socket.recvmsg_into

recvmsg_into(buffers[, ancbufsize[, flags]]) -> (nbytes, ancdata, msg_flags, address)

Receive normal data and ancillary data from the socket, scattering the
non-ancillary data into a series of buffers.  The buffers argument
must be an iterable of objects that export writable buffers
(e.g. bytearray objects); these will be filled with successive chunks
of the non-ancillary data until it has all been written or there are
no more buffers.  The ancbufsize argument sets the size in bytes of
the internal buffer used to receive the ancillary data; it defaults to
0, meaning that no ancillary data will be received.  Appropriate
buffer sizes for ancillary data can be calculated using CMSG_SPACE()
or CMSG_LEN(), and items which do not fit into the buffer might be
truncated or discarded.  The flags argument defaults to 0 and has the
same meaning as for recv().

The return value is a 4-tuple: (nbytes, ancdata, msg_flags, address).
The nbytes item is the total number of bytes of non-ancillary data
written into the buffers.  The ancdata item is a list of zero or more
tuples (cmsg_level, cmsg_type, cmsg_data) representing the ancillary
data (control messages) received: cmsg_level and cmsg_type are
integers specifying the protocol level and protocol-specific type
respectively, and cmsg_data is a bytes object holding the associated
data.  The msg_flags item is the bitwise OR of various flags
indicating conditions on the received message; see your system
documentation for details.  If the receiving socket is unconnected,
address is the address of the sending socket, if available; otherwise,
its value is unspecified.

If recvmsg_into() raises an exception after the system call returns,
it will first attempt to close any file descriptors received via the
SCM_RIGHTS mechanism.