Two-pass multi-run-safe micro (85 LOC) patcher in python

patch.py

#!/usr/bin/env python3
'''
Two-pass re-run safe micro (85 LOC) patcher in python.

Sample patch config (yes, it's in YAML):
---->8----
version: 0
title: tribute to sublimetext_4126_crack_linux.py by dmknght @github
file: /tmp/sublime_text
# size: 8862888 # optional check for file size
patch:
  - offset: 0x0002d78a
    value: 34 31 32 36 # "4126"
  - { offset: 0x00385797, value: 0f 84, replace: 0f 85 }
  - { offset: 0x0038583d, value: 74 1f, replace: 75 1f }
# vim:set ft=yaml ai et ts=2 sts=2 sw=2:EOF #
---->8----
'''
import sys, yaml, os

VERSION = 0

def hexx(z): return ' '.join(f'{b:02x}' for b in z)

def binn(p):
    data = ''.join(p.strip().split()).lower()
    assert data and len(data) % 2 == 0, f'bad data length {len(data)}'
    return bytes(int(data[i:i+2], 16) for i in range(0, len(data), 2))

def read_at(f, pos, size):
    assert f.seek(pos, os.SEEK_SET) == pos
    return f.read(size)

def write_at(f, pos, data):
    if data:
        print(f"\t{pos:08x}", len(data), '/', hexx(data))
        assert f.seek(pos, os.SEEK_SET) == pos
        f.write(data)

def verify(f, check, n):
    offset, pattern, repl = check['offset'], binn(check['value']), check.get('replace')
    if repl:
        repl = binn(repl)
        value = read_at(f, offset, len(repl))
        if value == repl:
            print(f"{n:6d}: {offset:08x}", len(value), '=', hexx(value), '!=', hexx(pattern), 'patched')
            return None
    value = read_at(f, offset, len(pattern))
    assert pattern == value, f"at {offset:08x}: [{hexx(value)}] != [{hexx(pattern)}]"
    print(f"{n:6d}: {offset:08x}", len(pattern), '=', hexx(pattern), 'ok,', 'patch' if repl else 'keep')
    return repl

def check(cf):
    print('check>', cf['file'], f'({len(cf["patch"])})')
    with open(cf['file'], 'rb') as f:
        size = cf.get('size')
        assert not size or size == f.seek(0, os.SEEK_END), f'File size not matched {size}'
        return [p for i, p in enumerate(cf['patch']) if verify(f, p, i + 1)]

def apply(cf, patches):
    if patches:
        print('patch>', cf['file'], f'({len(patches)} patch{"es" if len(patches) > 1 else ""} to apply)')
        with open(cf['file'], 'rb+') as f:
            for i, patch in enumerate(patches):
                write_at(f, patch['offset'], verify(f, patch, i + 1))
        print('*', cf['file'], 'patched using', cf['__self'])
    else:
        print('*', cf['file'], 'has already been patched using', cf['__self'], 'or alike')

def patch(cf):
    if cf.get('title'): print('#', cf.get('title'))
    apply(cf, check(cf))

try:
    for arg in sys.argv[1:]:
        print('@', arg)
        with open(arg) as f:
            cf = yaml.load(f, yaml.SafeLoader)
            cf['__self'] = arg
        assert cf.get('version') == VERSION, f'Patch version is not {VERSION!r} in {cf["__self"]!r}'
        patch(cf)
except Exception as e:
    print('!', e.__class__.__name__ + ':', e, file=sys.stderr)
    sys.exit(1)
# vim:set ft=python ai et ts=4 sts=4 sw=4 cc=80:EOF #

patch.yaml

version: 0
title: tribute to sublimetext_4126_crack_linux.py by dmknght @github
file: /tmp/sublime_text
size: 8862888 # optional
patch:
  - offset: 0x0002d78a
    value: 34 31 32 36 # "4126", just to check, no "replace:" part
  - { offset: 0x00385797, value: 0f 84, replace: 0f 85 } # one may have fun writing
  - { offset: 0x0038583d, value: 74 1f, replace: 75 1f } # patches in "table form"
# vim:set ft=yaml ai et ts=2 sts=2 sw=2:EOF #

sample-run.txt

$ cp /snap/sublime-text/112/opt/sublime_text/sublime_text /tmp/

$ ./patch.py patch.pth 
@ patch.pth
# tribute to sublimetext_4126_crack_linux.py by dmknght @github
check> /tmp/sublime_text (3)
     1: 0002d78a 4 = 34 31 32 36 ok, keep
     2: 00385797 2 = 0f 84 ok, patch
     3: 0038583d 2 = 74 1f ok, patch
patch> /tmp/sublime_text (2 patches to apply)
     1: 00385797 2 = 0f 84 ok, patch
	00385797 2 / 0f 85
     2: 0038583d 2 = 74 1f ok, patch
	0038583d 2 / 75 1f
* /tmp/sublime_text patched using patch.pth

$ ./patch.py patch.pth 
@ patch.pth
# tribute to sublimetext_4126_crack_linux.py by dmknght @github
check> /tmp/sublime_text (3)
     1: 0002d78a 4 = 34 31 32 36 ok, keep
     2: 00385797 2 = 0f 85 != 0f 84 patched
     3: 0038583d 2 = 75 1f != 74 1f patched
* /tmp/sublime_text has already been patched using patch.pth or alike