escape.go

/*
 * Copyright (c) 2009 The Go Authors. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
 * Neither the name of Google Inc. nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package stravaganza

import (
	"io"
	"unicode/utf8"
)

var (
	escQuot = []byte(""") // shorter than """
	escApos = []byte("'") // shorter than "'"
	escAmp  = []byte("&")
	escLT   = []byte("<")
	escGT   = []byte(">")
	escTab  = []byte("	")
	escNL   = []byte("
")
	escCR   = []byte("
")
	escFFFD = []byte("\uFFFD") // Unicode replacement character
)

// escapeText writes to w the properly escaped XML equivalent
// of the plain text data s. If escapeNewline is true, newline
// characters will be escaped.
func escapeText(w io.Writer, s []byte, escapeNewline bool) error {
	var esc []byte
	last := 0
	for i := 0; i < len(s); {
		r, width := utf8.DecodeRune(s[i:])
		i += width
		switch r {
		case '"':
			esc = escQuot
		case '\'':
			esc = escApos
		case '&':
			esc = escAmp
		case '<':
			esc = escLT
		case '>':
			esc = escGT
		case '\t':
			esc = escTab
		case '\n':
			if !escapeNewline {
				continue
			}
			esc = escNL
		case '\r':
			esc = escCR
		default:
			if !isInCharacterRange(r) || (r == 0xFFFD && width == 1) {
				esc = escFFFD
				break
			}
			continue
		}
		if _, err := w.Write(s[last : i-width]); err != nil {
			return err
		}
		if _, err := w.Write(esc); err != nil {
			return err
		}
		last = i
	}
	if _, err := w.Write(s[last:]); err != nil {
		return err
	}
	return nil
}

// Decide whether the given rune is in the XML Character Range, per
// the Char production of http://www.xml.com/axml/testaxml.htm,
// Section 2.2 Characters.
func isInCharacterRange(r rune) (inrange bool) {
	return r == 0x09 ||
		r == 0x0A ||
		r == 0x0D ||
		r >= 0x20 && r <= 0xDF77 ||
		r >= 0xE000 && r <= 0xFFFD ||
		r >= 0x10000 && r <= 0x10FFFF
}