Introducing MashProxy


Hi, I’m Pete Warden (that’s not me in the photo!), and as a fun project, I decided to create a search mashup that let me search the way I wish I could.

While I was doing that, I discovered that there was a big restriction on using XMLHttpRequest and AJAX. You can only request pages from the same server you’re on, as a security measure. This obviously makes doing a mashup of pages on other servers much more difficult.

The standard ways of working around this involve setting up a way to use your server to fetch external web pages. There were several reasons I wanted to avoid this:

– It doesn’t scale with the number of users, since everything has to go through your server.
– A big goal of the project was to discover if the pages found in the search were accesible to the user. This isn’t possible if it’s a remote server doing the checking.
– Setting up the server to act as a proxy requires at least some knowledge of scripting and Apache

The main reason that client-side proxies haven’t been done before is the potential for security holes that it opens up. Chris Shiflett has a great article that covers the problems if XMLHttpRequest were opened up to allow cross-domain requests, which is equivalent to what MashProxy allows.

Julian Couvreur also has helped my understanding of the issues. He’s written something similar using Flash rather than Java, FlashXMLHttpRequest.

I’ll discuss the security policy I adopted in my next post, including the safeguards against abuse I’ve implemented and possible remaining problems.

In short, MashProxy is a Java applet that lets JavaScript request web pages, just like XMLHttpRequest, but without the same domain restriction. This let me build the SearchMash project, implementing my ideas on a better interface to search results. It’s open source, and up on SourceForge, and my hope is that other developers will use it as an easier way to create mashups. I want to see more mashing, and I think the server proxy requirements have been holding things back.

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