#!/usr/bin/env python
#
# Copyright (c) 2016-2017, NORDUnet A/S All rights reserved.
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"""
Implementation of Cryptech RPC protocol multiplexer in Python.

Unlike the original C implementation, this uses SLIP encapsulation
over a SOCK_STREAM channel, because support for SOCK_SEQPACKET is not
what we might wish.  We outsource all the heavy lifting for serial and
network I/O to the PySerial and Tornado libraries, respectively.
"""

import os
import sys
import time
import struct
import atexit
import weakref
import logging
import argparse

import serial

import tornado.tcpserver
import tornado.iostream
import tornado.netutil
import tornado.ioloop
import tornado.queues
import tornado.locks
import tornado.gen


logger = logging.getLogger("cryptech_muxd")


SLIP_END     = chr(0300)        # Indicates end of SLIP packet
SLIP_ESC     = chr(0333)        # Indicates byte stuffing
SLIP_ESC_END = chr(0334)        # ESC ESC_END means END data byte
SLIP_ESC_ESC = chr(0335)        # ESC ESC_ESC means ESC data byte


def slip_encode(buffer):
    "Encode a buffer using SLIP encapsulation."
    return SLIP_END + buffer.replace(SLIP_ESC, SLIP_ESC + SLIP_ESC_ESC).replace(SLIP_END, SLIP_ESC + SLIP_ESC_END) + SLIP_END

def slip_decode(buffer):
    "Decode a SLIP-encapsulated buffer."
    return buffer.strip(SLIP_END).replace(SLIP_ESC + SLIP_ESC_END, SLIP_END).replace(SLIP_ESC + SLIP_ESC_ESC, SLIP_ESC)


def client_handle_get(msg):
    "Extract client_handle field from a Cryptech RPC message."
    return struct.unpack(">L", msg[4:8])[0]

def client_handle_set(msg, handle):
    "Replace client_handle field in a Cryptech RPC message."
    return msg[:4] + struct.pack(">L", handle) + msg[8:]


class SerialIOStream(tornado.iostream.BaseIOStream):
    """
    Implementation of a Tornado IOStream over a PySerial device.
    """

    def __init__(self, device, baudrate = 921600, *pargs, **kwargs):
        self.serial = serial.Serial(device, baudrate, timeout = 0, write_timeout = 0)
        super(SerialIOStream, self).__init__(*pargs, **kwargs)

    def fileno(self):
        return self.serial.fileno()

    def close_fd(self):
        self.serial.close()

    def write_to_fd(self, data):
        return self.serial.write(data)

    def read_from_fd(self):
        return self.serial.read(self.read_chunk_size) or None


class PFUnixServer(tornado.tcpserver.TCPServer):
    """
    Variant on tornado.tcpserver.TCPServer, listening on a PF_UNIX
    (aka PF_LOCAL) socket instead of a TCP socket.
    """

    def listen(self, filename, mode = 0600):
        self.socket_filename = filename
        self.add_socket(tornado.netutil.bind_unix_socket(filename, mode))
        atexit.register(self.atexit_unlink)

    def atexit_unlink(self):
        try:
            os.unlink(self.socket_filename)
        except:
            pass


class RPCIOStream(SerialIOStream):
    """
    Tornado IOStream for a serial RPC channel.
    """

    def __init__(self, *pargs, **kwargs):
        super(RPCIOStream, self).__init__(*pargs, **kwargs)
        self.queues = weakref.WeakValueDictionary()
        self.rpc_input_lock = tornado.locks.Lock()

    @tornado.gen.coroutine
    def rpc_input(self, query, handle, queue):
        "Send a query to the HSM."
        logger.debug("rpc send: %s", ":".join("{:02x}".format(ord(c)) for c in query))
        self.queues[handle] = queue
        with (yield self.rpc_input_lock.acquire()):
            yield self.write(query)

    @tornado.gen.coroutine
    def rpc_output_loop(self):
        "Handle reply stream HSM -> network."
        while True:
            try:
                reply = yield self.read_until(SLIP_END)
            except tornado.iostream.StreamClosedError:
                logger.info("rpc uart closed")
                for q in self.queues.itervalues():
                    q.put_nowait(None)
                return
            logger.debug("rpc recv: %s", ":".join("{:02x}".format(ord(c)) for c in reply))
            try:
                handle = client_handle_get(slip_decode(reply))
            except:
                continue
            self.queues[handle].put_nowait(reply)


class QueuedStreamClosedError(tornado.iostream.StreamClosedError):
    "Deferred StreamClosedError passed throught a Queue."


class RPCServer(PFUnixServer):
    """
    Serve multiplexed Cryptech RPC over a PF_UNIX socket.
    """

    def set_serial(self, serial_stream):
        self.serial = serial_stream

    @tornado.gen.coroutine
    def handle_stream(self, stream, address):
        "Handle one network connection."
        logger.info("rpc connected %r", stream)
        handle = stream.socket.fileno()
        queue  = tornado.queues.Queue()
        while True:
            try:
                query = yield stream.read_until(SLIP_END)
                if len(query) < 9:
                    continue
                query = slip_encode(client_handle_set(slip_decode(query), handle))
                yield self.serial.rpc_input(query, handle, queue)
                reply = yield queue.get()
                if reply is None:
                    raise QueuedStreamClosedError()
                yield stream.write(SLIP_END + reply)
            except tornado.iostream.StreamClosedError:
                logger.info("rpc closing %r", stream)
                stream.close()
                return

class CTYIOStream(SerialIOStream):
    """
    Tornado IOStream for a serial console channel.
    """

    def __init__(self, *pargs, **kwargs):
        super(CTYIOStream, self).__init__(*pargs, **kwargs)
        self.attached_cty = None

    @tornado.gen.coroutine
    def cty_output_loop(self):
        while True:
            try:
                buffer = yield self.read_bytes(1024, partial = True)
            except tornado.iostream.StreamClosedError:
                logger.info("cty uart closed")
                if self.attached_cty is not None:
                    self.attached_cty.close()
                return
            try:
                if self.attached_cty is not None:
                    yield self.attached_cty.write(buffer)
            except tornado.iostream.StreamClosedError:
                pass


class CTYServer(PFUnixServer):
    """
    Serve Cryptech console over a PF_UNIX socket.
    """

    def set_serial(self, serial_stream):
        self.serial = serial_stream

    @tornado.gen.coroutine
    def handle_stream(self, stream, address):
        "Handle one network connection."

        if self.serial.attached_cty is not None:
            yield stream.write("[Console already in use, sorry]\n")
            stream.close()
            return

        logger.info("cty connected to %r", stream)

        try:
            self.serial.attached_cty = stream
            while self.serial.attached_cty is stream:
                yield self.serial.write((yield stream.read_bytes(1024, partial = True)))
        except tornado.iostream.StreamClosedError:
            stream.close()
        finally:
            logger.info("cty disconnecting from %r", stream)
            if self.serial.attached_cty is stream:
                self.serial.attached_cty = None


@tornado.gen.coroutine
def main():
    parser = argparse.ArgumentParser(formatter_class = argparse.ArgumentDefaultsHelpFormatter)
    parser.add_argument("-v", "--verbose",  action = "store_true",  help = "produce human-readable output")
    parser.add_argument("-d", "--debug",    action = "store_true",  help = "blather about what we're doing")

    parser.add_argument("--rpc-device",            help = "RPC serial device name",
                        default = os.getenv("CRYPTECH_RPC_CLIENT_SERIAL_DEVICE", "/dev/ttyUSB0"))
    parser.add_argument("--rpc-socket",            help = "RPC PF_UNIX socket name",
                        default = os.getenv("CRYPTECH_RPC_CLIENT_SOCKET_NAME", "/tmp/.cryptech_muxd.rpc"))

    parser.add_argument("--cty-device",            help = "CTY serial device name",
                        default = os.getenv("CRYPTECH_CTY_CLIENT_SERIAL_DEVICE", "/dev/ttyUSB0"))
    parser.add_argument("--cty-socket",            help = "CTY PF_UNIX socket name",
                        default = os.getenv("CRYPTECH_CTY_CLIENT_SOCKET_NAME", "/tmp/.cryptech_muxd.cty"))

    args = parser.parse_args()

    futures = []

    rpc_stream = RPCIOStream(device = args.rpc_device)
    rpc_server = RPCServer()
    rpc_server.set_serial(rpc_stream)
    rpc_server.listen(args.rpc_socket)
    futures.append(rpc_stream.rpc_output_loop())

    cty_stream = CTYIOStream(device = args.cty_device)
    cty_server = CTYServer()
    cty_server.set_serial(cty_stream)
    cty_server.listen(args.cty_socket)
    futures.append(cty_stream.cty_output_loop())

    # Might want to use WaitIterator(dict(...)) here so we can
    # diagnose and restart output loops if they fail.  Worry about
    # that when we get to automatic device probing.

    yield futures

if __name__ == "__main__":
    try:
        #logging.basicConfig(level = logging.DEBUG)
        tornado.ioloop.IOLoop.current().run_sync(main)
    except KeyboardInterrupt:
        pass