cmd.py

# Copyright (C) 2008, 2009 Michael Trier (mtrier@gmail.com) and contributors
#
# This module is part of GitPython and is released under the
# 3-Clause BSD License: https://opensource.org/license/bsd-3-clause/

from __future__ import annotations

import re
import contextlib
import io
import logging
import os
import signal
from subprocess import Popen, PIPE, DEVNULL
import subprocess
import threading
from textwrap import dedent
from pathlib import Path

from git.compat import defenc, force_bytes, safe_decode
from git.exc import (
    CommandError,
    GitCommandError,
    GitCommandNotFound,
    UnsafeOptionError,
    UnsafeProtocolError,
)
from git.util import (
    LazyMixin,
    cygpath,
    expand_path,
    is_cygwin_git,
    patch_env,
    remove_password_if_present,
    stream_copy,
)

# typing ---------------------------------------------------------------------------

from typing import (
    Any,
    AnyStr,
    BinaryIO,
    Callable,
    Dict,
    IO,
    Iterator,
    List,
    Mapping,
    Optional,
    Sequence,
    TYPE_CHECKING,
    TextIO,
    Tuple,
    Union,
    cast,
    overload,
)

from git.types import PathLike, Literal, TBD

if TYPE_CHECKING:
    from git.repo.base import Repo
    from git.diff import DiffIndex


# ---------------------------------------------------------------------------------

execute_kwargs = {
    "istream",
    "with_extended_output",
    "with_exceptions",
    "as_process",
    "output_stream",
    "stdout_as_string",
    "kill_after_timeout",
    "with_stdout",
    "universal_newlines",
    "shell",
    "env",
    "max_chunk_size",
    "strip_newline_in_stdout",
}

log = logging.getLogger(__name__)
log.addHandler(logging.NullHandler())

__all__ = ("Git",)


# ==============================================================================
## @name Utilities
# ------------------------------------------------------------------------------
# Documentation
## @{


def handle_process_output(
    process: "Git.AutoInterrupt" | Popen,
    stdout_handler: Union[
        None,
        Callable[[AnyStr], None],
        Callable[[List[AnyStr]], None],
        Callable[[bytes, "Repo", "DiffIndex"], None],
    ],
    stderr_handler: Union[None, Callable[[AnyStr], None], Callable[[List[AnyStr]], None]],
    finalizer: Union[None, Callable[[Union[Popen, "Git.AutoInterrupt"]], None]] = None,
    decode_streams: bool = True,
    kill_after_timeout: Union[None, float] = None,
) -> None:
    """Register for notifications to learn that process output is ready to read, and
    dispatch lines to the respective line handlers.

    This function returns once the finalizer returns.

    :param process: :class:`subprocess.Popen` instance
    :param stdout_handler: f(stdout_line_string), or None
    :param stderr_handler: f(stderr_line_string), or None
    :param finalizer: f(proc) - wait for proc to finish
    :param decode_streams:
        Assume stdout/stderr streams are binary and decode them before pushing
        their contents to handlers.
        Set it to False if ``universal_newlines == True`` (then streams are in
        text mode) or if decoding must happen later (i.e. for Diffs).
    :param kill_after_timeout:
        float or None, Default = None
        To specify a timeout in seconds for the git command, after which the process
        should be killed.
    """

    # Use 2 "pump" threads and wait for both to finish.
    def pump_stream(
        cmdline: List[str],
        name: str,
        stream: Union[BinaryIO, TextIO],
        is_decode: bool,
        handler: Union[None, Callable[[Union[bytes, str]], None]],
    ) -> None:
        try:
            for line in stream:
                if handler:
                    if is_decode:
                        assert isinstance(line, bytes)
                        line_str = line.decode(defenc)
                        handler(line_str)
                    else:
                        handler(line)

        except Exception as ex:
            log.error(f"Pumping {name!r} of cmd({remove_password_if_present(cmdline)}) failed due to: {ex!r}")
            if "I/O operation on closed file" not in str(ex):
                # Only reraise if the error was not due to the stream closing
                raise CommandError([f"<{name}-pump>"] + remove_password_if_present(cmdline), ex) from ex
        finally:
            stream.close()

    if hasattr(process, "proc"):
        process = cast("Git.AutoInterrupt", process)
        cmdline: str | Tuple[str, ...] | List[str] = getattr(process.proc, "args", "")
        p_stdout = process.proc.stdout if process.proc else None
        p_stderr = process.proc.stderr if process.proc else None
    else:
        process = cast(Popen, process)  # type: ignore [redundant-cast]
        cmdline = getattr(process, "args", "")
        p_stdout = process.stdout
        p_stderr = process.stderr

    if not isinstance(cmdline, (tuple, list)):
        cmdline = cmdline.split()

    pumps: List[Tuple[str, IO, Callable[..., None] | None]] = []
    if p_stdout:
        pumps.append(("stdout", p_stdout, stdout_handler))
    if p_stderr:
        pumps.append(("stderr", p_stderr, stderr_handler))

    threads: List[threading.Thread] = []

    for name, stream, handler in pumps:
        t = threading.Thread(target=pump_stream, args=(cmdline, name, stream, decode_streams, handler))
        t.daemon = True
        t.start()
        threads.append(t)

    # FIXME: Why join? Will block if stdin needs feeding...
    for t in threads:
        t.join(timeout=kill_after_timeout)
        if t.is_alive():
            if isinstance(process, Git.AutoInterrupt):
                process._terminate()
            else:  # Don't want to deal with the other case.
                raise RuntimeError(
                    "Thread join() timed out in cmd.handle_process_output()."
                    f" kill_after_timeout={kill_after_timeout} seconds"
                )
            if stderr_handler:
                error_str: Union[str, bytes] = (
                    "error: process killed because it timed out." f" kill_after_timeout={kill_after_timeout} seconds"
                )
                if not decode_streams and isinstance(p_stderr, BinaryIO):
                    #  Assume stderr_handler needs binary input.
                    error_str = cast(str, error_str)
                    error_str = error_str.encode()
                # We ignore typing on the next line because mypy does not like
                # the way we inferred that stderr takes str or bytes.
                stderr_handler(error_str)  # type: ignore

    if finalizer:
        finalizer(process)


def _safer_popen_windows(
    command: Union[str, Sequence[Any]],
    *,
    shell: bool = False,
    env: Optional[Mapping[str, str]] = None,
    **kwargs: Any,
) -> Popen:
    """Call :class:`subprocess.Popen` on Windows but don't include a CWD in the search.

    This avoids an untrusted search path condition where a file like ``git.exe`` in a
    malicious repository would be run when GitPython operates on the repository. The
    process using GitPython may have an untrusted repository's working tree as its
    current working directory. Some operations may temporarily change to that directory
    before running a subprocess. In addition, while by default GitPython does not run
    external commands with a shell, it can be made to do so, in which case the CWD of
    the subprocess, which GitPython usually sets to a repository working tree, can
    itself be searched automatically by the shell. This wrapper covers all those cases.

    :note: This currently works by setting the ``NoDefaultCurrentDirectoryInExePath``
        environment variable during subprocess creation. It also takes care of passing
        Windows-specific process creation flags, but that is unrelated to path search.

    :note: The current implementation contains a race condition on :attr:`os.environ`.
        GitPython isn't thread-safe, but a program using it on one thread should ideally
        be able to mutate :attr:`os.environ` on another, without unpredictable results.
        See comments in https://github.com/gitpython-developers/GitPython/pull/1650.
    """
    # CREATE_NEW_PROCESS_GROUP is needed for some ways of killing it afterwards. See:
    # https://docs.python.org/3/library/subprocess.html#subprocess.Popen.send_signal
    # https://docs.python.org/3/library/subprocess.html#subprocess.CREATE_NEW_PROCESS_GROUP
    creationflags = subprocess.CREATE_NO_WINDOW | subprocess.CREATE_NEW_PROCESS_GROUP

    # When using a shell, the shell is the direct subprocess, so the variable must be
    # set in its environment, to affect its search behavior. (The "1" can be any value.)
    if shell:
        safer_env = {} if env is None else dict(env)
        safer_env["NoDefaultCurrentDirectoryInExePath"] = "1"
    else:
        safer_env = env

    # When not using a shell, the current process does the search in a CreateProcessW
    # API call, so the variable must be set in our environment. With a shell, this is
    # unnecessary, in versions where https://github.com/python/cpython/issues/101283 is
    # patched. If not, in the rare case the ComSpec environment variable is unset, the
    # shell is searched for unsafely. Setting NoDefaultCurrentDirectoryInExePath in all
    # cases, as here, is simpler and protects against that. (The "1" can be any value.)
    with patch_env("NoDefaultCurrentDirectoryInExePath", "1"):
        return Popen(
            command,
            shell=shell,
            env=safer_env,
            creationflags=creationflags,
            **kwargs,
        )


if os.name == "nt":
    safer_popen = _safer_popen_windows
else:
    safer_popen = Popen


def dashify(string: str) -> str:
    return string.replace("_", "-")


def slots_to_dict(self: "Git", exclude: Sequence[str] = ()) -> Dict[str, Any]:
    return {s: getattr(self, s) for s in self.__slots__ if s not in exclude}


def dict_to_slots_and__excluded_are_none(self: object, d: Mapping[str, Any], excluded: Sequence[str] = ()) -> None:
    for k, v in d.items():
        setattr(self, k, v)
    for k in excluded:
        setattr(self, k, None)


## -- End Utilities -- @}


class Git(LazyMixin):
    """The Git class manages communication with the Git binary.

    It provides a convenient interface to calling the Git binary, such as in::

     g = Git( git_dir )
     g.init()                   # calls 'git init' program
     rval = g.ls_files()        # calls 'git ls-files' program

    ``Debugging``
        Set the GIT_PYTHON_TRACE environment variable print each invocation
        of the command to stdout.
        Set its value to 'full' to see details about the returned values.
    """

    __slots__ = (
        "_working_dir",
        "cat_file_all",
        "cat_file_header",
        "_version_info",
        "_git_options",
        "_persistent_git_options",
        "_environment",
    )

    _excluded_ = ("cat_file_all", "cat_file_header", "_version_info")

    re_unsafe_protocol = re.compile(r"(.+)::.+")

    def __getstate__(self) -> Dict[str, Any]:
        return slots_to_dict(self, exclude=self._excluded_)

    def __setstate__(self, d: Dict[str, Any]) -> None:
        dict_to_slots_and__excluded_are_none(self, d, excluded=self._excluded_)

    # CONFIGURATION

    git_exec_name = "git"
    """Default git command that should work on Linux, Windows, and other systems."""

    GIT_PYTHON_TRACE = os.environ.get("GIT_PYTHON_TRACE", False)
    """Enables debugging of GitPython's git commands."""

    USE_SHELL = False
    """Deprecated. If set to True, a shell will be used when executing git commands.

    Prior to GitPython 2.0.8, this had a narrow purpose in suppressing console windows
    in graphical Windows applications. In 2.0.8 and higher, it provides no benefit, as
    GitPython solves that problem more robustly and safely by using the
    ``CREATE_NO_WINDOW`` process creation flag on Windows.

    Code that uses ``USE_SHELL = True`` or that passes ``shell=True`` to any GitPython
    functions should be updated to use the default value of ``False`` instead. ``True``
    is unsafe unless the effect of shell expansions is fully considered and accounted
    for, which is not possible under most circumstances.

    See:
    - :meth:`Git.execute` (on the ``shell`` parameter).
    - https://github.com/gitpython-developers/GitPython/commit/0d9390866f9ce42870d3116094cd49e0019a970a
    - https://learn.microsoft.com/en-us/windows/win32/procthread/process-creation-flags
    """

    _git_exec_env_var = "GIT_PYTHON_GIT_EXECUTABLE"
    _refresh_env_var = "GIT_PYTHON_REFRESH"

    GIT_PYTHON_GIT_EXECUTABLE = None
    """Provide the full path to the git executable. Otherwise it assumes git is in the path.

    Note that the git executable is actually found during the refresh step in
    the top level ``__init__``.
    """

    _bash_exec_env_var = "GIT_PYTHON_BASH_EXECUTABLE"

    bash_exec_name = "bash"
    """Default bash command."""

    GIT_PYTHON_BASH_EXECUTABLE = None
    """
    Provides the path to the bash executable used for commit hooks.  This is
    ordinarily set by `Git.refresh_bash()`.  Note that the default behavior of
    invoking commit hooks on Windows has changed to not prefer WSL bash with
    the introduction of this variable.  See the `Git.refresh_bash()`
    documentation for details on the default values and search paths.
    """

    @classmethod
    def _get_default_bash_path(cls) -> str:
        # Assumes that, if user is running in Windows, they probably are using
        # Git for Windows, which includes Git BASH and should be associated
        # with the configured Git command set in `refresh()`.
        # Uses the output of `git --exec-path` for the currently configured
        # Git command to find its `git-core` directory.  If one assumes that
        # the `git-core` directory is always three levels deeper than the
        # root directory of the Git installation, we can try going up three
        # levels and then navigating to (root)/bin/bash.exe.  If this exists,
        # prefer it over the WSL version in System32, direct access to which
        # is reportedly deprecated.  Fail back to default "bash.exe" if
        # the Git for Windows lookup doesn't work.
        #
        # This addresses issues where git hooks are intended to run assuming
        # the "native" Windows environment as seen by git.exe rather than
        # inside the git sandbox of WSL, which is likely configured
        # independently of the Windows Git.  A noteworthy example are repos
        # with Git LFS, where Git LFS may be installed in Windows but not
        # in WSL.
        if os.name != "nt":
            return "bash"
        gitcore = Path(cls()._call_process("--exec-path"))
        gitroot = gitcore.parent.parent.parent
        gitbash = gitroot / "bin" / "bash.exe"
        return str(gitbash) if gitbash.exists() else "bash.exe"

    @classmethod
    def refresh_bash(cls, path: Union[None, PathLike] = None) -> bool:
        """
        Refreshes the cached path to the bash executable used for executing
        commit hook scripts.  This gets called by the top-level `refresh()`
        function on initial package import (see the top level __init__), but
        this method may be invoked manually if the path changes after import.

        This method only checks one path for a valid bash executable at a time,
        using the first non-empty path provided in the following priority
        order:

          1. the explicit `path` argument to this method
          2. the environment variable `GIT_PYTHON_BASH_EXECUTABLE` if it is set
             and available via `os.environ` upon calling this method
          3. if the current platform is not Windows, the simple string `"bash"`
          4. if the current platform is Windows, inferred from the current
             provided Git executable assuming it is part of a Git for Windows
             distribution.

        The current platform is checked based on the call `os.name`.

        This is a change to the default behavior from previous versions of
        GitPython.  In the event backwards compatibility is needed, the `path`
        argument or the environment variable may be set to the string
        `"bash.exe"`, which on most systems invokes the WSL bash by default.

        This change to default behavior addresses issues where git hooks are
        intended to run assuming the "native" Windows environment as seen by
        git.exe rather than inside the git sandbox of WSL, which is likely
        configured independently of the Windows Git.  A noteworthy example are
        repos with Git LFS, where Git LFS may be installed in Windows but not
        in WSL.
        """
        # Discern which path to refresh with.
        if path is not None:
            new_bash = os.path.expanduser(path)
            # new_bash = os.path.abspath(new_bash)
        else:
            new_bash = os.environ.get(cls._bash_exec_env_var)
            if not new_bash:
                new_bash = cls._get_default_bash_path()

        # Keep track of the old and new bash executable path.
        # old_bash = cls.GIT_PYTHON_BASH_EXECUTABLE
        cls.GIT_PYTHON_BASH_EXECUTABLE = new_bash

        # Test if the new git executable path exists.
        has_bash = Path(cls.GIT_PYTHON_BASH_EXECUTABLE).exists()
        return has_bash

    @classmethod
    def refresh(cls, path: Union[None, PathLike] = None) -> bool:
        """
        This gets called by the refresh function (see the top level __init__).

        Note that calling this method directly does not automatically update
        the cached path to `bash`; either invoke the top level `refresh()`
        function or call `Git.refresh_bash()` directly.
        """
        # Discern which path to refresh with.
        if path is not None:
            new_git = os.path.expanduser(path)
            new_git = os.path.abspath(new_git)
        else:
            new_git = os.environ.get(cls._git_exec_env_var, cls.git_exec_name)

        # Keep track of the old and new git executable path.
        old_git = cls.GIT_PYTHON_GIT_EXECUTABLE
        cls.GIT_PYTHON_GIT_EXECUTABLE = new_git

        # Test if the new git executable path is valid. A GitCommandNotFound error is
        # spawned by us. A PermissionError is spawned if the git executable cannot be
        # executed for whatever reason.
        has_git = False
        try:
            cls().version()
            has_git = True
        except (GitCommandNotFound, PermissionError):
            pass

        # Warn or raise exception if test failed.
        if not has_git:
            err = (
                dedent(
                    """\
                Bad git executable.
                The git executable must be specified in one of the following ways:
                    - be included in your $PATH
                    - be set via $%s
                    - explicitly set via git.refresh()
                """
                )
                % cls._git_exec_env_var
            )

            # Revert to whatever the old_git was.
            cls.GIT_PYTHON_GIT_EXECUTABLE = old_git

            if old_git is None:
                # On the first refresh (when GIT_PYTHON_GIT_EXECUTABLE is None) we only
                # are quiet, warn, or error depending on the GIT_PYTHON_REFRESH value.

                # Determine what the user wants to happen during the initial refresh we
                # expect GIT_PYTHON_REFRESH to either be unset or be one of the
                # following values:
                #
                #   0|q|quiet|s|silence|n|none
                #   1|w|warn|warning
                #   2|r|raise|e|error

                mode = os.environ.get(cls._refresh_env_var, "raise").lower()

                quiet = ["quiet", "q", "silence", "s", "none", "n", "0"]
                warn = ["warn", "w", "warning", "1"]
                error = ["error", "e", "raise", "r", "2"]

                if mode in quiet:
                    pass
                elif mode in warn or mode in error:
                    err = (
                        dedent(
                            """\
                        %s
                        All git commands will error until this is rectified.

                        This initial warning can be silenced or aggravated in the future by setting the
                        $%s environment variable. Use one of the following values:
                            - %s: for no warning or exception
                            - %s: for a printed warning
                            - %s: for a raised exception

                        Example:
                            export %s=%s
                        """
                        )
                        % (
                            err,
                            cls._refresh_env_var,
                            "|".join(quiet),
                            "|".join(warn),
                            "|".join(error),
                            cls._refresh_env_var,
                            quiet[0],
                        )
                    )

                    if mode in warn:
                        print("WARNING: %s" % err)
                    else:
                        raise ImportError(err)
                else:
                    err = (
                        dedent(
                            """\
                        %s environment variable has been set but it has been set with an invalid value.

                        Use only the following values:
                            - %s: for no warning or exception
                            - %s: for a printed warning
                            - %s: for a raised exception
                        """
                        )
                        % (
                            cls._refresh_env_var,
                            "|".join(quiet),
                            "|".join(warn),
                            "|".join(error),
                        )
                    )
                    raise ImportError(err)

                # We get here if this was the init refresh and the refresh mode was not
                # error. Go ahead and set the GIT_PYTHON_GIT_EXECUTABLE such that we
                # discern the difference between a first import and a second import.
                cls.GIT_PYTHON_GIT_EXECUTABLE = cls.git_exec_name
            else:
                # After the first refresh (when GIT_PYTHON_GIT_EXECUTABLE is no longer
                # None) we raise an exception.
                raise GitCommandNotFound("git", err)

        return has_git

    @classmethod
    def is_cygwin(cls) -> bool:
        return is_cygwin_git(cls.GIT_PYTHON_GIT_EXECUTABLE)

    @overload
    @classmethod
    def polish_url(cls, url: str, is_cygwin: Literal[False] = ...) -> str:
        ...

    @overload
    @classmethod
    def polish_url(cls, url: str, is_cygwin: Union[None, bool] = None) -> str:
        ...

    @classmethod
    def polish_url(cls, url: str, is_cygwin: Union[None, bool] = None) -> PathLike:
        """Remove any backslashes from urls to be written in config files.

        Windows might create config files containing paths with backslashes,
        but git stops liking them as it will escape the backslashes. Hence we
        undo the escaping just to be sure.
        """
        if is_cygwin is None:
            is_cygwin = cls.is_cygwin()

        if is_cygwin:
            url = cygpath(url)
        else:
            url = os.path.expandvars(url)
            if url.startswith("~"):
                url = os.path.expanduser(url)
            url = url.replace("\\\\", "\\").replace("\\", "/")
        return url

    @classmethod
    def check_unsafe_protocols(cls, url: str) -> None:
        """Check for unsafe protocols.

        Apart from the usual protocols (http, git, ssh),
        Git allows "remote helpers" that have the form ``<transport>::<address>``.
        One of these helpers (``ext::``) can be used to invoke any arbitrary command.

        See:

        - https://git-scm.com/docs/gitremote-helpers
        - https://git-scm.com/docs/git-remote-ext
        """
        match = cls.re_unsafe_protocol.match(url)
        if match:
            protocol = match.group(1)
            raise UnsafeProtocolError(
                f"The `{protocol}::` protocol looks suspicious, use `allow_unsafe_protocols=True` to allow it."
            )

    @classmethod
    def check_unsafe_options(cls, options: List[str], unsafe_options: List[str]) -> None:
        """Check for unsafe options.

        Some options that are passed to `git <command>` can be used to execute
        arbitrary commands, this are blocked by default.
        """
        # Options can be of the form `foo` or `--foo bar` `--foo=bar`,
        # so we need to check if they start with "--foo" or if they are equal to "foo".
        bare_unsafe_options = [option.lstrip("-") for option in unsafe_options]
        for option in options:
            for unsafe_option, bare_option in zip(unsafe_options, bare_unsafe_options):
                if option.startswith(unsafe_option) or option == bare_option:
                    raise UnsafeOptionError(
                        f"{unsafe_option} is not allowed, use `allow_unsafe_options=True` to allow it."
                    )

    class AutoInterrupt:
        """Process wrapper that terminates the wrapped process on finalization.

        This kills/interrupts the stored process instance once this instance goes out of
        scope. It is used to prevent processes piling up in case iterators stop reading.

        All attributes are wired through to the contained process object.

        The wait method is overridden to perform automatic status code checking and
        possibly raise.
        """

        __slots__ = ("proc", "args", "status")

        # If this is non-zero it will override any status code during
        # _terminate, used to prevent race conditions in testing.
        _status_code_if_terminate: int = 0

        def __init__(self, proc: Union[None, subprocess.Popen], args: Any) -> None:
            self.proc = proc
            self.args = args
            self.status: Union[int, None] = None

        def _terminate(self) -> None:
            """Terminate the underlying process."""
            if self.proc is None:
                return

            proc = self.proc
            self.proc = None
            if proc.stdin:
                proc.stdin.close()
            if proc.stdout:
                proc.stdout.close()
            if proc.stderr:
                proc.stderr.close()
            # Did the process finish already so we have a return code?
            try:
                if proc.poll() is not None:
                    self.status = self._status_code_if_terminate or proc.poll()
                    return
            except OSError as ex:
                log.info("Ignored error after process had died: %r", ex)

            # It can be that nothing really exists anymore...
            if os is None or getattr(os, "kill", None) is None:
                return

            # Try to kill it.
            try:
                proc.terminate()
                status = proc.wait()  # Ensure the process goes away.

                self.status = self._status_code_if_terminate or status
            except OSError as ex:
                log.info("Ignored error after process had died: %r", ex)
            # END exception handling

        def __del__(self) -> None:
            self._terminate()

        def __getattr__(self, attr: str) -> Any:
            return getattr(self.proc, attr)

        # TODO: Bad choice to mimic `proc.wait()` but with different args.
        def wait(self, stderr: Union[None, str, bytes] = b"") -> int:
            """Wait for the process and return its status code.

            :param stderr: Previously read value of stderr, in case stderr is already closed.
            :warn: May deadlock if output or error pipes are used and not handled separately.
            :raise GitCommandError: If the return status is not 0.
            """
            if stderr is None:
                stderr_b = b""
            stderr_b = force_bytes(data=stderr, encoding="utf-8")
            status: Union[int, None]
            if self.proc is not None:
                status = self.proc.wait()
                p_stderr = self.proc.stderr
            else:  # Assume the underlying proc was killed earlier or never existed.
                status = self.status
                p_stderr = None

            def read_all_from_possibly_closed_stream(stream: Union[IO[bytes], None]) -> bytes:
                if stream:
                    try:
                        return stderr_b + force_bytes(stream.read())
                    except (OSError, ValueError):
                        return stderr_b or b""
                else:
                    return stderr_b or b""

            # END status handling

            if status != 0:
                errstr = read_all_from_possibly_closed_stream(p_stderr)
                log.debug("AutoInterrupt wait stderr: %r" % (errstr,))
                raise GitCommandError(remove_password_if_present(self.args), status, errstr)
            return status

    # END auto interrupt

    class CatFileContentStream:
        """Object representing a sized read-only stream returning the contents of
        an object.

        This behaves like a stream, but counts the data read and simulates an empty
        stream once our sized content region is empty.

        If not all data are read to the end of the object's lifetime, we read the
        rest to ensure the underlying stream continues to work.
        """

        __slots__: Tuple[str, ...] = ("_stream", "_nbr", "_size")

        def __init__(self, size: int, stream: IO[bytes]) -> None:
            self._stream = stream
            self._size = size
            self._nbr = 0  # Number of bytes read.

            # Special case: If the object is empty, has null bytes, get the
            # final newline right away.
            if size == 0:
                stream.read(1)
            # END handle empty streams

        def read(self, size: int = -1) -> bytes:
            bytes_left = self._size - self._nbr
            if bytes_left == 0:
                return b""
            if size > -1:
                # Ensure we don't try to read past our limit.
                size = min(bytes_left, size)
            else:
                # They try to read all, make sure it's not more than what remains.
                size = bytes_left
            # END check early depletion
            data = self._stream.read(size)
            self._nbr += len(data)

            # Check for depletion, read our final byte to make the stream usable by others.
            if self._size - self._nbr == 0:
                self._stream.read(1)  # final newline
            # END finish reading
            return data

        def readline(self, size: int = -1) -> bytes:
            if self._nbr == self._size:
                return b""

            # Clamp size to lowest allowed value.
            bytes_left = self._size - self._nbr
            if size > -1:
                size = min(bytes_left, size)
            else:
                size = bytes_left
            # END handle size

            data = self._stream.readline(size)
            self._nbr += len(data)

            # Handle final byte.
            if self._size - self._nbr == 0:
                self._stream.read(1)
            # END finish reading

            return data

        def readlines(self, size: int = -1) -> List[bytes]:
            if self._nbr == self._size:
                return []

            # Leave all additional logic to our readline method, we just check the size.
            out = []
            nbr = 0
            while True:
                line = self.readline()
                if not line:
                    break
                out.append(line)
                if size > -1:
                    nbr += len(line)
                    if nbr > size:
                        break
                # END handle size constraint
            # END readline loop
            return out

        # skipcq: PYL-E0301
        def __iter__(self) -> "Git.CatFileContentStream":
            return self

        def __next__(self) -> bytes:
            line = self.readline()
            if not line:
                raise StopIteration

            return line

        next = __next__

        def __del__(self) -> None:
            bytes_left = self._size - self._nbr
            if bytes_left:
                # Read and discard - seeking is impossible within a stream.
                # This includes any terminating newline.
                self._stream.read(bytes_left + 1)
            # END handle incomplete read

    def __init__(self, working_dir: Union[None, PathLike] = None):
        """Initialize this instance with:

        :param working_dir:
           Git directory we should work in. If None, we always work in the current
           directory as returned by :func:`os.getcwd`.
           It is meant to be the working tree directory if available, or the
           ``.git`` directory in case of bare repositories.
        """
        super().__init__()
        self._working_dir = expand_path(working_dir)
        self._git_options: Union[List[str], Tuple[str, ...]] = ()
        self._persistent_git_options: List[str] = []

        # Extra environment variables to pass to git commands
        self._environment: Dict[str, str] = {}

        # Cached command slots
        self.cat_file_header: Union[None, TBD] = None
        self.cat_file_all: Union[None, TBD] = None

    def __getattr__(self, name: str) -> Any:
        """A convenience method as it allows to call the command as if it was
        an object.

        :return:
            Callable object that will execute call :meth:`_call_process` with
            your arguments.
        """
        if name[0] == "_":
            return LazyMixin.__getattr__(self, name)
        return lambda *args, **kwargs: self._call_process(name, *args, **kwargs)

    def set_persistent_git_options(self, **kwargs: Any) -> None:
        """Specify command line options to the git executable for subsequent
        subcommand calls.

        :param kwargs:
            A dict of keyword arguments.
            These arguments are passed as in :meth:`_call_process`, but will be
            passed to the git command rather than the subcommand.
        """

        self._persistent_git_options = self.transform_kwargs(split_single_char_options=True, **kwargs)

    def _set_cache_(self, attr: str) -> None:
        if attr == "_version_info":
            # We only use the first 4 numbers, as everything else could be strings in fact (on Windows).
            process_version = self._call_process("version")  # Should be as default *args and **kwargs used.
            version_numbers = process_version.split(" ")[2]

            self._version_info = cast(
                Tuple[int, int, int, int],
                tuple(int(n) for n in version_numbers.split(".")[:4] if n.isdigit()),
            )
        else:
            super()._set_cache_(attr)
        # END handle version info

    @property
    def working_dir(self) -> Union[None, PathLike]:
        """:return: Git directory we are working on"""
        return self._working_dir

    @property
    def version_info(self) -> Tuple[int, int, int, int]:
        """
        :return: tuple(int, int, int, int) tuple with integers representing the major, minor
            and additional version numbers as parsed from git version.

            This value is generated on demand and is cached.
        """
        return self._version_info

    @overload
    def execute(self, command: Union[str, Sequence[Any]], *, as_process: Literal[True]) -> "AutoInterrupt":
        ...

    @overload
    def execute(
        self,
        command: Union[str, Sequence[Any]],
        *,
        as_process: Literal[False] = False,
        stdout_as_string: Literal[True],
    ) -> Union[str, Tuple[int, str, str]]:
        ...

    @overload
    def execute(
        self,
        command: Union[str, Sequence[Any]],
        *,
        as_process: Literal[False] = False,
        stdout_as_string: Literal[False] = False,
    ) -> Union[bytes, Tuple[int, bytes, str]]:
        ...

    @overload
    def execute(
        self,
        command: Union[str, Sequence[Any]],
        *,
        with_extended_output: Literal[False],
        as_process: Literal[False],
        stdout_as_string: Literal[True],
    ) -> str:
        ...

    @overload
    def execute(
        self,
        command: Union[str, Sequence[Any]],
        *,
        with_extended_output: Literal[False],
        as_process: Literal[False],
        stdout_as_string: Literal[False],
    ) -> bytes:
        ...

    def execute(
        self,
        command: Union[str, Sequence[Any]],
        istream: Union[None, BinaryIO] = None,
        with_extended_output: bool = False,
        with_exceptions: bool = True,
        as_process: bool = False,
        output_stream: Union[None, BinaryIO] = None,
        stdout_as_string: bool = True,
        kill_after_timeout: Union[None, float] = None,
        with_stdout: bool = True,
        universal_newlines: bool = False,
        shell: Union[None, bool] = None,
        env: Union[None, Mapping[str, str]] = None,
        max_chunk_size: int = io.DEFAULT_BUFFER_SIZE,
        strip_newline_in_stdout: bool = True,
        **subprocess_kwargs: Any,
    ) -> Union[str, bytes, Tuple[int, Union[str, bytes], str], AutoInterrupt]:
        R"""Handle executing the command, and consume and return the returned
        information (stdout).

        :param command:
            The command argument list to execute.
            It should be a sequence of program arguments, or a string. The
            program to execute is the first item in the args sequence or string.

        :param istream:
            Standard input filehandle passed to :class:`subprocess.Popen`.

        :param with_extended_output:
            Whether to return a (status, stdout, stderr) tuple.

        :param with_exceptions:
            Whether to raise an exception when git returns a non-zero status.

        :param as_process:
            Whether to return the created process instance directly from which
            streams can be read on demand. This will render `with_extended_output`
            and `with_exceptions` ineffective - the caller will have to deal with
            the details. It is important to note that the process will be placed
            into an :class:`AutoInterrupt` wrapper that will interrupt the process
            once it goes out of scope. If you use the command in iterators, you
            should pass the whole process instance instead of a single stream.

        :param output_stream:
            If set to a file-like object, data produced by the git command will be
            output to the given stream directly.
            This feature only has any effect if `as_process` is False. Processes will
            always be created with a pipe due to issues with subprocess.
            This merely is a workaround as data will be copied from the
            output pipe to the given output stream directly.
            Judging from the implementation, you shouldn't use this parameter!

        :param stdout_as_string:
            If False, the command's standard output will be bytes. Otherwise, it will be
            decoded into a string using the default encoding (usually UTF-8).
            The latter can fail, if the output contains binary data.

        :param kill_after_timeout:
            Specifies a timeout in seconds for the git command, after which the process
            should be killed. This will have no effect if `as_process` is set to True.
            It is set to None by default and will let the process run until the timeout
            is explicitly specified. Uses of this feature should be carefully
            considered, due to the following limitations:

            1. This feature is not supported at all on Windows.
            2. Effectiveness may vary by operating system. ``ps --ppid`` is used to
               enumerate child processes, which is available on most GNU/Linux systems
               but not most others.
            3. Deeper descendants do not receive signals, though they may sometimes
               terminate as a consequence of their parent processes being killed.
            4. `kill_after_timeout` uses ``SIGKILL``, which can have negative side
               effects on a repository. For example, stale locks in case of ``git gc``
               could render the repository incapable of accepting changes until the lock
               is manually removed.

        :param with_stdout:
            If True, default True, we open stdout on the created process.

        :param universal_newlines:
            if True, pipes will be opened as text, and lines are split at
            all known line endings.

        :param shell:
            Whether to invoke commands through a shell (see `Popen(..., shell=True)`).
            If this is not `None`, it overrides :attr:`USE_SHELL`.

            Passing ``shell=True`` to this or any other GitPython function should be
            avoided, as it is unsafe under most circumstances. This is because it is
            typically not feasible to fully consider and account for the effect of shell
            expansions, especially when passing ``shell=True`` to other methods that
            forward it to :meth:`Git.execute`. Passing ``shell=True`` is also no longer
            needed (nor useful) to work around any known operating system specific
            issues.

        :param env:
            A dictionary of environment variables to be passed to :class:`subprocess.Popen`.

        :param max_chunk_size:
            Maximum number of bytes in one chunk of data passed to the output_stream in
            one invocation of write() method. If the given number is not positive then
            the default value is used.

        :param strip_newline_in_stdout:
            Whether to strip the trailing ``\n`` of the command stdout.

        :param subprocess_kwargs:
            Keyword arguments to be passed to :class:`subprocess.Popen`. Please note
            that some of the valid kwargs are already set by this method; the ones you
            specify may not be the same ones.

        :return:
            * str(output) if extended_output = False (Default)
            * tuple(int(status), str(stdout), str(stderr)) if extended_output = True

            If output_stream is True, the stdout value will be your output stream:
            * output_stream if extended_output = False
            * tuple(int(status), output_stream, str(stderr)) if extended_output = True

            Note that git is executed with ``LC_MESSAGES="C"`` to ensure consistent
            output regardless of system language.

        :raise GitCommandError:

        :note:
           If you add additional keyword arguments to the signature of this method,
           you must update the execute_kwargs tuple housed in this module.
        """
        # Remove password for the command if present.
        redacted_command = remove_password_if_present(command)
        if self.GIT_PYTHON_TRACE and (self.GIT_PYTHON_TRACE != "full" or as_process):
            log.info(" ".join(redacted_command))

        # Allow the user to have the command executed in their working dir.
        try:
            cwd = self._working_dir or os.getcwd()  # type: Union[None, str]
            if not os.access(str(cwd), os.X_OK):
                cwd = None
        except FileNotFoundError:
            cwd = None

        # Start the process.
        inline_env = env
        env = os.environ.copy()
        # Attempt to force all output to plain ASCII English, which is what some parsing
        # code may expect.
        # According to https://askubuntu.com/a/311796, we are setting LANGUAGE as well
        # just to be sure.
        env["LANGUAGE"] = "C"
        env["LC_ALL"] = "C"
        env.update(self._environment)
        if inline_env is not None:
            env.update(inline_env)

        if os.name == "nt":
            cmd_not_found_exception = OSError
            if kill_after_timeout is not None:
                raise GitCommandError(
                    redacted_command,
                    '"kill_after_timeout" feature is not supported on Windows.',
                )
        else:
            cmd_not_found_exception = FileNotFoundError
        # END handle

        stdout_sink = PIPE if with_stdout else getattr(subprocess, "DEVNULL", None) or open(os.devnull, "wb")
        if shell is None:
            shell = self.USE_SHELL
        log.debug(
            "Popen(%s, cwd=%s, stdin=%s, shell=%s, universal_newlines=%s)",
            redacted_command,
            cwd,
            "<valid stream>" if istream else "None",
            shell,
            universal_newlines,
        )
        try:
            proc = safer_popen(
                command,
                env=env,
                cwd=cwd,
                bufsize=-1,
                stdin=(istream or DEVNULL),
                stderr=PIPE,
                stdout=stdout_sink,
                shell=shell,
                universal_newlines=universal_newlines,
                **subprocess_kwargs,
            )
        except cmd_not_found_exception as err:
            raise GitCommandNotFound(redacted_command, err) from err
        else:
            # Replace with a typeguard for Popen[bytes]?
            proc.stdout = cast(BinaryIO, proc.stdout)
            proc.stderr = cast(BinaryIO, proc.stderr)

        if as_process:
            return self.AutoInterrupt(proc, command)

        def kill_process(pid: int) -> None:
            """Callback to kill a process."""
            if os.name == "nt":
                raise AssertionError("Bug: This callback would be ineffective and unsafe on Windows, stopping.")
            p = Popen(["ps", "--ppid", str(pid)], stdout=PIPE)
            child_pids = []
            if p.stdout is not None:
                for line in p.stdout:
                    if len(line.split()) > 0:
                        local_pid = (line.split())[0]
                        if local_pid.isdigit():
                            child_pids.append(int(local_pid))
            try:
                os.kill(pid, signal.SIGKILL)
                for child_pid in child_pids:
                    try:
                        os.kill(child_pid, signal.SIGKILL)
                    except OSError:
                        pass
                kill_check.set()  # Tell the main routine that the process was killed.
            except OSError:
                # It is possible that the process gets completed in the duration after
                # timeout happens and before we try to kill the process.
                pass
            return

        # END kill_process

        if kill_after_timeout is not None:
            kill_check = threading.Event()
            watchdog = threading.Timer(kill_after_timeout, kill_process, args=(proc.pid,))

        # Wait for the process to return.
        status = 0
        stdout_value: Union[str, bytes] = b""
        stderr_value: Union[str, bytes] = b""
        newline = "\n" if universal_newlines else b"\n"
        try:
            if output_stream is None:
                if kill_after_timeout is not None:
                    watchdog.start()
                stdout_value, stderr_value = proc.communicate()
                if kill_after_timeout is not None:
                    watchdog.cancel()
                    if kill_check.is_set():
                        stderr_value = 'Timeout: the command "%s" did not complete in %d ' "secs." % (
                            " ".join(redacted_command),
                            kill_after_timeout,
                        )
                        if not universal_newlines:
                            stderr_value = stderr_value.encode(defenc)
                # Strip trailing "\n".
                if stdout_value.endswith(newline) and strip_newline_in_stdout:  # type: ignore
                    stdout_value = stdout_value[:-1]
                if stderr_value.endswith(newline):  # type: ignore
                    stderr_value = stderr_value[:-1]

                status = proc.returncode
            else:
                max_chunk_size = max_chunk_size if max_chunk_size and max_chunk_size > 0 else io.DEFAULT_BUFFER_SIZE
                stream_copy(proc.stdout, output_stream, max_chunk_size)
                stdout_value = proc.stdout.read()
                stderr_value = proc.stderr.read()
                # Strip trailing "\n".
                if stderr_value.endswith(newline):  # type: ignore
                    stderr_value = stderr_value[:-1]
                status = proc.wait()
            # END stdout handling
        finally:
            proc.stdout.close()
            proc.stderr.close()

        if self.GIT_PYTHON_TRACE == "full":
            cmdstr = " ".join(redacted_command)

            def as_text(stdout_value: Union[bytes, str]) -> str:
                return not output_stream and safe_decode(stdout_value) or "<OUTPUT_STREAM>"

            # END as_text

            if stderr_value:
                log.info(
                    "%s -> %d; stdout: '%s'; stderr: '%s'",
                    cmdstr,
                    status,
                    as_text(stdout_value),
                    safe_decode(stderr_value),
                )
            elif stdout_value:
                log.info("%s -> %d; stdout: '%s'", cmdstr, status, as_text(stdout_value))
            else:
                log.info("%s -> %d", cmdstr, status)
        # END handle debug printing

        if with_exceptions and status != 0:
            raise GitCommandError(redacted_command, status, stderr_value, stdout_value)

        if isinstance(stdout_value, bytes) and stdout_as_string:  # Could also be output_stream.
            stdout_value = safe_decode(stdout_value)

        # Allow access to the command's status code.
        if with_extended_output:
            return (status, stdout_value, safe_decode(stderr_value))
        else:
            return stdout_value

    def environment(self) -> Dict[str, str]:
        return self._environment

    def update_environment(self, **kwargs: Any) -> Dict[str, Union[str, None]]:
        """Set environment variables for future git invocations. Return all changed
        values in a format that can be passed back into this function to revert the
        changes.

        ``Examples``::

            old_env = self.update_environment(PWD='/tmp')
            self.update_environment(**old_env)

        :param kwargs: Environment variables to use for git processes

        :return: Dict that maps environment variables to their old values
        """
        old_env = {}
        for key, value in kwargs.items():
            # Set value if it is None.
            if value is not None:
                old_env[key] = self._environment.get(key)
                self._environment[key] = value
            # Remove key from environment if its value is None.
            elif key in self._environment:
                old_env[key] = self._environment[key]
                del self._environment[key]
        return old_env

    @contextlib.contextmanager
    def custom_environment(self, **kwargs: Any) -> Iterator[None]:
        """A context manager around the above :meth:`update_environment` method to
        restore the environment back to its previous state after operation.

        ``Examples``::

            with self.custom_environment(GIT_SSH='/bin/ssh_wrapper'):
                repo.remotes.origin.fetch()

        :param kwargs: See :meth:`update_environment`
        """
        old_env = self.update_environment(**kwargs)
        try:
            yield
        finally:
            self.update_environment(**old_env)

    def transform_kwarg(self, name: str, value: Any, split_single_char_options: bool) -> List[str]:
        if len(name) == 1:
            if value is True:
                return ["-%s" % name]
            elif value not in (False, None):
                if split_single_char_options:
                    return ["-%s" % name, "%s" % value]
                else:
                    return ["-%s%s" % (name, value)]
        else:
            if value is True:
                return ["--%s" % dashify(name)]
            elif value is not False and value is not None:
                return ["--%s=%s" % (dashify(name), value)]
        return []

    def transform_kwargs(self, split_single_char_options: bool = True, **kwargs: Any) -> List[str]:
        """Transform Python style kwargs into git command line options."""
        args = []
        for k, v in kwargs.items():
            if isinstance(v, (list, tuple)):
                for value in v:
                    args += self.transform_kwarg(k, value, split_single_char_options)
            else:
                args += self.transform_kwarg(k, v, split_single_char_options)
        return args

    @classmethod
    def _unpack_args(cls, arg_list: Sequence[str]) -> List[str]:
        outlist = []
        if isinstance(arg_list, (list, tuple)):
            for arg in arg_list:
                outlist.extend(cls._unpack_args(arg))
        else:
            outlist.append(str(arg_list))

        return outlist

    def __call__(self, **kwargs: Any) -> "Git":
        """Specify command line options to the git executable for a subcommand call.

        :param kwargs:
            A dict of keyword arguments.
            These arguments are passed as in :meth:`_call_process`, but will be
            passed to the git command rather than the subcommand.

        ``Examples``::
            git(work_tree='/tmp').difftool()
        """
        self._git_options = self.transform_kwargs(split_single_char_options=True, **kwargs)
        return self

    @overload
    def _call_process(self, method: str, *args: None, **kwargs: None) -> str:
        ...  # If no args were given, execute the call with all defaults.

    @overload
    def _call_process(
        self,
        method: str,
        istream: int,
        as_process: Literal[True],
        *args: Any,
        **kwargs: Any,
    ) -> "Git.AutoInterrupt":
        ...

    @overload
    def _call_process(
        self, method: str, *args: Any, **kwargs: Any
    ) -> Union[str, bytes, Tuple[int, Union[str, bytes], str], "Git.AutoInterrupt"]:
        ...

    def _call_process(
        self, method: str, *args: Any, **kwargs: Any
    ) -> Union[str, bytes, Tuple[int, Union[str, bytes], str], "Git.AutoInterrupt"]:
        """Run the given git command with the specified arguments and return
        the result as a string.

        :param method:
            The command. Contained ``_`` characters will be converted to dashes,
            such as in ``ls_files`` to call ``ls-files``.

        :param args:
            The list of arguments. If None is included, it will be pruned.
            This allows your commands to call git more conveniently as None
            is realized as non-existent.

        :param kwargs:
            Contains key-values for the following:
            - The :meth:`execute()` kwds, as listed in :var:`execute_kwargs`.
            - "Command options" to be converted by :meth:`transform_kwargs`.
            - The `'insert_kwargs_after'` key which its value must match one of ``*args``.
            It also contains any command options, to be appended after the matched arg.

        Examples::

            git.rev_list('master', max_count=10, header=True)

        turns into::

           git rev-list max-count 10 --header master

        :return: Same as :meth:`execute`.
            If no args are given, used :meth:`execute`'s default (especially
            ``as_process = False``, ``stdout_as_string = True``) and return str.
        """
        # Handle optional arguments prior to calling transform_kwargs.
        # Otherwise these'll end up in args, which is bad.
        exec_kwargs = {k: v for k, v in kwargs.items() if k in execute_kwargs}
        opts_kwargs = {k: v for k, v in kwargs.items() if k not in execute_kwargs}

        insert_after_this_arg = opts_kwargs.pop("insert_kwargs_after", None)

        # Prepare the argument list.

        opt_args = self.transform_kwargs(**opts_kwargs)
        ext_args = self._unpack_args([a for a in args if a is not None])

        if insert_after_this_arg is None:
            args_list = opt_args + ext_args
        else:
            try:
                index = ext_args.index(insert_after_this_arg)
            except ValueError as err:
                raise ValueError(
                    "Couldn't find argument '%s' in args %s to insert cmd options after"
                    % (insert_after_this_arg, str(ext_args))
                ) from err
            # END handle error
            args_list = ext_args[: index + 1] + opt_args + ext_args[index + 1 :]
        # END handle opts_kwargs

        call = [self.GIT_PYTHON_GIT_EXECUTABLE]

        # Add persistent git options.
        call.extend(self._persistent_git_options)

        # Add the git options, then reset to empty to avoid side effects.
        call.extend(self._git_options)
        self._git_options = ()

        call.append(dashify(method))
        call.extend(args_list)

        return self.execute(call, **exec_kwargs)

    def _parse_object_header(self, header_line: str) -> Tuple[str, str, int]:
        """
        :param header_line:
            <hex_sha> type_string size_as_int

        :return: (hex_sha, type_string, size_as_int)

        :raise ValueError: If the header contains indication for an error due to
            incorrect input sha
        """
        tokens = header_line.split()
        if len(tokens) != 3:
            if not tokens:
                err_msg = (
                    f"SHA is empty, possible dubious ownership in the repository "
                    f"""at {self._working_dir}.\n            If this is unintended run:\n\n         """
                    f"""             "git config --global --add safe.directory {self._working_dir}" """
                )
                raise ValueError(err_msg)
            else:
                raise ValueError("SHA %s could not be resolved, git returned: %r" % (tokens[0], header_line.strip()))
            # END handle actual return value
        # END error handling

        if len(tokens[0]) != 40:
            raise ValueError("Failed to parse header: %r" % header_line)
        return (tokens[0], tokens[1], int(tokens[2]))

    def _prepare_ref(self, ref: AnyStr) -> bytes:
        # Required for command to separate refs on stdin, as bytes.
        if isinstance(ref, bytes):
            # Assume 40 bytes hexsha - bin-to-ascii for some reason returns bytes, not text.
            refstr: str = ref.decode("ascii")
        elif not isinstance(ref, str):
            refstr = str(ref)  # Could be ref-object.
        else:
            refstr = ref

        if not refstr.endswith("\n"):
            refstr += "\n"
        return refstr.encode(defenc)

    def _get_persistent_cmd(self, attr_name: str, cmd_name: str, *args: Any, **kwargs: Any) -> "Git.AutoInterrupt":
        cur_val = getattr(self, attr_name)
        if cur_val is not None:
            return cur_val

        options = {"istream": PIPE, "as_process": True}
        options.update(kwargs)

        cmd = self._call_process(cmd_name, *args, **options)
        setattr(self, attr_name, cmd)
        cmd = cast("Git.AutoInterrupt", cmd)
        return cmd

    def __get_object_header(self, cmd: "Git.AutoInterrupt", ref: AnyStr) -> Tuple[str, str, int]:
        if cmd.stdin and cmd.stdout:
            cmd.stdin.write(self._prepare_ref(ref))
            cmd.stdin.flush()
            return self._parse_object_header(cmd.stdout.readline())
        else:
            raise ValueError("cmd stdin was empty")

    def get_object_header(self, ref: str) -> Tuple[str, str, int]:
        """Use this method to quickly examine the type and size of the object behind
        the given ref.

        :note: The method will only suffer from the costs of command invocation
            once and reuses the command in subsequent calls.

        :return: (hexsha, type_string, size_as_int)
        """
        cmd = self._get_persistent_cmd("cat_file_header", "cat_file", batch_check=True)
        return self.__get_object_header(cmd, ref)

    def get_object_data(self, ref: str) -> Tuple[str, str, int, bytes]:
        """As get_object_header, but returns object data as well.

        :return: (hexsha, type_string, size_as_int, data_string)
        :note: Not threadsafe.
        """
        hexsha, typename, size, stream = self.stream_object_data(ref)
        data = stream.read(size)
        del stream
        return (hexsha, typename, size, data)

    def stream_object_data(self, ref: str) -> Tuple[str, str, int, "Git.CatFileContentStream"]:
        """As get_object_header, but returns the data as a stream.

        :return: (hexsha, type_string, size_as_int, stream)
        :note: This method is not threadsafe, you need one independent Command instance per thread to be safe!
        """
        cmd = self._get_persistent_cmd("cat_file_all", "cat_file", batch=True)
        hexsha, typename, size = self.__get_object_header(cmd, ref)
        cmd_stdout = cmd.stdout if cmd.stdout is not None else io.BytesIO()
        return (hexsha, typename, size, self.CatFileContentStream(size, cmd_stdout))

    def clear_cache(self) -> "Git":
        """Clear all kinds of internal caches to release resources.

        Currently persistent commands will be interrupted.

        :return: self
        """
        for cmd in (self.cat_file_all, self.cat_file_header):
            if cmd:
                cmd.__del__()

        self.cat_file_all = None
        self.cat_file_header = None
        return self