mitogen/ansible_mitogen/parsing.py

# Copyright 2019, David Wilson
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"""
Classes to detect each case from [0] and prepare arguments necessary for the
corresponding Runner class within the target, including preloading requisite
files/modules known missing.

[0] "Ansible Module Architecture", developing_program_flow_modules.html
"""

from __future__ import absolute_import
from __future__ import unicode_literals

import mitogen.core


def parse_script_interpreter(source):
    """
    Parse the script interpreter portion of a UNIX hashbang using the rules
    Linux uses.

    :param str source: String like "/usr/bin/env python".

    :returns:
        Tuple of `(interpreter, arg)`, where `intepreter` is the script
        interpreter and `arg` is its sole argument if present, otherwise
        :py:data:`None`.
    """
    # Find terminating newline. Assume last byte of binprm_buf if absent.
    nl = source.find(b'\n', 0, 128)
    if nl == -1:
        nl = min(128, len(source))

    # Split once on the first run of whitespace. If no whitespace exists,
    # bits just contains the interpreter filename.
    bits = source[0:nl].strip().split(None, 1)
    if len(bits) == 1:
        return mitogen.core.to_text(bits[0]), None
    return mitogen.core.to_text(bits[0]), mitogen.core.to_text(bits[1])


def parse_hashbang(source):
    """
    Parse a UNIX "hashbang line" using the syntax supported by Linux.

    :param str source: String like "#!/usr/bin/env python".

    :returns:
        Tuple of `(interpreter, arg)`, where `intepreter` is the script
        interpreter and `arg` is its sole argument if present, otherwise
        :py:data:`None`.
    """
    # Linux requires first 2 bytes with no whitespace, pretty sure it's the
    # same everywhere. See binfmt_script.c.
    if not source.startswith(b'#!'):
        return None, None

    return parse_script_interpreter(source[2:])