private async Task <Page> ReadPageAsync(int pageNum, ushort pageSize, CancellationToken cancellationToken)
{
// Sanity checks
if (stream == null)
{
// TODO - create custom exception
throw new Exception("Block store is not open!");
}
// Seek to the proper spot
SeekToPage(pageNum);
// Read the bytes for the page
var bytes = new byte[pageSize];
await stream.ReadAsync(bytes, 0, pageSize);
// Peek at the page type and build the proper page type.
// TODO - a big switch statement is ugly...find a better way.
var pageType = BitConverter.ToUInt16(bytes, 1);
Page page = null;
switch (pageType)
{
case ZeroPage.PageId:
page = new ZeroPage();
break;
case HeaderPage.PageId:
page = new HeaderPage();
break;
default:
throw new Exception($"Unhandled page type: {pageType}.");
}
// Have the page deserialize itself
page.Deserialize(bytes);
// And return whatever we've got.
return(page);
}
/// <summary>
/// Create a new file.
/// </summary>
/// <param name="path">The path of the file.</param>
/// <param name="cancellationToken">The cancellation token.</param>
/// <returns>A task that can be awaited.</returns>
public async Task CreateAsync(string path, CancellationToken cancellationToken)
{
// Create the stream, read/write, no sharing.
stream = new FileStream(path, FileMode.CreateNew, FileAccess.ReadWrite, FileShare.None);
// Set up
// TODO - accept a config lambda to get page size and whatnot
PageSize = 2 * MinPageSize; // TODO - bump default to 4096 or 8192
// Initialize and write the zero-page, which always uses the minimum page size.
var zeroPage = new ZeroPage
{
PageSize = PageSize
};
await WritePageAsync(0, zeroPage, MinPageSize, cancellationToken);
// Write the two header pages.
var header1 = new HeaderPage();
var header2 = new HeaderPage();
await WritePageAsync(1, header1, cancellationToken);
await WritePageAsync(2, header2, cancellationToken);
}