Inline MHTML+Data URIs

October 3rd, 2010. Tagged: CSS, HTTP, IE, images, performance

MHTML and Data URIs in the same CSS file is totally doable and gives us nice support for IE6+ and all modern browsers. But the question is - what about inline styles. In other words can you have a single-request web application which bundles together markup, inline styles, inline scripts, inline images? With data URIs - yes, clearly. But MHTML?

I remember hacker extraordinaire Hedger Wang coming up with a test page, which proved it's doable. Problems with the test are that a/ I can't find the page anymore, his domain has expired b/ there was some funky IE7/Vista stuff (probably now solvable) in there which even included an undesired redirect c/ was complex - the whole HTML becomes a multipart document, if I remember correctly there was something that required html served as text/plain....

So I tried something simple - shove an MHTML doc inside an inline style comment. It so totally worked! Including IE6 and IE8 in IE7 mode on Windows 7 (which in my experience behaves as badly as IE7 proper on Vista)

Here's the test page. Look ma', no extra HTTP requests :)

So it's a simple HTML doc:

<!doctype html>
    <title>Look Ma' No HTTP requests</title>
    <style type="text/css">
/* magic here */
    <h1>MHTML + Data:URIs inline in a <code>style</code> element</h1>
    <p class="image1">hello<br>hello</p>
    <p class="image2">bonjour<br>bonjour</p>

And the magic is two parts: the MHTML doc inside a CSS comment and the actual CSS which uses data URIs for normal browsers and refers to the MHTML parts in IE6,7.

Content-Type: multipart/related; boundary="_"
iVBORw0KGgoAAAAN ... [more crazyness]... QmCC
iVBORw0KGgoAAAANSUh ... [moarrr] ... ggg==
.image1 {
  background-image: url("data:image/png;base64,iVBORw0KGgoAAAAN ... QmCC"); 
  *background-image: url(mhtml:!locoloco); 
.image2 {
  background-image: url("data:image/png;base64,iVBORw0KGgoAAAANSUh ... ggg=="); 
  *background-image: url(mhtml:!polloloco); 
body {
  font: bold 24px Arial;

How cool is that!

Please report any issues you might find in any browser/os combination

The obvious drawback is repeating the long base64'd image content twice, but it's solvable with either server-side sniffing or... one crazy hack, found on the Russian site I should talk about it separately and help spread the word to the larger English-speaking audience, but for the impatient - click!

So there you go - MHTML inline in CSS inline in HTML or building single-request x-browser web apps :)

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