Adding bech32 spending example

[mrx23dot]

Please add native-segwit utxo signing example.
I couldn't find any other python lib that would support signing this.

[dgpv]

You can look into python-elementstx examples for the code that spends p2wsh address: https://github.com/Simplexum/python-elementstx/blob/4858587d27c9cdc16eb4d1556f95be33e7406abe/examples/confidential-cross-chain-atomic-swap.py#L602-L646

or look into implementation of PartiallySignedTransaction.sign() - it has code that signs various types of inputs.

more example code is of course welcome if you or anyone are willing to create that.

[mrx23dot]

Thank you, I will give it a go.

[mrx23dot]

Some minimal help would be appreciated, all I'm trying to do is transfer from bc1xx to bc1xx.

No idea what to do with these, big example mentions 3 alice,bob and contract keys.

  spend_key=None # from privkeyBytes parameter ?
  btc_contract='?'

I guess branch_condition true is to not to use lock times.
Do we know the numof vBytes in advance to calculate the fee?

This is what I have:

from bitcointx.wallet import CCoinAddress
from bitcointx.core import CMutableTransaction,CTxIn, CTxOut,COutPoint,lx,CTxInWitness
from bitcointx.core.script import SIGHASH_ALL,SIGVERSION_WITNESS_V0, DATA,CScriptWitness,CBitcoinScript

def sweep_bech32_tx(utxos, toAddrStr, privkeyB, feeSat=200):

  spend_key=None # from privkeyB parameter ?
  btc_contract='?'

  in_amount = sum([amntSat for txid,vout_n,amntSat in utxos])
  out_amount = in_amount - feeSat

  # Create the unsigned transaction.
  tx = CMutableTransaction(
    vin=[CTxIn(prevout=COutPoint(hash=lx(txid), n=vout_n)) for txid,vout_n,amntSat in utxos],

    vout=[CTxOut(nValue=out_amount, scriptPubKey=CCoinAddress(toAddrStr).to_scriptPubKey())]
  )
  cond = b'\x01' # branch_condition true
  # We used P2WSHCoinAddress to create the address that we sent bitcoin to, so we know that we need to use SIGVERSION_WITNESS_V0
  sighash = btc_contract.sighash(tx, 0, SIGHASH_ALL, amount=in_amount, sigversion=SIGVERSION_WITNESS_V0)
  spend_sig = spend_key.sign(sighash) + bytes([SIGHASH_ALL])
  # This is script witness, not script. The condition for OP_IF
  # in our script is directly encoded as data in the witness.
  # We cannot use OP_TRUE/OP_FALSE here. We use DATA guard is to ensure that.
  witness = CScriptWitness([spend_sig, DATA(cond), btc_contract])
  # empty scriptSig, because segwit
  tx.vin[0].scriptSig = CBitcoinScript([])
  # all data to check the spend conditions is in the witness
  tx.wit.vtxinwit[0] = CTxInWitness(witness)
  # VerifyScript not working
  return tx

# inputs: (txid, vout_n, amntSat)
utxos = [
  ('097fed228b1c4afb9dc8df2ae137e4be5e1c1376541c2db3b1c74a6166e7842b', 0, 178876), 
]
tx = sweep_bech32_tx(utxos, toAddrStr='bc1..', privkeyB=bytes.fromhex('11'*32))
print(tx) 

[dgpv]

Hmm, I guess linking to python-elementstx example was not helpful, because that example uses custom bitcoin scripts and that is not the same as signing simple keypath spending.

You probably better use PartiallySignedTransaction's sign() method, you can create psbt from CTransaction like in this test code: https://github.com/Simplexum/python-bitcointx/blob/master/bitcointx/tests/test_psbt.py#L401 and then call psbt.sign(keystore) where keystore is an instance of KeyStore which contains your keys