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;;; ietf-drums.el --- Functions for parsing RFC 2822 headers -*- lexical-binding:t -*-
;; Copyright (C) 1998-2025 Free Software Foundation, Inc.
;; Author: Lars Magne Ingebrigtsen <larsi@gnus.org>
;; 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 3 of the License, 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. If not, see <https://www.gnu.org/licenses/>.
;;; Commentary:
;; DRUMS is an IETF Working Group that worked on Internet RFC 2822,
;; the successor to RFC 822 and the predecessor of RFC 5322. This
;; library is based on draft-ietf-drums-msg-fmt-05.txt, released on
;; 1998-08-05.
;;; Code:
(eval-when-compile (require 'cl-lib))
(defvar ietf-drums-no-ws-ctl-token "\001-\010\013\014\016-\037\177"
"US-ASCII control characters excluding CR, LF and white space.")
(defvar ietf-drums-text-token "\001-\011\013\014\016-\177"
"US-ASCII characters excluding CR and LF.")
(defvar ietf-drums-specials-token "()<>[]:;@\\,.\""
"Special characters.")
(defvar ietf-drums-quote-token "\\"
"Quote character.")
(defvar ietf-drums-wsp-token " \t"
"White space.")
(defvar ietf-drums-fws-regexp
(concat "[" ietf-drums-wsp-token "]*\n[" ietf-drums-wsp-token "]+")
"Folding white space.")
(defvar ietf-drums-atext-token "-^a-zA-Z0-9!#$%&'*+/=?_`{|}~"
"Textual token.")
(defvar ietf-drums-dot-atext-token "-^a-zA-Z0-9!#$%&'*+/=?_`{|}~."
"Textual token including full stop.")
(defvar ietf-drums-qtext-token
(concat ietf-drums-no-ws-ctl-token "\041\043-\133\135-\177")
"Non-white-space control characters, plus the rest of ASCII excluding
backslash and doublequote.")
(defvar ietf-drums-tspecials "][()<>@,;:\\\"/?="
"Tspecials.")
(defvar ietf-drums-syntax-table
(let ((table (copy-syntax-table emacs-lisp-mode-syntax-table)))
(modify-syntax-entry ?\\ "/" table)
(modify-syntax-entry ?< "(" table)
(modify-syntax-entry ?> ")" table)
(modify-syntax-entry ?@ "w" table)
(modify-syntax-entry ?/ "w" table)
(modify-syntax-entry ?* "_" table)
(modify-syntax-entry ?\; "_" table)
(modify-syntax-entry ?\' "_" table)
table))
(defvar ietf-drums-comment-syntax-table
(let ((table (copy-syntax-table ietf-drums-syntax-table)))
(modify-syntax-entry ?\" "w" table)
table)
"In comments, DQUOTE is normal and does not start a string.")
(defun ietf-drums--skip-comment ()
;; From just before the start of a comment, go to the end. Returns
;; point. If the comment is unterminated, go to point-max.
(condition-case ()
(with-syntax-table ietf-drums-comment-syntax-table
(forward-sexp 1))
(scan-error (goto-char (point-max))))
(point))
(defun ietf-drums-token-to-list (token)
"Translate TOKEN into a list of characters."
(let ((i 0)
b c out range)
(while (< i (length token))
(setq c (aref token i))
(cl-incf i)
(cond
((eq c ?-)
(if b
(setq range t)
(push c out)))
(range
(while (<= b c)
(push (make-char 'ascii b) out)
(cl-incf b))
(setq range nil))
((= i (length token))
(push (make-char 'ascii c) out))
(t
(when b
(push (make-char 'ascii b) out))
(setq b c))))
(nreverse out)))
(defsubst ietf-drums-init (string)
(set-syntax-table ietf-drums-syntax-table)
(insert string)
(ietf-drums-unfold-fws)
(goto-char (point-min)))
(defun ietf-drums-remove-comments (string)
"Remove comments from STRING."
(with-temp-buffer
(let (c)
(ietf-drums-init string)
(while (not (eobp))
(setq c (char-after))
(cond
((eq c ?\")
(condition-case nil
(forward-sexp 1)
(error (goto-char (point-max)))))
((eq c ?\()
(delete-region (point) (ietf-drums--skip-comment)))
(t
(forward-char 1))))
(buffer-string))))
(defun ietf-drums-remove-whitespace (string)
"Remove whitespace from STRING."
(with-temp-buffer
(ietf-drums-init string)
(let (c)
(while (not (eobp))
(setq c (char-after))
(cond
((eq c ?\")
(condition-case ()
(forward-sexp 1)
(scan-error (goto-char (point-max)))))
((eq c ?\()
(ietf-drums--skip-comment))
((memq c '(?\ ?\t ?\n ?\r))
(delete-char 1))
(t
(forward-char 1))))
(buffer-string))))
(defun ietf-drums-get-comment (string)
"Return the last comment in STRING."
(with-temp-buffer
(ietf-drums-init string)
(let (result c)
(while (not (eobp))
(setq c (char-after))
(cond
((eq c ?\")
(forward-sexp 1))
((eq c ?\()
(setq result
(buffer-substring
(1+ (point))
(progn (forward-sexp 1) (1- (point))))))
(t
(forward-char 1))))
result)))
(defun ietf-drums-strip (string)
"Remove comments and whitespace from STRING."
(ietf-drums-remove-whitespace (ietf-drums-remove-comments string)))
(defun ietf-drums-remove-garbage (string)
"Remove some garbage from STRING."
(while (string-match "[][()<>@,;:\\\"/?=]+" string)
(setq string (concat (substring string 0 (match-beginning 0))
(substring string (match-end 0)))))
string)
(defun ietf-drums-strip-cte (string)
"Remove comments, whitespace and garbage from STRING.
STRING is assumed to be a string that is extracted from
the Content-Transfer-Encoding header of a mail."
(ietf-drums-remove-garbage (inline (ietf-drums-strip string))))
(declare-function rfc2047-decode-string "rfc2047" (string &optional address-mime))
(defun ietf-drums-parse-address (string &optional decode)
"Parse STRING and return a MAILBOX / DISPLAY-NAME pair.
STRING here is supposed to be an RFC822(bis) mail address, and
will commonly look like, for instance:
\"=?utf-8?Q?Andr=C3=A9?= <andre@example.com>\"
If you have an already-decoded address, like
\"André <andre@example.com>\"
this function can't be used to parse that. Instead, use
`mail-header-parse-address-lax' to make a guess at what's the
name and what's the address.
If DECODE, the DISPLAY-NAME will have RFC2047 decoding performed
(that's the \"=?utf...q...=?\") stuff."
(when decode
(require 'rfc2047))
(with-temp-buffer
(let (display-name mailbox c display-string)
(ietf-drums-init string)
(while (not (eobp))
(setq c (char-after))
;; If we have an uneven number of quote characters,
;; `forward-sexp' will fail. In these cases, just delete the
;; final of these quote characters.
(when (and (eq c ?\")
(not
(save-excursion
(ignore-errors
(forward-sexp 1)
t))))
(delete-char 1)
(setq c (char-after)))
(cond
((or (eq c ? )
(eq c ?\t))
(forward-char 1))
((eq c ?\()
(forward-sexp 1))
((eq c ?\")
(push (buffer-substring
(1+ (point)) (progn (forward-sexp 1) (1- (point))))
display-name))
((looking-at (concat "[" ietf-drums-atext-token "@" "]"))
(push (buffer-substring (point) (progn (forward-sexp 1) (point)))
display-name))
((eq c ?<)
(setq mailbox
(ietf-drums-remove-whitespace
(ietf-drums-remove-comments
(buffer-substring
(1+ (point))
(progn (forward-sexp 1) (1- (point))))))))
(t
(forward-char 1))))
;; If we found no display-name, then we look for comments.
(if display-name
(setq display-string
(mapconcat #'identity (reverse display-name) " "))
(setq display-string (ietf-drums-get-comment string)))
(if (not mailbox)
(when (and display-string
(string-search "@" display-string))
(cons
(mapconcat #'identity (nreverse display-name) "")
(ietf-drums-get-comment string)))
(cons mailbox (if (and decode display-string)
(rfc2047-decode-string display-string)
display-string))))))
(defun ietf-drums-parse-addresses (string &optional rawp)
"Parse STRING and return a list of MAILBOX / DISPLAY-NAME pairs.
If RAWP, don't actually parse the addresses, but instead return
a list of address strings."
(if (null string)
nil
(with-temp-buffer
(ietf-drums-init string)
(let ((beg (point))
pairs c address)
(while (not (eobp))
(setq c (char-after))
(cond
((eq c ?:)
(setq beg (1+ (point)))
(skip-chars-forward "^;")
(when-let ((address
(condition-case nil
(ietf-drums-parse-addresses
(buffer-substring beg (point)) rawp)
(error nil))))
(if (listp address)
(setq pairs (append address pairs))
(push address pairs)))
(condition-case nil
(forward-char 1)
(error nil))
(setq beg (point)))
((memq c '(?\" ?< ?\())
(condition-case nil
(forward-sexp 1)
(error
(skip-chars-forward "^,"))))
((eq c ?,)
(setq address
(if rawp
(buffer-substring beg (point))
(condition-case nil
(ietf-drums-parse-address
(buffer-substring beg (point)))
(error nil))))
(when (or (consp address)
(and (stringp address) (< 0 (length address))))
(push address pairs))
(forward-char 1)
(setq beg (point)))
((not (eobp))
(forward-char 1))))
(setq address
(if rawp
(buffer-substring beg (point))
(condition-case nil
(ietf-drums-parse-address
(buffer-substring beg (point)))
(error nil))))
(when (or (consp address)
(and (stringp address) (< 0 (length address))))
(push address pairs))
(nreverse pairs)))))
(defun ietf-drums-unfold-fws ()
"Unfold folding white space in the current buffer."
(goto-char (point-min))
(while (re-search-forward ietf-drums-fws-regexp nil t)
(replace-match " " t t))
(goto-char (point-min)))
(declare-function ietf-drums-parse-date-string "ietf-drums-date"
(time-string &optional error? no-822?))
(defun ietf-drums-parse-date (string)
"Return an Emacs time spec from STRING."
(require 'ietf-drums-date)
(encode-time (ietf-drums-parse-date-string string)))
(defun ietf-drums-narrow-to-header ()
"Narrow to the header section in the current buffer."
(narrow-to-region
(goto-char (point-min))
(if (re-search-forward "^\r?$" nil 1)
(match-beginning 0)
(point-max)))
(goto-char (point-min)))
(defun ietf-drums-quote-string (string)
"Quote string if it needs quoting to be displayed in a header."
(if (string-match (concat "[^" ietf-drums-atext-token "]") string)
(concat "\"" string "\"")
string))
(defun ietf-drums-make-address (name address)
(if name
(concat (ietf-drums-quote-string name) " <" address ">")
address))
(provide 'ietf-drums)
;;; ietf-drums.el ends here
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