Expire URL items from the on-disk cache once in a while

* url.el (url-retrieve-number-of-calls): New variable.
(url-retrieve-internal): Use it to expire the cache once in a
while.

* url-cache.el (url-cache-prune-cache): New function.

lisp/url/ChangeLog

@@ -1,5 +1,11 @@
 2012-02-06  Lars Ingebrigtsen  <larsi@gnus.org>
 
+	* url-cache.el (url-cache-prune-cache): New function.
+
+	* url.el (url-retrieve-number-of-calls): New variable.
+	(url-retrieve-internal): Use it to expire the cache once in a
+	while.
+
 	* url-queue.el (url-queue-setup-runners): New function that uses
 	`run-with-idle-timer' for extra asynchronicity.
 	(url-queue-remove-jobs-from-host): New function.

lisp/url/url-cache.el

@@ -209,6 +209,32 @@ If `url-standalone-mode' is non-nil, cached items never expire."
 	    (seconds-to-time (or expire-time url-cache-expire-time)))
 	   (current-time))))))
 
+(defun url-cache-prune-cache (&optional directory)
+  "Remove all expired files from the cache.
+`url-cache-expire-time' says how old a file has to be to be
+considered \"expired\"."
+  (let ((current-time (current-time))
+	(total-files 0)
+	(deleted-files 0))
+    (dolist (file (directory-files (or directory url-cache-directory) t))
+      (unless (member (file-name-nondirectory file) '("." ".."))
+	(setq total-files (1+ total-files))
+	(cond
+	 ((file-directory-p file)
+	  (when (url-cache-prune-cache file)
+	    (setq deleted-files (1+ deleted-files))))
+	 ((time-less-p
+	   (time-add
+	    (nth 5 (file-attributes file))
+	    (seconds-to-time url-cache-expire-time))
+	   current-time)
+	  (delete-file file)
+	  (setq deleted-files (1+ deleted-files))))))
+    (if (< deleted-files total-files)
+	nil
+      (delete-directory directory)
+      t)))
+
 (provide 'url-cache)
 
 ;;; url-cache.el ends here

lisp/url/url.el

@@ -119,6 +119,9 @@ Sometimes while retrieving a URL, the URL library needs to use another buffer
 than the one returned initially by `url-retrieve'.  In this case, it sets this
 variable in the original buffer as a forwarding pointer.")
 
+(defvar url-retrieve-number-of-calls 0)
+(autoload 'url-cache-prune-cache "url-cache")
+
 ;;;###autoload
 (defun url-retrieve (url callback &optional cbargs silent)
   "Retrieve URL asynchronously and call CALLBACK with CBARGS when finished.
@@ -174,6 +177,10 @@ If SILENT, don't message progress reports and the like."
   (unless (url-type url)
     (error "Bad url: %s" (url-recreate-url url)))
   (setf (url-silent url) silent)
+  ;; Once in a while, remove old entries from the URL cache.
+  (when (zerop (% url-retrieve-number-of-calls 1000))
+    (url-cache-prune-cache))
+  (setq url-retrieve-number-of-calls (1+ url-retrieve-number-of-calls))
   (let ((loader (url-scheme-get-property (url-type url) 'loader))
 	(url-using-proxy (if (url-host url)
 			     (url-find-proxy-for-url url (url-host url))))