[emacs-berlin] Code review for a simple HTTP async client

[Diez B. Roggisch]

I haven’t done anything with callbacks so far, but needing global to convey operation reduces utility IMHO. Isn’t there some sort of await or synchronization primitive available? 

Diez 
Mobile Mail. Excuse brevity. 


> Am 22.10.2023 um 22:55 schrieb jman <emacs-berlin at city17.xyz>:
> 
> 
> Hello everyone!
> 
> I have adventured myself into porting into elisp the following simple
> bash script:
> 
> ----------s---------s----------
> # Use cURL to query a remote server using a HTTP HEAD
> # isolate the Location header returned
> function http_head_no_redirect ()
> {
>    URL="${1}"
>    UA="User-Agent: Mozilla/5.0 (compatible; Googlebot/2.1; +google.com/bot.html)"
>    location=`curl -fsS "${URL}" -H "${UA}" -I | grep location | tr -d '\n' | tr -d '\r' | sed "s/location: //"`
>    print "The redirect points to location: %s" $location
> }
> ----------e---------e----------
> 
> The following code is the solution I've found. It works but I'm sure it
> can be improved while preserving readability.
> 
> The main thing I couldn't figure out is that since `url-retrieve` is
> asynchronous the function returns nil because the http call completes
> later, so it will not return the `Location` header. As a workaround I
> set a global variable and set that ^^'
> 
> Any suggestions?
> 
> ----------s---------s----------
> (defvar test-302 "https://httpbin.org/status/302")
> (defvar redirect-url nil)
> (defvar ua-google "User-Agent: Mozilla/5.0 (compatible; Googlebot/2.1; +google.com/bot.html)")
> 
> (defun http-get-no-redirect (url)
>  "Send a HTTP HEAD request to URL. Don't follow redirects.
> Return the URL to which the request would be redirected."
>  (let ((url-user-agent ua-google)(url-request-method "HEAD")(url-max-redirections 0))
>    (url-retrieve
>     url
>     (lambda (status)
>       (when (eq (car status) :redirect)
>         (message "location: %s" (cadr status))
>         (setq redirect-url (cadr status)))))))
> 
> ;; testing
> (http-get-no-redirect test-302)
> (message "Redirect location is: %s" redirect-url)
> ----------e---------e----------
> _______________________________________________
> emacs-berlin mailing list
> emacs-berlin at emacs-berlin.org
> https://mailb.org/mailman/listinfo/emacs-berlin