web3 | Ethereum Blockchain | TestRPC | Python 3

# Author............: Noelle Milton Vega

# Creation Date.....: 01/04/2016 (Monday)

# Description.......: Foundations for Blockchain and Smart-Contracts via Ethereum Crypto/Network.

# A programmatic perspective.

import web3

import random, string, pprint, sys

# ============================================================================

# Ethereum is a specification of RPC methods that client-libraries can implement.

# testrpc(8) is one such library, and it has nodejs and Python implementations,

# respectively, testrpc and testrpc-py. We are using testrpc-py here.

# It is started and running in the background like this:

# nmvega@fedora$ testrpc-py | ganache-*.AppImage

# ============================================================================

#endpoint = 'http://localhost:8545' # Testrpc or Ganache-cli

#endpoint = 'https://ropsten.infura.io/v3/myHash' # Infuria TestNet (One of three offered).

endpoint = 'http://localhost:7545' # Ganache UI: https://truffleframework.com/ganache

w3 = web3.Web3(web3.providers.rpc.HTTPProvider(endpoint))

# ============================================================================

# Various helper functions used later on ...

# ============================================================================

# ----------------------------------------------------------------------------

# From the list() of 10-accounts returned by testrpc(8), provide a public

# key for the desired account to get its current ETH balance.

# ----------------------------------------------------------------------------

accnt_ETH_balance = lambda account: w3.fromWei(w3.eth.getBalance(account), 'ether')

# ----------------------------------------------------------------------------

# Print accounts and their balances in ETH ...

# ----------------------------------------------------------------------------

def get_balances():

for accnt_pubKey in w3.eth.accounts:

print('%s ETH balance: %s' % (accnt_pubKey, accnt_ETH_balance(accnt_pubKey)))

# ----------------------------------------------------------------------------

# A function to build a transaction JSON/dict() data structure from a transaction

# attributes-tuple that specifies the following (noting that 'metaData' is

# optional): (srcAccnt, dstAccnt, ethValue, gas, gasPrice, metaData)

# ----------------------------------------------------------------------------

build_txn = lambda txn_attribs_tuple : { "to" : txn_attribs_tuple[1],

"value" : txn_attribs_tuple[2],

"gas" : txn_attribs_tuple[3],

"gasPrice" : txn_attribs_tuple[4],

"nonce" : w3.eth.getTransactionCount(txn_attribs_tuple[0]),

"data" : b'' if len(txn_attribs_tuple) < 6 else txn_attribs_tuple[5] }

# ----------------------------------------------------------------------------

# Creates a "signable" equivalent of transaction JSON/dict() by converting

# VALUES for all KEYS (except "from" and "to" keys) into Hexadecimal equivalent

# values. This is the RAW representation, and is required for sending raw

# transactions (useful when pre-signing them). Note: We never use this function

# because higher level abstractions in the Web3 library do this under the hood.

# It is included here just for knowledge and completeness. =:)

# ----------------------------------------------------------------------------

txn_raw = lambda txn: { k : v if k in ("from", "to") else w3.toHex(v)

for (k,v) in txn.items() }

# ============================================================================

# Using Web3 to generate a PUBLIC/PRIVATE blockchain keypair. DEMO ONLY!

# ============================================================================

# Note: Please read BITCOIN IMPROVEMENT PROGRAM (BIP) and ETHEREUM IMPROVEMENT

# PROGRAM (EIP) for best-practices on key pair generation.

# ============================================================================

# Note that w3.eth.account.create() generates a different account object each

# time it's run; even if a 'seed' were omitted (which we added to help randomness).

# ============================================================================

seed = ''.join(random.choices(string.printable, k=128))

pub_priv_address_pair = w3.eth.account.create(seed) # Not idempotent. Good!

public_key = pub_priv_address_pair.address[2:].lower() # 40-hex-chars (0x prefix removed)

private_key = pub_priv_address_pair.privateKey.hex()[2:].lower() # 64-hex-chars (0x prefix removed)

# ============================================================================

# Ex: public_key = 46FC666ea7a328.............. (length 40)

# private_key = 8107d1756216623a0f2611bf.... (length 64)

# Check if public-key has ever been used on blockchain: https://etherscan.io

# Not being present on a Blockchain doesn't mean it hasn't been assigned!

# ============================================================================

# ETH, WEI and GAS mathematics ...

# Charging ETH/WEI for operations (ops) on Ethereum has two perposes:

# ============================================================================

# 1) Prevents DDoS attacks. Per "Touring's Halting Problem", there's no way

# to determine if a combination PROGRAM + INPUTS will ever terminate.

# So running out of GAS will halt it.

#

# 2) Compensate miners for transactions that do not involve Cryptocurrency

# exchange. Example: If a miner is mining the insertion of a medical

# record onto the blockchain, there's no fraction of cryptocurrency that

# he can take. Eth/Wei solves this.

# ============================================================================

# https://is.gd/evm_op_codes # OP-Code definitions.

# https://is.gd/evm_gas_costs # GAS cost for each OP-Code.

# ============================================================================

# Example: A "Generate Transaction" op (op-code 'GTX') costs 21,000 GAS. So

# if a transaction, say, transfers currency (or whatever item of value) from

# one account to another, it always costs 21,000 GAS. The unit-cost of GAS in

# Eth/Wei is what varies over time. To see the current price of Gas in Wei

# visit: https://ethstats.net

# ============================================================================

GTX_op_gasCost = 21000 # 21,000 Gas for an Ethereum "Transaction".

gwei_per_unit_gas = 1.11 # Update this from: https://ethstats.net

wei_per_unit_gas = w3.toWei(gwei_per_unit_gas, 'gwei')

wei_per_GTX_op = wei_per_unit_gas * GTX_op_gasCost

eth_per_GTX_op = w3.fromWei(wei_per_GTX_op, 'ether')

#print(eth_per_GTX_op) # 0.00002331 Eth. Now go to web and convert this to U.S. dollars.

# ============================================================================

# Send transactions to blockchain: AUTO-SIGNED and MANUAL-SIGNED variants ...

# ============================================================================

# Ethereun Transaction (op-code GTX): Send 1.0 Eth from account1 to account2.

# Note: Get account1_privKey from testrpc/Ganache UI. Not possible to get programmatically!

# ============================================================================

account1_privKey = '..... 64-character Hexadecimal string .....'

account1_pubKey = w3.eth.accounts[0] # Public-key of 1st testrpc account (src).

account2_pubKey = w3.eth.accounts[1] # Public-key of 2nd testrpc account (dest).

value = w3.toWei(1, 'ether') # We'll sent 1.0 Ether from account1 to account2

gas = 21000 # Published GTX op-cost is 21,000 gas

gasPrice = 1 # When working off-chain, this can be arbitrarily set.

data = b'' # SEE: https://web3py.readthedocs.io/en/stable/web3.eth.html?highlight=sendTransaction

txn_attribs_tuple = (account1_pubKey, account2_pubKey, value, gas, gasPrice, data)

# ============================================================================

# -----------------------------------------------------------

# AUTOMATIC SIGNING way to do it (say, by client or wallet) ...

# -----------------------------------------------------------

print("=" * 80)

autoSigned_txn = build_txn(txn_attribs_tuple) # Build base transaction JSON.

autoSigned_txn["from"] = txn_attribs_tuple[0] # Add "from" field b/c unsigned (i.e. auto-signed) txns require it.

print('Transmitting autoSigned transaction:'); pprint.pprint(autoSigned_txn)

autoSigned_txn_receipt = w3.eth.sendTransaction(autoSigned_txn) # 64-hex-char HexBytes object/type.

print('\nautoSigned_txn_receipt: %s' % autoSigned_txn_receipt.hex())

print('\nautoSigned transaction BlockChain record:\n\t%s' % w3.eth.getTransaction(autoSigned_txn_receipt))

print("=" * 80, '\n')

# -----------------------------------------------------------

# MANUAL PRE-SIGNING way to do it (by, say, us offline) ...

# -----------------------------------------------------------

print("=" * 80)

selfSigned_txn = build_txn(txn_attribs_tuple) # Build base transaction JSON.

selfSigned_txn = w3.eth.account.signTransaction(selfSigned_txn, account1_privKey)

# -----------------------------------------------------------

# SITENOTE: Notice above that we SIGNED our transaction offline, and the resulting

# object attribute, selfSigned_txn.rawTransaction, contains all of the data

# required to submit it to the Blockchain. While we submit it programmatically

# next, we could easily store it on a USB stick, pass it around, and submit it

# later on elsewhere; for example here: https://etherscan.io/pushTx

# -----------------------------------------------------------

print('Transmitting selfSigned Raw Transaction: %s\n' % selfSigned_txn.rawTransaction.hex()[2:])

selfSigned_txn_receipt = w3.eth.sendRawTransaction(selfSigned_txn.rawTransaction)

print('selfSigned_txn_receipt: %s\n' % selfSigned_txn_receipt.hex())

print('selfSigned transaction BlockChain record:\n\t%s' % w3.eth.getTransaction(selfSigned_txn_receipt))

print("=" * 80, '\n')

# ============================================================================

print("=" * 80)

print('New account1 ETH balance: %s' % accnt_ETH_balance(account1_pubKey)) # e.g.: 98.9999922

print('New account2 ETH balance: %s' % accnt_ETH_balance(account2_pubKey)) # e.g.: 101

print("=" * 80)

# ============================================================================

# w3.eth.getTransaction(receipt) looks like this ...

# ============================================================================

# AttributeDict({

# 'hash': HexBytes('0x7e51e692accd3d80dc3d1120c6d80b2c33b39f1ef4e5873dd989c6b3d9020404'),

# 'nonce': 23,

# 'blockHash': HexBytes('0x4038ace16e914bb35ee97eccda18d88c5cec6cc857e10b946a731f4d0b569fdf'),

# 'blockNumber': 24,

# 'transactionIndex': 0,

# 'from': '0xd046443e436C21631Cdb23b344305e51C457D7Ca',

# 'to': '0xc3D981622b48535509374BB64e8AAE758C04e3ab',

# 'value': 1000000000000000000,

# 'gas': 21000,

# 'gasPrice': 1,

# 'input': '0x0',

# # The next three k/v pairs are only found in Signed Transactions!

# 'v': 28,

# 'r': HexBytes('0x5de8a34e536b78447ee863b11f19b04bcd009b58d919413a0915c188096baa2e'),

# 's': HexBytes('0x08145aabb144f7e17ecb76d7ca347818cf0ffb8a2aa0ce2093eeb741cae9b9a7')})

# ============================================================================

# Notes on attributes in the output:

# ============================================================================

# 'nonce'.............: Same as: w3.eth.getTransactionCount(account1) before sending.

# 'hash'..............: Same value as tx_receipt that we received on transaction submission.

# 'blockHash'.........: A hash of the BLOCK the transaction was mind in, and it will be

# included in the NEXT BLOCK mined.

# 'blockNumber'.......: The blockchain block-number that this transaction iside of. We have

# a tiny personal blockchain. =:)

# 'transactionIndex...: Blockchain blocks include multiple transactions in them, each with a

# a transaction index number. Since this is our personal blockchain,

# each mined block has only one transaction, so this number is always

# zero (qty. 0) for us. =:)

# 'input'.............: Our tx dict() could have included an 'input' key/value

# pair where we could include arbitrary input data. Default: 0x0

# ============================================================================

# A note about transaction NONCES from an account. Above, we could specify a

# nonce key/value pair in the 'tx' dict(). If we don't, the next one is automatically

# generated for us when the transaction is submitted. However, whether manually

# specified or automatically generated, the nonce must NOT already exist on

# the blockchain for that account (i.e. it cannot have been previously used).

# Nonces are monotically increasing values, and depending on the node server

# (e.g. testrpc, geth, infurium) it may be possible to specify a nonce

# that is much larger than the current one for an account (i.e. a "future" one

# instead of the next sequential nonce). For use-cases for this, see this

# explanation on StackOverflow:

# https://ethereum.stackexchange.com/questions/ +

# 2808/what-happens-when-a-transaction-nonce-is-too-high

# ============================================================================

# Nonces is the means by which "replay attacks" (i.e. sending the exact

# same HTTP or Blockchain transaction again and again) is prevented. For

# explanation, see: https://en.wikipedia.org/wiki/Cryptographic_nonce

# Let's see this in action.

# ============================================================================