Using OpenLayers Script protocol callback?

Question

I have a layer with a BBOX strategy with a script protocol to get the data from our server. I'd like make use of the callback function http://dev.openlayers.org/docs/files/OpenLayers/Protocol/Script-js.html#OpenLayers.Protocol.Script.callback to intercept the server response and modify it based on the current state of the map (due to user interactions) If I understand it correctly, that function should get the 'raw' response of the server. But for now it just doesn't do anything:

this.layer = new OpenLayers.Layer.Vector("POI",{
 strategies: [
 new OpenLayers.Strategy.BBOX({
 resFactor: 2,
 active: false,
 autoActivate: false,
 ratio: 1.3,
 noAbort: true
 }), 
 new OpenLayers.Strategy.Cluster({
 distance: this.clusterDistance,
 threshold: this.clusterThreshold
 })
 ],
 protocol: new OpenLayers.Protocol.Script({
 url: 'http://localhost/tests/poi',
 callback: tbPoi.myOwnCallback,
 callbackKey: 'callback',
 format: new OpenLayers.Format.GeoJSON(in_options),
 params: {
 poi: tbPoi.getPoi,
 geozone: tbPoi.getGeozone
 }
 }),
 styleMap: new OpenLayers.StyleMap({
 "default": style,
 "vertex": tbMap.vertexStyle
 }, {extendDefault: false})
 });
myOwnCallback: function(data){
 console.log(data);
},

The myOwnCallback function is completely ignored. I have no idea how to make this work. I searched for examples but couldn't find one.

I want this function to test if individual features returned by the server are also on my drawing layer (if a user is modifying one) So I don't get duplicates on the map.

Answer 1

OK, I've figured this out. You can use the option: parseFeatures in the protocol:

protocol: new OpenLayers.Protocol.Script({
 url: 'http://localhost/tests/poi',
 callback: tbPoi.myOwnCallback,
 callbackKey: 'callback',
 format: new OpenLayers.Format.GeoJSON(in_options),
 parseFeatures: myOwnCallback,
 params: {
 poi: tbPoi.getPoi,
 geozone: tbPoi.getGeozone
 }
}),

The myOwnCallback function should use the formatter to give the correct return.

myOwnCallback: function(data) {
 return this.format.read(data);
},

The data it receives is the GeoJSON object as returned by the server. So in the function you can deconstruct and change it any way you like. I've made a new array with the features that are not on the drawing layer and put that back as the feature part of the data object.

data.features = temp;

works great.