Ecco un wrapper per rendere qualsiasi Stream
disponibile per leggere le operazioni.
Funziona memorizzando nella cache le letture dal flusso sottostante, fino al numero di byte specificato nel costruttore. Questo sarà utile quando i vincoli della memoria vietano la soluzione di Marc Gravell.
supportati operazioni di ricerca:
- cerca avanti utilizzando
SeekOrigin.Current
e SeekOrigin.Begin
lavori per spostamenti arbitrari
- cerca all'indietro utilizzando
SeekOrigin.Current
e SeekOrigin.Begin
opere per giù a -seekBackBufferSize
byte dalla posizione corrente nel flusso sottostante (che può differire da readSeekableStream.Position
dopo una ricerca precedente a ritroso)
- che cerca di utilizzare
SeekOrigin.End
opere per offset >= -seekBackBufferSize && offset <= 0
Osservazioni generali
- il metodo
Seek
e la proprietà Position
sono completamente gestite internamente e non comportano il flusso sottostante (che sarebbe solo un tiro in ogni caso)
- seeking colpisce il leggere parte del flusso solo, da cui il nome della classe
- tutte le operazioni di scrittura sono semplicemente delegate attraverso il flusso sottostante
- avvolgimento già flussi ricercabile con questo sarebbe uno spreco di risorse
- alcuni problemi affrontati da
ReadSeekableStream
di seguito possono anche essere risolti con la mia classe PeekableStream
Questa implementazione è fresco e non ancora agguerriti. Ho comunque testato l'unità per un bel po 'di casi di ricerca/lettura e casi angolari, confrontandola con un (liberamente ricercabile) MemoryStream
.
public class ReadSeekableStream : Stream
{
private long _underlyingPosition;
private readonly byte[] _seekBackBuffer;
private int _seekBackBufferCount;
private int _seekBackBufferIndex;
private readonly Stream _underlyingStream;
public ReadSeekableStream(Stream underlyingStream, int seekBackBufferSize)
{
if (!underlyingStream.CanRead)
throw new Exception("Provided stream " + underlyingStream + " is not readable");
_underlyingStream = underlyingStream;
_seekBackBuffer = new byte[seekBackBufferSize];
}
public override bool CanRead { get { return true; } }
public override bool CanSeek { get { return true; } }
public override int Read(byte[] buffer, int offset, int count)
{
int copiedFromBackBufferCount = 0;
if (_seekBackBufferIndex < _seekBackBufferCount)
{
copiedFromBackBufferCount = Math.Min(count, _seekBackBufferCount - _seekBackBufferIndex);
Buffer.BlockCopy(_seekBackBuffer, _seekBackBufferIndex, buffer, offset, copiedFromBackBufferCount);
offset += copiedFromBackBufferCount;
count -= copiedFromBackBufferCount;
_seekBackBufferIndex += copiedFromBackBufferCount;
}
int bytesReadFromUnderlying = 0;
if (count > 0)
{
bytesReadFromUnderlying = _underlyingStream.Read(buffer, offset, count);
if (bytesReadFromUnderlying > 0)
{
_underlyingPosition += bytesReadFromUnderlying;
var copyToBufferCount = Math.Min(bytesReadFromUnderlying, _seekBackBuffer.Length);
var copyToBufferOffset = Math.Min(_seekBackBufferCount, _seekBackBuffer.Length - copyToBufferCount);
var bufferBytesToMove = Math.Min(_seekBackBufferCount - 1, copyToBufferOffset);
if (bufferBytesToMove > 0)
Buffer.BlockCopy(_seekBackBuffer, _seekBackBufferCount - bufferBytesToMove, _seekBackBuffer, 0, bufferBytesToMove);
Buffer.BlockCopy(buffer, offset, _seekBackBuffer, copyToBufferOffset, copyToBufferCount);
_seekBackBufferCount = Math.Min(_seekBackBuffer.Length, _seekBackBufferCount + copyToBufferCount);
_seekBackBufferIndex = _seekBackBufferCount;
}
}
return copiedFromBackBufferCount + bytesReadFromUnderlying;
}
public override long Seek(long offset, SeekOrigin origin)
{
if (origin == SeekOrigin.End)
return SeekFromEnd((int) Math.Max(0, -offset));
var relativeOffset = origin == SeekOrigin.Current
? offset
: offset - Position;
if (relativeOffset == 0)
return Position;
else if (relativeOffset > 0)
return SeekForward(relativeOffset);
else
return SeekBackwards(-relativeOffset);
}
private long SeekForward(long origOffset)
{
long offset = origOffset;
var seekBackBufferLength = _seekBackBuffer.Length;
int backwardSoughtBytes = _seekBackBufferCount - _seekBackBufferIndex;
int seekForwardInBackBuffer = (int) Math.Min(offset, backwardSoughtBytes);
offset -= seekForwardInBackBuffer;
_seekBackBufferIndex += seekForwardInBackBuffer;
if (offset > 0)
{
// first completely fill seekBackBuffer to remove special cases from while loop below
if (_seekBackBufferCount < seekBackBufferLength)
{
var maxRead = seekBackBufferLength - _seekBackBufferCount;
if (offset < maxRead)
maxRead = (int) offset;
var bytesRead = _underlyingStream.Read(_seekBackBuffer, _seekBackBufferCount, maxRead);
_underlyingPosition += bytesRead;
_seekBackBufferCount += bytesRead;
_seekBackBufferIndex = _seekBackBufferCount;
if (bytesRead < maxRead)
{
if (_seekBackBufferCount < offset)
throw new NotSupportedException("Reached end of stream seeking forward " + origOffset + " bytes");
return Position;
}
offset -= bytesRead;
}
// now alternate between filling tempBuffer and seekBackBuffer
bool fillTempBuffer = true;
var tempBuffer = new byte[seekBackBufferLength];
while (offset > 0)
{
var maxRead = offset < seekBackBufferLength ? (int) offset : seekBackBufferLength;
var bytesRead = _underlyingStream.Read(fillTempBuffer ? tempBuffer : _seekBackBuffer, 0, maxRead);
_underlyingPosition += bytesRead;
var bytesReadDiff = maxRead - bytesRead;
offset -= bytesRead;
if (bytesReadDiff > 0 /* reached end-of-stream */ || offset == 0)
{
if (fillTempBuffer)
{
if (bytesRead > 0)
{
Buffer.BlockCopy(_seekBackBuffer, bytesRead, _seekBackBuffer, 0, bytesReadDiff);
Buffer.BlockCopy(tempBuffer, 0, _seekBackBuffer, bytesReadDiff, bytesRead);
}
}
else
{
if (bytesRead > 0)
Buffer.BlockCopy(_seekBackBuffer, 0, _seekBackBuffer, bytesReadDiff, bytesRead);
Buffer.BlockCopy(tempBuffer, bytesRead, _seekBackBuffer, 0, bytesReadDiff);
}
if (offset > 0)
throw new NotSupportedException("Reached end of stream seeking forward " + origOffset + " bytes");
}
fillTempBuffer = !fillTempBuffer;
}
}
return Position;
}
private long SeekBackwards(long offset)
{
var intOffset = (int)offset;
if (offset > int.MaxValue || intOffset > _seekBackBufferIndex)
throw new NotSupportedException("Cannot currently seek backwards more than " + _seekBackBufferIndex + " bytes");
_seekBackBufferIndex -= intOffset;
return Position;
}
private long SeekFromEnd(long offset)
{
var intOffset = (int) offset;
var seekBackBufferLength = _seekBackBuffer.Length;
if (offset > int.MaxValue || intOffset > seekBackBufferLength)
throw new NotSupportedException("Cannot seek backwards from end more than " + seekBackBufferLength + " bytes");
// first completely fill seekBackBuffer to remove special cases from while loop below
if (_seekBackBufferCount < seekBackBufferLength)
{
var maxRead = seekBackBufferLength - _seekBackBufferCount;
var bytesRead = _underlyingStream.Read(_seekBackBuffer, _seekBackBufferCount, maxRead);
_underlyingPosition += bytesRead;
_seekBackBufferCount += bytesRead;
_seekBackBufferIndex = Math.Max(0, _seekBackBufferCount - intOffset);
if (bytesRead < maxRead)
{
if (_seekBackBufferCount < intOffset)
throw new NotSupportedException("Could not seek backwards from end " + intOffset + " bytes");
return Position;
}
}
else
{
_seekBackBufferIndex = _seekBackBufferCount;
}
// now alternate between filling tempBuffer and seekBackBuffer
bool fillTempBuffer = true;
var tempBuffer = new byte[seekBackBufferLength];
while (true)
{
var bytesRead = _underlyingStream.Read(fillTempBuffer ? tempBuffer : _seekBackBuffer, 0, seekBackBufferLength);
_underlyingPosition += bytesRead;
var bytesReadDiff = seekBackBufferLength - bytesRead;
if (bytesReadDiff > 0) // reached end-of-stream
{
if (fillTempBuffer)
{
if (bytesRead > 0)
{
Buffer.BlockCopy(_seekBackBuffer, bytesRead, _seekBackBuffer, 0, bytesReadDiff);
Buffer.BlockCopy(tempBuffer, 0, _seekBackBuffer, bytesReadDiff, bytesRead);
}
}
else
{
if (bytesRead > 0)
Buffer.BlockCopy(_seekBackBuffer, 0, _seekBackBuffer, bytesReadDiff, bytesRead);
Buffer.BlockCopy(tempBuffer, bytesRead, _seekBackBuffer, 0, bytesReadDiff);
}
_seekBackBufferIndex -= intOffset;
return Position;
}
fillTempBuffer = !fillTempBuffer;
}
}
public override long Position
{
get { return _underlyingPosition - (_seekBackBufferCount - _seekBackBufferIndex); }
set { Seek(value, SeekOrigin.Begin); }
}
protected override void Dispose(bool disposing)
{
if (disposing)
_underlyingStream.Close();
base.Dispose(disposing);
}
public override bool CanTimeout { get { return _underlyingStream.CanTimeout; } }
public override bool CanWrite { get { return _underlyingStream.CanWrite; } }
public override long Length { get { return _underlyingStream.Length; } }
public override void SetLength(long value) { _underlyingStream.SetLength(value); }
public override void Write(byte[] buffer, int offset, int count) { _underlyingStream.Write(buffer, offset, count); }
public override void Flush() { _underlyingStream.Flush(); }
}
'MemoryStream'? 'BufferedStream'? –
Se si considera l'implementazione di BufferedStream, si noterà che non consente effettivamente le operazioni di ricerca quando lo streaming di base non le consente. MemoryStream non ha costruttori che adottano un parametro Stream. – Brannon
È possibile riprodurre da un flusso di rete MP3 in NAudio e l'app NAudioDemo mostra come eseguire questa operazione. Mp3FileReader è per la lettura dei file, quindi si aspetta che siano cercabili. Creare un TOC in anticipo ci permette di supportare repository molto veloci e accurati in un VBR MP3. Tuttavia, sono d'accordo che sarebbe bello per un futuro NAudio supportare flussi non ricercabili passati in Mp3FileReader. –