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using System;
using System.IO;
using System.Threading;
#if NETCOREAPP1_0_OR_GREATER || NET45_OR_GREATER || NETSTANDARD1_0_OR_GREATER
using System.Threading.Tasks;
#endif
namespace Org.BouncyCastle.Utilities.IO
{
public class PushbackStream
: FilterStream
{
private int m_buf = -1;
public PushbackStream(Stream s)
: base(s)
{
}
#if NETCOREAPP2_0_OR_GREATER || NETSTANDARD2_1_OR_GREATER
public override void CopyTo(Stream destination, int bufferSize)
{
if (m_buf != -1)
{
destination.WriteByte((byte)m_buf);
m_buf = -1;
}
Streams.CopyTo(s, destination, bufferSize);
}
#endif
#if NETCOREAPP1_0_OR_GREATER || NET45_OR_GREATER || NETSTANDARD1_0_OR_GREATER
public override async Task CopyToAsync(Stream destination, int bufferSize, CancellationToken cancellationToken)
{
if (m_buf != -1)
{
byte[] buffer = new byte[1]{ (byte)m_buf };
await destination.WriteAsync(buffer, 0, 1, cancellationToken).ConfigureAwait(false);
m_buf = -1;
}
await Streams.CopyToAsync(s, destination, bufferSize, cancellationToken);
}
#endif
public override int Read(byte[] buffer, int offset, int count)
{
Streams.ValidateBufferArguments(buffer, offset, count);
if (m_buf != -1)
{
if (count < 1)
return 0;
buffer[offset] = (byte)m_buf;
m_buf = -1;
return 1;
}
return s.Read(buffer, offset, count);
}
#if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1_OR_GREATER
public override int Read(Span<byte> buffer)
{
if (m_buf != -1)
{
if (buffer.IsEmpty)
return 0;
buffer[0] = (byte)m_buf;
m_buf = -1;
return 1;
}
return s.Read(buffer);
}
public override ValueTask<int> ReadAsync(Memory<byte> buffer, CancellationToken cancellationToken = default)
{
if (m_buf != -1)
{
if (buffer.IsEmpty)
return new ValueTask<int>(0);
buffer.Span[0] = (byte)m_buf;
m_buf = -1;
return new ValueTask<int>(1);
}
return Streams.ReadAsync(s, buffer, cancellationToken);
}
#endif
public override int ReadByte()
{
if (m_buf != -1)
{
int tmp = m_buf;
m_buf = -1;
return tmp;
}
return s.ReadByte();
}
public virtual void Unread(int b)
{
if (m_buf != -1)
throw new InvalidOperationException("Can only push back one byte");
m_buf = b & 0xFF;
}
}
}
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