Patch `libbackend.so` of Turing Complete's bleeding edge build to use `xterm` rather than `gnome-terminal`. `click` version

patch-backend.py

#!/usr/bin/env python3

from __future__ import annotations

import hashlib
import sys

from pathlib import Path

import click

from typing import TYPE_CHECKING
if TYPE_CHECKING:
    from typing import Literal


LIBBACKEND_FILENAME = 'libbackend.so'

OLD = b'gnome-terminal -- bash -ic "./si'
NEW = b'setsid -f xterm -e bash -c "./si'


def hexdigest(data: bytes) -> str:
    return hashlib.md5(data, usedforsecurity=False).hexdigest()


def patch_backend(file: Path, action: Literal['do', 'undo', 'view']) -> None:

    orig_content = file.read_bytes()
    count_old = orig_content.count(OLD)
    count_new = orig_content.count(NEW)
    old_content = orig_content.replace(NEW, OLD)
    new_content = orig_content.replace(OLD, NEW)

    if action == 'view':
        print(f"Found {count_old} occurrences of the original byte sequence and {count_new} of the replacement.")
        print(f"  md5sum with original byte sequence:      {hexdigest(old_content)}")
        print(f"  md5sum with current file content:        {hexdigest(orig_content)}")
        print(f"  md5sum with replacement byte sequence:   {hexdigest(new_content)}")
        return

    if count_old + count_new == 0:
        raise ValueError("Found neither original nor replacement byte sequence in file.")

    if count_old + count_new > 1:
        raise ValueError("Found more than one occurrence of original or replacement byte sequence in file.")

    byte_offset = orig_content.find(OLD) if count_old else orig_content.find(NEW)
    if byte_offset < 1024 or (byte_offset & 0xF) != 0:
        raise ValueError(f"Found byte sequence at suspicious offset {byte_offset} / {byte_offset:#x}.")

    match action:
        case 'do':
            if count_old == 0:
                print("Original byte sequence does not occur in file.", file=sys.stderr)
                print(f"  md5sum:   {hexdigest(orig_content)}", file=sys.stderr)

            else:
                print(f"  md5sum was:      {hexdigest(orig_content)}", file=sys.stderr)
                file.write_bytes(new_content)
                print(f"  md5sum now is:   {hexdigest(new_content)}", file=sys.stderr)

        case 'undo':
            if count_new == 0:
                print("Replacement byte sequence does not occur in file.", file=sys.stderr)
                print(f"  md5sum:   {hexdigest(orig_content)}", file=sys.stderr)

            else:
                print(f"  md5sum was:      {hexdigest(orig_content)}", file=sys.stderr)
                file.write_bytes(old_content)
                print(f"  md5sum now is:   {hexdigest(old_content)}", file=sys.stderr)

        case _:
            raise NotImplementedError(f"unimplemented action {action!r}")


@click.command()
@click.argument('file', required=False, type=click.Path(exists=True, file_okay=True, dir_okay=False, readable=True, path_type=Path))
@click.option('--do',         'action', flag_value='do',   help='Replace gnome-terminal with xterm.', default=True, show_default=True)
@click.option('--undo', '-u', 'action', flag_value='undo', help='Go back to using gnome-terminal.')
@click.option('--view', '-n', 'action', flag_value='view', help='Count the occurrences and view the checksums.')
def cli(file: Path | None, action: str) -> None:
    """Replace debug terminal app in Turing Complete's libbackend.so."""

    try:
        patch_backend(
            file = Path(file) if file is not None else Path(sys.argv[0]).parent / LIBBACKEND_FILENAME,
            action = action,
        )

    except Exception as e:
        raise SystemExit(e)


if __name__ == '__main__':
    cli()