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;;; nxml-enc.el --- XML encoding auto-detection -*- lexical-binding:t -*-
;; Copyright (C) 2003, 2007-2024 Free Software Foundation, Inc.
;; Author: James Clark
;; Keywords: text, hypermedia, languages, XML
;; 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:
;; User entry points are nxml-start-auto-coding and
;; nxml-stop-auto-coding. This is separate from nxml-mode, because
;; this cannot be autoloaded. It may use
;; `xmltok-get-declared-encoding-position' which can be autoloaded.
;; It's separate from rng-auto.el so it can be byte-compiled, and
;; because it provides independent, useful functionality.
;;; Code:
(defvar nxml-file-name-ignore-case
(memq system-type '(windows-nt)))
(defvar nxml-cached-file-name-auto-coding-regexp nil)
(defvar nxml-cached-auto-mode-alist nil)
(defun nxml-file-name-auto-coding-regexp ()
"Return regexp for filenames for which XML auto-coding should be done."
(if (eq auto-mode-alist nxml-cached-auto-mode-alist)
nxml-cached-file-name-auto-coding-regexp
(let ((alist auto-mode-alist)
(case-fold-search nxml-file-name-ignore-case)
regexps)
(setq nxml-cached-auto-mode-alist alist)
(while alist
(when (eq (cdar alist) 'nxml-mode)
(setq regexps (cons (caar alist) regexps)))
(setq alist (cdr alist)))
(setq nxml-cached-file-name-auto-coding-regexp
(if (null (cdr regexps))
(car regexps)
(mapconcat (lambda (r)
(concat "\\(?:" r "\\)"))
regexps
"\\|"))))))
(defvar nxml-non-xml-set-auto-coding-function nil
"The function that `set-auto-coding-function' should call for non-XML files.")
(defun nxml-set-auto-coding (file-name size)
(if (let ((case-fold-search nxml-file-name-ignore-case)
(regexp (nxml-file-name-auto-coding-regexp)))
(and regexp
(string-match regexp file-name)))
(nxml-set-xml-coding file-name size)
(and nxml-non-xml-set-auto-coding-function
(funcall nxml-non-xml-set-auto-coding-function file-name size))))
(defun nxml-set-xml-coding (_file-name size)
"Function to use as `set-auto-coding-function' when file is known to be XML."
(nxml-detect-coding-system (+ (point) (min size 1024))))
(declare-function xmltok-get-declared-encoding-position "xmltok"
(&optional limit)) ; autoloaded
(defun nxml-detect-coding-system (limit)
(if (< limit (+ (point) 2))
(if (eq (char-after) 0) 'no-conversion 'utf-8)
(let ((first-two-chars (list (char-after)
(char-after (1+ (point))))))
(cond ((equal first-two-chars '(#xFE #xFF))
(and (coding-system-p 'utf-16-be) 'utf-16-be))
((equal first-two-chars '(#xFF #xFE))
(and (coding-system-p 'utf-16-le) 'utf-16-le))
((memq 0 first-two-chars)
;; Certainly not well-formed XML;
;; perhaps UTF-16 without BOM.
;; In any case, we can't handle it.
;; no-conversion gives the user a chance to fix it.
'no-conversion)
;; There are other things we might try here in the future
;; eg UTF-8 BOM, UTF-16 with no BOM
;; translate to EBCDIC
(t
(let ((enc-pos (xmltok-get-declared-encoding-position limit)))
(cond ((consp enc-pos)
(or (nxml-mime-charset-coding-system
(buffer-substring-no-properties (car enc-pos)
(cdr enc-pos)))
;; We have an encoding whose name we don't recognize.
;; What to do?
;; raw-text seems the best bet: since we got
;; the XML decl it must be a superset of ASCII,
;; so we don't need to go to no-conversion
'raw-text))
(enc-pos 'utf-8)
;; invalid XML declaration
(t nil))))))))
(defun nxml-mime-charset-coding-system (charset)
(let ((charset-sym (intern (downcase charset)))
(coding-systems (coding-system-list t))
coding-system ret)
(while (and coding-systems (not ret))
(setq coding-system (car coding-systems))
(if (eq (coding-system-get coding-system 'mime-charset)
charset-sym)
(setq ret coding-system)
(setq coding-systems (cdr coding-systems))))
ret))
(defun nxml-start-auto-coding ()
"Do encoding auto-detection as specified in the XML standard.
Applied to any files that `auto-mode-alist' says should be handled by
`nxml-mode'."
(interactive)
(unless (eq set-auto-coding-function 'nxml-set-auto-coding)
(let ((inhibit-quit t))
(setq nxml-non-xml-set-auto-coding-function set-auto-coding-function)
(setq set-auto-coding-function 'nxml-set-auto-coding))))
(defun nxml-stop-auto-coding ()
"Stop doing encoding auto-detection as specified in the XML standard."
(interactive)
(when (eq set-auto-coding-function 'nxml-set-auto-coding)
(let ((inhibit-quit t))
(setq set-auto-coding-function nxml-non-xml-set-auto-coding-function)
(setq nxml-non-xml-set-auto-coding-function nil))))
;; Emacs 22 makes us-ascii an alias for iso-safe without
;; giving it a mime-charset property.
(unless (coding-system-get 'us-ascii 'mime-charset)
(coding-system-put 'us-ascii 'mime-charset 'us-ascii))
(provide 'nxml-enc)
;;; nxml-enc.el ends here
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