Finds which .dat file contains the block

find_block.py

#! /usr/bin/env python

# Finds which .dat file contains the block.
# Warning: this will most likely corrupt the block index. You are strongly advised to copy the index (around 100MB) to a different location and
# run the script in that location (change path below).
#
# Path to index: $datadir/blocks/index

import sys
import plyvel

index_path = "/path/to/index-copy"
block_prefix = "62"

if len(sys.argv) < 2:
	print(f"usage: {sys.argv[0]} <blockhash>", file = sys.stderr)
	sys.exit(1)

blockhash = sys.argv[1]

def read_varint(asInt):
	global pos
	global raw
	value = bytearray()
  
	while raw[pos] >> 7 == 1:
		if asInt:
			value.append(raw[pos] + 1)
		else:
			value.append(raw[pos])
		pos += 1
 
	value.append(raw[pos])
	pos += 1
 
	return bytes(value)

def varint_as_int():
	data = read_varint(True)
	number = 0
	for b in data:
		bits = b & 0b01111111
		number = number << 7 | bits
  
	return number

def varint_as_raw():
  return read_varint(False)


db = plyvel.DB(index_path, create_if_missing = False)

key = bytes.fromhex(f"{block_prefix}{blockhash}")

raw = db.get(key)
if raw is None:
	rev = bytearray.fromhex(f"{blockhash}{block_prefix}")
	rev.reverse()
	raw = db.get(bytes(rev))
	if raw is None:
		print("Block not found")
		sys.exit(0)

db.close()

print(f"Raw data: {raw.hex()}")
print()

pos = 0

client = varint_as_raw()

print(f"Block recorded by client version {client.hex()}")
print()

height = varint_as_int()
print(f"Height: {height}")

varint_as_raw() # flags

txCount = varint_as_int()
print(f"Transactions in block: {txCount}")

fileNumber = str(varint_as_int()).rjust(5, "0")
print(f"Filename: blk{fileNumber}.dat")

offset = varint_as_int()
print(f"File offset: {offset}")

varint_as_int() # offset rev file

print()
header = raw[pos : pos + 80]
print(f"Header: {header.hex()}")