Prior to this change, it's necessary to implement the entirety of the
`WalletRead` trait in order to be able to use the input selection
functionality provided by `zcash_client_backend::data_api::input_selection`.
This change factors out the minimal operations required for transaction
proposal construction to better reflect the principle of least authority
and make the input selection code reusable in more contexts.
In order to minimize the operations of the newly-created `InputSource`
and `ShieldingSource` traits, this change also removes the
`min_confirmations` field from transaction proposals, in favor of
storing explicit target and anchor heights. This has the effect of
limiting the lifetime of transaction proposals to `PRUNING_DEPTH -
min_confirmations` blocks.
The MSRV for the main crates is 1.65, which is higher than the Rust
version that stabilised workplace dependencies (1.64). The implicit MSRV
for the component crates is still lower than this, so we don't migrate
these crates.
Now that the librustzcash crate has been removed from the repository and
workspace, there are no crates that generate binary artifacts, and cargo
ignores Cargo.lock when publishing library crates.
Uses the addchain crate to obtain an addition chain for the exponent,
and then generates the corresponding constant-time square-and-multiply
algorithm.
The main design goals of this mmr implementation were
1. Avoid database callbacks. As it is implemented, calling side must just smartly pre-load MMR nodes from the database (about log2(tree length) for append, twice as much for deletion).
2. Reuse as much code/logic between rust and c++ clients.
3. Close to zero memory consumption.
Checking for spent notes in a block is still not completely constant
time, due to filtering out negative results of the constant-time
comparison.
Part of #84.