Viacoin Core 0.16.3

Downgrading warning

Wallets created in 0.16.3 and later are not compatible with versions prior to 0.16.3
and will not work if you try to use newly created wallets in older versions. Existing
wallets that were created with older versions are not affected by this.

Segwit Wallet

Viacoin Core 0.16.3 introduces full support for segwit in the wallet and user interfaces. A new -addresstype argument has been added, which supports legacy, p2sh-segwit (default), and bech32 addresses. It controls what kind of addresses are produced by getnewaddress, getaccountaddress, and createmultisigaddress. A -changetype argument has also been added, with the same options, and by default equal to -addresstype, to control which kind of change is used.

A new address_type parameter has been added to the getnewaddress and addmultisigaddress RPCs to specify which type of address to generate.
A change_type argument has been added to the fundrawtransaction RPC to override the -changetype argument for specific transactions.

• All segwit addresses created through getnewaddress or *multisig RPCs explicitly get their redeemscripts added to the wallet file. This means that downgrading after creating a segwit address will work, as long as the wallet file is up to date.
• All segwit keys in the wallet get an implicit redeemscript added, without it being written to the file. This means recovery of an old backup will work, as long as you use new software.
• All keypool keys that are seen used in transactions explicitly get their redeemscripts added to the wallet files. This means that downgrading after recovering from a backup that includes a segwit address will work

Note that some RPCs do not yet support segwit addresses. Notably, signmessage/verifymessage doesn't support segwit addresses, nor does importmulti at this time. Support for segwit in those RPCs will continue to be added in future versions.

P2WPKH change outputs are now used by default if any destination in the transaction is a P2WPKH or P2WSH output. This is done to ensure the change output is as indistinguishable from the other outputs as possible in either case.

BIP173 (Bech32) Address support ("via1..." addresses)

Full support for native segwit addresses (BIP173 / Bech32) has now been added.
This includes the ability to send to BIP173 addresses (including non-v0 ones), and generating these
addresses (including as default new addresses, see above).

A checkbox has been added to the GUI to select whether a Bech32 address or P2SH-wrapped address should be generated when using segwit addresses. When launched with -addresstype=bech32 it is checked by default. When launched with -addresstype=legacy it is unchecked and disabled.

HD-wallets by default

Due to a backward-incompatible change in the wallet database, wallets created
with version 0.16.3 will be rejected by previous versions. Also, version 0.16.3
will only create hierarchical deterministic (HD) wallets. Note that this only applies
to new wallets; wallets made with previous versions will not be upgraded to be HD.

Wallets directory configuration (-walletdir)

Viacoin Core now has more flexibility in where the wallets directory can be
located. Previously wallet database files were stored at the top level of the
viacoin data directory. The behavior is now:

• For new installations (where the data directory doesn't already exist),
  wallets will now be stored in a new wallets/ subdirectory inside the data
  directory by default.
• For existing nodes (where the data directory already exists), wallets will be
  stored in the data directory root by default. If a wallets/ subdirectory
  already exists in the data directory root, then wallets will be stored in the
  wallets/ subdirectory by default.
• The location of the wallets directory can be overridden by specifying a
  -walletdir=<path> option where <path> can be an absolute path to a
  directory or directory symlink.

Care should be taken when choosing the wallets directory location, as if it
becomes unavailable during operation, funds may be lost.

Performance: SHA256 assembly enabled by default

The SHA256 hashing optimizations for architectures supporting SSE4, which lead to ~50% speedups in SHA256 on supported hardware (~5% faster synchronization and block validation), have now been enabled by default. In previous versions they were enabled using the --enable-experimental-asm flag when building, but are now the default and no longer deemed experimental.

RPC changes

New rescanblockchain RPC

A new RPC rescanblockchain has been added to manually invoke a blockchain rescan.
The RPC supports start and end-height arguments for the rescan, and can be used in a
multiwallet environment to rescan the blockchain at runtime.

New savemempool RPC

A new savemempool RPC has been added which allows the current mempool to be saved to
disk at any time to avoid it being lost due to crashes / power loss.

Safe mode disabled by default

Safe mode is now disabled by default and must be manually enabled (with -disablesafemode=0) if you wish to use it. Safe mode is a feature that disables a subset of RPC calls - mostly related to the wallet and sending - automatically in case certain problem conditions with the network are detected. However, developers have come to regard these checks as not reliable enough to act on automatically. Even with safe mode disabled, they will still cause warnings in the warnings field of the getneworkinfo RPC and launch the -alertnotify command.

Renamed script for creating JSON-RPC credentials

The share/rpcuser/rpcuser.py script was renamed to share/rpcauth/rpcauth.py. This script can be
used to create rpcauth credentials for a JSON-RPC user.

Validateaddress improvements

The validateaddress RPC output has been extended with a few new fields, and support for segwit addresses (both P2SH and Bech32). Specifically:

• A new field iswitness is True for P2WPKH and P2WSH addresses ("bc1..." addresses), but not for P2SH-wrapped segwit addresses (see below).
• The existing field isscript will now also report True for P2WSH addresses.
• A new field embedded is present for all script addresses where the script is known and matches something that can be interpreted as a known address. This is particularly true for P2SH-P2WPKH and P2SH-P2WSH addresses. The value for embedded includes much of the information validateaddress would report if invoked directly on the embedded address.
• For multisig scripts a new pubkeys field was added that reports the full public keys involved in the script (if known). This is a replacement for the existing addresses field (which reports the same information but encoded as P2PKH addresses), represented in a more useful and less confusing way. The addresses field remains present for non-segwit addresses for backward compatibility.
• For all single-key addresses with known key (even when wrapped in P2SH or P2WSH), the pubkey field will be present. In particular, this means that invoking validateaddress on the output of getnewaddress will always report the pubkey, even when the address type is P2SH-P2WPKH.

Low-level changes

• The deprecated RPC getinfo was removed. It is recommended that the more specific RPCs are used:
  • getblockchaininfo
  • getnetworkinfo
  • getwalletinfo
  • getmininginfo
• The wallet RPC getreceivedbyaddress will return an error if called with an address not in the wallet.
• The wallet RPC addwitnessaddress was deprecated and will be removed in version 0.17,
  set the address_type argument of getnewaddress, or option -addresstype=[bech32|p2sh-segwit] instead.
• dumpwallet now includes hex-encoded scripts from the wallet in the dumpfile, and
  importwallet now imports these scripts, but corresponding addresses may not be added
  correctly or a manual rescan may be required to find relevant transactions.
• The RPC getblockchaininfo now includes an errors field.
• A new blockhash parameter has been added to the getrawtransaction RPC which allows for a raw transaction to be fetched from a specific block if known, even without -txindex enabled.
• The decoderawtransaction and fundrawtransaction RPCs now have optional iswitness parameters to override the
  heuristic witness checks if necessary.
• The walletpassphrase timeout is now clamped to 2^30 seconds.
• Using addresses with the createmultisig RPC is now deprecated, and will be removed in a later version. Public keys should be used instead.
• Blockchain rescans now no longer lock the wallet for the entire rescan process, so other RPCs can now be used at the same time (although results of balances / transactions may be incorrect or incomplete until the rescan is complete).
• The logging RPC has now been made public rather than hidden.
• An initialblockdownload boolean has been added to the getblockchaininfo RPC to indicate whether the node is currently in IBD or not.
• minrelaytxfee is now included in the output of getmempoolinfo

Miner block size removed

The -blockmaxsize option for miners to limit their blocks' sizes was
deprecated in version 0.15.1, and has now been removed. Miners should use the
-blockmaxweight option if they want to limit the weight of their blocks'
weights.

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