Tag Archives: ie

WP redirects confuse IE

Some users were having problems on a community site that was implemented using WordPress+BuddyPress. After some testing the issue involved users visiting the site with Internet Explorer (IE). These users were receiving error pages instead of site content. Other web browsers did not have similar issues.

The cause of the problem turns out to be a confluence of issues:

  • The site is hosted on a Windows+IIS server, a rare platform for WordPress (and even more so for BuddyPress) and one that probably doesn’t receive full attention during quality assurance testing.
  • How WordPress performs redirects on IIS is a bit quirky. BuddyPress issues a lot of redirects so this redirect quirk comes into play quite often. The issue is that when WordPress needs to perform a redirect on IIS it returns a “refresh” header pointing to the new page rather than a “location” header.
  • IE’s attempt to make the Internet more friendly; specifically IE’s use of “friendly error pages.” These friendly error pages replace the content delivered by the server (if that content falls below a certain size in KB).

Normally none of these issue are a problem by themselves and a web browser (including IE) will load the page indicated by the redirect. However, all three of the above issues taken together result in a situation where IE never sees the header refresh and so doesn’t redirect the user to the correct location.

The fix is fairly simple: change the headers that WordPress sends to include the standard “location” header. To do this you modify wordpress/wp-includes/pluggable.php@wp_redirect() so that it reads as follows (line 14 is new):

function wp_redirect($location, $status = 302) {
	global $is_IIS;

	$location = apply_filters('wp_redirect', $location, $status);
	$status = apply_filters('wp_redirect_status', $status, $location);

	if ( !$location ) // allows the wp_redirect filter to cancel a redirect
		return false;

	$location = wp_sanitize_redirect($location);

	if ( $is_IIS ) {
		header("Refresh: 0;url=$location");
		header("Location: $location", true, $status);
	} else {
		if ( php_sapi_name() != 'cgi-fcgi' )
			status_header($status); // This causes problems on IIS and some FastCGI setups
		header("Location: $location", true, $status);

Updates for IE8

With the release of IE8 getting closer I took a moment to check out our web site and Benchmarks Online in the new browser. As I suspected, the incompatibilities on our web site were of the same ilk as when IE7 was released and required minor updates. The updates to Benchmarks were also fairly minor, though did require a bit of effort to track down. Luckily IE8 includes developer tools right in the browser, making debugging web content much easier.

While I was at it, I decided to see how the JS+CSS was working in Safari (latest version on Windows and Mac) and Opera (latest versions on Windows). There were some minor issues with these browsers that I fixed as well. Quickly, Safari and Opera both were having trouble displaying the bullets in my ordered list when the pseudo multi-column-styling was applied. The odd thing is that the numbers were there, just not visible until an element was forced on top of them.

Finally, I decided to update the multi-column list code on the web site to that used in Benchmarks (which is more robust). I did run across one problem in the update that I may have to investigate further. Essentially, the script was not correctly positioning the second+ columns if a margin was specified on the container OL/UL.

Internet Explorer blocks Firefox downloads

When designing the school reports I decided to use a GET request on form submission so that it would be easier to bookmark or share a report. I knew at the time that using GET might cause problems down the road, but the utility/programming trade-off seemed worthwhile.

Long URLs

The main problem with GET is that the total size a URL is allowed to be (and thus the amount of data passed) is fairly limited when compared to POST. The exact limit varies by browser and web server, but a practical limit is the lowest limit across platforms. In this case that is 2083 characters in Internet Explorer.

Since each report has to pass the list of included packets and items, the URL could easily surpass this limit. Recently one user generated a report that went over the IE limit. Figuring this out, though, proved to be somewhat difficult.

Held up at security

The user in question was using Firefox to access the utility. The report in question was generating and displaying just fine. However, when the user tried to download the report an error would result. It seemed odd that the browser would display the report on screen without issue then error out when attempting to download the same report.

I tried many options, but no matter what I did I was unable to download the report in Firefox. Next I tried the same report in IE and the situation started to clarify. IE would not even display the report. So now I was beginning to think that maybe the GET request was causing problems. Still it was difficult to fathom Firefox displaying the report on screen but refusing to download it.

A little web research finally clarified everything. Firefox attempts to honor the Windows Internet security zone settings for downloaded files. In order to apply the security zone settings Windows has to pass the URL to the IE engine for analysis. Firefox allows URLs of significantly larger size than IE, so the same URL that displays correctly on Firefox will thus cause IE to error out. Since Firefox attempts to honors the security settings, when IE coughs up a hairball due to the URL length the download is aborted.

Solving the problem

Initially I thought to just shorten the request by modifying the variable names on the form. This worked well enough for the problem at hand, but I could easily see having to address the problem again in the future. In the end I decided to modify the code behind the page so that the report parameters are submitted by POST instead of GET. It required more work up front, but will prevent this problem from cropping up in the future.

Plus, the utility has an option to save reports, so bookmarking/sharing is not as much of an issue.