#!/usr/bin/env python
#
# Copyright (c) 2016, NORDUnet A/S All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are
# met:
# - Redistributions of source code must retain the above copyright notice,
#   this list of conditions and the following disclaimer.
#
# - Redistributions in binary form must reproduce the above copyright
#   notice, this list of conditions and the following disclaimer in the
#   documentation and/or other materials provided with the distribution.
#
# - Neither the name of the NORDUnet nor the names of its contributors may
#   be used to endorse or promote products derived from this software
#   without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
# IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
# 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,
# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
# TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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"""
Utility to probe USB serial port(s) trying to figure out which one(s)
we have plugged in today.  stdout is environment variable settings,
suitable for use in bash with "eval `cryptech_probe`"; all other output
goes to stderr.
"""

import sys
import time
import argparse
import serial.tools.list_ports_posix

class positive_integer(int):
    def __init__(self, value):
        if self <= 0:
            raise ValueError

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("--no-cleanup",       action = "store_true",   help = "don't send cleanup sequences after probing")
parser.add_argument("--read-buffer-size", type = positive_integer, help = "size of read buffer", default = 1024)
args = parser.parse_args()

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

Control_U    = chr(0025)        # Console: clear line
Control_M    = chr(0015)        # Console: end of line

RPC_query    = chr(0) * 8       # client_handle = 0, function code = RPC_FUNC_GET_VERSION
RPC_reply    = chr(0) * 12      # opcode = RPC_FUNC_GET_VERSION, client_handle = 0, valret = HAL_OK

# This is the query string we send to each USB port we find.  It's
# intended to be relatively harmless, at least for either of the HSM
# ports: the final Control-U should prevent the console from trying to
# interpret the RPC command, and the SLIP_END markers should cause
# the RPC server to treat the ASCII control characters as noise.
#
# Yes, this is a total kludge.  Useful identifiers for the USB ports
# are are on the wish list for a future revision of the hardware, but
# for the moment, we do what we can with what we have.

probe_string = SLIP_END + Control_U + SLIP_END + RPC_query + SLIP_END + Control_U + Control_M

ports = [port for port, desc, hwid in serial.tools.list_ports_posix.comports()
         if "VID:PID=0403:6014" in hwid]

if not ports:
    sys.exit("Couldn't find any likely USB ports")

if args.debug:
    sys.stderr.write("Candidate USB ports: {}\n".format(", ".join(ports)))

env = {}

for port in ports:

    while True:
        try:
            tty = serial.Serial(port, 921600, timeout=0.1)
            break
        except serial.SerialException:
            time.sleep(0.2)

    for c in probe_string:
        tty.write(c)
        time.sleep(0.1)

    response = tty.read(args.read_buffer_size)
    if args.debug:
        sys.stderr.write("Received from {}: {!r} ({})\n".format(port, response, ":".join("{:02x}".format(ord(c)) for c in response)))

    # Check whether we got a known console prompt.

    is_cty = any(prompt in response for prompt in ("Username:", "Password:", "cryptech>"))

    # Check whether we got something that looks like the response to an RPC version query.
    # We skip over the version value itself, as it might change, but we check that it's
    # terminated properly.  This is fragile, and will need to handle SLIP decoding if
    # we ever bump one of the version fields up into the range where the SLIP control
    # characters live, but it will do for the moment.

    try:
        is_hsm = response[response.index(SLIP_END + RPC_reply) + len(SLIP_END + RPC_reply) + 4] == SLIP_END
    except ValueError:
        is_hsm = False
    except IndexError:
        is_hsm = False

    if is_cty and args.verbose:
        sys.stderr.write("{} looks like the Cryptech HSM console port\n".format(port))

    if is_hsm and args.verbose:
        sys.stderr.write("{} looks like the Cryptech HSM RPC port\n".format(port))

    if is_cty:
        env.update(CRYPTECH_CTY_CLIENT_SERIAL_DEVICE = port)

    if is_hsm:
        env.update(CRYPTECH_RPC_CLIENT_SERIAL_DEVICE = port)

    if (is_cty or is_hsm) and not args.no_cleanup:
        if is_cty:
            tty.write(Control_U)
        if is_hsm:
            tty.write(SLIP_END)
        while tty.read(args.read_buffer_size):
            pass

    tty.close()

if env:
    sys.stdout.write("export {}\n".format(
        " ".join("{}='{}'".format(var, env[var]) for var in sorted(env))))