webSPAD is a project in progress and its goal is to provide web services for FriCAS and friends. Eventually it shall serve to write a new Jupyter kernel for those systems.
The documentation sources are in the folder sphinx
whereas the built
HTML files will go to docs
(GitHub pages:
https://nilqed.github.io/webSPAD).
Below is an excerpt from the appendix in order to demonstrate the idea.
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.
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)
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) ->
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)
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.
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
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 characters have a special meaning in an URL, so url encoding must follow some rules (HTML URL Encoding Reference).
There are some online URL en/decoders which will encode more complex input, for instance:
integrate(1/(1+x^2),x)
reads in encoded form as:
integrate(1%2F(1%2Bx%5E2)%2Cx)
The latter string can be used in a url, whereas the former will not be
accepted (e.g. due to the plus character +
).
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.
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.
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 ;-)