Implement transaction decoding and TxID calculation

[d3adlast45-commits]

Added functions to decode variable integers and transactions from hex strings, including legacy serialization for TxID calculation. gh pr checkout 2587import binascii
import struct

raw_tx = "020000000257ded1c7a09c2965a12a486b4ad37c45da485a94ab96347e0400294d445380510900000000fdffffff57ded1c7a09c2965a12a486b4ad37c45da485a94ab96347e0400294d445380510b00000000fdffffff010000000000000000296a2765766572797468696e6727732066696e65207c204f6e207369676e6574207765206c6561726e2e32a70400"
bytes_tx = binascii.unhexlify(raw_tx)

Decode

version = bytes_tx[0:4]

inputs

num_inputs = bytes_tx[4]

Input 1

in1_txid = bytes_tx[5:37]
in1_vout = bytes_tx[37:41]

... variable length script sig ...

Wait, the provided hex has "00" scriptSig length?

Let's parse dynamically.

offset = 4
num_inputs = bytes_tx[offset]
offset += 1
inputs = []
for i in range(num_inputs):
txid = bytes_tx[offset:offset+32]
offset += 32
vout = bytes_tx[offset:offset+4]
offset += 4
script_len = bytes_tx[offset]
offset += 1
script = bytes_tx[offset:offset+script_len]
offset += script_len
sequence = bytes_tx[offset:offset+4]
offset += 4
inputs.append({"txid": binascii.hexlify(txid[::-1]), "vout": struct.unpack("<I", vout)[0], "seq": binascii.hexlify(sequence)})

num_outputs = bytes_tx[offset]
offset += 1
outputs = []
for i in range(num_outputs):
value = bytes_tx[offset:offset+8]
offset += 8
script_len = bytes_tx[offset]
offset += 1
script = bytes_tx[offset:offset+script_len]
offset += script_len
outputs.append({"value": struct.unpack("<Q", value)[0], "script": binascii.hexlify(script)})

locktime = bytes_tx[offset:offset+4]

print(f"Inputs: {inputs}")
print(f"Outputs: {outputs}")
print(f"Locktime: {binascii.hexlify(locktime)}")

message

msg_hex = outputs[0]['script'][4:] # Skip 6a (OP_RETURN) and 27 (len)
print(f"Message: {binascii.unhexlify(msg_hex)}")