lisp/mail/mailheader.el

   1 ;;; mailheader.el --- mail header parsing, merging, formatting
   2
   3 ;; Copyright (C) 1996, 2002, 2003, 2004, 2005,
   4 ;;   2006 Free Software Foundation, Inc.
   5
   6 ;; Author: Erik Naggum <erik@naggum.no>
   7 ;; Keywords: tools, mail, news
   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 2, or (at your option)
  14 ;; 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; see the file COPYING.  If not, write to
  23 ;; the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  24 ;; Boston, MA 02110-1301, USA.
  25
  26 ;;; Commentary:
  27
  28 ;; This package provides an abstraction to RFC822-style messages, used in
  29 ;; mail, news, and some other systems.  The simple syntactic rules for such
  30 ;; headers, such as quoting and line folding, are routinely reimplemented
  31 ;; in many individual packages.  This package removes the need for this
  32 ;; redundancy by representing message headers as association lists,
  33 ;; offering functions to extract the set of headers from a message, to
  34 ;; parse individual headers, to merge sets of headers, and to format a set
  35 ;; of headers.
  36
  37 ;; The car of each element in the message-header alist is a symbol whose
  38 ;; print name is the name of the header, in all lower-case.  The cdr of an
  39 ;; element depends on the operation.  After extracting headers from a
  40 ;; message, it is a string, the value of the header.  An extracted set of
  41 ;; headers may be parsed further, which may turn it into a list, whose car
  42 ;; is the original value and whose subsequent elements depend on the
  43 ;; header.  For formatting, it is evaluated to obtain the strings to be
  44 ;; inserted.  For merging, one set of headers consists of strings, while
  45 ;; the other set will be evaluated with the symbols in the first set of
  46 ;; headers bound to their respective values.
  47
  48 ;;; Code:
  49
  50 (eval-when-compile
  51   (require 'cl))
  52
  53 ;; Make the byte-compiler shut up.
  54 (defvar headers)
  55
  56 (defun mail-header-extract ()
  57   "Extract headers from current buffer after point.
  58 Returns a header alist, where each element is a cons cell (name . value),
  59 where NAME is a symbol, and VALUE is the string value of the header having
  60 that name."
  61   (let ((message-headers ()) (top (point))
  62         start end)
  63     (while (and (setq start (point))
  64                 (> (skip-chars-forward "^\0- :") 0)
  65                 (= (following-char) ?:)
  66                 (setq end (point))
  67                 (progn (forward-char)
  68                        (> (skip-chars-forward " \t") 0)))
  69       (let ((header (intern (downcase (buffer-substring start end))))
  70             (value (list (buffer-substring
  71                           (point) (progn (end-of-line) (point))))))
  72         (while (progn (forward-char) (> (skip-chars-forward " \t") 0))
  73           (push (buffer-substring (point) (progn (end-of-line) (point)))
  74                 value))
  75         (push (if (cdr value)
  76                   (cons header (mapconcat #'identity (nreverse value) " "))
  77                   (cons header (car value)))
  78               message-headers)))
  79     (goto-char top)
  80     (nreverse message-headers)))
  81
  82 (defun mail-header-extract-no-properties ()
  83   "Extract headers from current buffer after point, without properties.
  84 Returns a header alist, where each element is a cons cell (name . value),
  85 where NAME is a symbol, and VALUE is the string value of the header having
  86 that name."
  87   (mapcar
  88    (lambda (elt)
  89      (set-text-properties 0 (length (cdr elt)) nil (cdr elt))
  90      elt)
  91    (mail-header-extract)))
  92
  93 (defun mail-header-parse (parsing-rules headers)
  94   "Apply PARSING-RULES to HEADERS.
  95 PARSING-RULES is an alist whose keys are header names (symbols) and whose
  96 value is a parsing function.  The function takes one argument, a string,
  97 and return a list of values, which will destructively replace the value
  98 associated with the key in HEADERS, after being prepended with the original
  99 value."
 100   (dolist (rule parsing-rules)
 101     (let ((header (assq (car rule) headers)))
 102       (when header
 103         (if (consp (cdr header))
 104             (setf (cddr header) (funcall (cdr rule) (cadr header)))
 105           (setf (cdr header)
 106                 (cons (cdr header) (funcall (cdr rule) (cdr header))))))))
 107   headers)
 108
 109 (defsubst mail-header (header &optional header-alist)
 110   "Return the value associated with header HEADER in HEADER-ALIST.
 111 If the value is a string, it is the original value of the header.  If the
 112 value is a list, its first element is the original value of the header,
 113 with any subsequent elements being the result of parsing the value.
 114 If HEADER-ALIST is nil, the dynamically bound variable `headers' is used."
 115   (cdr (assq header (or header-alist headers))))
 116
 117 (defun mail-header-set (header value &optional header-alist)
 118   "Set the value associated with header HEADER to VALUE in HEADER-ALIST.
 119 HEADER-ALIST defaults to the dynamically bound variable `headers' if nil.
 120 See `mail-header' for the semantics of VALUE."
 121   (let* ((alist (or header-alist headers))
 122         (entry (assq header alist)))
 123     (if entry
 124         (setf (cdr entry) value)
 125         (nconc alist (list (cons header value)))))
 126   value)
 127
 128 (defsetf mail-header (header &optional header-alist) (value)
 129   `(mail-header-set ,header ,value ,header-alist))
 130
 131 (defun mail-header-merge (merge-rules headers)
 132   "Return a new header alist with MERGE-RULES applied to HEADERS.
 133 MERGE-RULES is an alist whose keys are header names (symbols) and whose
 134 values are forms to evaluate, the results of which are the new headers.  It
 135 should be a string or a list of string.  The first element may be nil to
 136 denote that the formatting functions must use the remaining elements, or
 137 skip the header altogether if there are no other elements.
 138   The macro `mail-header' can be used to access headers in HEADERS."
 139   (mapcar
 140    (lambda (rule)
 141      (cons (car rule) (eval (cdr rule))))
 142    merge-rules))
 143
 144 (defvar mail-header-format-function
 145   (lambda (header value)
 146     "Function to format headers without a specified formatting function."
 147     (insert (capitalize (symbol-name header))
 148             ": "
 149             (if (consp value) (car value) value)
 150             "\n")))
 151
 152 (defun mail-header-format (format-rules headers)
 153   "Use FORMAT-RULES to format HEADERS and insert into current buffer.
 154 HEADERS should be an alist of the form (HEADER . VALUE),
 155 where HEADER is a header field name (a symbol or a string),
 156 and VALUE is the contents for that header field.
 157
 158 FORMAT-RULES is an alist of elements (HEADER . FUNCTION) Here HEADER
 159 is a header field name (a symbol), and FUNCTION is how to format that
 160 header field, if it appears in HEADERS.  Each FUNCTION should take two
 161 arguments: the header symbol, and the value of that header.  The value
 162 returned by FUNCTION is inserted in the buffer unless it is nil.
 163
 164 If the function for a header field is nil, or if no function is
 165 specified for a particular header field, the default action is to
 166 insert the value of the header, unless it is nil.
 167
 168 The headers are inserted in the order of the FORMAT-RULES.
 169 A key of t in FORMAT-RULES represents any otherwise unmentioned headers.
 170 A key of nil has as its value a list of defaulted headers to ignore."
 171   (let ((ignore (append (cdr (assq nil format-rules))
 172                         (mapcar #'car format-rules))))
 173     (dolist (rule format-rules)
 174       (let* ((header (car rule))
 175             (value (mail-header header)))
 176         (if (stringp header)
 177             (setq header (intern header)))
 178         (cond ((null header) 'ignore)
 179               ((eq header t)
 180                (dolist (defaulted headers)
 181                  (unless (memq (car defaulted) ignore)
 182                    (let* ((header (car defaulted))
 183                           (value (cdr defaulted)))
 184                      (if (cdr rule)
 185                          (funcall (cdr rule) header value)
 186                        (funcall mail-header-format-function header value))))))
 187               (value
 188                (if (cdr rule)
 189                    (funcall (cdr rule) header value)
 190                  (funcall mail-header-format-function header value))))))
 191     (insert "\n")))
 192
 193 (provide 'mailheader)
 194
 195 ;;; arch-tag: 6e7aa221-80b5-4b3d-b46f-fd66ab567be0
 196 ;;; mailheader.el ends here