Size iFrame height to content height

I'm loading a site cross-domain in an iFrame. I'd like to resize the iFrame to match the height of the site I'm loading. Sniply does exactly this, and I'd like to mimic the functionality. Anyone have any idea what sort of wizardry they're performing here?

http://snip.ly/Z9nv#https://forums.eveonline.com/default.aspx?g=posts&m=5009807

It seems as they aren't only accessing the document from a cross-domain site, but with differing protocols (HTTP/HTTPS). Any insight? It looks like they may be setting the iFrame's height to some impossibly high value and somehow stopping the scroll when it hits the bottom. Help!

EDIT: Some additional details.. I'm using some plugins on the backend to do some analysis on the URL i'm trying to submit: https://github.com/mikeal/request and https://github.com/tmpvar/jsdom. Are there requests I can make using one of these two plugins that would let me get the height of the document?

EDIT2: I don't want to scroll within the iframe - I want it to match the height of the document it contains.

I think you have to set css. You can use a class if there are more iframes.

iframe {
position: absolute;
left: 0;
right: 0;
top: 0;
bottom: 0;
border: 0;
height: 100%;
min-width: 100%;
width: 10px;
-webkit-overflow-scrolling: touch;
overflow: scroll;
}

You have to set your own element as position:fixed.

Setting the CSS to this seems to work

iframe {
  position: absolute;
  left: 0;
  right: 0;
  top: 0;
  bottom: 0;
  border: 0;
  height: 100%;
  min-width: 100%;
  width: 10px;
}

Here's a live sample http://jsfiddle.net/greggman/vso8L8sz/