In preparation for out-of-order range-based scanning, it is necessary
to ensure that the size of the Sapling note commitment tree is carried
along through the scan process and that stored blocks are always
persisted with the updated note commitment tree size.
Local chain validation will be performed internal to
`scan_cached_blocks`, and as handling of chain reorgs will need to
change to support out-of-order scanning, the `validate_chain` method
will be superfluous. It is removed in advance of other changes in order
to avoid updating it to reflect the forthcoming changes.
This better reflects the semantics of wallet behavior. Also, this
adds a `zcash_client_backend::WalletRead::get_min_unspent_height`
method that replaces the deprecated & removed (and misleadingly
named) `get_rewind_height` method.
This change makes it possible for wallets using the
`zcash_client_backend::data_api::wallet` module to perform transaction
preparation, including input selection and fee calculation, as an
independent step prior to creating proofs and signatures. This can be
used to improve user experience by making it possible to report the
proposed effects of the transaction to the wallet user (including
privacy implications) prior to authorizing the transaction.
This allows callers to validate smaller intervals of the given
`BlockSourceT` shortening processing times of the function call at the
expense of obtaining a partial result on a given section of interest of
the block source.
`params: &ParamsT` has been removed from the arguments since they were
only needed to fall back to `sapling_activation_height` when `None` as
passed as the `validate_from` argument. Passing `None` as validation
start point on a pre-populated `block_source` would result in an error
`ChainError::block_height_discontinuity(sapling_activation_height - 1, current_height)`
With this new API callers must specify a concrete `validate_from`
argument and assume that `validate_chain` will not take any default
fallbacks to chain `ParamsT`.
The addition of a `limit` to the chain validation function changes the
meaning of its successful output, being now a `BlockHeight, BlockHash)`
tuple indicating the block height and block hash up to which the chain
as been validated on its continuity of heights and hashes. Callers
providing a `limit` aregument are responsible of subsequent calls to
`validate_chain()` to complete validating the remaining blocks stored on
the `block_source`.
Closeszcash/librustzcash#705
The MSRVs of the component crates are left as-is, partly because our
dependencies don't require us to bump them, and partly because those
crates have no pending changes and are relatively stable. We also plan
to split the component crates out into a separate repository, where it
will be easier to have a separate MSRV.
Closeszcash/librustzcash#759.
Kris Nuttycombe
Kris Nuttycombe
Jack Grigg
Francisco Gindre