如何在Common Lisp中读取HTTP cookie？

Question

I would like to make a single CGI program in Common Lisp, that reads a cookie.

It is clear to me that I can send a Cookie by sending HTTP headers. Yet, I would like to know how to read a cookie on a server, through CGI program, from the client who is accessing the program.

Answer 1

Based on Kaz answer, we need to get an environment variable. But I won't refer to the cl-cookbook[1], now we have this solution that comes with asdf:

(uiop:getenv)

Also the Osicat library (os, files and directories) has (environment-variable name) for posix systems, incl. windows.

[1] the cl-cookbook on sourceforge is old and sometimes outdated. There is a copy on github, maintained (well, a bit) and editable: https://lispcookbook.github.io/cl-cookbook/os.html ( https://github.com/LispCookbook/cl-cookbook/ ).

edit : the cookbook on github has been edited accordingly and should be deployed soon on https://lispcookbook.github.io/cl-cookbook/os.html

Answer 2

The CGI mechanism passes the cookie using the HTTP_COOKIE environment variable. ANSI Common Lisp doesn't have any API for accessing POSIX and Windows system environment variables. Implementation-specific functions, or else an implementation's FFI, is used to achieve the equivalent of C's getenv .

The Common Lisp Cookbook suggests this:

* (defun my-getenv (name &optional default)
    #+CMU
    (let ((x (assoc name ext:*environment-list*
                    :test #'string=)))
      (if x (cdr x) default))
    #-CMU
    (or
     #+Allegro (sys:getenv name)
     #+CLISP (ext:getenv name)
     #+ECL (si:getenv name)
     #+SBCL (sb-unix::posix-getenv name)
     #+LISPWORKS (lispworks:environment-variable name)
     default))
MY-GETENV
* (my-getenv "HOME")
"/home/edi"
* (my-getenv "HOM")
NIL
* (my-getenv "HOM" "huh?")
"huh?"

Before using, I'd slightly modify this to:

(or #+CMU (let ((x ...)) (if ...))
    #+Allegro ...
    #+CLISP
    ...
    default)