Create a composer

To create a composer, you must implement the IComposer interface.

We will be using the WallItem model we created from create a model.

Implement the IComposer interface

Add the IComposer interface and its Compose method implementation to your model. In Compose you have access to the PacketWriter that allows you to write primitive types to the packet. This is where you construct the packet by writing each of the values from the object.

public class WallItem : IComposer
{
    // Define properties here...

    public void Compose(in PacketWriter p)
    {
        // Write each property to the packet.
        // We convert the Id to a string here, so it is in the correct type for the packet.
        p.WriteString(Id.ToString());
        p.WriteInt(Kind);
        p.WriteString(Location);
        p.WriteString(Data);
        p.WriteInt(SecondsUntilExpiration);
        p.WriteInt(UsagePolicy);
        p.WriteId(OwnerId);
        p.WriteString(OwnerName);
    }
}

In action

Now that we have created our own composer, we are able to write it to a packet.

Let's send a new wall item to the client when we activate the extension. Add the following event handler to your extension:

ext.Activated += () => {
    // Create a new WallItem.
    var item = new WallItem
    {
        Id = 1,
        Kind = 4001,
        Data = "501",
        Location = ":w=10,10 l=0,0 r",
        OwnerId = 1,
        OwnerName = "xabbo"
    };
    // Send the WallItem to the client.
    ext.Send(In.ItemAdd, item);
};

When you run the extension and activate it, you should see a Jolly Roger appear somewhere in your room:

Caution

You must make sure that the packet structure and its data is correctly formatted. Sending a malformed packet to the client can cause it to crash with a black screen, and you will have to close the game and log back in.

ADDITIONAL INFO

If you removed the IComposer interface from your class and attempted to compile the above example, the xabbo analyzer would emit an error because it cannot be written to a packet:

❯ dotnet build
MSBuild version 17.8.5+b5265ef37 for .NET
  Determining projects to restore...
  All projects are up-to-date for restore.
/tmp/composer/Program.cs(26,26): error XABBO012: 'Examples.Composer.WallItem' is not a packet primitive or IComposer implementation [/tmp/composer/Examples.Composer.csproj]

Build FAILED.

/tmp/composer/Program.cs(26,26): error XABBO012: 'Examples.Composer.WallItem' is not a packet primitive or IComposer implementation [/tmp/composer/Examples.Composer.csproj]
    0 Warning(s)
    1 Error(s)

Time Elapsed 00:00:01.29