clack-cors - A Clack middleware to set CORS related HTTP headers.

CLACK-CORS ASDF System Details

Installation

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

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

Usage

function
clack-cors:make-cors-middleware
app &key (allowed-origin \*default-allowed-origin\*) (allowed-headers \*default-allowed-headers\*) (allowed-methods \*default-allowed-methods\*) (error-response \*default-error-response\*)

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.

variable
clack-cors:*default-allowed-origin*
nil

Default value to return as Access-Control-Allow-Origin HTTP header.

variable
clack-cors:*default-allowed-headers*
nil

Default value to return as Access-Control-Allow-Headers HTTP header.

variable
clack-cors:*default-allowed-methods*
nil

Default value to return as Access-Control-Allow-Methods HTTP header.

variable
clack-cors:*default-error-response*
(500 (:CONTENT-TYPE "application/json") ("{\"code\": -1, \"message\": \"Unhandled error.\"}"))

Default value to return if main app will not return a list of three items.