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OP_RETURN on Bitcoin Regtest
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| import bitcoin.main as vitalik # vitalik's bitcoin lib | |
| import bitcoin as bitcoinlib # python-bitcoinlib | |
| import bitcoin.core as bitcoinlibcore | |
| import bitcoin.rpc as bitcoinlibrpc | |
| import bitcoin.transaction as bitcoinlibtransaction | |
| import binascii | |
| import requests | |
| # THIS IS THE MESSAGE TO WRITE ON THE BLOCKCHAIN | |
| msg = "Alberto G. Toribio" | |
| nbrSatIn1BTC = 1e8 | |
| UINT_MAX = 4294967295 # use for sequence number in tx ins | |
| # examle of how to use mainnet | |
| # bitcoinlib.SelectParams('mainnet') | |
| bitcoinlib.SelectParams('regtest') | |
| msgHex = binascii.hexlify(msg.encode('utf-8')).decode('utf-8') | |
| lengthMsg = int(len(msgHex)/2) # length in bytes. 2 hex for 1 byte | |
| lengthMsgHex = hex(lengthMsg) | |
| lengthMsgHex = lengthMsgHex[2:] # remove 0x from the beginning of the string | |
| if len(lengthMsgHex) == 1: | |
| lengthMsgHex = "0" + lengthMsgHex | |
| # OP_RETURN message should be 80 bytes max | |
| if lengthMsg > 80: | |
| print("Your message's size is greater than 80 bytes. Please start again and choose a smaller message. Size: ", lengthMsg, "bytes\n") | |
| quit() | |
| # | |
| # display the balance of the wallet | |
| # | |
| rpc = bitcoinlibrpc.Proxy() | |
| # | |
| # Take the first UXTO found on the wallet | |
| # | |
| listUTXOs = rpc.listunspent(1) | |
| if len(listUTXOs) == 0: | |
| print("There is no UTXO available. Please create an address and send funds to it.\n") | |
| quit() | |
| theUTXO = listUTXOs[0] | |
| # | |
| # Create a new address for the change | |
| # | |
| changeAddress = rpc.getnewaddress() | |
| privKeyChangeAddress = rpc.dumpprivkey(changeAddress) | |
| pubKeyChangeAddress = vitalik.privtopub(privKeyChangeAddress) | |
| hashPubKeyChangeAddress = vitalik.hash160(pubKeyChangeAddress) | |
| # | |
| # fee | |
| # | |
| # length of our transaction with 1 input and 2 outputs including one OP_RETURN is around 200 bytes + the message if the input is compressed, around 230 bytes + the message if the input is not compressed. We pessimistically choose 230 bytes and add the size of the message (80 bytes max). There is no need to be more precise here, as the fee / byte is anyway an estimation. | |
| sizeTX = 230 + lengthMsg # bytes | |
| # estimation of fee as sat/B | |
| feePerByte = rpc._call("estimatesmartfee", 2) # second parameter is the number of blocks we are ok to wait. We choose 2. The result from estimatesmartfee is in BTC/kB | |
| if 'feerate' in feePerByte: # if no error from estimatesmartfee | |
| feePerByte = float(feePerByte['feerate']) * nbrSatIn1BTC / 1000 # BTC/kB -> sat/B | |
| else: # if error from estimatesmartfee, fallback to a call to blockcypher api | |
| urlFeeAPI = "https://api.blockcypher.com/v1/btc/test3" | |
| responseFeeAPI = requests.get(urlFeeAPI) | |
| if responseFeeAPI.ok: | |
| feePerByte = responseFeeAPI.json()['low_fee_per_kb'] / 1000 # sat/kB -> sat/B | |
| else: | |
| feePerByte = 5.0 # if both methods return an error, fallback to 5 sat/B | |
| feeTX = int(feePerByte * sizeTX) # in sat | |
| # stop if fee is too high to avoid losing too much BTC. | |
| if feeTX > 1e6: | |
| print("Fee is too high. There must be an error. Please try again. Fee: ", feeTX, "sat") | |
| quit() | |
| amount = theUTXO['amount'] - feeTX # the amount to send to the change address is the amount of the UTXO minus the fee. | |
| if amount < 0: | |
| print("You chose a UTXO with not enough fund. Please restart and choose a UTXO with more than ", feeTX, "sat\n") | |
| quit() | |
| # | |
| # construct transaction | |
| # | |
| # script 1st output (OP_RETURN) | |
| opReturnScript = "6a" # OP_RETURN | |
| opReturnScript += lengthMsgHex # hex value of length of message | |
| opReturnScript += msgHex # hex value of message | |
| # lock script 2nd output (change address) | |
| lockScriptChangeAddr = "76" # OP_DUP | |
| lockScriptChangeAddr += "a9" # OP_HASH160 | |
| lockScriptChangeAddr += "14" # hex value of length of public key hash (decimal: 20) | |
| lockScriptChangeAddr += hashPubKeyChangeAddress # the hash of pub key of the change address | |
| lockScriptChangeAddr += "88" # OP_EQUALVERIFY | |
| lockScriptChangeAddr += "ac" # OP_CHECKSIG | |
| mainTX = { | |
| 'ins':[ | |
| { | |
| 'script': '', | |
| 'outpoint': { | |
| 'index': theUTXO['outpoint'].n, | |
| 'hash': bitcoinlibcore.b2lx(theUTXO['outpoint'].hash) | |
| }, | |
| 'sequence': UINT_MAX | |
| } | |
| ], | |
| 'outs':[ | |
| { | |
| 'script': opReturnScript, | |
| 'value': 0 | |
| }, | |
| { | |
| 'script': lockScriptChangeAddr, | |
| 'value': amount | |
| } | |
| ], | |
| 'locktime': 0, | |
| 'version': 1 | |
| } | |
| rawMainTX = bitcoinlibtransaction.serialize(mainTX) | |
| ## uncomment the next 3 lines if need to debug the transaction | |
| # deserializedRawMainTX = bitcoinlibtransaction.deserialize(rawMainTX) | |
| # print(deserializedRawMainTX) | |
| # print("\n") | |
| # | |
| # sign raw transaction | |
| # | |
| signedRawMainTX = rpc._call("signrawtransaction", rawMainTX) # I directly call the rpc method instead of using the lib rpc.signrawtransaction function as that function is expecting a transaction object. For the sake of the exercise, I construct the transaction manually. There are other methods to make the transaction, for instance: https://github.com/petertodd/python-bitcoinlib/blob/master/examples/spend-p2pkh-txout.py | |
| # | |
| # send raw transaction | |
| # | |
| sentRawMainTX = rpc._call("sendrawtransaction", signedRawMainTX['hex']) | |
| print("Transaction sent successfully. TXID: ") | |
| print(sentRawMainTX) | |
| print("\n") |
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