public async Task OpenAsync()
{
try
{
await _blob.FetchAttributesAsync();
_commitPosition = Get_Committed_Position();
}
catch (StorageException ex)
{
if (ex.RequestInformation.HttpStatusCode != 404)
throw;
_commitPosition = Position.Start;
}
byte[] lastPage = new byte[PageSize];
if (_commitPosition.ToLinearAddress() != 0)
{
using (var stream = _blob.OpenRead())
{
stream.Seek(_commitPosition.Page * PageSize, SeekOrigin.Begin);
await stream.ReadAsync(lastPage, 0, PageSize);
}
}
_lastPage = new Page(_commitPosition, lastPage);
}
async Task Commit_new_length_if_it_grew(long newLength, Page lastPage)
{
if (_commitPosition.ToLinearAddress() < newLength)
{
await Commit_Position(newLength);
_lastPage = lastPage;
}
}
Page Retrieve_Page_At(int position)
{
if (position == _commitPosition.ToLinearAddress())
return _lastPage;
else
{
var page = new Page(position);
page.FillFromBlob(_blob);
return page;
}
}
async Task<PreparedPages> PreparePages(int position, Stream stream)
{
int count = (int)stream.Length;
int copied = 0;
int currentPosition = position;
int firstPageNumber = position / PageSize;
int lastPageNumber = ((position + count) / PageSize);
Page firstPage = Retrieve_Page_At(position);
Page lastPage = new Page(position + count);
Task lastFilling = null;
if (firstPageNumber == lastPageNumber)
lastPage = firstPage;
else
if (lastPage.GetBaseAddress() < _commitPosition.ToLinearAddress())
lastFilling = lastPage.FillFromBlobAsync(_blob);
var bufferedPages = new StreamJoiner();
if (firstPage.Is_empty_and_can_contain_all_data___or___Is_not_empty(count))
{
copied = firstPage.Append(stream);
bufferedPages.Append(firstPage.ToStream());
currentPosition = position + copied;
}
if (copied < count)
{
int rem;
int fullPages = Math.DivRem(count - copied, PageSize, out rem);
if (fullPages > 0)
{
bufferedPages.Append(stream, copied, count - copied - rem);
copied += fullPages * PageSize;
currentPosition = position + copied;
stream.Seek(copied, SeekOrigin.Begin);
}
if (copied < count)
{
Debug.Assert(rem > 0);
if (lastFilling != null)
await lastFilling;
else
lastPage = new Page(position + copied);
lastPage.Fill_From(stream);
bufferedPages.Append(lastPage.ToStream());
copied += rem;
currentPosition = position + copied;
}
}
Debug.Assert(position + count == currentPosition);
Debug.Assert(copied == count);
return new PreparedPages
{
Position = position,
CurrentPosition = currentPosition,
Pages = bufferedPages,
LastPage = lastPage
};
}
