first_same_block_spend.py

"""Find first block has a TXO created and spent in the same block

Using a remote API because this should be a fast search early in the blockchain
"""
import json
from time import sleep
import requests

BLOCK_HEIGHT_URL = "https://blockchain.info/block-height/{height}?format=json"
TX_INDEX_URL = "https://blockchain.info/tx-index/{tx_index}/{txo_n}?format=json"
TX_URL = "https://blockchain.info/tx/{txid}?format=json"

NUM_TRIES = 10

class NoMoreTriesError(Exception):
    """Ran out of tries"""
    pass

def _get_json(url):
    tries = NUM_TRIES
    while tries > 0:
        resp = requests.get(url)
        if hasattr(resp, 'status_code') and resp.status_code == 200 and hasattr(resp, 'text'):
            return json.loads(resp.text)
        print "\tFailed to fetch {url}".format(url=url)
        sleep(1)
        tries -= 1
    raise NoMoreTriesError('{tries} failures in a row. Stopping!'.format(
        tries=NUM_TRIES))


def _main():
    height = 0
    while True:
        print "Checking block at height {height} for same-block spends".format(
            height=height)
        block_height_json = _get_json(BLOCK_HEIGHT_URL.format(height=height))
        assert 'blocks' in block_height_json
        assert len(block_height_json['blocks']) == 1
        block = block_height_json['blocks'][0] #one authoritative block at each height
        assert 'tx' in block
        assert 'hash' in block
        #block_hash = block['hash']
        for txn in block['tx']:
            #go through each tx spent and see if prev_out mined in same block
            if 'inputs' in txn:
                for inpt in txn['inputs']:
                    if 'prev_out' in inpt:
                        tx_index = inpt['prev_out']['tx_index']
                        txo_n = inpt['prev_out']['n']
                        tx_index_json = _get_json(TX_INDEX_URL.format(
                            tx_index=tx_index, txo_n=txo_n))

                        #sanity checks
                        assert 'out' in tx_index_json
                        assert len(tx_index_json['out']) >= txo_n + 1

                        assert 'block_height' in tx_index_json
                        int(tx_index_json['block_height'])
                        if tx_index_json['block_height'] == height:
                            tx_hash = tx_index_json['hash']
                            print("Found transaction created and spent at "
                                  "block height {height}").format(height=height)
                            print "\tBlockchain.info tx_index: {index}".format(
                                index=tx_index)
                            print "\ttxid:{hash}".format(hash=tx_hash)
                            print "\ttxo_n:{txo_n}".format(txo_n=txo_n)
        height += 1

if __name__ == '__main__':
    _main()