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+;;; gnus-nocem.el --- NoCeM pseudo-cancellation treatment
+;; Copyright (C) 1995,96 Free Software Foundation, Inc.
+
+;; Author: Lars Magne Ingebrigtsen <larsi@ifi.uio.no>
+;; Keywords: news
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation; either version 2, or (at your option)
+;; any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs; see the file COPYING.  If not, write to the
+;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+;; Boston, MA 02111-1307, USA.
+
+;;; Commentary:
+
+;;; Code:
+
+(require 'gnus)
+(require 'nnmail)
+(eval-when-compile (require 'cl))
+
+(defvar gnus-nocem-groups 
+  '("alt.nocem.misc" "news.admin.net-abuse.announce")
+  "*List of groups that will be searched for NoCeM messages.")
+
+(defvar gnus-nocem-issuers 
+  '("Automoose-1" ; The CancelMoose[tm] on autopilot.
+    "clewis@ferret.ocunix.on.ca;" ; Chris Lewis -- Canadian angel & despammer.
+    "jem@xpat.com;"  ; John Milburn -- despammer in Korea.
+    "red@redpoll.mrfs.oh.us (Richard E. Depew)" ; Spew/bincancel guy.
+    )
+  "*List of NoCeM issuers to pay attention to.")
+
+(defvar gnus-nocem-directory 
+  (concat (file-name-as-directory gnus-article-save-directory) "NoCeM/")
+  "*Directory where NoCeM files will be stored.")
+
+(defvar gnus-nocem-expiry-wait 15
+  "*Number of days to keep NoCeM headers in the cache.")
+
+(defvar gnus-nocem-verifyer nil
+  "*Function called to verify that the NoCeM message is valid.
+One likely value is `mc-verify'.  If the function in this variable
+isn't bound, the message will be used unconditionally.")
+
+;;; Internal variables
+
+(defvar gnus-nocem-active nil)
+(defvar gnus-nocem-alist nil)
+(defvar gnus-nocem-touched-alist nil)
+(defvar gnus-nocem-hashtb nil)
+
+;;; Functions
+
+(defun gnus-nocem-active-file ()
+  (concat (file-name-as-directory gnus-nocem-directory) "active"))
+
+(defun gnus-nocem-cache-file ()
+  (concat (file-name-as-directory gnus-nocem-directory) "cache"))
+
+(defun gnus-nocem-scan-groups ()
+  "Scan all NoCeM groups for new NoCeM messages."
+  (interactive)
+  (let ((groups gnus-nocem-groups)
+	group active gactive articles)
+    (or (file-exists-p gnus-nocem-directory)
+	(make-directory gnus-nocem-directory t))
+    ;; Load any previous NoCeM headers.
+    (gnus-nocem-load-cache)
+    ;; Read the active file if it hasn't been read yet.
+    (and (file-exists-p (gnus-nocem-active-file))
+	 (not gnus-nocem-active)
+	 (condition-case ()
+	     (load (gnus-nocem-active-file) t t t)
+	   (error nil)))
+    ;; Go through all groups and see whether new articles have
+    ;; arrived.  
+    (while (setq group (pop groups))
+      (if (not (setq gactive (gnus-activate-group group)))
+	  () ; This group doesn't exist.
+	(setq active (nth 1 (assoc group gnus-nocem-active)))
+	(when (and (not (< (cdr gactive) (car gactive))) ; Empty group.
+		   (or (not active)
+		       (< (cdr active) (cdr gactive))))
+	  ;; Ok, there are new articles in this group, se we fetch the
+	  ;; headers.
+	  (save-excursion
+	    (let ((dependencies (make-vector 10 nil))
+		  (buffer (nnheader-set-temp-buffer " *Gnus NoCeM*"))
+		  headers)
+	      (setq headers
+		    (if (eq 'nov
+			    (gnus-retrieve-headers 
+			     (setq articles
+				   (gnus-uncompress-range
+				    (cons 
+				     (if active (1+ (cdr active)) 
+				       (car gactive))
+				     (cdr gactive))))
+			     group))
+			(gnus-get-newsgroup-headers-xover 
+			 articles nil dependencies)
+		      (gnus-get-newsgroup-headers dependencies)))
+	      (while headers
+		;; We take a closer look on all articles that have
+		;; "@@NCM" in the subject.  
+		(when (string-match "@@NCM"
+				    (mail-header-subject (car headers)))
+		  (gnus-nocem-check-article group (car headers)))
+		(setq headers (cdr headers)))
+	      (kill-buffer (current-buffer)))))
+	(setq gnus-nocem-active
+	      (cons (list group gactive) 
+		    (delq (assoc group gnus-nocem-active)
+			  gnus-nocem-active)))))
+    ;; Save the results, if any.
+    (gnus-nocem-save-cache)
+    (gnus-nocem-save-active)))
+
+(defun gnus-nocem-check-article (group header)
+  "Check whether the current article is an NCM article and that we want it."
+  ;; Get the article.
+  (gnus-message 7 "Checking article %d in %s for NoCeM..."
+		(mail-header-number header) group)
+  (let ((date (mail-header-date header))
+	issuer b e)
+    (when (or (not date)
+	      (nnmail-time-less 
+	       (nnmail-time-since (nnmail-date-to-time date))
+	       (nnmail-days-to-time gnus-nocem-expiry-wait)))
+      (gnus-request-article-this-buffer (mail-header-number header) group)
+      ;; The article has to have proper NoCeM headers.
+      (when (and (setq b (search-forward "\n@@BEGIN NCM HEADERS\n" nil t))
+		 (setq e (search-forward "\n@@BEGIN NCM BODY\n" nil t)))
+	;; We get the name of the issuer.
+	(narrow-to-region b e)
+	(setq issuer (mail-fetch-field "issuer"))
+	(and (member issuer gnus-nocem-issuers) ; We like her...
+	     (gnus-nocem-verify-issuer issuer) ; She is who she says she is..
+	     (gnus-nocem-enter-article)))))) ; We gobble the message.
+  
+(defun gnus-nocem-verify-issuer (person)
+  "Verify using PGP that the canceler is who she says she is."
+  (widen)
+  (if (fboundp gnus-nocem-verifyer)
+      (funcall gnus-nocem-verifyer)
+    ;; If we don't have MailCrypt, then we use the message anyway.
+    t))
+
+(defun gnus-nocem-enter-article ()
+  "Enter the current article into the NoCeM cache."
+  (goto-char (point-min))
+  (let ((b (search-forward "\n@@BEGIN NCM BODY\n" nil t))
+	(e (search-forward "\n@@END NCM BODY\n" nil t))
+	(buf (current-buffer))
+	ncm id)
+    (when (and b e)
+      (narrow-to-region b (1+ (match-beginning 0)))
+      (goto-char (point-min))
+      (while (search-forward "\t" nil t)
+	(when (condition-case nil
+		  (boundp (let ((obarray gnus-active-hashtb)) (read buf)))
+		(error nil))
+	  (beginning-of-line)
+	  (while (= (following-char) ?\t)
+	    (forward-line -1))
+	  (setq id (buffer-substring (point) (1- (search-forward "\t"))))
+	  (push id ncm)
+	  (gnus-sethash id t gnus-nocem-hashtb)
+	  (forward-line 1)
+	  (while (= (following-char) ?\t)
+	    (forward-line 1))))
+      (when ncm
+	(setq gnus-nocem-touched-alist t)
+	(push (cons (let ((time (current-time))) (setcdr (cdr time) nil) time)
+		    ncm) 
+	      gnus-nocem-alist)))))
+
+(defun gnus-nocem-load-cache ()
+  "Load the NoCeM cache."
+  (unless gnus-nocem-alist
+    ;; The buffer doesn't exist, so we create it and load the NoCeM
+    ;; cache.  
+    (when (file-exists-p (gnus-nocem-cache-file))
+      (load (gnus-nocem-cache-file) t t t)
+      (gnus-nocem-alist-to-hashtb))))
+      
+(defun gnus-nocem-save-cache ()
+  "Save the NoCeM cache."
+  (when (and gnus-nocem-alist
+	     gnus-nocem-touched-alist)
+    (nnheader-temp-write (gnus-nocem-cache-file)
+      (prin1 `(setq gnus-nocem-alist ',gnus-nocem-alist) (current-buffer)))
+    (setq gnus-nocem-touched-alist nil)))
+
+(defun gnus-nocem-save-active ()
+  "Save the NoCeM active file."
+  (nnheader-temp-write (gnus-nocem-active-file)
+    (prin1 `(setq gnus-nocem-active ',gnus-nocem-active) (current-buffer))))
+
+(defun gnus-nocem-alist-to-hashtb ()
+  "Create a hashtable from the Message-IDs we have."
+  (let* ((alist gnus-nocem-alist)
+	 (pprev (cons nil alist))
+	 (prev pprev)
+	 (expiry (nnmail-days-to-time gnus-nocem-expiry-wait))
+	 entry)
+    (setq gnus-nocem-hashtb (gnus-make-hashtable (* (length alist) 51)))
+    (while (setq entry (car alist))
+      (if (not (nnmail-time-less (nnmail-time-since (car entry)) expiry))
+	  ;; This entry has expired, so we remove it.
+	  (setcdr prev (cdr alist))
+	(setq prev alist)
+	;; This is ok, so we enter it into the hashtable.
+	(setq entry (cdr entry))
+	(while entry
+	  (gnus-sethash (car entry) t gnus-nocem-hashtb)
+	  (setq entry (cdr entry))))
+      (setq alist (cdr alist)))))
+
+(gnus-add-shutdown 'gnus-nocem-close 'gnus)
+
+(defun gnus-nocem-close ()
+  "Clear internal NoCeM variables."
+  (setq gnus-nocem-alist nil
+	gnus-nocem-hashtb nil
+	gnus-nocem-active nil
+	gnus-nocem-touched-alist nil))
+
+(defun gnus-nocem-unwanted-article-p (id)
+  "Say whether article ID in the current group is wanted."
+  (gnus-gethash id gnus-nocem-hashtb))
+
+(provide 'gnus-nocem)
+
+;;; gnus-nocem.el ends here