• Description: A Clack middleware to set CORS related HTTP headers.
• Licence: Unlicense
• Author: Alexander Artemenko [email protected]
• Homepage: https://40ants.com/clack-cors/
• Bug tracker: https://github.com/40ants/clack-cors/issues
• Source control: GIT
• Depends on: alexandria, log4cl, serapeum

You can install this library from Quicklisp, but you want to receive updates quickly, then install it from Ultralisp.org:

(ql-dist:install-dist "https://dist.ultralisp.org/"
                      :prompt nil)
(ql:quickload :clack-cors)

Returns a Clack middleware which can be used to override CORS HTTP headers in response.

You can pass arguments ALLOWED-ORIGIN, ALLOWED-HEADERS and ALLOWED-METHODS to override corresponding headers.

If given, these arguments are extend headers, returned by the main application. For example, if main application already returns Access-Control-Allow-Headers with value Content-Type, then it will be overwritten with the value Authorization. To implement a smarter logic, pass as an argument a function of two variables - initial env plist and resulting headers plist. The function should return a string which will be used to replace a header value.

Also, you can provide a ERROR-RESPONSE argument which will be used as response in case if original APP returns response other than a list of three items. This argument should be a list like this:

(list 500
     (list :Content-Type "application/json")
     (list "{\"code\": -1, \"message\": \"Unhandled error.\"}"))

All arguments can be given as a function of two argument, in this case a function will be called with Lack's env plist and a plist of headers returned by the main application. Most useful keys in the env plist are :REQUEST-METHOD and :REQUEST-URI.