source: box/trunk/lib/common/BufferedStream.cpp @ 2728

// --------------------------------------------------------------------------
//
// File
//              Name:    BufferedStream.cpp
//              Purpose: Buffering read-only wrapper around IOStreams
//              Created: 2007/01/16
//
// --------------------------------------------------------------------------

#include "Box.h"
#include "BufferedStream.h"
#include "CommonException.h"

#include <string.h>

#include "MemLeakFindOn.h"

// --------------------------------------------------------------------------
//
// Function
//              Name:    BufferedStream::BufferedStream(const char *, int, int)
//              Purpose: Constructor, set up buffer
//              Created: 2007/01/16
//
// --------------------------------------------------------------------------
BufferedStream::BufferedStream(IOStream& rSource)
: mrSource(rSource), mBufferSize(0), mBufferPosition(0)
{ }


// --------------------------------------------------------------------------
//
// Function
//              Name:    BufferedStream::Read(void *, int)
//              Purpose: Reads bytes from the file
//              Created: 2007/01/16
//
// --------------------------------------------------------------------------
int BufferedStream::Read(void *pBuffer, int NBytes, int Timeout)
{
        if (mBufferSize == mBufferPosition)
        {
                // buffer is empty, fill it.

                int numBytesRead = mrSource.Read(mBuffer, sizeof(mBuffer), 
                        Timeout);

                if (numBytesRead < 0)
                {
                        return numBytesRead;
                }

                mBufferSize = numBytesRead;
        }

        int sizeToReturn = mBufferSize - mBufferPosition;

        if (sizeToReturn > NBytes)
        {
                sizeToReturn = NBytes;
        }

        memcpy(pBuffer, mBuffer + mBufferPosition, sizeToReturn);
        mBufferPosition += sizeToReturn;

        if (mBufferPosition == mBufferSize)
        {
                // clear out the buffer
                mBufferSize = 0;
                mBufferPosition = 0;
        }

        return sizeToReturn;
}


// --------------------------------------------------------------------------
//
// Function
//              Name:    BufferedStream::BytesLeftToRead()
//              Purpose: Returns number of bytes to read (may not be most efficient function ever)
//              Created: 2007/01/16
//
// --------------------------------------------------------------------------
IOStream::pos_type BufferedStream::BytesLeftToRead()
{
        return mrSource.BytesLeftToRead() + mBufferSize - mBufferPosition;
}


// --------------------------------------------------------------------------
//
// Function
//              Name:    BufferedStream::Write(void *, int)
//              Purpose: Writes bytes to the underlying stream (not supported)
//              Created: 2003/07/31
//
// --------------------------------------------------------------------------
void BufferedStream::Write(const void *pBuffer, int NBytes)
{
        THROW_EXCEPTION(CommonException, NotSupported);
}


// --------------------------------------------------------------------------
//
// Function
//              Name:    BufferedStream::GetPosition()
//              Purpose: Get position in stream
//              Created: 2003/08/21
//
// --------------------------------------------------------------------------
IOStream::pos_type BufferedStream::GetPosition() const
{
        return mrSource.GetPosition() - mBufferSize + mBufferPosition;
}


// --------------------------------------------------------------------------
//
// Function
//              Name:    BufferedStream::Seek(pos_type, int)
//              Purpose: Seeks within file, as lseek, invalidate buffer
//              Created: 2003/07/31
//
// --------------------------------------------------------------------------
void BufferedStream::Seek(IOStream::pos_type Offset, int SeekType)
{
        switch (SeekType)
        {
                case SeekType_Absolute:
                {
                        // just go there
                        mrSource.Seek(Offset, SeekType);
                }
                break;

                case SeekType_Relative:
                {
                        // Actual underlying file position is 
                        // (mBufferSize - mBufferPosition) ahead of us.
                        // Need to subtract that amount from the seek
                        // to seek forward that much less, putting the 
                        // real pointer in the right place.
                        mrSource.Seek(Offset - mBufferSize + mBufferPosition, 
                                SeekType);
                }
                break;

                case SeekType_End:
                {
                        // Actual underlying file position is 
                        // (mBufferSize - mBufferPosition) ahead of us.
                        // Need to add that amount to the seek
                        // to seek backwards that much more, putting the 
                        // real pointer in the right place.
                        mrSource.Seek(Offset + mBufferSize - mBufferPosition, 
                                SeekType);
                }
        }

        // always clear the buffer for now (may be slightly wasteful)
        mBufferSize = 0;
        mBufferPosition = 0;
}


// --------------------------------------------------------------------------
//
// Function
//              Name:    BufferedStream::Close()
//              Purpose: Closes the underlying stream (not needed)
//              Created: 2003/07/31
//
// --------------------------------------------------------------------------
void BufferedStream::Close()
{
        THROW_EXCEPTION(CommonException, NotSupported);
}


// --------------------------------------------------------------------------
//
// Function
//              Name:    BufferedStream::StreamDataLeft()
//              Purpose: Any data left to write?
//              Created: 2003/08/02
//
// --------------------------------------------------------------------------
bool BufferedStream::StreamDataLeft()
{
        return mrSource.StreamDataLeft();
}

// --------------------------------------------------------------------------
//
// Function
//              Name:    BufferedStream::StreamClosed()
//              Purpose: Is the stream closed?
//              Created: 2003/08/02
//
// --------------------------------------------------------------------------
bool BufferedStream::StreamClosed()
{
        return mrSource.StreamClosed();
}