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;;; traclicker.el -- fight email click trackers -*- lexical-binding: t -*-
;; Copyright (C) 2023 Free Software Foundation, Inc.
;; Author: Yuchen Pei <id@ypei.org>
;; Package-Requires: ((emacs "28.2"))
;; This file is part of traclicker.
;; traclicker is free software: you can redistribute it and/or modify it under
;; the terms of the GNU Affero General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.
;; traclicker 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 Affero General
;; Public License for more details.
;; You should have received a copy of the GNU Affero General Public
;; License along with traclicker. If not, see <https://www.gnu.org/licenses/>.
;;; Commentary:
;; traclicker is a tool that protects user privacy against email click
;; trackers by sending a HEAD request to all urls in these emails and
;; recording the real urls.
;;; Code:
(require 'gnus-util)
(require 'ol)
(require 'mm-decode)
(defvar tracli-senders
nil
"List of email addresses.")
(defvar tracli-db-file (locate-user-emacs-file "traclicker.eld")
"Database file to read.")
(defvar tracli-maildirs '("~/mail")
"List of maildirs to scan and process urls.
Will scan from both cur and new subdirs.")
(defun tracli-read-data ()
"Read data from `tracli-db-file'."
(when (file-exists-p tracli-db-file)
(with-temp-buffer
(insert-file-contents tracli-db-file)
(goto-char (point-min))
(read (current-buffer)))))
(defun tracli-scan (&optional after)
"Scan emails and get redirect urls.
Only scan emails that are sent by `tracli-senders', delivered
after AFTER (in epoch), in `tracli-maildirs'.
If AFTER is nil, use the timestamp in `tracli-db-file', or an
empty string (i.e. scan all mails)."
(let* ((sender-re (format "<%s>" (regexp-opt tracli-senders)))
(counter 0)
(data (tracli-read-data))
(now (format-time-string "%s" (current-time)))
(urls (or (alist-get 'urls data)
(make-hash-table :test 'equal))))
(setq after (or after
(alist-get 'timestamp data)
""))
(dolist (maildir tracli-maildirs)
(dolist (subdir '("new" "cur"))
(dolist (file (directory-files (file-name-concat maildir subdir)))
(when (and (string-match "^\\([0-9]+\\)\\." file)
(string> (match-string 1 file) after))
(with-temp-buffer
(insert-file-contents (file-name-concat maildir subdir file))
(goto-char (point-min))
(when (and
;; Only scan if the email is not a reply.
(not (gnus-fetch-field "In-Reply-To"))
(string-match sender-re (gnus-fetch-field "From")))
(message "Processing mail from %s with subject %s..."
(gnus-fetch-field "From")
(gnus-fetch-field "Subject"))
(setq counter (1+ counter))
(pcase-dolist (`(,source . ,target)
(tracli-get-buffer-redirect-urls))
(puthash source target urls))))))))
(setf (alist-get 'timestamp data) now)
(setf (alist-get 'urls data) urls)
(with-temp-buffer
(insert (prin1-to-string data))
(write-region nil nil tracli-db-file))
(message "Processed %d mails" counter)))
(defun tracli-get-redirect-url (url)
"Get redirect link of URL.
Sends a HEAD request."
(let* ((url-request-method "HEAD")
(url-max-redirections 0)
(buffer (url-retrieve-synchronously url))
(inhibit-message t))
(with-current-buffer buffer
(goto-char (point-min))
(when (re-search-forward "^Location: \\(.*\\)$" nil t)
(match-string 1)))))
(defun tracli-collect-urls ()
"Collect all http/https urls in the current buffer."
(save-excursion
(let ((results))
(while (re-search-forward org-link-plain-re nil t)
(let ((scheme (match-string 1))
(url (match-string 0)))
(when (and (member scheme '("http" "https"))
(not (member url results)))
(push url results))))
(reverse results))))
(defun tracli-get-buffer-redirect-urls ()
"Get a list of redirect urls in the current buffer."
(let ((parsed (tracli-parse-buffer)))
(with-temp-buffer
(insert (format "%s" parsed))
(goto-char (point-min))
(mapcar (lambda (url)
(cons url (tracli-get-redirect-url url)))
(tracli-collect-urls)))))
(defun tracli-parse-buffer ()
"Parse a buffer."
(let ((handles (mm-dissect-buffer t t)))
(with-temp-buffer
(tracli-parse-first handles))))
(defun tracli-parse-first (handle)
"Parse the first handle in the tree of HANDLE's."
(if (stringp (car handle))
(tracli-parse-first (cadr handle))
(tracli-parse handle)))
(defun tracli-parse (handle)
"Parse a mime HANDLE.
Adapted from `mm-shr'."
(let ((shr-width (if shr-use-fonts
nil
fill-column))
(shr-content-function (lambda (id)
(let ((handle (mm-get-content-id id)))
(when handle
(mm-with-part handle
(buffer-string))))))
(shr-inhibit-images t)
(shr-blocked-images ".*")
charset coding char)
(mm-with-part (or handle (setq handle (mm-dissect-buffer t)))
(setq case-fold-search t)
(or (setq charset
(mail-content-type-get (mm-handle-type handle) 'charset))
(progn
(goto-char (point-min))
(and (re-search-forward "\
<meta\\s-+http-equiv=[\"']?content-type[\"']?\\s-+content=[\"']?\
text/html;\\s-*charset=\\([^\t\n\r \"'>]+\\)[^>]*>" nil t)
(setq coding (mm-charset-to-coding-system (match-string 1)
nil t))))
(setq charset mail-parse-charset))
(when (and (or coding
(setq coding (mm-charset-to-coding-system charset nil t)))
(not (eq coding 'ascii)))
(insert (prog1
(decode-coding-string (buffer-string) coding)
(erase-buffer)
(set-buffer-multibyte t))))
(goto-char (point-min))
(while (re-search-forward
"&#\\(?:x\\([89][0-9a-f]\\)\\|\\(1[2-5][0-9]\\)\\);" nil t)
(when (setq char
(cdr (assq (if (match-beginning 1)
(string-to-number (match-string 1) 16)
(string-to-number (match-string 2)))
mm-extra-numeric-entities)))
(replace-match (char-to-string char))))
;; Remove "soft hyphens".
(goto-char (point-min))
(while (search-forward "" nil t)
(replace-match "" t t))
(buffer-substring-no-properties (point-min) (point-max)))))
(provide 'traclicker)
;;; traclicker.el ends here
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