Question

In the classic "RESTful Web Services" book (O Reilly, ISBN 978-0-596-52926-0) it says on page 251 "Some firewalls block HTTP PUT and DELETE but not POST."

Is this still true?

If it s true I have to allow overloaded POST to substitute for DELETE.

Answer 1

Firewalls blocking HTTP PUT/DELETE are typically blocking incoming connections (to servers behind the firewall). Assuming you have controls over the firewall protecting your application, you shouldn t need to worry about it.

Also, firewalls can only block PUT/DELETE if they are performing deep inspection on the network traffic. Encryption will prevent firewalls from analyzing the URL, so if you re using HTTPS (you are protecting your data with SSL, right?) clients accessing your web service will be able to use any of the standard four HTTP verbs.

Answer 2

Some 7 layer firewalls could analyze traffic to this degree. But I m not sure how many places would configure them as such. You might check on serverfault.com to see how popular such a config might be (you could also always check with your IT staff)

Answer 3

I would not worry about overloading a POST to support a DELETE request.

HTML 4.0 and XHTML 1.0 only support GET and POST requests (via ) so it is commonplace to tunnel a PUT/DELETE via a hidden form field which is read by the server and dispathced appropriately. This technique preserves compatibility across browsers and allows you to ignore any firewall issues.

Ruby On Rails and .NET both handle RESTful requests in this fashion.

As an aside GET, POST, PUT & DELETE requests are fully supported through the XMLHttpRequest request object at present. XHTML 2.0 s officially supports GET, POST, PUT & DELETE as well.

Answer 4

You can configure a firewall to whatever you want ( at least in theory ) so don t be surprised if some sys admins do block HTTP PUT/DELETE.

The danger of HTTP PUT/DELETE is concerning some mis-configured servers: PUT replaces documents (and DELETE deletes them ;-) on the target server. So some sys admins decide up right to block PUT in case a crack is opened somewhere.

Of course we are talking about Firewalls acting at "layer 7" and not just at the IP layer ;-)

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