Awesome

drakma-async

This is a port of the wonderful drakma library to run on top of cl-async.

This library is now API-compatible with drakma 1.3.4.

Documentation

drakma-async:http-request takes the same arguments as drakma:http-request, and does its absolute best to have the exact same behavior, except instead of returning the values of the HTTP request made, it returns a cl-async future that is finished with the values of the HTTP request.

Here's a simple usage example (using the blackbird promise implementation):

(defun my-http-request ()
  (catcher
    (multiple-promise-bind (body status headers)
        (das:http-request "https://www.google.com/")
      (format t "Status: ~a~%" status)
      (format t "Headers: ~s~%" headers)
      (format t "Body: ~a~%" (if (stringp body) body (babel:octets-to-string body))))
    (das:http-eof ()
      (format t "Server hung up unexpectedly =[~%"))
    (error (e)
      (format t "Error: ~a~%" e))))

(as:start-event-loop #'my-http-request)

Tests

drakma-async comes with a test suite:

(ql:quickload :drakma-async-test)

(drakma-async-test:run-tests)

Carrier

drakma-async works well, but for an HTTP client that supports streaming (both upload and download) more natively, check out carrier. Carrier is built specifically to be used in an asynchronous setting, and may eventually deprecate drakma-async.

SSL

This library makes use of the cl-async-ssl package, which is an add-on package for cl-async to provide SSL functionality. drakma-async will use SSL by default, unless :drakma-no-ssl is present in *features* during load/compile time.

Same goes for the test suite: if :drakma-no-ssl is present in *features* when the tests are loaded, no SSL tests are performed.

Notes

drakma-async provides a function in the drakma package called http-request-async which mirrors drakma:http-request, except for that the final value returned is a closure instead of the finished request values. This closure is to be called when all content in the response has been returned. This is handled by the http-stream implementation which is able to tell when a response has been completely downloaded. Once the closure is called, it reads all the data from the http-stream the request was sent on, and parses it via drakma's normal capabilities.

Obviously the downside to this is that the entire response has to be held in memory. For this reason, this library would be best used for smaller requests and sending large amounts of data as opposed to downloading large amounts of data. Note that there is an issue outlining this problem and a potential fix, but it hasn't been worked on YET.

Porting of drakma:http-request to drakma:http-request-async is now completely automated through the use of the rewrite-http-request macro (along with some tree search/replace functions in util.lisp). This makes upgrading drakma-async to use the latest version of drakma as simple as copying the http-request function from drakma's request.lisp and pasting it inside the (rewrite-http-request ...) macro in drakma-aync's hijack.lisp. This saves me a lot of time doing manual porting, and makes it easy to use another version of drakma if that's required.