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//------------------------------------------------------------------------------
// <copyright file="Utf16StringValidator.cs" company="Microsoft">
// Copyright (c) Microsoft Corporation. All rights reserved.
// </copyright>
//------------------------------------------------------------------------------
namespace System.Web.Util {
using System;
// This class contains utility methods for dealing with security contexts when crossing AppDomain boundaries.
internal static class Utf16StringValidator {
private const char UNICODE_NULL_CHAR = '\0';
private const char UNICODE_REPLACEMENT_CHAR = '\uFFFD';
private static readonly bool _skipUtf16Validation = AppSettings.AllowRelaxedUnicodeDecoding;
public static string ValidateString(string input) {
return ValidateString(input, _skipUtf16Validation);
}
// only internal for unit testing
internal static string ValidateString(string input, bool skipUtf16Validation) {
if (skipUtf16Validation || String.IsNullOrEmpty(input)) {
return input;
}
// locate the first surrogate character
int idxOfFirstSurrogate = -1;
for (int i = 0; i < input.Length; i++) {
if (Char.IsSurrogate(input[i])) {
idxOfFirstSurrogate = i;
break;
}
}
// fast case: no surrogates = return input string
if (idxOfFirstSurrogate < 0) {
return input;
}
// slow case: surrogates exist, so we need to validate them
char[] chars = input.ToCharArray();
for (int i = idxOfFirstSurrogate; i < chars.Length; i++) {
char thisChar = chars[i];
// If this character is a low surrogate, then it was not preceded by
// a high surrogate, so we'll replace it.
if (Char.IsLowSurrogate(thisChar)) {
chars[i] = UNICODE_REPLACEMENT_CHAR;
continue;
}
if (Char.IsHighSurrogate(thisChar)) {
// If this character is a high surrogate and it is followed by a
// low surrogate, allow both to remain.
if (i + 1 < chars.Length && Char.IsLowSurrogate(chars[i + 1])) {
i++; // skip the low surrogate also
continue;
}
// If this character is a high surrogate and it is not followed
// by a low surrogate, replace it.
chars[i] = UNICODE_REPLACEMENT_CHAR;
continue;
}
// Otherwise, this is a non-surrogate character and just move to the
// next character.
}
return new String(chars);
}
}
}
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