Thursday, March 01, 2012

Tweak OpenLayers to get parse GetCapabilities working in IE

It happened to me recently that I needed OpenLayers (version 2.11) to parse a GetCapabilities response from Geoserver to present the user a list of layers to pick from.

The capabilites request is made through a Sproutcore request, which is basically a jQuery ajax object in disguise.
This of course works beautifully in every browser with the notable execption of ... IE (IE9 included).

The cause is that IE will helpfully xml-parse a response whose content-type is text/xml, but will refuse to parse a document whose content-type is application/vnd.ogc.request+xml. To add comedy to the drama the responseXML attribute of response is not null, as one would expect, but is instead set to reference an empty dom.

The workaround is to put a giant browser-sniffing if in your javascript to handle IE differently.
The code is like the following and please note that it is Sproutcore code, so browser sniffing and other amenities are peculiar to Sproutcore:

// God mess IE
if(SC.$.browser.msie) {
    content=response.responseText;
    var xmlDoc = new ActiveXObject("Microsoft.XMLDOM");
    // required or IE will attempt to validate against DTD, which could fail
    // because the dtd is not accessibile and we don't really care
    // we will notice later if any layer was loaded from the response anyway
    xmlDoc.async = false;
    xmlDoc.validateOnParse = false;
    xmlDoc.resolveExternals = false;
    var parsed=xmlDoc.loadXML(content);
    if(!parsed) {
        var myErr = xmlDoc.parseError;
        alert(myErr.reason);
    } else {
        content=xmlDoc;
    }
}

var wmsCapabilities = new OpenLayers.Format.WMSCapabilities();
var capabilities = wmsCapabilities.read(content);
// use the capabilities as you wish


IMPORTANT: remember to set the Proxy Base Url in the Geoserver Global configuration page to the correct value if using a reverse proxy.

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