Minimal embedding of Hunchentoot¶

The following code provides a concise example how to embed Hunchentoot into a running FriCAS instance. The GET and POST method will be demonstrated by using urls in a web-browser and a short Python code respectively.

The code¶

Paste the following code into a file minserver.lisp

(load "~/quicklisp/setup")
(ql:quickload :hunchentoot)


(in-package :boot)

;;; Config
(defparameter +port+ 4242)

;;; SPAD eval

(defun spad_eval (code)
  (let ((*package* (find-package :boot))
        (alg (boot::|parseAndEvalToString| code)))
          (format nil "~{~A~%~}" alg)))

;;; WEB server
(hunchentoot:define-easy-handler (fricas-eval :uri "/eval") (code)
  (setf (hunchentoot:content-type*) "text/plain")
    (format nil "~A~%" (spad_eval code)))

(hunchentoot:start (make-instance 'hunchentoot:easy-acceptor :port +port+))

;;; add :address "localhost"  if you wish local access only!
;;; test example: http://localhost:4242/eval?code=D(x^n,x,6)

Load server¶

We will do all steps manually for the sake of clarity. Start FriCAS and load the file minserver.lisp:

$ fricas

                           FriCAS Computer Algebra System
                         Version: FriCAS 2016-08-28
                  Timestamp: Sam Sep 17 00:34:49 CEST 2016
---------------------------------------------------------------------------
   Issue )copyright to view copyright notices.
   Issue )summary for a summary of useful system commands.
   Issue )quit to leave FriCAS and return to shell.
---------------------------------------------------------------------------

(1) -> )lisp (load "minserver")
To load "hunchentoot":
  Load 1 ASDF system:
    hunchentoot
; Loading "hunchentoot"
............
Value = T
(1) ->

Open a web browser¶

Now open a web browser (some terminal based browsers like w3m, lynx or links, do not accept all urls as e.g. Firefox does, however, when using quotes most urls will work). Enter the following url:

http://localhost:4242/eval?code=D(x^n,x,6)

The result in the browser window should exactly look like as below:

  6      5      4       3       2         n - 6
(n  - 15n  + 85n  - 225n  + 274n  - 120n)x
                                                 Type: Expression(Integer)

Explanation¶

The connection of the url example above with the lisp code is almost obvious:

(fricas-eval :uri "/eval") (code)

The easy handler expects a query ? and one variable code. Then this query will be evaluated and the result formatted and written to the client.

GET and POST¶

Source:	http://www.w3schools.com/TAGS/ref_httpmethods.asp

Two commonly used methods for a request-response between a client and server are:

GET and POST.

GET - Requests data from a specified resource
POST - Submits data to be processed to a specified resource

The GET Method¶

Note that the query string (name/value pairs) is sent in the URL of a GET request:

/test/demo_form.asp?name1=value1&name2=value2

Restrictions:	The GET method adds the data to the URL; and the length of a

URL is limited (maximum URL length is 2048 characters and ASCII characters only are allowed.

Certain character have a special meaning in an URL, so url encoding must follow some rules (HTML URL Encoding Reference).

The POST Method¶

Note that the query string (name/value pairs) is sent in the HTTP message body of a POST request:

POST /test/demo_form.asp HTTP/1.1
Host: w3schools.com
name1=value1&name2=value2

The restrictions of the GET method do not apply here, however, to get a full overview consult the link above. There also are other HTTP request possibilities.

Python example for POST¶

import requests
url = 'http://localhost:4242/eval'
payload = {'code': 'D(x^n,x,8)'}

r = requests.post(url, data=payload)

print(r.text)

Live action:

C:\Users\nilqed>python
Python 2.7.10 (default, May 23 2015, 09:40:32) [MSC v.1500 32 bit (Intel)]
Type "help", "copyright", "credits" or "license" for more information.
>>> import requests
>>> url = 'http://localhost:4242/eval'
>>> payload = {'code': 'D(x^n,x,8)'}
>>> r = requests.post(url, data=payload)
>>> r
<Response [200]>
>>> print(r.text)

     8      7       6        5        4         3         2          n - 8
   (n  - 28n  + 322n  - 1960n  + 6769n  - 13132n  + 13068n  - 5040n)x

                                                  Type: Expression(Integer)


>>>

With the POST method we can use high payloads and there are many languages with HTTP support libraries.

Conclusion¶

This skeleton example shows the general method and of course only uses the most basic features of Hunchentoot. We can define many more easy handlers and other - even more sophisticated - methods to access the internals of FriCAS by HTTP requests. The sky is the limit ;-)