Interpret a log output based on a location database

interpret.py

# usage python generate_loc_db.py <database> 

import sys
import json

# We will read from stdin, for simplicity sake

# Load the previously generated data from the json
db = None
with open(sys.argv[1]) as f:
    db = json.load(f)

# We need to functions: one to read integers as binary and one to read the strings.
def read_ptr():
  # We read eight bytes since I am using this on an x64 machine. This needs to adjusted to the pointer size on the target
  # This can be detected by sending a proper header before the pointer, but we skip that for the example.
  bytes = sys.stdin.buffer.read(8)
  
  # This means it's closed, so we stop execution.
  if len(bytes) == 0: 
      return None
  
  # We also assume little endian, you can adjust that.
  return int.from_bytes(bytes, byteorder="little")
  
# Secondly read the string until the null terminator
def read_string():
  chars = bytearray()
  while True:
    c = sys.stdin.buffer.read(1)
    if c == b'\x00': # Null terminator, so return the previous bytes decoded as a string
      return chars.decode()
    chars.extend(c)

# Alright, so let's read the address of main.

main_addr = read_ptr()

offset = main_addr - db['main']['address']
while True: 
  addr_raw = read_ptr()
  if addr_raw is None:
      break
  
  addr = addr_raw - offset

  msg = read_string()
  # Now find the address in the saved marks. If that throws StopIterator we have an error in the pre generated data
  mark = next(mark for mark in db['marks'] if mark['address'] == addr)

  # This is the formatting to so we get {filename}({line}): {message}
  print('{}({}): {}'.format(mark['filename'], mark['line'], msg))