# -*- test-case-name: twext.internet.test.test_sendfdport -*-
##
# Copyright (c) 2010-2016 Apple Inc. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
##

"""
Implementation of a TCP/SSL port that uses send1msg/recv1msg as implemented by
L{twisted.python.sendfd}.
"""

from os import close
from errno import EAGAIN, ENOBUFS
from socket import (
    socketpair, fromfd, error as SocketError, AF_UNIX, SOCK_STREAM, SOCK_DGRAM
)

from zope.interface import Interface

from twisted.python.sendmsg import send1msg, recv1msg, getsockfam
from twisted.internet.abstract import FileDescriptor
from twisted.internet.protocol import Protocol, Factory

from twext.python.log import Logger
from twext.python.sendfd import sendfd, recvfd

log = Logger()


class InheritingProtocol(Protocol, object):
    """
    When a connection comes in on this protocol, stop reading and writing, and
    dispatch the socket to another process via its factory.
    """

    def connectionMade(self):
        """
        A connection was received; transmit the file descriptor to another
        process via L{InheritingProtocolFactory} and remove my transport from
        the reactor.
        """
        self.transport.stopReading()
        self.transport.stopWriting()
        skt = self.transport.getHandle()
        self.factory.sendSocket(skt)


class InheritingProtocolFactory(Factory, object):
    """
    An L{InheritingProtocolFactory} is a protocol factory which listens for
    incoming connections in a I{master process}, then sends those connections
    off to be inherited by a I{worker process} via an
    L{InheritedSocketDispatcher}.

    L{InheritingProtocolFactory} is instantiated in the master process.

    @ivar dispatcher: an L{InheritedSocketDispatcher} to use to dispatch
        incoming connections to an appropriate subprocess.

    @ivar description: the string to send along with connections received on
        this factory.
    """

    protocol = InheritingProtocol

    def __init__(self, dispatcher, description):
        self.dispatcher = dispatcher
        self.description = description

    def sendSocket(self, socketObject):
        """
        Send the given socket object on to my dispatcher.
        """
        self.dispatcher.sendFileDescriptor(socketObject, self.description)


class _SubprocessSocket(FileDescriptor, object):
    """
    A socket in the master process pointing at a file descriptor that can be
    used to transmit sockets to a subprocess.

    @ivar outSocket: the UNIX socket used as the send1msg() transport.
    @type outSocket: L{socket.socket}

    @ivar outgoingSocketQueue: an outgoing queue of sockets to send to the
        subprocess, along with their descriptions (strings describing their
        protocol so that the subprocess knows how to handle them; as of this
        writing, either C{"TCP"} or C{"SSL"})
    @ivar outgoingSocketQueue: a C{list} of 2-tuples of C{(socket-object,
        bytes)}

    @ivar status: a record of the last status message received (via
        L{recv1msg}) from the subprocess: this is an application-specific
        indication of how ready this subprocess is to receive more connections.
        A typical usage would be to count the open connections: this is what is
        passed to
    @type status: See L{IStatusWatcher} for an explanation of which methods
        determine this type.

    @ivar dispatcher: The socket dispatcher that owns this L{_SubprocessSocket}
    @type dispatcher: L{InheritedSocketDispatcher}
    """

    def __init__(self, dispatcher, inSocket, outSocket, status, slavenum):
        FileDescriptor.__init__(self, dispatcher.reactor)
        self.status = status
        self.slavenum = slavenum
        self.dispatcher = dispatcher
        self.inSocket = inSocket
        self.outSocket = outSocket   # XXX needs to be set non-blocking by somebody
        self.fileno = outSocket.fileno
        self.outgoingSocketQueue = []
        self.pendingCloseSocketQueue = []

    def childSocket(self):
        """
        Return the socket that the child process will use to communicate with the master.
        """
        return self.inSocket

    def start(self):
        """
        The master process monitor is about to start the child process associated with this socket.
        Update status to ensure dispatcher know what is going on.
        """
        self.status.start()
        self.dispatcher.statusChanged()

    def restarted(self):
        """
        The child process associated with this socket has signaled it is ready.
        Update status to ensure dispatcher know what is going on.
        """
        self.status.restarted()
        self.dispatcher.statusChanged()

    def stop(self):
        """
        The master process monitor has determined the child process associated with this socket
        has died. Update status to ensure dispatcher know what is going on.
        """
        self.status.stop()
        self.dispatcher.statusChanged()

    def remove(self):
        """
        Remove this socket.
        """
        self.status.stop()
        self.dispatcher.statusChanged()
        self.dispatcher.removeSocket()

    def sendSocketToPeer(self, skt, description):
        """
        Enqueue a socket to send to the subprocess.
        """
        self.outgoingSocketQueue.append((skt, description))
        self.startWriting()

    def doRead(self, recvmsg=recv1msg):
        """
        Receive a status / health message and record it.
        """
        try:
            data, _ignore_flags, _ignore_ancillary = recvmsg(
                self.outSocket.fileno()
            )
        except SocketError, se:
            if se.errno not in (EAGAIN, ENOBUFS):
                raise
        else:
            closeCount = self.dispatcher.statusMessage(self, data)
            for ignored in xrange(closeCount):
                self.pendingCloseSocketQueue.pop(0).close()

    def doWrite(self, sendfd=sendfd):
        """
        Transmit as many queued pending file descriptors as we can.
        """
        while self.outgoingSocketQueue:
            skt, desc = self.outgoingSocketQueue.pop(0)
            try:
                sendfd(self.outSocket.fileno(), skt.fileno(), desc)
            except SocketError, se:
                if se.errno in (EAGAIN, ENOBUFS):
                    self.outgoingSocketQueue.insert(0, (skt, desc))
                    return
                raise

            # Ready to close this socket; wait until it is acknowledged.
            self.pendingCloseSocketQueue.append(skt)

        if not self.outgoingSocketQueue:
            self.stopWriting()


class IStatus(Interface):
    """
    Defines the status of a socket. This keeps track of active connections etc.
    """

    def effective():
        """
        The current effective load.

        @return: The current effective load.
        @rtype: L{int}
        """

    def active():
        """
        Whether the socket should be active (able to be dispatched to).

        @return: Active state.
        @rtype: L{bool}
        """

    def start():
        """
        Worker process is starting. Mark status accordingly but do not make
        it active.

        @return: C{self}
        """

    def restarted():
        """
        Worker process has signaled it is ready so make this active.

        @return: C{self}
        """

    def stop():
        """
        Worker process has stopped so make this inactive.

        @return: C{self}
        """


class IStatusWatcher(Interface):
    """
    A provider of L{IStatusWatcher} tracks the I{status messages} reported by
    the worker processes over their control sockets, and computes internal
    I{status values} for those messages.  The I{messages} are individual
    octets, representing one of three operations.  C{0} meaning "a new worker
    process has started, with zero connections being processed", C{+} meaning
    "I have received and am processing your request; I am confirming that my
    requests-being-processed count has gone up by one", and C{-} meaning "I
    have completed processing a request, my requests-being-processed count has
    gone down by one".  The I{status value} tracked by
    L{_SubprocessSocket.status} is an integer, indicating the current
    requests-being-processed value.  (FIXME: the intended design here is
    actually just that all I{this} object knows about is that
    L{_SubprocessSocket.status} is an orderable value, and that this
    C{statusWatcher} will compute appropriate values so the status that I{sorts
    the least} is the socket to which new connections should be directed; also,
    the format of the status messages is only known / understood by the
    C{statusWatcher}, not the L{InheritedSocketDispatcher}.  It's hard to
    explain it in that manner though.)

    @note: the intention of this interface is to eventually provide a broader
        notion of what might constitute 'status', so the above explanation just
        explains the current implementation, in for expediency's sake, rather
        than the somewhat more abstract language that would be accurate.
    """

    def initialStatus():
        """
        A new socket was created and added to the dispatcher.  Compute an
        initial value for its status.

        @return: the new status.
        """

    def newConnectionStatus(previousStatus):
        """
        A new connection was sent to a given socket.  Compute its status based
        on the previous status of that socket.

        @param previousStatus: A status value for the socket being sent work,
            previously returned by one of the methods on this interface.

        @return: the socket's status after incrementing its outstanding work.
        """

    def statusFromMessage(previousStatus, message):
        """
        A status message was received by a worker.  Convert the previous status
        value (returned from L{newConnectionStatus}, L{initialStatus}, or
        L{statusFromMessage}).

        @param previousStatus: A status value for the socket being sent work,
            previously returned by one of the methods on this interface.

        @return: the socket's status after taking the reported message into
            account.
        """

    def closeCountFromStatus(previousStatus):
        """
        Based on a status previously returned from a method on this
        L{IStatusWatcher}, determine how many sockets may be closed.

        @return: a 2-tuple of C{number of sockets that may safely be closed},
            C{new status}.
        @rtype: 2-tuple of (C{int}, C{<opaque>})
        """


class InheritedSocketDispatcher(object):
    """
    Used by one or more L{InheritingProtocolFactory}s, this keeps track of a
    list of available sockets that connect to I{worker process}es and sends
    inbound connections to be inherited over those sockets, by those processes.

    L{InheritedSocketDispatcher} is therefore instantiated in the I{master
    process}.

    @ivar statusWatcher: The object which will handle status messages and
        convert them into current statuses, as well as .
    @type statusWatcher: L{IStatusWatcher}
    """

    def __init__(self, statusWatcher):
        """
        Create a socket dispatcher.
        """
        self._subprocessSockets = []
        self.statusWatcher = statusWatcher
        from twisted.internet import reactor
        self.reactor = reactor
        self._isDispatching = False

    @property
    def statuses(self):
        """
        Yield the current status of all subprocess sockets in the current priority order.
        """
        for subsocket in self._subprocessSockets:
            yield subsocket.status

    @property
    def slavestates(self):
        """
        Yield the current status of all subprocess sockets, ordered by slave number.
        """
        for subsocket in sorted(self._subprocessSockets, key=lambda x: x.slavenum):
            yield (subsocket.slavenum, subsocket.status,)

    def statusChanged(self):
        """
        Someone is telling us a child socket status changed.
        """
        self.statusWatcher.statusesChanged(self.statuses)

    def statusMessage(self, subsocket, message):
        """
        The status of a connection has changed; update all registered status
        change listeners.
        """
        status = self.statusWatcher.statusFromMessage(subsocket.status, message)
        closeCount, subsocket.status = self.statusWatcher.closeCountFromStatus(status)
        self.statusChanged()
        return closeCount

    def sendFileDescriptor(self, skt, description):
        """
        A connection has been received.  Dispatch it to active sockets, sorted by
        how much work they have.

        @param skt: the I{connection socket} (i.e.: not the listening socket)
        @type skt: L{socket.socket}

        @param description: some text to identify to the subprocess's
            L{InheritedPort} what type of transport to create for this socket.
        @type description: C{bytes}
        """
        self._subprocessSockets.sort(key=lambda x: x.status.effective())
        selectedSocket = filter(lambda x: x.status.active(), self._subprocessSockets)[0]
        selectedSocket.sendSocketToPeer(skt, description)
        # XXX Maybe want to send along 'description' or 'skt' or some
        # properties thereof? -glyph
        selectedSocket.status = self.statusWatcher.newConnectionStatus(
            selectedSocket.status
        )
        self.statusChanged()

    def startDispatching(self):
        """
        Start listening on all subprocess sockets.
        """
        self._isDispatching = True
        for subSocket in self._subprocessSockets:
            subSocket.startReading()

    def addSocket(self, slavenum=0, socketpair=lambda: socketpair(AF_UNIX, SOCK_DGRAM)):
        """
        Add a L{send1msg}-oriented AF_UNIX socket to the pool of sockets being
        used for transmitting file descriptors to child processes.

        @return: a socket object for the receiving side; pass this object's
            C{fileno()} as part of the C{childFDs} argument to
            C{spawnProcess()}, then close it.
        """
        i, o = socketpair()
        i.setblocking(False)
        o.setblocking(False)
        a = _SubprocessSocket(self, i, o, self.statusWatcher.initialStatus(), slavenum)
        self._subprocessSockets.append(a)
        if self._isDispatching:
            a.startReading()
        return a

    def removeSocket(self, skt):
        """
        Removes a previously added socket from the pool of sockets being used
        for transmitting file descriptors to child processes.
        """
        self._subprocessSockets.remove(skt)


class InheritedPort(FileDescriptor, object):
    """
    An L{InheritedPort} is an L{IReadDescriptor}/L{IWriteDescriptor} created in
    the I{worker process} to handle incoming connections dispatched via
    L{send1msg}.
    """

    def __init__(self, fd, transportFactory, protocolFactory):
        """
        @param fd: the file descriptor representing a UNIX socket connected to
            a I{master process}.  We will call L{recv1msg} on this socket to
            receive file descriptors.
        @type fd: C{int}

        @param transportFactory: a 4-argument function that takes the socket
            object produced from the file descriptor, the peer address of that
            socket, the (non-ancillary) data sent along with the incoming file
            descriptor, and the protocol built along with it, and returns an
            L{ITransport} provider.  Note that this should NOT call
            C{makeConnection} on the protocol that it produces, as this class
            will do that.

        @param protocolFactory: an L{IProtocolFactory}
        """
        FileDescriptor.__init__(self)
        self.fd = fd
        self.transportFactory = transportFactory
        self.protocolFactory = protocolFactory
        self.statusQueue = []

    def fileno(self):
        """
        Get the FD number for this socket.
        """
        return self.fd

    def doRead(self):
        """
        A message is ready to read.  Receive a file descriptor from our parent
        process.
        """
        try:
            fd, description = recvfd(self.fd)
        except SocketError, se:
            if se.errno != EAGAIN:
                raise
        else:
            try:
                skt = fromfd(fd, getsockfam(fd), SOCK_STREAM)
                close(fd)       # fromfd() calls dup()
                try:
                    peeraddr = skt.getpeername()
                except SocketError:
                    peeraddr = ('0.0.0.0', 0)
                # FIXME: when using UNIX Domain sockets, peeraddr = ""
                if not peeraddr:
                    peeraddr = ('0.0.0.0', 0)
                protocol = self.protocolFactory.buildProtocol(peeraddr)
                transport = self.transportFactory(skt, peeraddr,
                                                  description, protocol)
                protocol.makeConnection(transport)
            except:
                log.failure("doRead()")

    def doWrite(self):
        """
        Write some data.
        """
        while self.statusQueue:
            msg = self.statusQueue.pop(0)
            try:
                send1msg(self.fd, msg, 0)
            except SocketError, se:
                if se.errno in (EAGAIN, ENOBUFS):
                    self.statusQueue.insert(0, msg)
                    return
                raise
        self.stopWriting()

    def reportStatus(self, statusMessage):
        """
        Report a status message to the L{_SubprocessSocket} monitoring this
        L{InheritedPort}'s health in the master process.
        """
        self.statusQueue.append(statusMessage)
        self.startWriting()