Create a model

To create a parser or composer, we must first define a model containing all of the properties of the object we want to create a parser or composer for.

Analyze the packet structure

As an example, let's create a model for a wall item when it is placed in the room. Take a look at the packet in G-Earth's packet logger when you place a wall item:

[ItemAdd]
Incoming[3171] -> [0][0][0]:[12]c[0][10]2147418112[0][0][17]+[0][15]:w=9,1 l=0,50 r[0][0]ÿÿÿÿ[0][0][0][0][2]ø¢[132][0][5]xabbo[10]
{in:ItemAdd}{s:"2147418112"}{i:4395}{s:":w=9,1 l=0,50 r"}{s:""}{i:-1}{i:0}{i:49848964}{s:"xabbo"}

We can see that we have several fields in the packet expression. Here is what they are:

Expression	Type	Description
{s:"2147418112"}	string	Unique ID of the item.
{i:4395}	int	Furni kind (furni type ID). In this case, 4395 is the "Crazed Rorshach Inkblot".
{s:":w=9,1 l=0,50 r"}	string	Wall location.
{s:""}	string	Item data. This could specify a poster variant or other information.
{i:-1}	int	Seconds until expiration.
{i:0}	int	Usage policy. This specifies whether everyone, users with rights, or only the owner can use the furni.
{i:49848964}	int	Owner ID.
{s:"xabbo"}	string	Owner name.

A parser should read each of these fields and store them into the properties of an object.
A composer must write each of these fields in their correct order and format to construct a valid packet.

Define the model

Define a class with the relevant properties and types from the packet structure. For the Id and OwnerId we are using the Id type from Xabbo.Common. It is good practice to use this type for all IDs as it adjusts for different clients.

public class WallItem
{
    public Id Id { get; set; }
    public int Kind { get; set; }
    public string Location { get; set; } = "";
    public string Data { get; set; } = "";
    public int SecondsUntilExpiration { get; set; }
    public int UsagePolicy { get; set; }
    public Id OwnerId { get; set; }
    public string OwnerName { get; set; } = "";
}

Note

Although the the item ID in the packet is a string, we have defined it in our model with the type Id. This makes the model easier to work with as it is a numeric type, and also makes it consistent with OwnerId. We will handle converting the Id to/from a string in our parser/composer implementation.

Using this model as a base, we can continue on to creating a parser or composer.