Apache CORS Headers

It is possible to add multiple domains by using the following:

Header set Access-Control-Allow-Origin "http://domain1.com"
Header add Access-Control-Allow-Origin "http://domain2.net"
Header add Access-Control-Allow-Origin "http://domain3.org"

However, it doesn't work entirely as expected and it also exposes all your API clients to anyone interested. Not a big deal, but why expose more info than necessary?

So, to only have valid requests return one single domain (the accepted Origin) we can configure Apache to dynamically check and return only one permitted domain:

SetEnvIf Origin "(http|https)://(domain1.com|domain2.net|domain3.org)$" RequestOrigin=$0
Header always set Access-Control-Allow-Origin %{RequestOrigin}e env=RequestOrigin

This will return http://domain2.net if the request has an Origin of http://domain2.net. If the request has an origin that isn't matched by the regular expression in the SetEnvIf command, then it will not return any Access-Control-Allow-Origin header at all!

Some other headers I always include:

Header set Access-Control-Allow-Methods 'GET,PUT,POST,DELETE,OPTIONS'
Header set Access-Control-Allow-Credentials true

HTTP PATCH Explained

A very concise article about how the PATCH verb should be used can be found here.

In essence it should be treated as a set of operations to apply a delta to the existing resource. It is NOT the same as a partial PUT.

Going home from work...

Its nice to take a 20 minute boat-trip to get home when the weather is like this:

Regular Expressions

To match a floating point value in a substring I currently use the following regular expression:

(\d+(?:\.\d+)?(?:[eE][-+]?[0-9]+)?)

This matches:

• 123
• 123.4
• 123.4E3
• 123.4e-4
• etc...

Does anyone have a better expression that matches example strings?
Please post in the comments below, thanks.

Installing "Glances" system monitor on ubuntu 12.04

Glances is a curses based tool for monitoring your system - kind of like top on steroids. There is a small issue with using the version in the PPA on Ubuntu 12.04 (specifically the 12.04.2 minimal install); it crashes on startup with the following error:

Traceback (most recent call last):
  File "/usr/bin/glances", line 5, in
    from pkg_resources import load_entry_point
ImportError: No module named pkg_resources

To fix it I manually had to install the package python-pkg-resources.