Re: Avoid a redirect loop in url-http

[Chong Yidong <cyd@stupidchicken.com>]

Diane Murray <disumu@x3y2z1.net> writes:

> There are sites that for some reason or another keep returning
> redirect responses.  Some redirect to the same host and file path
> but with slightly different query arguments, possibly because the
> page expects a cookie to be set and url-cookie doesn't allow it.
> Other mischievous sites might do something similar just to try and
> cause problems.  Since these are all distinct URLs, they won't be
> equal, which is why I suggested checking how many times the request
> has been redirected.

I see.

How about this patch?

*** emacs/lisp/url/url-vars.el.~1.16.~	2007-01-20 22:24:41.000000000 -0500
--- emacs/lisp/url/url-vars.el	2007-04-12 11:32:34.000000000 -0400
***************
*** 320,325 ****
--- 320,331 ----
    "\\`\\([-a-zA-Z0-9+.]+:\\)"
    "A regular expression that will match an absolute URL.")
  
+ (defcustom url-max-redirections 30
+   "*The maximum number of redirection requests to honor in a HTTP connection.
+ A negative number means to honor an unlimited number of redirection requests."
+   :type 'integer
+   :group 'url)
+ 
  (defcustom url-confirmation-func 'y-or-n-p
    "*What function to use for asking yes or no functions.
  Possible values are `yes-or-no-p' or `y-or-n-p', or any function that
*** emacs/lisp/url/url-http.el.~1.52.~	2007-04-01 11:32:35.000000000 -0400
--- emacs/lisp/url/url-http.el	2007-04-12 11:44:48.000000000 -0400
***************
*** 556,561 ****
--- 556,575 ----
             (let ((url-request-method url-http-method)
  		 (url-request-data url-http-data)
  		 (url-request-extra-headers url-http-extra-headers))
+ 	     ;; Check existing number of redirects
+ 	     (if (or (< url-max-redirections 0)
+ 		     (and (> url-max-redirections 0)
+ 			  (let ((events (car url-callback-arguments))
+ 				(old-redirects 0))
+ 			    (while events
+ 			      (if (eq (car events) :redirect)
+ 				  (setq old-redirects (1+ old-redirects)))
+ 			      (and (setq events (cdr events))
+ 				   (setq events (cdr events))))
+ 			    (< old-redirects url-max-redirections))))
+ 		 ;; url-max-redirections hasn't been reached, so go
+ 		 ;; ahead and redirect.
+ 		 (progn
  	     ;; Remember that the request was redirected.
  	     (setf (car url-callback-arguments)
  		   (nconc (list :redirect redirect-uri)
***************
*** 570,576 ****
  		   (url-retrieve-internal
  		    redirect-uri url-callback-function
  		    url-callback-arguments))
! 	      (url-mark-buffer-as-dead (current-buffer))))))
        (4				; Client error
         ;; 400 Bad Request
         ;; 401 Unauthorized
--- 584,598 ----
  		   (url-retrieve-internal
  		    redirect-uri url-callback-function
  		    url-callback-arguments))
! 	      (url-mark-buffer-as-dead (current-buffer)))
! 	       ;; We hit url-max-redirections, so issue an error and
! 	       ;; stop redirecting.
! 	       (setf (car url-callback-arguments)
! 		     (nconc (list :error (list 'error
! 					       'http
! 					       url-http-response-status))
! 			    (car url-callback-arguments)))
! 	       (setq success t))))))
        (4				; Client error
         ;; 400 Bad Request
         ;; 401 Unauthorized