#!/usr/bin/env python
#
# Copyright (c) 2016, NORDUnet A/S All rights reserved.
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#   this list of conditions and the following disclaimer.
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# - Redistributions in binary form must reproduce the above copyright
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# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
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# TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
# PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
# HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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# TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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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 argparse

import serial

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


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, debug = False, *pargs, **kwargs):
        self.serial = serial.Serial(device, baudrate, timeout = 0, write_timeout = 0)
        self.queues = weakref.WeakValueDictionary()
        self.debug = debug
        self.hsm_write_lock = tornado.locks.Lock()
        super(SerialIOStream, self).__init__(*pargs, **kwargs)

    # The next four methods are required: BaseIOStream is an abstract
    # class, we provide a driver by overriding them.

    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

    @tornado.gen.coroutine
    def hsm_write(self, query, handle, queue):
        "Send a query to the HSM."
        if self.debug:
            sys.stdout.write("+send: {}\n".format(":".join("{:02x}".format(ord(c)) for c in query)))
        self.queues[handle] = queue
        with (yield self.hsm_write_lock.acquire()):
            yield self.write(query)

    @tornado.gen.coroutine
    def hsm_read_loop(self):
        "Handle reply stream HSM -> network."
        while True:
            reply = yield self.read_until(SLIP_END)
            if self.debug:
                sys.stdout.write("+recv: {}\n".format(":".join("{:02x}".format(ord(c)) for c in reply)))
            if len(reply) < 9:
                continue
            handle = client_handle_get(slip_decode(reply))
            self.queues[handle].put_nowait(reply)


class UnixServer(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.add_socket(tornado.netutil.bind_unix_socket(filename, mode))

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

    @tornado.gen.coroutine
    def handle_stream(self, stream, address):
        "Handle one network connection."
        handle = stream.socket.fileno()
        queue  = tornado.queues.Queue()
        closed = False
        while not closed:
            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.hsm_write(query, handle, queue)
                reply = yield queue.get()
                yield stream.write(SLIP_END + reply)
            except tornado.iostream.StreamClosedError:
                closed = True


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("device",           nargs = "?",            help = "serial device name",
                    default = os.getenv("CRYPTECH_RPC_CLIENT_SERIAL_DEVICE", "/dev/ttyUSB0"))
parser.add_argument("socket",           nargs = "?",            help = "PF_UNIX socket name",
                    default = os.getenv("CRYPTECH_RPC_CLIENT_SOCKET_NAME", "/tmp/.cryptech_rpcmuxd"))
args = parser.parse_args()

serial_stream = SerialIOStream(device = args.device, debug = args.debug)

unix_server = UnixServer()
unix_server.set_serial(serial_stream)
unix_server.listen(args.socket)

atexit.register(os.unlink, args.socket)

tornado.ioloop.IOLoop.current().run_sync(serial_stream.hsm_read_loop)