xml_spaces.ml

(*
 * Copyright (C) 2006-2009 Citrix Systems Inc.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published
 * by the Free Software Foundation; version 2.1 only. with the special
 * exception on linking described in file LICENSE.
 *
 * This program 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 Lesser General Public License for more details.
 *)
(* we pick here a valid XML character which is not used too often in state.db (ie. not '\') *)
let protect_char = '%'

type change =
	| No_change
	| Replace of char * char (* replace 2 chars by 2 other chars                         *)
	| Compress of char       (* replace 2 chars by 1 char                                *)
	| Expand of char * char  (* replace the first char of 2 chars by 2 chars             *)

(* remark: every real operation makes the map2 function to create a new buffer (even the for the replace operation). *)
(* Indeed, we  want to keep the string immutable in xapi, in order to avoid nasty string modifications.              *)
let map2_unlikely f s =
	let changed = ref false in
	let m = ref 0 in
	let i = ref 0 in
	let buf = Buffer.create 0 in
	let length_s = String.length s in
	let aux c d =
		match f (c, d) with
		| No_change -> ()
		| Replace (c,d) ->
			changed := true;
			Buffer.add_substring buf s !m (!i - !m);
			Buffer.add_char buf c;
			Buffer.add_char buf d;
			incr i;
			m := !i + 1
		| Compress char ->
			changed := true;
			Buffer.add_substring buf s !m (!i - !m);
			Buffer.add_char buf char;
			incr i;
			m := !i + 1
		| Expand (c,d) ->
			changed := true;
			Buffer.add_substring buf s !m (!i - !m);
			Buffer.add_char buf c;
			Buffer.add_char buf d;
			m := !i + 1
	in
	(* main loop *)
	while !i <= length_s - 2 do
		aux s.[!i] (Some s.[!i+1]);
		incr i;
	done;
	(* process the last character *)
	if !i = length_s - 1 
	then aux s.[!i] None;
	if !changed then begin
		Buffer.add_substring buf s !m (String.length s - !m);
		Buffer.contents buf
	end else
		s

let protect_fn = function
	|  ' ', Some ' ' -> Replace (protect_char, '_' )
	| '\t',       _  -> Expand  (protect_char, 't' )
	| '\n',       _  -> Expand  (protect_char, 'n' )
	| '\r',       _  -> Expand  (protect_char, 'r' )
	|   c,        _ when c = protect_char -> 
	                    Expand (protect_char, protect_char)
	|   _ ,       _  -> No_change

let unprotect_fn = function
	| c, Some '_' when c=protect_char -> Replace (' ', ' ')
	| c, Some 't' when c=protect_char -> Compress '\t'
	| c, Some 'n' when c=protect_char -> Compress '\n'
	| c, Some 'r' when c=protect_char -> Compress '\r'
	| c, Some  d  when c=protect_char && d=protect_char ->
	                                     Compress protect_char
	| _ ,      _                      -> No_change

let protect = map2_unlikely protect_fn
let unprotect = map2_unlikely unprotect_fn