rswiki-book/src/Class-Check.md

Class check

The class check originated with the new Runescape engine update which took place around the 4xx revisions. It gives the Jagex servers the ability to check the modifiers, update, or fetch the value for a field. It also gives functionality to invoke a method with parameters and get it's return value, or check it's modifiers. Each of these functionalities are described with a request type. A class check request is built up with many of these request types. Each request is tagged with an unique id.

Request format

unsigned byte numberOfRequests;
int uid;
byte[] requests_block;

The requests_block is comprised of multiple requests, each with the following format:

unsigned byte type;
type-dependent data;

Response format

int uid;
byte[] responses_block;
short payloadCrc;

The responses_block is comprised of multiple responses, each with the following format:

byte responseCode;
type-dependent data;

Request Types

For request types 0, 2, 4 there will only be one successful response code and a short value of the value being requested will be sent. For request type 1, only the successful response code will be used but no value will be sent back.

Opcode	Name	Description
0	Fetch fumeric field	Fetches the value of a numeric field.
1	Update numeric field	Updates the value of a numeric field.
2	Get field modifiers	Gets the modifiers of a field.
3	Invoke method	Invokes a method and sends back its return object.
4	Get method modifiers	Gets the modifiers of a method.

Return Codes

For opcode 0, there are cases where a numeric value is sent to the server on fetch requests. This value is always a short.

For a method invoke request, there isn't a value that is sent to the server. It is just assumed that there wasn't a return object from the invoked method.

Opcode	Name	On Receive/Response	Description
0	Successful	Response	Successfully executed the request.
1	Successful - Returned numeric value	Response	Successfully executed the request, and returned a numeric value.
2	Successful - Returned string value	Response	Successfully executed the request, and returned a string value.
4	Successful - Returned object value	Response	Successfully executed the request, and returned an object value.
-1	ClassNotFoundException	Receive	A ClassNotFoundException was thrown while receiving a request from the server.
-2	SecurityException	Receive	A SecurityException was thrown while receiving a request from the server.
-3	NullPointerException	Receive	A NullPointerException was thrown while receiving a request from the server.
-4	Exception	Receive	An Exception was thrown while receiving a request from the server.
-5	Throwable	Receive	An error or exception was thrown while receiving a request from the server.
-10	ClassNotFoundException	Response	A ClassNotFoundException was thrown while responding to a request from the server.
-11	InvalidClassException	Response	An InvalidClassException was thrown while responding to a request from the server.
-12	StreamCorruptedException	Response	A StreamCorruptedException was thrown while responding to a request from the server.
-13	OptionDataException	Response	An OptionDataException was thrown while responding to a request from the server.
-14	IllegalAccessException	Response	An IllegalAccessException was thrown while responding to a request from the server.
-15	IllegalArgumentException	Response	An IllegalArgumentException was thrown while responding to a request from the server.
-16	InvocationTargetException	Response	An InvocationTargetException was thrown while responding to a request from the server.
-17	SecurityException	Response	A SecurityException was thrown while responding to a request from the server.
-18	IOException	Response	An IOException was thrown while responding to a request from the server.
-19	NullPointerException	Response	A NullPointerException was thrown while responding to a request from the server.
-20	Exception	Response	An Exception was thrown while responding to a request from the server.
-21	Throwable	Response	An error or exception was thrown while receiving a request from the server.