/// <summary>
/// Return the start offset for piece number pieceNumber.
/// </summary>
/// <remarks>
/// pieceNumber is assumed to be a valid number. If it isn't, an assertion will fail.
/// </remarks>
internal long GetStartOffset(int pieceNumber)
{
//Make sure that the stream has been initialized for this piece number
PieceStreamInfo pieceStreamInfo = RetrievePiece(pieceNumber);
return(pieceStreamInfo.StartOffset);
}
//------------------------------------------------------
//
// Internal Methods
//
//------------------------------------------------------
/// <summary>
/// Given an offset in the part, locate the piece that contains it.
/// </summary>
internal int GetPieceNumberFromOffset(long offset)
{
// Find the piece whose range includes offset.
PieceStreamInfo temporaryPieceInfo = new PieceStreamInfo(_temporaryMemoryStream, offset);
int pieceNumber = _pieceStreamInfoList.BinarySearch(temporaryPieceInfo);
if (pieceNumber >= 0)
{
// Found the piece that starts at offset 'offset'.
return(pieceNumber);
}
// ~pieceNumber represents the place at which we would insert a piece starting at offset.
// offset belongs therefore to the preceding piece.
pieceNumber = (~pieceNumber - 1);
// If the list contains data about pieces following pieceNumber, then we know offset precedes those
// and is therefore in the scope of the piece at pieceNumber.
if (pieceNumber < _indexOfLastPieceStreamInfoAccessed)
{
return(pieceNumber);
}
// The following tests may have to be repeated until we load enough descriptors to cover offset.
// If there is no error in part numbering, we'll eventually find either the last part
// or an intermediate part whose range contains offset.
while (pieceNumber < _lastPieceIndex)
{
// Make sure we have a descriptor and stream for piece pieceNumber.
PieceStreamInfo currentPieceInfo = RetrievePiece(pieceNumber);
// If the piece at pieceNumber is not expandable, then its length has to be taken into account.
// currentPieceInfo.Stream is guaranteed to be non-null
if (offset < checked (currentPieceInfo.StartOffset + currentPieceInfo.Stream.Length))
{
break;
}
// offset is not covered by any piece whose descriptor has been loaded.
// Keep loading piece descriptors.
checked
{
++pieceNumber;
}
}
// If pieceNumber is the number of the last piece in the part, it is expandable and therefore
// contains offset.
// Else the pieceNumber should be less than the _lastPieceIndex
Invariant.Assert(pieceNumber <= _lastPieceIndex, "We should have found the valid pieceNumber earlier");
return(pieceNumber);
}
//------------------------------------------------------
//
// Private Methods
//
//------------------------------------------------------
/// <summary>
/// Return the descriptor for piece number pieceNumber.
/// This method does lazy initializations of the streams corresponding
/// to the pieces that make up the part.
/// </summary>
/// <remarks>
/// pieceNumber is assumed to be a valid number. If it isn't, an assertion will fail.
/// </remarks>
private PieceStreamInfo RetrievePiece(int pieceNumber)
{
if (pieceNumber > _lastPieceIndex)
{
throw new ArgumentException(SR.Get(SRID.PieceDoesNotExist));
}
if (_indexOfLastPieceStreamInfoAccessed >= pieceNumber)
{
return(_pieceStreamInfoList[pieceNumber]);
}
// The search below supposes the list is initially non-empty.
// This invariant is enforced by the constructor.
// Load descriptors for all pieces from _indexOfLastPieceStreamInfoAccessed+1 through pieceNumber.
PieceStreamInfo currentPieceStreamInfo = _pieceStreamInfoList[_indexOfLastPieceStreamInfoAccessed];
//we retrieve piece streams "upto the requested piece number" rather than getting just the
//stream corresponding "to the requested piece number" for the following two reasons -
//a. We need to be able to calculate the correct startOffset and as such need the lengths
// of all the intermediate streams
//b. We also want to make sure that the intermediate streams do exists as it would be an
// error if they are missing or corrupt.
for (int i = _indexOfLastPieceStreamInfoAccessed + 1; i <= pieceNumber; ++i)
{
// Compute StartOffset.
long newStartOffset = checked (currentPieceStreamInfo.StartOffset + currentPieceStreamInfo.Stream.Length);
// Compute pieceInfoStream.Stream.
Stream pieceStream = _sortedPieceInfoList[pieceNumber].ZipFileInfo.GetStream(
_fileMode, _fileAccess);
// Update _pieceStreamInfoArray.
_indexOfLastPieceStreamInfoAccessed = i;
currentPieceStreamInfo = new PieceStreamInfo(pieceStream, newStartOffset);
// !!!Implementation Note!!!
// List<> always adds the new item at the end of the list.
// _sortedPieceInfoList is sorted by the piecenumbers and so, when we add
// members to _pieceStreamInfoList they also get added in a sorted manner.
// If every the implementation changes, we must make sure that the
// _pieceStreamInfoList still remains sorted by the piecenumbers as we
// perform a binary search on this list in GetPieceNumberFromOffset method
_pieceStreamInfoList.Add(currentPieceStreamInfo);
}
return(_pieceStreamInfoList[pieceNumber]);
}
/// <summary>
/// This method is called to implement SetLength. If it changes
/// the actual last piece, the next call to flush will perform the
/// necessary renaming and deletion(s).
/// </summary>
internal void SetLogicalLastPiece(int pieceNumber)
{
//The Logical piece that we are setting should not be greater than the
//last piece index
Invariant.Assert(pieceNumber <= _lastPieceIndex);
//Make sure that the stream has been initialized for this piece number
PieceStreamInfo piece = RetrievePiece(pieceNumber);
// Update _lastPiece and record whether this invalidates physical pieces.
if (_lastPieceIndex > pieceNumber)
{
_logicalEndPrecedesPhysicalEnd = true;
_lastPieceIndex = pieceNumber;
// To avoid any potential for confusion, remove any invalidated piece from _pieceStreamInfoArray.
_indexOfLastPieceStreamInfoAccessed = _lastPieceIndex;
_pieceStreamInfoList.RemoveRange(_indexOfLastPieceStreamInfoAccessed + 1, _pieceStreamInfoList.Count - (_indexOfLastPieceStreamInfoAccessed + 1));
}
}
