Is there a method to prevent a getfeatureinfo event listener to listen on certain conditions?

Question

I am working in OpenLayers 2, setting up a WMSFeatureinfo Object that has both 'beforegetfeatureinfo' and 'getfeatureinfo' event listeners. In the response I want to strip out all the WKT for the geometry and in order to do so I have to include in the "propertyName" vendorParams all the properties I want to filter (all apart from the geometry). This methods sometimes results in very long query strings that the server cannot handle getting a 502 response type.

Considered that I cannot change the server settings, I would like to count the query string length and in case this is longer that a certain number of characters exit the map init function and blocking the code execution, preventing the identify control to send the request.

I tried to put a try catch statement on the 'beforegetfeatureinfo' event listener but the request is sent anyway. Is there a method to exit the code and ignore the event listener before the request is sent?

identifyControl = new OpenLayers.Control.WMSGetFeatureInfo({
        url: dataurl,
        properties: getVisibleAttributes(),
        layers: getIdentifiableLayers(),
        queryVisible: false,
        format: new OpenLayers.Format.JSON,
        infoFormat: 'application/json',
        eventListeners: {
            'beforegetfeatureinfo': function (e) {
                identifyControl.layers = getIdentifiableLayers();
                identifyControl.url = dataurl + data.dataurlExt;
                this.vendorParams = {
                    STYLES: "",
                    PROPERTYNAME: this.formatPropertyNamesParameter()
                }
                try {
                    //here I check for the query string lenght
                    this.filterQueryString(this.vendorParams.PROPERTYNAME)
                }
                catch (err) {
                    // I would like to exit the code here but it does not happen
                    }
                }
            },
            'getfeatureinfo': function (e) {
                featuresCounter = 0;
                identifyLocation = map.getLonLatFromPixel(e.xy);
                //Filter here
                var finalResults = new Array();
                for (var i = 0; i < e.features.features.length; i++) {
                    var id = e.features.features[i].id;
                    var layer = id.substr(0, id.indexOf('.'));
                    //TODO: only request the attributes that are needed with GeoServer vendor parameter propertyName
                    var visibleAttributes = getVisibleLayerAttributes(layer);
                    var results = filterAttributes(visibleAttributes, e.features.features[i]);
                    if (results.length > 0) {
                        finalResults.push(results);
                    }
                }
                createPopupHTML(finalResults);
            },

    filterQueryString: function (queryString) {
        if (queryString.length > 705) {
            throw "The feature info request cannot be handled. Remove one or more layers and try again";
        }
    }
});

Answer 1

The obvious solution to this problem is to remove the geometry element after you get the response back, after all that is why you asked for JSON so you could manipulate it using a JavaScript function. That is why you asked for it right? not just because it's trendy?

The easier way to do this is to use one of the other formats that your server supports, for any recent GeoServer this is:

    <Format>text/plain</Format>
    <Format>application/vnd.ogc.gml</Format>
    <Format>text/xml</Format>
    <Format>application/vnd.ogc.gml/3.1.1</Format>
    <Format>text/xml; subtype=gml/3.1.1</Format>
    <Format>text/html</Format>
    <Format>application/json</Format>

Obviously the GML options are out if you don't want the geometries, which leaves us with text/plain, text/xml and text/html.

Text/plain gives me:

Results for FeatureType 'http://www.openplans.org/topp:states':
--------------------------------------------
the_geom = [GEOMETRY (Polygon) with 56 points]
STATE_NAME = Colorado
STATE_FIPS = 08
SUB_REGION = Mtn
STATE_ABBR = CO
LAND_KM = 268659.501
WATER_KM = 960.364
PERSONS = 3294394.0
FAMILIES = 854214.0
HOUSHOLD = 1282489.0
MALE = 1631295.0
FEMALE = 1663099.0
WORKERS = 1233023.0
DRVALONE = 1216639.0
CARPOOL = 210274.0
PUBTRANS = 46983.0
EMPLOYED = 1633281.0
UNEMPLOY = 99438.0
SERVICE = 421079.0
MANUAL = 181760.0
P_MALE = 0.495
P_FEMALE = 0.505
SAMP_POP = 512677.0
--------------------------------------------

Text/XML gives me GML so we can abandon that, and text/html gives:

<table class="featureInfo">
  <caption class="featureInfo">states</caption>
  <tr>
  <th>fid</th>
    <th >STATE_NAME</th>
    <th >STATE_FIPS</th>
    <th >SUB_REGION</th>
    <th >STATE_ABBR</th>
    <th >LAND_KM</th>
    <th >WATER_KM</th>
    <th >PERSONS</th>
    <th >FAMILIES</th>
    <th >HOUSHOLD</th>
    <th >MALE</th>
    <th >FEMALE</th>
    <th >WORKERS</th>
    <th >DRVALONE</th>
    <th >CARPOOL</th>
    <th >PUBTRANS</th>
    <th >EMPLOYED</th>
    <th >UNEMPLOY</th>
    <th >SERVICE</th>
    <th >MANUAL</th>
    <th >P_MALE</th>
    <th >P_FEMALE</th>
    <th >SAMP_POP</th>
  </tr>

    <tr>

  <td>states.6</td>    
      <td>Colorado</td>
      <td>08</td>
      <td>Mtn</td>
      <td>CO</td>
      <td>268659.501</td>
      <td>960.364</td>
      <td>3294394.0</td>
      <td>854214.0</td>
      <td>1282489.0</td>
      <td>1631295.0</td>
      <td>1663099.0</td>
      <td>1233023.0</td>
      <td>1216639.0</td>
      <td>210274.0</td>
      <td>46983.0</td>
      <td>1633281.0</td>
      <td>99438.0</td>
      <td>421079.0</td>
      <td>181760.0</td>
      <td>0.495</td>
      <td>0.505</td>
      <td>512677.0</td>
  </tr>
</table>

That's quite verbose but if all you plan to do is produce a tabular output then it might work for you.