#region Apache License
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//
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// Licensed to the Apache Software Foundation (ASF) under one or more
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// contributor license agreements. See the NOTICE file distributed with
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// this work for additional information regarding copyright ownership.
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// The ASF licenses this file to you under the Apache License, Version 2.0
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// (the "License"); you may not use this file except in compliance with
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// the License. You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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#endregion
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using System;
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using System.Text;
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using System.Xml;
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using System.Text.RegularExpressions;
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namespace log4net.Util
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{
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/// <summary>
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/// Utility class for transforming strings.
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/// </summary>
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/// <remarks>
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/// <para>
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/// Utility class for transforming strings.
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/// </para>
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/// </remarks>
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/// <author>Nicko Cadell</author>
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/// <author>Gert Driesen</author>
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public sealed class Transform
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{
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#region Private Instance Constructors
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/// <summary>
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/// Initializes a new instance of the <see cref="Transform" /> class.
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/// </summary>
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/// <remarks>
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/// <para>
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/// Uses a private access modifier to prevent instantiation of this class.
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/// </para>
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/// </remarks>
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private Transform()
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{
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}
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#endregion Private Instance Constructors
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#region XML String Methods
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/// <summary>
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/// Write a string to an <see cref="XmlWriter"/>
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/// </summary>
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/// <param name="writer">the writer to write to</param>
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/// <param name="textData">the string to write</param>
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/// <param name="invalidCharReplacement">The string to replace non XML compliant chars with</param>
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/// <remarks>
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/// <para>
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/// The test is escaped either using XML escape entities
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/// or using CDATA sections.
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/// </para>
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/// </remarks>
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public static void WriteEscapedXmlString(XmlWriter writer, string textData, string invalidCharReplacement)
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{
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string stringData = MaskXmlInvalidCharacters(textData, invalidCharReplacement);
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// Write either escaped text or CDATA sections
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int weightCData = 12 * (1 + CountSubstrings(stringData, CDATA_END));
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int weightStringEscapes = 3*(CountSubstrings(stringData, "<") + CountSubstrings(stringData, ">")) + 4*CountSubstrings(stringData, "&");
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if (weightStringEscapes <= weightCData)
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{
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// Write string using string escapes
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writer.WriteString(stringData);
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}
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else
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{
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// Write string using CDATA section
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int end = stringData.IndexOf(CDATA_END);
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if (end < 0)
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{
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writer.WriteCData(stringData);
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}
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else
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{
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int start = 0;
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while (end > -1)
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{
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writer.WriteCData(stringData.Substring(start, end - start));
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if (end == stringData.Length - 3)
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{
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start = stringData.Length;
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writer.WriteString(CDATA_END);
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break;
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}
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else
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{
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writer.WriteString(CDATA_UNESCAPABLE_TOKEN);
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start = end + 2;
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end = stringData.IndexOf(CDATA_END, start);
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}
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}
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if (start < stringData.Length)
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{
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writer.WriteCData(stringData.Substring(start));
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}
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}
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}
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}
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/// <summary>
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/// Replace invalid XML characters in text string
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/// </summary>
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/// <param name="textData">the XML text input string</param>
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/// <param name="mask">the string to use in place of invalid characters</param>
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/// <returns>A string that does not contain invalid XML characters.</returns>
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/// <remarks>
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/// <para>
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/// Certain Unicode code points are not allowed in the XML InfoSet, for
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/// details see: <a href="http://www.w3.org/TR/REC-xml/#charsets">http://www.w3.org/TR/REC-xml/#charsets</a>.
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/// </para>
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/// <para>
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/// This method replaces any illegal characters in the input string
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/// with the mask string specified.
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/// </para>
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/// </remarks>
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public static string MaskXmlInvalidCharacters(string textData, string mask)
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{
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return INVALIDCHARS.Replace(textData, mask);
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}
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#endregion XML String Methods
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#region Private Helper Methods
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/// <summary>
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/// Count the number of times that the substring occurs in the text
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/// </summary>
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/// <param name="text">the text to search</param>
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/// <param name="substring">the substring to find</param>
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/// <returns>the number of times the substring occurs in the text</returns>
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/// <remarks>
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/// <para>
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/// The substring is assumed to be non repeating within itself.
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/// </para>
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/// </remarks>
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private static int CountSubstrings(string text, string substring)
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{
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int count = 0;
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int offset = 0;
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int length = text.Length;
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int substringLength = substring.Length;
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if (length == 0)
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{
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return 0;
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}
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if (substringLength == 0)
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{
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return 0;
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}
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while(offset < length)
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{
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int index = text.IndexOf(substring, offset);
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if (index == -1)
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{
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break;
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}
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count++;
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offset = index + substringLength;
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}
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return count;
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}
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#endregion
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#region Private Static Fields
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private const string CDATA_END = "]]>";
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private const string CDATA_UNESCAPABLE_TOKEN = "]]";
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/// <summary>
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/// Characters illegal in XML 1.0
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/// </summary>
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private static Regex INVALIDCHARS=new Regex(@"[^\x09\x0A\x0D\x20-\uD7FF\uE000-\uFFFD]",RegexOptions.Compiled);
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#endregion Private Static Fields
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}
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}
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