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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.
// See the LICENSE file in the project root for more information.
using System.Diagnostics;
using System.Threading;
namespace System.Text
{
public abstract class EncoderFallback
{
private static EncoderFallback s_replacementFallback; // Default fallback, uses no best fit & "?"
private static EncoderFallback s_exceptionFallback;
// Get each of our generic fallbacks.
public static EncoderFallback ReplacementFallback
{
get
{
if (s_replacementFallback == null)
Interlocked.CompareExchange<EncoderFallback>(ref s_replacementFallback, new EncoderReplacementFallback(), null);
return s_replacementFallback;
}
}
public static EncoderFallback ExceptionFallback
{
get
{
if (s_exceptionFallback == null)
Interlocked.CompareExchange<EncoderFallback>(ref s_exceptionFallback, new EncoderExceptionFallback(), null);
return s_exceptionFallback;
}
}
// Fallback
//
// Return the appropriate unicode string alternative to the character that need to fall back.
// Most implementations will be:
// return new MyCustomEncoderFallbackBuffer(this);
public abstract EncoderFallbackBuffer CreateFallbackBuffer();
// Maximum number of characters that this instance of this fallback could return
public abstract int MaxCharCount { get; }
}
public abstract class EncoderFallbackBuffer
{
// Most implementations will probably need an implementation-specific constructor
// Public methods that cannot be overridden that let us do our fallback thing
// These wrap the internal methods so that we can check for people doing stuff that is incorrect
public abstract bool Fallback(char charUnknown, int index);
public abstract bool Fallback(char charUnknownHigh, char charUnknownLow, int index);
// Get next character
public abstract char GetNextChar();
// Back up a character
public abstract bool MovePrevious();
// How many chars left in this fallback?
public abstract int Remaining { get; }
// Not sure if this should be public or not.
// Clear the buffer
public virtual void Reset()
{
while (GetNextChar() != (char)0) ;
}
// Internal items to help us figure out what we're doing as far as error messages, etc.
// These help us with our performance and messages internally
internal unsafe char* charStart;
internal unsafe char* charEnd;
internal EncoderNLS encoder;
internal bool setEncoder;
internal bool bUsedEncoder;
internal bool bFallingBack = false;
internal int iRecursionCount = 0;
private const int iMaxRecursion = 250;
// Internal Reset
// For example, what if someone fails a conversion and wants to reset one of our fallback buffers?
internal unsafe void InternalReset()
{
charStart = null;
bFallingBack = false;
iRecursionCount = 0;
Reset();
}
// Set the above values
// This can't be part of the constructor because EncoderFallbacks would have to know how to implement these.
internal unsafe void InternalInitialize(char* charStart, char* charEnd, EncoderNLS encoder, bool setEncoder)
{
this.charStart = charStart;
this.charEnd = charEnd;
this.encoder = encoder;
this.setEncoder = setEncoder;
this.bUsedEncoder = false;
this.bFallingBack = false;
this.iRecursionCount = 0;
}
internal char InternalGetNextChar()
{
char ch = GetNextChar();
bFallingBack = (ch != 0);
if (ch == 0) iRecursionCount = 0;
return ch;
}
// Fallback the current character using the remaining buffer and encoder if necessary
// This can only be called by our encodings (other have to use the public fallback methods), so
// we can use our EncoderNLS here too.
// setEncoder is true if we're calling from a GetBytes method, false if we're calling from a GetByteCount
//
// Note that this could also change the contents of this.encoder, which is the same
// object that the caller is using, so the caller could mess up the encoder for us
// if they aren't careful.
internal unsafe virtual bool InternalFallback(char ch, ref char* chars)
{
// Shouldn't have null charStart
Debug.Assert(charStart != null,
"[EncoderFallback.InternalFallbackBuffer]Fallback buffer is not initialized");
// Get our index, remember chars was preincremented to point at next char, so have to -1
int index = (int)(chars - charStart) - 1;
// See if it was a high surrogate
if (char.IsHighSurrogate(ch))
{
// See if there's a low surrogate to go with it
if (chars >= this.charEnd)
{
// Nothing left in input buffer
// No input, return 0 if mustflush is false
if (this.encoder != null && !this.encoder.MustFlush)
{
// Done, nothing to fallback
if (this.setEncoder)
{
bUsedEncoder = true;
this.encoder._charLeftOver = ch;
}
bFallingBack = false;
return false;
}
}
else
{
// Might have a low surrogate
char cNext = *chars;
if (char.IsLowSurrogate(cNext))
{
// If already falling back then fail
if (bFallingBack && iRecursionCount++ > iMaxRecursion)
ThrowLastCharRecursive(char.ConvertToUtf32(ch, cNext));
// Next is a surrogate, add it as surrogate pair, and increment chars
chars++;
bFallingBack = Fallback(ch, cNext, index);
return bFallingBack;
}
// Next isn't a low surrogate, just fallback the high surrogate
}
}
// If already falling back then fail
if (bFallingBack && iRecursionCount++ > iMaxRecursion)
ThrowLastCharRecursive((int)ch);
// Fall back our char
bFallingBack = Fallback(ch, index);
return bFallingBack;
}
// private helper methods
internal void ThrowLastCharRecursive(int charRecursive)
{
// Throw it, using our complete character
throw new ArgumentException(
SR.Format(SR.Argument_RecursiveFallback,
charRecursive), "chars");
}
}
}
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