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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.Diagnostics;
using System.Runtime.InteropServices;
namespace System.Text
{
// An Encoder is used to encode a sequence of blocks of characters into
// a sequence of blocks of bytes. Following instantiation of an encoder,
// sequential blocks of characters are converted into blocks of bytes through
// calls to the GetBytes method. The encoder maintains state between the
// conversions, allowing it to correctly encode character sequences that span
// adjacent blocks.
//
// Instances of specific implementations of the Encoder abstract base
// class are typically obtained through calls to the GetEncoder method
// of Encoding objects.
//
public abstract class Encoder
{
internal EncoderFallback? _fallback;
internal EncoderFallbackBuffer? _fallbackBuffer;
protected Encoder()
{
// We don't call default reset because default reset probably isn't good if we aren't initialized.
}
public EncoderFallback? Fallback
{
get => _fallback;
set
{
ArgumentNullException.ThrowIfNull(value);
// Can't change fallback if buffer is wrong
if (_fallbackBuffer is not null && _fallbackBuffer.Remaining > 0)
throw new ArgumentException(
SR.Argument_FallbackBufferNotEmpty, nameof(value));
_fallback = value;
_fallbackBuffer = null;
}
}
// Note: we don't test for threading here because async access to Encoders and Decoders
// doesn't work anyway.
public EncoderFallbackBuffer FallbackBuffer
{
get
{
_fallbackBuffer ??= _fallback is not null ?
_fallback.CreateFallbackBuffer() :
EncoderFallback.ReplacementFallback.CreateFallbackBuffer();
return _fallbackBuffer;
}
}
internal bool InternalHasFallbackBuffer => _fallbackBuffer is not null;
// Reset the Encoder
//
// Normally if we call GetBytes() and an error is thrown we don't change the state of the encoder. This
// would allow the caller to correct the error condition and try again (such as if they need a bigger buffer.)
//
// If the caller doesn't want to try again after GetBytes() throws an error, then they need to call Reset().
//
// Virtual implementation has to call GetBytes with flush and a big enough buffer to clear a 0 char string
// We avoid GetMaxByteCount() because a) we can't call the base encoder and b) it might be really big.
public virtual void Reset()
{
char[] charTemp = Array.Empty<char>();
byte[] byteTemp = new byte[GetByteCount(charTemp, 0, 0, true)];
GetBytes(charTemp, 0, 0, byteTemp, 0, true);
_fallbackBuffer?.Reset();
}
// Returns the number of bytes the next call to GetBytes will
// produce if presented with the given range of characters and the given
// value of the flush parameter. The returned value takes into
// account the state in which the encoder was left following the last call
// to GetBytes. The state of the encoder is not affected by a call
// to this method.
//
public abstract int GetByteCount(char[] chars, int index, int count, bool flush);
// We expect this to be the workhorse for NLS encodings
// unfortunately for existing overrides, it has to call the [] version,
// which is really slow, so avoid this method if you might be calling external encodings.
[CLSCompliant(false)]
public virtual unsafe int GetByteCount(char* chars, int count, bool flush)
{
ArgumentNullException.ThrowIfNull(chars);
ArgumentOutOfRangeException.ThrowIfNegative(count);
char[] arrChar = new char[count];
for (int index = 0; index < count; index++)
arrChar[index] = chars[index];
return GetByteCount(arrChar, 0, count, flush);
}
public virtual unsafe int GetByteCount(ReadOnlySpan<char> chars, bool flush)
{
fixed (char* charsPtr = &MemoryMarshal.GetNonNullPinnableReference(chars))
{
return GetByteCount(charsPtr, chars.Length, flush);
}
}
// Encodes a range of characters in a character array into a range of bytes
// in a byte array. The method encodes charCount characters from
// chars starting at index charIndex, storing the resulting
// bytes in bytes starting at index byteIndex. The encoding
// takes into account the state in which the encoder was left following the
// last call to this method. The flush parameter indicates whether
// the encoder should flush any shift-states and partial characters at the
// end of the conversion. To ensure correct termination of a sequence of
// blocks of encoded bytes, the last call to GetBytes should specify
// a value of true for the flush parameter.
//
// An exception occurs if the byte array is not large enough to hold the
// complete encoding of the characters. The GetByteCount method can
// be used to determine the exact number of bytes that will be produced for
// a given range of characters. Alternatively, the GetMaxByteCount
// method of the Encoding that produced this encoder can be used to
// determine the maximum number of bytes that will be produced for a given
// number of characters, regardless of the actual character values.
//
public abstract int GetBytes(char[] chars, int charIndex, int charCount,
byte[] bytes, int byteIndex, bool flush);
// We expect this to be the workhorse for NLS Encodings, but for existing
// ones we need a working (if slow) default implementation)
//
// WARNING WARNING WARNING
//
// WARNING: If this breaks it could be a security threat. Obviously we
// call this internally, so you need to make sure that your pointers, counts
// and indexes are correct when you call this method.
//
// In addition, we have internal code, which will be marked as "safe" calling
// this code. However this code is dependent upon the implementation of an
// external GetBytes() method, which could be overridden by a third party and
// the results of which cannot be guaranteed. We use that result to copy
// the byte[] to our byte* output buffer. If the result count was wrong, we
// could easily overflow our output buffer. Therefore we do an extra test
// when we copy the buffer so that we don't overflow byteCount either.
[CLSCompliant(false)]
public virtual unsafe int GetBytes(char* chars, int charCount,
byte* bytes, int byteCount, bool flush)
{
ArgumentNullException.ThrowIfNull(chars);
ArgumentNullException.ThrowIfNull(bytes);
ArgumentOutOfRangeException.ThrowIfNegative(charCount);
ArgumentOutOfRangeException.ThrowIfNegative(byteCount);
// Get the char array to convert
char[] arrChar = new char[charCount];
for (int index = 0; index < charCount; index++)
arrChar[index] = chars[index];
// Get the byte array to fill
byte[] arrByte = new byte[byteCount];
// Do the work
int result = GetBytes(arrChar, 0, charCount, arrByte, 0, flush);
Debug.Assert(result <= byteCount, "Returned more bytes than we have space for");
// Copy the byte array
// WARNING: We MUST make sure that we don't copy too many bytes. We can't
// rely on result because it could be a 3rd party implementation. We need
// to make sure we never copy more than byteCount bytes no matter the value
// of result
if (result < byteCount)
byteCount = result;
// Don't copy too many bytes!
for (int index = 0; index < byteCount; index++)
bytes[index] = arrByte[index];
return byteCount;
}
public virtual unsafe int GetBytes(ReadOnlySpan<char> chars, Span<byte> bytes, bool flush)
{
fixed (char* charsPtr = &MemoryMarshal.GetNonNullPinnableReference(chars))
fixed (byte* bytesPtr = &MemoryMarshal.GetNonNullPinnableReference(bytes))
{
return GetBytes(charsPtr, chars.Length, bytesPtr, bytes.Length, flush);
}
}
// This method is used to avoid running out of output buffer space.
// It will encode until it runs out of chars, and then it will return
// true if it the entire input was converted. In either case it
// will also return the number of converted chars and output bytes used.
// It will only throw a buffer overflow exception if the entire length of bytes[] is
// too small to store the next byte. (like 0 or maybe 1 or 4 for some encodings)
// We're done processing this buffer only if completed returns true.
//
// Might consider checking Max...Count to avoid the extra counting step.
//
// Note that if all of the input chars are not consumed, then we'll do a /2, which means
// that its likely that we didn't consume as many chars as we could have. For some
// applications this could be slow. (Like trying to exactly fill an output buffer from a bigger stream)
public virtual void Convert(char[] chars, int charIndex, int charCount,
byte[] bytes, int byteIndex, int byteCount, bool flush,
out int charsUsed, out int bytesUsed, out bool completed)
{
ArgumentNullException.ThrowIfNull(chars);
ArgumentNullException.ThrowIfNull(bytes);
ArgumentOutOfRangeException.ThrowIfNegative(charIndex);
ArgumentOutOfRangeException.ThrowIfNegative(charCount);
ArgumentOutOfRangeException.ThrowIfNegative(byteIndex);
ArgumentOutOfRangeException.ThrowIfNegative(byteCount);
if (chars.Length - charIndex < charCount)
throw new ArgumentOutOfRangeException(nameof(chars),
SR.ArgumentOutOfRange_IndexCountBuffer);
if (bytes.Length - byteIndex < byteCount)
throw new ArgumentOutOfRangeException(nameof(bytes),
SR.ArgumentOutOfRange_IndexCountBuffer);
charsUsed = charCount;
// Its easy to do if it won't overrun our buffer.
// Note: We don't want to call unsafe version because that might be an untrusted version
// which could be really unsafe and we don't want to mix it up.
while (charsUsed > 0)
{
if (GetByteCount(chars, charIndex, charsUsed, flush) <= byteCount)
{
bytesUsed = GetBytes(chars, charIndex, charsUsed, bytes, byteIndex, flush);
completed = (charsUsed == charCount &&
(_fallbackBuffer == null || _fallbackBuffer.Remaining == 0));
return;
}
// Try again with 1/2 the count, won't flush then 'cause won't read it all
flush = false;
charsUsed /= 2;
}
// Oops, we didn't have anything, we'll have to throw an overflow
throw new ArgumentException(SR.Argument_ConversionOverflow);
}
// Same thing, but using pointers
//
// Might consider checking Max...Count to avoid the extra counting step.
//
// Note that if all of the input chars are not consumed, then we'll do a /2, which means
// that its likely that we didn't consume as many chars as we could have. For some
// applications this could be slow. (Like trying to exactly fill an output buffer from a bigger stream)
[CLSCompliant(false)]
public virtual unsafe void Convert(char* chars, int charCount,
byte* bytes, int byteCount, bool flush,
out int charsUsed, out int bytesUsed, out bool completed)
{
ArgumentNullException.ThrowIfNull(chars);
ArgumentNullException.ThrowIfNull(bytes);
ArgumentOutOfRangeException.ThrowIfNegative(charCount);
ArgumentOutOfRangeException.ThrowIfNegative(byteCount);
// Get ready to do it
charsUsed = charCount;
// Its easy to do if it won't overrun our buffer.
while (charsUsed > 0)
{
if (GetByteCount(chars, charsUsed, flush) <= byteCount)
{
bytesUsed = GetBytes(chars, charsUsed, bytes, byteCount, flush);
completed = (charsUsed == charCount &&
(_fallbackBuffer == null || _fallbackBuffer.Remaining == 0));
return;
}
// Try again with 1/2 the count, won't flush then 'cause won't read it all
flush = false;
charsUsed /= 2;
}
// Oops, we didn't have anything, we'll have to throw an overflow
throw new ArgumentException(SR.Argument_ConversionOverflow);
}
public virtual unsafe void Convert(ReadOnlySpan<char> chars, Span<byte> bytes, bool flush, out int charsUsed, out int bytesUsed, out bool completed)
{
fixed (char* charsPtr = &MemoryMarshal.GetNonNullPinnableReference(chars))
fixed (byte* bytesPtr = &MemoryMarshal.GetNonNullPinnableReference(bytes))
{
Convert(charsPtr, chars.Length, bytesPtr, bytes.Length, flush, out charsUsed, out bytesUsed, out completed);
}
}
}
}
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