08_build_and_send.py

# SPDX-License-Identifier: MIT
"""08 - Build, sign, and send a transaction using your node's wallet.

The wallet does the hard parts for you: it selects UTXOs, adds a change output, sets a
fee, signs, and broadcasts. This is the simplest correct way to send. For offline,
library-based building (no node), see the JavaScript recipe 08 (bitcoinjs-lib).

Fund your node's wallet first from cypherfaucet.com.

    RPC_USER=... RPC_PASS=... python 08_build_and_send.py <address> <amount-in-coins>

The amount is in whole coins (BTC/LTC), matching sendtoaddress. The JavaScript recipe
08 takes satoshis instead.
"""
import sys
import requests
from config import RPC_URL, RPC_USER, RPC_PASS


def rpc(method, params=None):
    payload = {"jsonrpc": "1.0", "id": "ex", "method": method, "params": params or []}
    try:
        r = requests.post(RPC_URL, json=payload, auth=(RPC_USER, RPC_PASS), timeout=30)
    except requests.exceptions.RequestException:
        raise SystemExit(f"could not reach your node at {RPC_URL}. is it running with RPC "
                         "enabled? see testnethub.com/run-node")
    if r.status_code == 401:
        raise SystemExit("the node rejected the login: set RPC_USER / RPC_PASS (see testnethub.com/rpc-safety)")
    body = r.json()
    if body.get("error"):
        raise SystemExit(f"the node rejected the call: {body['error']['message']}")
    return body["result"]


if len(sys.argv) < 3:
    sys.exit("usage: python 08_build_and_send.py <address> <amount-in-coins>")
address = sys.argv[1]
try:
    amount = float(sys.argv[2])
except ValueError:
    sys.exit("amount must be a number in coins, e.g. 0.001")

# One call that builds + funds + signs + broadcasts. If you want to see each step,
# the explicit path is: createrawtransaction -> fundrawtransaction ->
# signrawtransactionwithwallet -> sendrawtransaction.
txid = rpc("sendtoaddress", [address, amount])
print(f"sent {amount} to {address}")
print(f"txid: {txid}")
print(f"watch it: python 06_watch.py {txid}")