lisp/mail/mailheader.el

   1 ;;; mailheader.el --- mail header parsing, merging, formatting
   2
   3 ;; Copyright (C) 1996, 2001-2016 Free Software Foundation, Inc.
   4
   5 ;; Author: Erik Naggum <erik@naggum.no>
   6 ;; Keywords: tools, mail, news
   7 ;; Package: mail-utils
   8
   9 ;; This file is part of GNU Emacs.
  10
  11 ;; GNU Emacs is free software: you can redistribute it and/or modify
  12 ;; it under the terms of the GNU General Public License as published by
  13 ;; the Free Software Foundation, either version 3 of the License, or
  14 ;; (at your option) any later version.
  15
  16 ;; GNU Emacs is distributed in the hope that it will be useful,
  17 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  18 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19 ;; GNU General Public License for more details.
  20
  21 ;; You should have received a copy of the GNU General Public License
  22 ;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.
  23
  24 ;;; Commentary:
  25
  26 ;; This package provides an abstraction to RFC822-style messages, used in
  27 ;; mail, news, and some other systems.  The simple syntactic rules for such
  28 ;; headers, such as quoting and line folding, are routinely reimplemented
  29 ;; in many individual packages.  This package removes the need for this
  30 ;; redundancy by representing message headers as association lists,
  31 ;; offering functions to extract the set of headers from a message, to
  32 ;; parse individual headers, to merge sets of headers, and to format a set
  33 ;; of headers.
  34
  35 ;; The car of each element in the message-header alist is a symbol whose
  36 ;; print name is the name of the header, in all lower-case.  The cdr of an
  37 ;; element depends on the operation.  After extracting headers from a
  38 ;; message, it is a string, the value of the header.  An extracted set of
  39 ;; headers may be parsed further, which may turn it into a list, whose car
  40 ;; is the original value and whose subsequent elements depend on the
  41 ;; header.  For formatting, it is evaluated to obtain the strings to be
  42 ;; inserted.  For merging, one set of headers consists of strings, while
  43 ;; the other set will be evaluated with the symbols in the first set of
  44 ;; headers bound to their respective values.
  45
  46 ;;; Code:
  47
  48 (defun mail-header-extract ()
  49   "Extract headers from current buffer after point.
  50 Returns a header alist, where each element is a cons cell (name . value),
  51 where NAME is a symbol, and VALUE is the string value of the header having
  52 that name."
  53   (let ((message-headers ()) (top (point))
  54         start end)
  55     (while (and (setq start (point))
  56                 (> (skip-chars-forward "^\0- :") 0)
  57                 (= (following-char) ?:)
  58                 (setq end (point))
  59                 (progn (forward-char)
  60                        (> (skip-chars-forward " \t") 0)))
  61       (let ((header (intern (downcase (buffer-substring start end))))
  62             (value (list (buffer-substring
  63                           (point) (progn (end-of-line) (point))))))
  64         (while (progn (forward-char) (> (skip-chars-forward " \t") 0))
  65           (push (buffer-substring (point) (progn (end-of-line) (point)))
  66                 value))
  67         (push (if (cdr value)
  68                   (cons header (mapconcat #'identity (nreverse value) " "))
  69                   (cons header (car value)))
  70               message-headers)))
  71     (goto-char top)
  72     (nreverse message-headers)))
  73
  74 (defun mail-header-extract-no-properties ()
  75   "Extract headers from current buffer after point, without properties.
  76 Returns a header alist, where each element is a cons cell (name . value),
  77 where NAME is a symbol, and VALUE is the string value of the header having
  78 that name."
  79   (mapcar
  80    (lambda (elt)
  81      (set-text-properties 0 (length (cdr elt)) nil (cdr elt))
  82      elt)
  83    (mail-header-extract)))
  84
  85 (defun mail-header-parse (parsing-rules headers)
  86   "Apply PARSING-RULES to HEADERS.
  87 PARSING-RULES is an alist whose keys are header names (symbols) and whose
  88 value is a parsing function.  The function takes one argument, a string,
  89 and return a list of values, which will destructively replace the value
  90 associated with the key in HEADERS, after being prepended with the original
  91 value."
  92   (dolist (rule parsing-rules)
  93     (let ((header (assq (car rule) headers)))
  94       (when header
  95         (if (consp (cdr header))
  96             (setf (cddr header) (funcall (cdr rule) (cadr header)))
  97           (setf (cdr header)
  98                 (cons (cdr header) (funcall (cdr rule) (cdr header))))))))
  99   headers)
 100
 101 ;; Advertised part of the interface; see mail-header, mail-header-set.
 102 (defvar headers)
 103
 104 (defsubst mail-header (header &optional header-alist)
 105   "Return the value associated with header HEADER in HEADER-ALIST.
 106 If the value is a string, it is the original value of the header.  If the
 107 value is a list, its first element is the original value of the header,
 108 with any subsequent elements being the result of parsing the value.
 109 If HEADER-ALIST is nil, the dynamically bound variable `headers' is used."
 110   (declare (gv-setter (lambda (value)
 111                         `(mail-header-set ,header ,value ,header-alist))))
 112   (cdr (assq header (or header-alist headers))))
 113
 114 (defun mail-header-set (header value &optional header-alist)
 115   "Set the value associated with header HEADER to VALUE in HEADER-ALIST.
 116 HEADER-ALIST defaults to the dynamically bound variable `headers' if nil.
 117 See `mail-header' for the semantics of VALUE."
 118   (let* ((alist (or header-alist headers))
 119         (entry (assq header alist)))
 120     (if entry
 121         (setf (cdr entry) value)
 122         (nconc alist (list (cons header value)))))
 123   value)
 124
 125 (defun mail-header-merge (merge-rules headers)
 126   "Return a new header alist with MERGE-RULES applied to HEADERS.
 127 MERGE-RULES is an alist whose keys are header names (symbols) and whose
 128 values are forms to evaluate, the results of which are the new headers.  It
 129 should be a string or a list of string.  The first element may be nil to
 130 denote that the formatting functions must use the remaining elements, or
 131 skip the header altogether if there are no other elements.
 132   The macro `mail-header' can be used to access headers in HEADERS."
 133   (mapcar
 134    (lambda (rule)
 135      (cons (car rule) (eval (cdr rule))))
 136    merge-rules))
 137
 138 (defvar mail-header-format-function
 139   (lambda (header value)
 140     "Function to format headers without a specified formatting function."
 141     (insert (capitalize (symbol-name header))
 142             ": "
 143             (if (consp value) (car value) value)
 144             "\n")))
 145
 146 (defun mail-header-format (format-rules headers)
 147   "Use FORMAT-RULES to format HEADERS and insert into current buffer.
 148 HEADERS should be an alist of the form (HEADER . VALUE),
 149 where HEADER is a header field name (a symbol or a string),
 150 and VALUE is the contents for that header field.
 151
 152 FORMAT-RULES is an alist of elements (HEADER . FUNCTION) Here HEADER
 153 is a header field name (a symbol), and FUNCTION is how to format that
 154 header field, if it appears in HEADERS.  Each FUNCTION should take two
 155 arguments: the header symbol, and the value of that header.  The value
 156 returned by FUNCTION is inserted in the buffer unless it is nil.
 157
 158 If the function for a header field is nil, or if no function is
 159 specified for a particular header field, the default action is to
 160 insert the value of the header, unless it is nil.
 161
 162 The headers are inserted in the order of the FORMAT-RULES.
 163 A key of t in FORMAT-RULES represents any otherwise unmentioned headers.
 164 A key of nil has as its value a list of defaulted headers to ignore."
 165   (let ((ignore (append (cdr (assq nil format-rules))
 166                         (mapcar #'car format-rules))))
 167     (dolist (rule format-rules)
 168       (let* ((header (car rule))
 169             (value (mail-header header)))
 170         (if (stringp header)
 171             (setq header (intern header)))
 172         (cond ((null header) 'ignore)
 173               ((eq header t)
 174                (dolist (defaulted headers)
 175                  (unless (memq (car defaulted) ignore)
 176                    (let* ((header (car defaulted))
 177                           (value (cdr defaulted)))
 178                      (if (cdr rule)
 179                          (funcall (cdr rule) header value)
 180                        (funcall mail-header-format-function header value))))))
 181               (value
 182                (if (cdr rule)
 183                    (funcall (cdr rule) header value)
 184                  (funcall mail-header-format-function header value))))))
 185     (insert "\n")))
 186
 187 (provide 'mailheader)
 188
 189 ;;; mailheader.el ends here