This check does not have any impact on existing apps as in full verification mode the UTXO set is already effectively performing this check, and general SPV wallets don't verify inputs meaningfully anyway (they could just be random). However it's useful for Lighthouse and can't hurt - a tx with a duplicated outpoint is always invalid.
Instead of useDummySignatures flag there is now a MissingSigMode enum
allowing to specify what to do with missing signatures.
Available modes:
USE_OP_ZERO - do nothing. OP_0 will be left in place of missing
signature
USE_DUMMY_SIG - insert dummy signature in place of missing sig.
THROW - throw an exception. It would be either MissingSignatureException
for P2SH or MissingPrivateKeyException for other tx types
Default mode is USE_DUMMY_SIG (for backward compatibility)
Transaction inputs are now prepopulated with empty scriptSig. Each signer
is expected to update this scriptSig with a signature at a proper place.
There is a new method in RedeemData to locate index of the key/signature
within scriptSig/program.
To generalize an above approach for all supported types of inputs,
RedeemData can now represent data for any type of input. For
pay-to-address and pay-to-pubkey inputs it is expected to contain single
key and CHECKSIG program.
Signers now accept ProposedTransaction object that could carry additional
metadata shared between signers. For now it shares derivation path of the
signing key.
To preserve the dummy sig feature, a new flag was introduced in a SendRequest.
It specifies whether to fill empty sigs with dummies during tx completion
or not. Default value is true (for backward compatibility).
There is a CustomTransactionSigner class that may be used as a base for
simple third-party signers (or may be not). It is used in unit test which
may be treated as a usage example.
In the end the API evolved in such a way that changing this param isn't that useful. To do contracts you tend to work with transactions directly, and a Wallet subclass that needs to do special signing by default can override the signing engine used.
Introduced pluggable signers notion. Instances of
TransactionSigner could be added into the wallet, so that they subsequently
applied to transaction to complete it.
Existing signing code (Transaction.signInputs) was refactored into
LocalTransactionSigner, which is always implicitly added to any wallet.
Related pull request: #157
We were not previously triggering lookahead before calculating a Bloom filter, which means we might have missed transactions in some edge cases. Add a test to catch this and then fix up various unit tests to have fewer magic numbers and be more robust to changes.
For partial scriptSig OP_0 is used as a signature placeholder:
Pay-to-address: OP_0 [pubkey]
Pay-to-pubkey: OP_0
P2SH with 2-of-3 CHECKMULTISIG: OP_0 OP_0 OP_0 [redeem script]
Previously the codepath that was supposed to mark keys as used didn't work, and the lookahead calculation wasn't quite right. Now the current key advances correctly when an inbound tx is found that spends to it, including pending transactions. Additionally the lookahead zone now has the threshold zone after it, not inside it, meaning that if you request a lookahead size of 100 keys you'll actually always have at least 100 keys, never less.
