requestURI: failure callback/hook not invoked when used with a proxy

[slorber]

Hi.

When using requestURI, it is not always possible to know that there were a failure.

https://github.com/linkeddata/rdflib.js/blob/master/web.js#L1016

// Setup the request
        if (typeof jQuery !== 'undefined' && jQuery.ajax) {
            var xhr = jQuery.ajax({
                url: uri2,
                accepts: {'*': 'text/turtle,text/n3,application/rdf+xml'},
                processData: false,
                error: function(xhr, s, e) {
                    if (s == 'timeout')
                        sf.failFetch(xhr, "requestTimeout");
                    else
                        onerrorFactory(xhr)(e);
                },
                success: function(d, s, xhr) {
                    onreadystatechangeFactory(xhr)();
                }
            });
        } else {
            var xhr = $rdf.Util.XMLHTTPFactory();
            xhr.onerror = onerrorFactory(xhr);
            xhr.onreadystatechange = onreadystatechangeFactory(xhr);
            try {
                xhr.open('GET', uri2, this.async);
            } catch (er) {
                return this.failFetch(xhr, "XHR open for GET failed for <"+uri2+">:\n\t" + er);
            }
        }

With JQuery + usage of a proxy, the onreadystatechangeFactory will not fire the failFetch method which triggers the fail callback hook.

        var onerrorFactory = function(xhr) { return function(event) {
            if ($rdf.Fetcher.crossSiteProxyTemplate && document && document.location && !xhr.proxyUsed) { // In mashup situation
                 //


                 // NEVER CALLED: sf.failFetch(xhr, "XHR Error: "+event)
                 // But it seems to re-do the request again but 

               //
            } else {
                sf.failFetch(xhr, "XHR Error: "+event)
            }
        }; }

https://github.com/linkeddata/rdflib.js/blob/master/web.js#L693

As expected, the fail hook is correctly triggered when there is a no proxy.

So, when using this method with a proxy, there is no way to know that the request has terminated.

[slorber]

I think the default RDFLib behavior is to try to fetch the resource without the proxy and if there is an error, try too fetch the resource with the proxy.
I see 2 requestURI calls being triggered but no callback is invoked for the later