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Revision as of 17:25, 20 January 2012
Contents
Introduction
NOTE: All information within this document is subject to change until further notice.
The RAP Protocol is the JSON-based format used within the HTTP-Requests from a RAP-client to a RAP-server. Compared with the previously used JavaScript and HTTP-fields based communication it will provide a number of advantages:
- It allowes to move all client-specific code from the server to the client.
- It produces human readable messages, easing debugging.
- It allowes the client to create more informative error messages.
- It allowes to replace either ends as long as they process and create valid RAP-protocol messages.
- It allowes to add client-independent client-side scripting.
The protocol is currently beeing developed in CVS HEAD. Server-to-Client communication is completed for all RWT-Widgets and will be part of the 1.5 release. Client-to-Server communication will possibly be implemented after 1.5.
Protocol Format
The protocol is based on the JSON fromat as described here: [ http://www.json.org/ ]
Message
There is exactly one message in a response. A message contains of a meta part and a list of operations.
Message ::= { "meta" : Meta, "operations" : [ Operation* ] }
Meta
The meta object contains headers that describe the message.
Meta ::= { "requestCounter" : RequestCounter }
RequestCounter ::= { "requestCounter" : <number> // a positive integer that represents the sequential number of this message }
Operations
The operations are commands that the peer must execute in the order they appear in the message. There are different types of operations: create, set, call, listen, and destroy. Every operation has a target object. In case of a create operation, the target object is to be created, for all other operations, the target object must already exist.
Operation ::= CreateOperation | SetOperation | CallOperation | ListenOperation | DestroyOperation
Operations are processed in the order of their appearance in the message. Unkown operations will be ignored.
Create
A create operation advises the peer to create an object of the given type and attach a given id to it. The CreateProperties contain properties that should be initially set on the created objects.
CreateOperation ::= { "action" : "create", "target" : TargetId, "type" : TypeName, "properties" : { PropertyName : PropertyValue ( , PropertyName : PropertyValue )* } }
TargetId ::= <string> // the id of the object to create TypeName ::= <string> // the fully qualified name of the type PropertyName ::= <string> // the name of a property to set PropertyValue ::= <any JSON value> // the initial value for this property
Set
A set operation advises the peer to set a number of properties of the given target object.
SetOperation ::= { "action" : "set", "target" : TargetId, "properties" : { PropertyName : PropertyValue ( , PropertyName : PropertyValue )* } }
TargetId ::= <string> // the id of the object to set properties to PropertyName ::= <string> // the name of a property to set PropertyValue ::= <any JSON value> // the new value for this property
Call
A call operation advises the peer to call a method on the target object.
CallOperation ::= { "action" : "call", "target" : TargetId, "method" : MethodName, "properties" : { ParameterName : ParameterValue ( , ParameterName : ParameterValue )* } }
TargetId ::= <string> // the id of the object to call a method on MethodName ::= <string> // the name of the method to call ParameterName ::= <string> // the name of a method parameter ParameterValue ::= <any JSON value> // the value for the method parameter
Listen
A listen operation advises the peer to listen on certain types of events.
ListenOperation ::= { "action" : "listen", "target" : TargetId, "properties" : { EventName : ListenToEvent ( , EventName : ListenToEvent )* } }
TargetId ::= <string> // the id of the object to set properties to EventName ::= <string> // the name of an event ListenToEvent ::= <boolean> // whether to listen to the given event or not
Destroy
A destroy operation advises the peer to destroy the target object.
DestroyOperation ::= { "action" : "destroy", "target" : TargetId }
TargetId ::= <string> // the id of the object to destroy
Data Type Reference
In addition to the datatypes recognized by JSON itself, the RAP protocol also uses these composed types:
Bounds
[ int left, int top, int witdh, int height ]
Note that left and top may be negative. No value may be null.
Color
[ int red, int green, int blue, int alpha ]
All values are to be between 0 and 255. The alpha value may be ignored by the client unless its 0.
Image
[ String url, int width, int height ] | null
Gradient
[ Color[] colors, int[] stops, boolean verticalFlag ] | null
The number of colors must match the number of stops. Each stop is a value between 0 and 1, and has to be equal or higher then the previous stop.