Difference between revisions of "RAP/Protocol"

Revision as of 16:58, 20 January 2012

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.

{
  "meta" : Meta,
  "operations" : [ Operation* ]
}

Meta

{
  "requestCounter" : <integer number>
}

Operation

There are five different types of operations: create, set, call, listen, and destroy.

  Operation ::= CreateOperation | SetOperation | CallOperation | ListenOperation | DestroyOperation

Operations are processed in the order of their appearance in the message. Unkown operations will be ignored.

CreateOperation

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" : CreateProperties
}

SetOperation

A set operation advises the peer to set a number of properties of the given target object.

SetOperation ::= {
  "action" : "set",
  "target" : TargetId,
  "properties" : SetProperties
}

CallOperation

A call operation advises the peer to call a method on the target object.

CallOperation ::= { 
  "action" : "call",
  "target" : TargetId,
  "method" : MethodName,
  "properties" : CallProperties
}

ListenOperation

A listen operation advises the peer to listen on certain types of events.

ListenOperation ::= { 
  "action" : "listen",
  "target" : TargetId,
  "properties" : ListenProperties
}

DestroyOperation

A destroy operation advises the peer to destroy the target object.

DestroyOperation ::= { 
  "action" : "destroy",
  "target" : TargetId
}

TargetId

The id of the target object as string

TypeName

The name of the type to create

MethodName

The name of the method to call

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.

Object Type Reference

Server and JavaScript-Client API