Make an attempt to parse the response body as XML if the user is expecting XML, even if the Content-Type says otherwise.

Prior to this patch, if an XML document is sent with the wrong Content-Type (e.g. "text/html"), jQuery will return a parsererror, even if the response body is valid XML. This issue was discovered via a Rails bug in which cached content (in our case, an XML document) is returned with a Content-Type of "text/html" rather than the original Content-Type. See https://rails.lighthouseapp.com/projects/8994/tickets/1585-action-caching-sets-wrong-content-type-when-cache_path-is-a-string

Ticket #5764 (http://dev.jquery.com/ticket/5764)

Author: Brad Greenlee

src/ajax.js

@@ -558,6 +558,17 @@ jQuery.extend({
 		var ct = xhr.getResponseHeader("content-type"),
 			xml = type === "xml" || !type && ct && ct.indexOf("xml") >= 0,
 			data = xml ? xhr.responseXML : xhr.responseText;
+			
+		// if we're expecting xml and the content-type is wrong, try to parse the responseText
+		if (xml && !(data && data.documentElement)) {
+			if (window.DOMParser)
+			  data = new DOMParser().parseFromString(xhr.responseText, "text/xml");
+			else { // IE
+				data = new ActiveXObject("Microsoft.XMLDOM");
+				data.async = "false";
+				data.loadXML(xhr.responseText);
+			}
+		}
 
 		if ( xml && data.documentElement.nodeName === "parsererror" ) {
 			throw "parsererror";

test/data/xml_as_html.php

@@ -0,0 +1,10 @@
+<?php 
+  header("Content-Type: text/html"); 
+  echo '<?xml version="1.0" encoding="UTF-8"?>';
+?>	
+<root>
+	<nodes>
+		<node>Peanut Butter</node>
+		<node>Jelly</node>
+	</nodes>
+</root>

test/unit/ajax.js

@@ -1065,6 +1065,22 @@ test("jQuery.ajax - Etag support", function() {
 	});
 });
 
+test("jQuery.ajax - XML with wrong Content-Type", function() {
+	expect(1);
+	stop();
+	jQuery.ajax({
+		url: "data/xml_as_html.php",
+		dataType: "xml",
+		success: function(data) {
+			equals( jQuery("node", data).length, 2, 'nodes in responseXML' );			
+			start();
+		},
+		error: function(data, status) {
+			ok(false, "failed with status: " + status);
+			start();
+		}
+	});
+});
 }
 
 //}