* Allow Storage Backends to do their own Hashing
- Describes an optional interface 'SelfHashing' that a storage backend's type implementing 'PieceImpl' may also implement in order to calculate piece hashsums itself.
- Alters the 'hashPiece' function in the torrent package to look for types implementing 'SelfHashing' . If not implemented, calculate the hash as usual.
It was incorrect to assume piece hashing only operates on incomplete chunk data. This actually uncovered a bug where duplicate hash checks occurred, and the redundant checks would fail due to not reading the completed data.
This is now necessary because bolt doesn't allow multiple DB handles, so the bolt piece completion DB instance must be at the client level. The new method is not currently used from the Client however, this maybe necessary to avoid leaks.
This allows lots of behaviour to be baked into the new Client, Torrent and Piece wrappers, rather than duplicating (badly) them in all the backend implementations.
Matt Joiner
Alex Sharov
Zilog8