comparison mercurial/pure/osutil.py @ 49275:c6a3243567b6

chg: replace mercurial.util.recvfds() by simpler pure Python implementation

On Python 3, we have socket.socket.recvmsg(). This makes it possible to receive
FDs in pure Python code. The new code behaves like the previous
implementations, except that it’s more strict about the format of the ancillary
data. This works because we know in which format the FDs are passed.

Because the code is (and always has been) specific to chg (payload is 1 byte,
number of passed FDs is limited) and we now have only one implementation and
the code is very short, I decided to stop exposing a function in
mercurial.util.

Note on terminology: The SCM_RIGHTS mechanism is used to share open file
descriptions to another process over a socket. The sending side passes an array
of file descriptors and the receiving side receives an array of file
descriptors. The file descriptors are different in general on both sides but
refer to the same open file descriptions. The two terms are often conflated,
even in the official documentation. That’s why I used “FD” above, which could
mean both “file descriptor” and “file description”.

49273:34020d1f1635

import ctypes
import ctypes.util
import os
import socket
import stat as statmod

from ..pycompat import getattr
from .. import (
    encoding,

if not pycompat.iswindows:
    posixfile = open

    _SCM_RIGHTS = 0x01
    _socklen_t = ctypes.c_uint

    if pycompat.sysplatform.startswith(b'linux'):
        # socket.h says "the type should be socklen_t but the definition of
        # the kernel is incompatible with this."
        _cmsg_len_t = ctypes.c_size_t
        _msg_controllen_t = ctypes.c_size_t
        _msg_iovlen_t = ctypes.c_size_t
    else:
        _cmsg_len_t = _socklen_t
        _msg_controllen_t = _socklen_t
        _msg_iovlen_t = ctypes.c_int

    class _iovec(ctypes.Structure):
        _fields_ = [
            (u'iov_base', ctypes.c_void_p),
            (u'iov_len', ctypes.c_size_t),
        ]

    class _msghdr(ctypes.Structure):
        _fields_ = [
            (u'msg_name', ctypes.c_void_p),
            (u'msg_namelen', _socklen_t),
            (u'msg_iov', ctypes.POINTER(_iovec)),
            (u'msg_iovlen', _msg_iovlen_t),
            (u'msg_control', ctypes.c_void_p),
            (u'msg_controllen', _msg_controllen_t),
            (u'msg_flags', ctypes.c_int),
        ]

    class _cmsghdr(ctypes.Structure):
        _fields_ = [
            (u'cmsg_len', _cmsg_len_t),
            (u'cmsg_level', ctypes.c_int),
            (u'cmsg_type', ctypes.c_int),
            (u'cmsg_data', ctypes.c_ubyte * 0),
        ]

    _libc = ctypes.CDLL(ctypes.util.find_library(u'c'), use_errno=True)
    _recvmsg = getattr(_libc, 'recvmsg', None)
    if _recvmsg:
        _recvmsg.restype = getattr(ctypes, 'c_ssize_t', ctypes.c_long)
        _recvmsg.argtypes = (
            ctypes.c_int,
            ctypes.POINTER(_msghdr),
            ctypes.c_int,
        )
    else:
        # recvmsg isn't always provided by libc; such systems are unsupported
        def _recvmsg(sockfd, msg, flags):
            raise NotImplementedError(b'unsupported platform')

    def _CMSG_FIRSTHDR(msgh):
        if msgh.msg_controllen < ctypes.sizeof(_cmsghdr):
            return
        cmsgptr = ctypes.cast(msgh.msg_control, ctypes.POINTER(_cmsghdr))
        return cmsgptr.contents

    # The pure version is less portable than the native version because the
    # handling of socket ancillary data heavily depends on C preprocessor.
    # Also, some length fields are wrongly typed in Linux kernel.
    def recvfds(sockfd):
        """receive list of file descriptors via socket"""
        dummy = (ctypes.c_ubyte * 1)()
        iov = _iovec(ctypes.cast(dummy, ctypes.c_void_p), ctypes.sizeof(dummy))
        cbuf = ctypes.create_string_buffer(256)
        msgh = _msghdr(
            None,
            0,
            ctypes.pointer(iov),
            1,
            ctypes.cast(cbuf, ctypes.c_void_p),
            ctypes.sizeof(cbuf),
            0,
        )
        r = _recvmsg(sockfd, ctypes.byref(msgh), 0)
        if r < 0:
            e = ctypes.get_errno()
            raise OSError(e, os.strerror(e))
        # assumes that the first cmsg has fds because it isn't easy to write
        # portable CMSG_NXTHDR() with ctypes.
        cmsg = _CMSG_FIRSTHDR(msgh)
        if not cmsg:
            return []
        if (
            cmsg.cmsg_level != socket.SOL_SOCKET
            or cmsg.cmsg_type != _SCM_RIGHTS
        ):
            return []
        rfds = ctypes.cast(cmsg.cmsg_data, ctypes.POINTER(ctypes.c_int))
        rfdscount = (
            cmsg.cmsg_len - _cmsghdr.cmsg_data.offset
        ) // ctypes.sizeof(ctypes.c_int)
        return [rfds[i] for i in pycompat.xrange(rfdscount)]


else:
    import msvcrt

    _kernel32 = ctypes.windll.kernel32  # pytype: disable=module-attr

49275:c6a3243567b6

import ctypes
import ctypes.util
import os
import stat as statmod

from ..pycompat import getattr
from .. import (
    encoding,

if not pycompat.iswindows:
    posixfile = open


else:
    import msvcrt

    _kernel32 = ctypes.windll.kernel32  # pytype: disable=module-attr