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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
using System.Buffers;
using System.ComponentModel;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.IO;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Text.Unicode;
namespace System.Text.Encodings.Web
{
/// <summary>
/// An abstraction representing various text encoders.
/// </summary>
/// <remarks>
/// TextEncoder subclasses can be used to do HTML encoding, URI encoding, and JavaScript encoding.
/// Instances of such subclasses can be accessed using <see cref="HtmlEncoder.Default"/>, <see cref="UrlEncoder.Default"/>, and <see cref="JavaScriptEncoder.Default"/>.
/// </remarks>
public abstract class TextEncoder
{
private const int EncodeStartingOutputBufferSize = 1024; // bytes or chars, depending
/// <summary>
/// Encodes a Unicode scalar into a buffer.
/// </summary>
/// <param name="unicodeScalar">Unicode scalar.</param>
/// <param name="buffer">The destination of the encoded text.</param>
/// <param name="bufferLength">Length of the destination <paramref name="buffer"/> in chars.</param>
/// <param name="numberOfCharactersWritten">Number of characters written to the <paramref name="buffer"/>.</param>
/// <returns>Returns false if <paramref name="bufferLength"/> is too small to fit the encoded text, otherwise returns true.</returns>
/// <remarks>This method is seldom called directly. One of the TextEncoder.Encode overloads should be used instead.
/// Implementations of <see cref="TextEncoder"/> need to be thread safe and stateless.
/// </remarks>
[CLSCompliant(false)]
[EditorBrowsable(EditorBrowsableState.Never)]
public abstract unsafe bool TryEncodeUnicodeScalar(int unicodeScalar, char* buffer, int bufferLength, out int numberOfCharactersWritten);
[MethodImpl(MethodImplOptions.AggressiveInlining)]
private unsafe bool TryEncodeUnicodeScalar(uint unicodeScalar, Span<char> buffer, out int charsWritten)
{
fixed (char* pBuffer = &MemoryMarshal.GetReference(buffer))
{
return TryEncodeUnicodeScalar((int)unicodeScalar, pBuffer, buffer.Length, out charsWritten);
}
}
private bool TryEncodeUnicodeScalarUtf8(uint unicodeScalar, Span<char> utf16ScratchBuffer, Span<byte> utf8Destination, out int bytesWritten)
{
if (!TryEncodeUnicodeScalar(unicodeScalar, utf16ScratchBuffer, out int charsWritten))
{
// We really don't expect any encoder to exceed 24 escaped chars per input scalar.
// If this happens, throw an exception and we can figure out if we want to support it
// in the future.
ThrowArgumentException_MaxOutputCharsPerInputChar();
}
// Transcode chars -> bytes one at a time.
utf16ScratchBuffer = utf16ScratchBuffer.Slice(0, charsWritten);
int dstIdx = 0;
while (!utf16ScratchBuffer.IsEmpty)
{
if (Rune.DecodeFromUtf16(utf16ScratchBuffer, out Rune nextScalarValue, out int scalarUtf16CodeUnitCount) != OperationStatus.Done)
{
// Wrote bad UTF-16 data, we cannot transcode to UTF-8.
ThrowArgumentException_MaxOutputCharsPerInputChar();
}
uint utf8lsb = (uint)UnicodeHelpers.GetUtf8RepresentationForScalarValue((uint)nextScalarValue.Value);
do
{
if (SpanUtility.IsValidIndex(utf8Destination, dstIdx))
{
utf8Destination[dstIdx++] = (byte)utf8lsb;
}
else
{
bytesWritten = 0; // ran out of space in the destination
return false;
}
} while ((utf8lsb >>= 8) != 0);
utf16ScratchBuffer = utf16ScratchBuffer.Slice(scalarUtf16CodeUnitCount);
}
bytesWritten = dstIdx;
return true;
}
// all subclasses have the same implementation of this method.
// but this cannot be made virtual, because it will cause a virtual call to Encodes, and it destroys perf, i.e. makes common scenario 2x slower
/// <summary>
/// Finds index of the first character that needs to be encoded.
/// </summary>
/// <param name="text">The text buffer to search.</param>
/// <param name="textLength">The number of characters in the <paramref name="text"/>.</param>
/// <returns></returns>
/// <remarks>This method is seldom called directly. It's used by higher level helper APIs.</remarks>
[CLSCompliant(false)]
[EditorBrowsable(EditorBrowsableState.Never)]
public abstract unsafe int FindFirstCharacterToEncode(char* text, int textLength);
/// <summary>
/// Determines if a given Unicode scalar will be encoded.
/// </summary>
/// <param name="unicodeScalar">Unicode scalar.</param>
/// <returns>Returns true if the <paramref name="unicodeScalar"/> will be encoded by this encoder, otherwise returns false.</returns>
[EditorBrowsable(EditorBrowsableState.Never)]
public abstract bool WillEncode(int unicodeScalar);
// this could be a field, but I am trying to make the abstraction pure.
/// <summary>
/// Maximum number of characters that this encoder can generate for each input character.
/// </summary>
[EditorBrowsable(EditorBrowsableState.Never)]
public abstract int MaxOutputCharactersPerInputCharacter { get; }
/// <summary>
/// Encodes the supplied string and returns the encoded text as a new string.
/// </summary>
/// <param name="value">String to encode.</param>
/// <returns>Encoded string.</returns>
public virtual string Encode(string value)
{
if (value is null)
{
ThrowHelper.ThrowArgumentNullException(ExceptionArgument.value);
}
int indexOfFirstCharToEncode = FindFirstCharacterToEncode(value.AsSpan());
if (indexOfFirstCharToEncode < 0)
{
return value; // shortcut: there's no work to perform
}
// We optimize for the data having no "requires encoding" chars, so keep the
// real encoding logic out of the fast path.
return EncodeToNewString(value.AsSpan(), indexOfFirstCharToEncode);
}
private string EncodeToNewString(ReadOnlySpan<char> value, int indexOfFirstCharToEncode)
{
ReadOnlySpan<char> remainingInput = value.Slice(indexOfFirstCharToEncode);
ValueStringBuilder stringBuilder = new ValueStringBuilder(stackalloc char[EncodeStartingOutputBufferSize]);
#if !NET
// Can't call string.Concat later in the method, so memcpy now.
stringBuilder.Append(value.Slice(0, indexOfFirstCharToEncode));
#endif
// On each iteration of the main loop, we'll make sure we have at least this many chars left in the
// destination buffer. This should prevent us from making very chatty calls where we only make progress
// one char at a time.
int minBufferBumpEachIteration = Math.Max(MaxOutputCharactersPerInputCharacter, EncodeStartingOutputBufferSize);
do
{
// AppendSpan mutates the VSB length to include the newly-added span. This potentially overallocates.
Span<char> destBuffer = stringBuilder.AppendSpan(Math.Max(remainingInput.Length, minBufferBumpEachIteration));
EncodeCore(remainingInput, destBuffer, out int charsConsumedJustNow, out int charsWrittenJustNow, isFinalBlock: true);
if (charsWrittenJustNow == 0 || (uint)charsWrittenJustNow > (uint)destBuffer.Length)
{
ThrowArgumentException_MaxOutputCharsPerInputChar(); // couldn't make forward progress or returned bogus data
}
remainingInput = remainingInput.Slice(charsConsumedJustNow);
// It's likely we didn't populate the entire span. If this is the case, adjust the VSB length
// to reflect that there's unused buffer at the end of the VSB instance.
stringBuilder.Length -= destBuffer.Length - charsWrittenJustNow;
} while (!remainingInput.IsEmpty);
#if NET
string retVal = string.Concat(value.Slice(0, indexOfFirstCharToEncode), stringBuilder.AsSpan());
stringBuilder.Dispose();
return retVal;
#else
return stringBuilder.ToString();
#endif
}
/// <summary>
/// Encodes the supplied string into a <see cref="TextWriter"/>.
/// </summary>
/// <param name="output">Encoded text is written to this output.</param>
/// <param name="value">String to be encoded.</param>
public void Encode(TextWriter output, string value)
{
Encode(output, value, 0, value.Length);
}
/// <summary>
/// Encodes a substring into a <see cref="TextWriter"/>.
/// </summary>
/// <param name="output">Encoded text is written to this output.</param>
/// <param name="value">String whose substring is to be encoded.</param>
/// <param name="startIndex">The index where the substring starts.</param>
/// <param name="characterCount">Number of characters in the substring.</param>
public virtual void Encode(TextWriter output, string value, int startIndex, int characterCount)
{
if (output is null)
{
ThrowHelper.ThrowArgumentNullException(ExceptionArgument.output);
}
if (value is null)
{
ThrowHelper.ThrowArgumentNullException(ExceptionArgument.value);
}
ValidateRanges(startIndex, characterCount, actualInputLength: value.Length);
int indexOfFirstCharToEncode = FindFirstCharacterToEncode(value.AsSpan(startIndex, characterCount));
if (indexOfFirstCharToEncode < 0)
{
indexOfFirstCharToEncode = characterCount;
}
// memcpy all characters that don't require encoding, then encode any remaining chars
output.WritePartialString(value, startIndex, indexOfFirstCharToEncode);
if (indexOfFirstCharToEncode != characterCount)
{
EncodeCore(output, value.AsSpan(startIndex + indexOfFirstCharToEncode, characterCount - indexOfFirstCharToEncode));
}
}
/// <summary>
/// Encodes characters from an array into a <see cref="TextWriter"/>.
/// </summary>
/// <param name="output">Encoded text is written to the output.</param>
/// <param name="value">Array of characters to be encoded.</param>
/// <param name="startIndex">The index where the substring starts.</param>
/// <param name="characterCount">Number of characters in the substring.</param>
public virtual void Encode(TextWriter output, char[] value, int startIndex, int characterCount)
{
if (output is null)
{
ThrowHelper.ThrowArgumentNullException(ExceptionArgument.output);
}
if (value is null)
{
ThrowHelper.ThrowArgumentNullException(ExceptionArgument.value);
}
ValidateRanges(startIndex, characterCount, actualInputLength: value.Length);
int indexOfFirstCharToEncode = FindFirstCharacterToEncode(value.AsSpan(startIndex, characterCount));
if (indexOfFirstCharToEncode < 0)
{
indexOfFirstCharToEncode = characterCount;
}
output.Write(value, startIndex, indexOfFirstCharToEncode);
if (indexOfFirstCharToEncode != characterCount)
{
EncodeCore(output, value.AsSpan(startIndex + indexOfFirstCharToEncode, characterCount - indexOfFirstCharToEncode));
}
}
/// <summary>
/// Encodes the supplied UTF-8 text.
/// </summary>
/// <param name="utf8Source">A source buffer containing the UTF-8 text to encode.</param>
/// <param name="utf8Destination">The destination buffer to which the encoded form of <paramref name="utf8Source"/>
/// will be written.</param>
/// <param name="bytesConsumed">The number of bytes consumed from the <paramref name="utf8Source"/> buffer.</param>
/// <param name="bytesWritten">The number of bytes written to the <paramref name="utf8Destination"/> buffer.</param>
/// <param name="isFinalBlock"><see langword="true"/> if there is further source data that needs to be encoded;
/// <see langword="false"/> if there is no further source data that needs to be encoded.</param>
/// <returns>An <see cref="OperationStatus"/> describing the result of the encoding operation.</returns>
/// <remarks>The buffers <paramref name="utf8Source"/> and <paramref name="utf8Destination"/> must not overlap.</remarks>
public virtual OperationStatus EncodeUtf8(
ReadOnlySpan<byte> utf8Source,
Span<byte> utf8Destination,
out int bytesConsumed,
out int bytesWritten,
bool isFinalBlock = true)
{
// The Encode method is intended to be called in a loop, potentially where the source buffer
// is much larger than the destination buffer. We don't want to walk the entire source buffer
// on each invocation of this method, so we'll slice the source buffer to be no larger than
// the destination buffer to avoid performing unnecessary work. The potential exists for us to
// split the source in the middle of a UTF-8 multi-byte sequence. If this happens,
// FindFirstCharacterToEncodeUtf8 will report the split bytes as "needs encoding", we'll fall
// back down the slow path, and the slow path will handle the scenario appropriately.
ReadOnlySpan<byte> sourceSearchSpace = utf8Source;
if (utf8Destination.Length < utf8Source.Length)
{
sourceSearchSpace = utf8Source.Slice(0, utf8Destination.Length);
}
int idxOfFirstByteToEncode = FindFirstCharacterToEncodeUtf8(sourceSearchSpace);
if (idxOfFirstByteToEncode < 0)
{
idxOfFirstByteToEncode = sourceSearchSpace.Length;
}
utf8Source.Slice(0, idxOfFirstByteToEncode).CopyTo(utf8Destination); // memcpy data that doesn't need to be encoded
if (idxOfFirstByteToEncode == utf8Source.Length)
{
bytesConsumed = utf8Source.Length;
bytesWritten = utf8Source.Length;
return OperationStatus.Done; // memcopied all bytes, nothing more to do
}
// If we got to this point, we couldn't memcpy the entire source buffer into the destination.
// Either the destination was too short or we found data that needs to be encoded.
OperationStatus status = EncodeUtf8Core(utf8Source.Slice(idxOfFirstByteToEncode), utf8Destination.Slice(idxOfFirstByteToEncode), out int innerBytesConsumed, out int innerBytesWritten, isFinalBlock);
bytesConsumed = idxOfFirstByteToEncode + innerBytesConsumed;
bytesWritten = idxOfFirstByteToEncode + innerBytesWritten;
return status;
}
// skips the call to FindFirstCharacterToEncodeUtf8
private protected virtual OperationStatus EncodeUtf8Core(
ReadOnlySpan<byte> utf8Source,
Span<byte> utf8Destination,
out int bytesConsumed,
out int bytesWritten,
bool isFinalBlock)
{
int originalUtf8SourceLength = utf8Source.Length;
int originalUtf8DestinationLength = utf8Destination.Length;
const int TempUtf16CharBufferLength = 24; // arbitrarily chosen, but sufficient for any reasonable implementation
Span<char> utf16ScratchBuffer = stackalloc char[TempUtf16CharBufferLength];
while (!utf8Source.IsEmpty)
{
OperationStatus opStatus = Rune.DecodeFromUtf8(utf8Source, out Rune scalarValue, out int bytesConsumedJustNow);
if (opStatus != OperationStatus.Done)
{
if (!isFinalBlock && opStatus == OperationStatus.NeedMoreData)
{
goto NeedMoreData;
}
Debug.Assert(scalarValue == Rune.ReplacementChar); // DecodeFromUtf8 should've performed substitution
goto MustEncode;
}
if (!WillEncode(scalarValue.Value))
{
uint utf8lsb = (uint)UnicodeHelpers.GetUtf8RepresentationForScalarValue((uint)scalarValue.Value);
int dstIdxTemp = 0;
do
{
if ((uint)dstIdxTemp >= (uint)utf8Destination.Length)
{
goto DestinationTooSmall;
}
utf8Destination[dstIdxTemp++] = (byte)utf8lsb;
} while ((utf8lsb >>= 8) != 0);
utf8Source = utf8Source.Slice(bytesConsumedJustNow);
utf8Destination = utf8Destination.Slice(dstIdxTemp);
continue;
}
MustEncode:
if (!TryEncodeUnicodeScalarUtf8((uint)scalarValue.Value, utf16ScratchBuffer, utf8Destination, out int bytesWrittenJustNow))
{
goto DestinationTooSmall;
}
utf8Source = utf8Source.Slice(bytesConsumedJustNow);
utf8Destination = utf8Destination.Slice(bytesWrittenJustNow);
}
// And we're finished!
OperationStatus retVal = OperationStatus.Done;
ReturnCommon:
bytesConsumed = originalUtf8SourceLength - utf8Source.Length;
bytesWritten = originalUtf8DestinationLength - utf8Destination.Length;
return retVal;
NeedMoreData:
retVal = OperationStatus.NeedMoreData;
goto ReturnCommon;
DestinationTooSmall:
retVal = OperationStatus.DestinationTooSmall;
goto ReturnCommon;
}
/// <summary>
/// Encodes the supplied characters.
/// </summary>
/// <param name="source">A source buffer containing the characters to encode.</param>
/// <param name="destination">The destination buffer to which the encoded form of <paramref name="source"/>
/// will be written.</param>
/// <param name="charsConsumed">The number of characters consumed from the <paramref name="source"/> buffer.</param>
/// <param name="charsWritten">The number of characters written to the <paramref name="destination"/> buffer.</param>
/// <param name="isFinalBlock"><see langword="true"/> if there is further source data that needs to be encoded;
/// <see langword="false"/> if there is no further source data that needs to be encoded.</param>
/// <returns>An <see cref="OperationStatus"/> describing the result of the encoding operation.</returns>
/// <remarks>The buffers <paramref name="source"/> and <paramref name="destination"/> must not overlap.</remarks>
public virtual OperationStatus Encode(
ReadOnlySpan<char> source,
Span<char> destination,
out int charsConsumed,
out int charsWritten,
bool isFinalBlock = true)
{
// The Encode method is intended to be called in a loop, potentially where the source buffer
// is much larger than the destination buffer. We don't want to walk the entire source buffer
// on each invocation of this method, so we'll slice the source buffer to be no larger than
// the destination buffer to avoid performing unnecessary work. The potential exists for us to
// split the source in the middle of a UTF-16 surrogate pair. If this happens,
// FindFirstCharacterToEncode will report the split surrogate as "needs encoding", we'll fall
// back down the slow path, and the slow path will handle the surrogate appropriately.
ReadOnlySpan<char> sourceSearchSpace = source;
if (destination.Length < source.Length)
{
sourceSearchSpace = source.Slice(0, destination.Length);
}
int idxOfFirstCharToEncode = FindFirstCharacterToEncode(sourceSearchSpace);
if (idxOfFirstCharToEncode < 0)
{
idxOfFirstCharToEncode = sourceSearchSpace.Length;
}
source.Slice(0, idxOfFirstCharToEncode).CopyTo(destination); // memcpy data that doesn't need to be encoded
if (idxOfFirstCharToEncode == source.Length)
{
charsConsumed = source.Length;
charsWritten = source.Length;
return OperationStatus.Done; // memcopied all chars, nothing more to do
}
// If we got to this point, we couldn't memcpy the entire source buffer into the destination.
// Either the destination was too short or we found data that needs to be encoded.
OperationStatus status = EncodeCore(source.Slice(idxOfFirstCharToEncode), destination.Slice(idxOfFirstCharToEncode), out int innerCharsConsumed, out int innerCharsWritten, isFinalBlock);
charsConsumed = idxOfFirstCharToEncode + innerCharsConsumed;
charsWritten = idxOfFirstCharToEncode + innerCharsWritten;
return status;
}
// skips the call to FindFirstCharacterToEncode
private protected virtual OperationStatus EncodeCore(ReadOnlySpan<char> source, Span<char> destination, out int charsConsumed, out int charsWritten, bool isFinalBlock)
{
int originalSourceLength = source.Length;
int originalDestinationLength = destination.Length;
while (!source.IsEmpty)
{
OperationStatus status = Rune.DecodeFromUtf16(source, out Rune scalarValue, out int charsConsumedJustNow);
if (status != OperationStatus.Done)
{
if (!isFinalBlock && status == OperationStatus.NeedMoreData)
{
goto NeedMoreData;
}
Debug.Assert(scalarValue == Rune.ReplacementChar); // should be replacement char
goto MustEncode;
}
if (!WillEncode(scalarValue.Value))
{
if (!scalarValue.TryEncodeToUtf16(destination, out _))
{
goto DestinationTooSmall;
}
source = source.Slice(charsConsumedJustNow);
destination = destination.Slice(charsConsumedJustNow); // reflecting input directly to the output, same # of chars written
continue;
}
MustEncode:
if (!TryEncodeUnicodeScalar((uint)scalarValue.Value, destination, out int charsWrittenJustNow))
{
goto DestinationTooSmall;
}
source = source.Slice(charsConsumedJustNow);
destination = destination.Slice(charsWrittenJustNow);
}
// And we're finished!
OperationStatus retVal = OperationStatus.Done;
ReturnCommon:
charsConsumed = originalSourceLength - source.Length;
charsWritten = originalDestinationLength - destination.Length;
return retVal;
NeedMoreData:
retVal = OperationStatus.NeedMoreData;
goto ReturnCommon;
DestinationTooSmall:
retVal = OperationStatus.DestinationTooSmall;
goto ReturnCommon;
}
// skips call to FindFirstCharacterToEncode
private void EncodeCore(TextWriter output, ReadOnlySpan<char> value)
{
Debug.Assert(output != null);
Debug.Assert(!value.IsEmpty, "Caller should've special-cased 'no encoding needed'.");
// On each iteration of the main loop, we'll make sure we have at least this many chars left in the
// destination buffer. This should prevent us from making very chatty calls where we only make progress
// one char at a time.
int minBufferBumpEachIteration = Math.Max(MaxOutputCharactersPerInputCharacter, EncodeStartingOutputBufferSize);
char[] rentedArray = ArrayPool<char>.Shared.Rent(Math.Max(value.Length, minBufferBumpEachIteration));
Span<char> scratchBuffer = rentedArray;
do
{
EncodeCore(value, scratchBuffer, out int charsConsumedJustNow, out int charsWrittenJustNow, isFinalBlock: true);
if (charsWrittenJustNow == 0 || (uint)charsWrittenJustNow > (uint)scratchBuffer.Length)
{
ThrowArgumentException_MaxOutputCharsPerInputChar(); // couldn't make forward progress or returned bogus data
}
output.Write(rentedArray, 0, charsWrittenJustNow); // write char[], not Span<char>, for best compat & performance
value = value.Slice(charsConsumedJustNow);
} while (!value.IsEmpty);
ArrayPool<char>.Shared.Return(rentedArray);
}
private protected virtual unsafe int FindFirstCharacterToEncode(ReadOnlySpan<char> text)
{
// Default implementation calls the unsafe overload
fixed (char* pText = &MemoryMarshal.GetReference(text))
{
return FindFirstCharacterToEncode(pText, text.Length);
}
}
/// <summary>
/// Given a UTF-8 text input buffer, finds the first element in the input buffer which would be
/// escaped by the current encoder instance.
/// </summary>
/// <param name="utf8Text">The UTF-8 text input buffer to search.</param>
/// <returns>
/// The index of the first element in <paramref name="utf8Text"/> which would be escaped by the
/// current encoder instance, or -1 if no data in <paramref name="utf8Text"/> requires escaping.
/// </returns>
[EditorBrowsable(EditorBrowsableState.Never)]
public virtual int FindFirstCharacterToEncodeUtf8(ReadOnlySpan<byte> utf8Text)
{
int utf8TextOriginalLength = utf8Text.Length;
while (!utf8Text.IsEmpty)
{
OperationStatus opStatus = Rune.DecodeFromUtf8(utf8Text, out Rune scalarValue, out int bytesConsumed);
if (opStatus != OperationStatus.Done || WillEncode(scalarValue.Value))
{
break;
}
utf8Text = utf8Text.Slice(bytesConsumed);
}
return (utf8Text.IsEmpty) ? -1 : utf8TextOriginalLength - utf8Text.Length;
}
internal static bool TryCopyCharacters(string source, Span<char> destination, out int numberOfCharactersWritten)
{
Debug.Assert(!string.IsNullOrEmpty(source));
if (destination.Length < source.Length)
{
numberOfCharactersWritten = 0;
return false;
}
for (int i = 0; i < source.Length; i++)
{
destination[i] = source[i];
}
numberOfCharactersWritten = source.Length;
return true;
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
internal static bool TryWriteScalarAsChar(int unicodeScalar, Span<char> destination, out int numberOfCharactersWritten)
{
Debug.Assert(unicodeScalar < ushort.MaxValue);
if (destination.IsEmpty)
{
numberOfCharactersWritten = 0;
return false;
}
destination[0] = (char)unicodeScalar;
numberOfCharactersWritten = 1;
return true;
}
private static void ValidateRanges(int startIndex, int characterCount, int actualInputLength)
{
if (startIndex < 0 || startIndex > actualInputLength)
{
throw new ArgumentOutOfRangeException(nameof(startIndex));
}
if (characterCount < 0 || characterCount > (actualInputLength - startIndex))
{
throw new ArgumentOutOfRangeException(nameof(characterCount));
}
}
[DoesNotReturn]
private static void ThrowArgumentException_MaxOutputCharsPerInputChar()
{
throw new ArgumentException(SR.TextEncoderDoesNotImplementMaxOutputCharsPerInputChar);
}
}
}
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