Incorrect Seek Operations in SftpFileStream #909
Description
When SftpFileStream.Seek() is called with the origin parameter set to SeekOrigin.End and a negative offset, the resulting position is greater than the size of the stream. This is because the negative offset is subtracted from the total size, instead of added.
size offset
1000 - (-42) = 1042
1000 + (-42) = 958
Failed test using SftpFileStream.Seek():
FluentAssertions.Execution.AssertionFailedException
HResult=0x80131500
Message=Expected stream.Seek(-5, SeekOrigin.End) to be 22L, but found 32L.
Furthermore, the tests for SftpFileStream only cover cases with the origin set to SeekOrigin.Begin, and not SeekOrigin.Current or SeekOrigin.End.