojang launcher debug.log is found in .minecraft\logs.


Curse/Overwolf: If you are using the Curse Launcher, their configurations break Forge's log settings, fortunately there is an easier workaround than I originally thought, this works even with Curse's installation of the Minecraft launcher as long as it is not launched THROUGH Twitch:

  1. Make sure you have the correct version of Forge installed (some packs are heavily dependent on one specific build of Forge)
  2. Make a launcher profile targeting this version of Forge.
  3. Set the launcher profile's GameDir property to the pack's instance folder (not the instances folder, the folder that has the pack's name on it).
  4. Now launch the pack through that profile and follow the "Mojang Launcher" instructions above.






or alternately, 


Fallback ("No logs are generated"):

If you don't see logs generated in the usual place, provide the launcher_log.txt from .minecraft


Server Not Starting:


If your server does not start or a command window appears and immediately goes away, run the jar manually and provide the output.


Reporting Illegal/Inappropriate Adfocus Ads:


Get a screenshot of the URL bar or copy/paste the whole URL into a thread on the General Discussion board with a description of the Ad.

Lex will need the Ad ID contained in that URL to report it to Adfocus' support team.


Posting your mod as a GitHub Repo:


When you have an issue with your mod the most helpful thing you can do when asking for help is to provide your code to those helping you. The most convenient way to do this is via GitHub or another source control hub.

When setting up a GitHub Repo it might seem easy to just upload everything, however this method has the potential for mistakes that could lead to trouble later on, it is recommended to use a Git client or to get comfortable with the Git command line. The following instructions will use the Git Command Line and as such they assume you already have it installed and that you have created a repository.


  1. Open a command prompt (CMD, Powershell, Terminal, etc).
  2. Navigate to the folder you extracted Forge’s MDK to (the one that had all the licenses in).
  3. Run the following commands:
    1. git init
    2. git remote add origin [Your Repository's URL]
      • In the case of GitHub it should look like: https://GitHub.com/[Your Username]/[Repo Name].git
    3. git fetch
    4. git checkout --track origin/master
    5. git stage *
    6. git commit -m "[Your commit message]"
    7. git push
  4. Navigate to GitHub and you should now see most of the files.
    • note that it is intentional that some are not synced with GitHub and this is done with the (hidden) .gitignore file that Forge’s MDK has provided (hence the strictness on which folder git init is run from)
  5. Now you can share your GitHub link with those who you are asking for help.

[Workaround line, please ignore]


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38 minutes ago, diesieben07 said:

On the server NetworkEvent.Context#getSender gives you the player that sent the packet.

Thanks, got it!


8 hours ago, DaemonUmbra said:

Who told you to use OnlyIn everywhere?

No one. It was my own conclusion from documentation and tutorials. When you asked, I read about @OnlyIn one more time, and see - my conclusion was fully wrong. I even thinked @OnlyIn work with logical sides, but specification says - physical. So I should make a refactorng. Thanks for get my attention.

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