comm.py

#!/usr/bin/env python3


"""
Copyright (C) 2016 Interactive Brokers LLC. All rights reserved.  This code is
subject to the terms and conditions of the IB API Non-Commercial License or the
 IB API Commercial License, as applicable. 
"""


"""
This module has tools for implementing the IB low level messaging.
"""


import struct

from common import UNSET_INTEGER, UNSET_DOUBLE
from logger import LOGGER


def make_msg(text) -> bytes:
    """ adds the length prefix """
    #msg = array.array('B', 
    msg = struct.pack("!I%ds" % len(text), len(text), str.encode(text))
    return msg


def make_field(val) -> bytes:
    """ adds the NULL string terminator """

    if val is None:
        raise ValueError("Cannot send None to TWS")

    # bool type is encoded as int
    if type(val) is bool:
        val = int(val)

    field = str(val) + '\0'
    return field


def make_field_handle_empty(val) -> bytes:

    if val is None:
        raise ValueError("Cannot send None to TWS")

    if UNSET_INTEGER == val or UNSET_DOUBLE == val:
        val = ""

    return make_field(val)


def read_msg(buf: bytes) -> tuple:
    """ first the size prefix and then the corresponding msg payload """
    size = struct.unpack("!I", buf[0:4])[0]
    LOGGER.debug("read_msg: size: %d", size)
    text = struct.unpack("!%ds" % size, buf[4:4+size])[0]

    return (size, text, buf[4+size:])
     

def read_fields(buf: bytes) -> tuple:
    """ msg payload is made of fields terminated/separated by NULL chars """
    fields = buf.split(b"\0")

    return fields[0:-1]   #last one is empty; this may slow dow things though, TODO