This began as a change to improve the fee calculation code and evolved
into a much larger refactor which improves the readability and
modularity of all of the transaction creation code.
Transaction fee calculations have been switched from full increments
of the relay fee to a proportion based on the transaction size. This
means that for a relay fee of 1e3 satoshis/kB, a 500 byte transaction
is only required to pay a 5e2 satoshi fee and a 1500 byte transaction
only need pay a 1.5e3 fee. The previous code would end up estimating
these fees to be 1e3 and 2e3 respectively.
Because the previous code would add more fee than needed in almost
every case, the transaction size estimations were optimistic
(best/smallest case) and signing was done in a loop where the fee was
incremented by the relay fee again each time the actual size of the
signed transaction rendered the fee too low. This has switched to
using worst case transaction size estimates rather than best case, and
signing is only performed once.
Transaction input signature creation has switched from using
txscript.SignatureScript to txscript.SignTxOutput. The new API is
able to redeem outputs other than just P2PKH, so the previous
restrictions about P2SH outputs being unspendable (except through the
signrawtransaction RPC) no longer hold.
Several new public packages have been added:
wallet/txauthor - transaction authoring and signing
wallet/txfees - fee estimations and change output inclusion
wallet/txrules - simple consensus and mempool policy rule checks
Along with some internal packages:
wallet/internal/txsizes - transaction size estimation
internal/helpers - context free convenience functions
The txsizes package is internal as the estimations it provides are
specific for the algorithms used by these new packages.
Rather than the main package being responsible for opening the address
and transaction managers, the namespaces of these components are
passed as parameters to the wallet.Open function.
Additionally, the address manager Options struct has been split into
two: ScryptOptions which holds the scrypt parameters needed during
passphrase key derivation, and OpenCallbacks which is only passed to
the Open function to allow the caller to provide additional details
during upgrades.
These changes are being done in preparation for a notification server
in the wallet package, with callbacks passed to the Open and Create
functions in waddrmgr and wtxmgr. Before this could happen, the
wallet package had to be responsible for actually opening the managers
from their namespaces.
This a refactor of the btcwallet main package to create a new wallet
package.
The main feature of this package is the integration of all the other
wallet components (waddrmgr, txstore, and chain) and the Wallet type is
'runnable', so it will be continuously updating itself against changes
notified by the remote btcd instance.
It also includes several methods which provide access to information
necessary to run a wallet RPC server.
