bitcoin-s/docs/wallet/wallet-rescan.md

title	id
Wallet Rescans	wallet-rescan

With BIP157 you can cache block filters locally to use later for rescans in the case you need to restore your wallets. Our chain project gives us an API with the ability to query for filters.

Rescan from CLI

To execute a rescan from the cli because you are restoring a wallet or it has gotten out of sync is fairly simple.

If you have an empty wallet it can be done by simply calling rescan

./bitcoin-s-cli rescan

If your wallet is not empty then you will need to call it with the force command

./bitcoin-s-cli rescan --force

You can also specify start and stop heights

./bitcoin-s-cli rescan --start <start height> --stop <stop height>

By default, if you do not set the start height, the rescan will begin at your wallet's creation time. If you wish to ignore this and start from genesis use the ignorecreationtime flag

./bitcoin-s-cli rescan --ignorecreationtime

Code Example

You can rescan your wallet with filters with WalletApi.rescanNeutrinoWallet()

To run this example you need to make sure you have access to a bitcoind binary. You can download this with bitcoin-s by doing sbt downloadBitcoind

import org.bitcoins.testkit.BitcoinSTestAppConfig
import org.bitcoins.testkit.fixtures._
import org.bitcoins.testkit.wallet._
import org.bitcoins.server.BitcoinSAppConfig
import org.bitcoins.wallet.config.WalletAppConfig
import akka.actor.ActorSystem
import scala.concurrent.{ExecutionContext, Future, Await}
import scala.concurrent.duration.DurationInt

//we need an actor system and app config to power this
implicit val system: ActorSystem = ActorSystem(s"wallet-rescan-example")
implicit val ec: ExecutionContext = system.dispatcher
implicit val appConfig: BitcoinSAppConfig = BitcoinSTestAppConfig.getNeutrinoTestConfig()
implicit val walletAppConfig: WalletAppConfig = appConfig.walletConf

val bip39PasswordOpt = None
//ok now let's spin up a bitcoind and a bitcoin-s wallet with funds in it
val walletWithBitcoindF = for {
  bitcoind <- BitcoinSFixture.createBitcoindWithFunds()
  walletWithBitcoind <- BitcoinSWalletTest.createWalletWithBitcoindCallbacks(bitcoind, bip39PasswordOpt)
} yield walletWithBitcoind

val walletF = walletWithBitcoindF.map(_.wallet)

val bitcoindF = walletWithBitcoindF.map(_.bitcoind)

//let's see what our initial wallet balance is
val initBalanceF = for {
  w <- walletF
  balance <- w.getBalance()
} yield {
  println(s"Initial wallet balance=${balance}")
  balance
}

//ok great! We have money in the wallet to start,
//now let's delete our internal tables that hold our utxos
//and addresses so that we end up with a 0 balance
val clearedWalletF = for {
  w <- walletF
  _ <- initBalanceF
  clearedWallet <- w.clearAllUtxosAndAddresses()
  zeroBalance <- clearedWallet.getBalance()
} yield {
  println(s"Balance after clearing utxos: ${zeroBalance}")
  clearedWallet
}

//we need to pick how many addresses we want to generate off of our keychain
//when doing a rescan, this means we are generating 100 addrsses
//and then looking for matches. If we find a match, we generate _another_
//100 fresh addresses and search those. We keep doing this until we find
//100 addresses that do not contain a match.
val addrBatchSize = 100
//ok now that we have a cleared wallet, we need to rescan and find our fudns again!
val rescannedBalanceF = for {
  w <- clearedWalletF
  _ <- w.fullRescanNeutrinoWallet(addrBatchSize)
  balanceAfterRescan <- w.getBalance()
} yield {
  println(s"Wallet balance after rescan: ${balanceAfterRescan}")
  ()
}

//cleanup
val cleanupF = for {
  _ <- rescannedBalanceF
  walletWithBitcoind <- walletWithBitcoindF
  _ <- BitcoinSWalletTest.destroyWalletWithBitcoind(walletWithBitcoind)
} yield ()

Await.result(cleanupF, 60.seconds)