Things to change in v4 (maybe)

[sappenin]

• Transaction Flags are technically optional, so the Java API should make them optional in each Transaction child class.
  • E.g., in Payment, the API should be Optional<PaymentFlags> flags() with the default implementation removed.
  • This is more idiomatically Java than the v3 solution, which was implemented via Allow for empty/omitted transaction flags #425.
  • Note that LedgerObject flags are not optional, so we need to make sure that classes like AccountRootObject do not make their flags Optional.
  • For Transaction objects, builder.build() should by default have an empty flags in it.
  • For LedgerObjects, builder.build() should by default have flags set to Flags.UNSET because these objects always have flags, but by default they're 0.
  • For all builders, we remove the concept of tfFullyCanonicalSig (e.g., here).
• Consider making the default LedgerSpecifier in any request builder to be LedgerSpecifier.VALIDATED instead of LedgerSpecifier.CURRENT.
• Remove Secp256k1.java which was deprecated as part of Fixes #446 (Consistent secp256k1 Curve) #447
• Consider concrete subclasses of TransactionMetadata for NFTs (fields added here); Payments (delivered_amount); and metadata that shows up in all transactions.
• Add an UnknownTransaction object that can take the place of a transaction that xrpl4j doesn't yet support. For example, loading ledgers (and transactions) from the Hooks devnet should not blow-up (but currently they would).
• Implement: Add optional support for XRPL API v2 #481
• Add overt input length checks into PublicKey constructors (similar to the constructors for PrivateKey)
• Consider a new type of wrapper that enforces the number of bytes (e.g., PrivateKeyUnsignedByteArray) that gives a value, and a paddedValue, or similar? See Inconsistent Length of Private Key Byte Array in deriveKeyPair Method #486 for inspiration.

[sappenin]

Consider this list for any new API endpoints or breaking changes: https://github.com/XRPLF/rippled/issues?q=label%3A%22API+Change%22+is%3Aclosed