Python Calling An SDK Function In DLL Of A Sensor That Takes Pointer IP And Port And Return A Void* (void* A Handle To The Profile Sensor.)

I am just new in Python. I am trying to connect to a laser sensor through its DLL library. The SDK functions in this Library are compiled in C++ language. By using ctypes in pytho

Solution 1:

I want to start by pointing out [Python 3.Docs]: ctypes - A foreign function library for Python.

I'm going to post an answer based on some assumptions:

1. The sensor you're talking about is the same one as described in [FoxControls]: acuity-ap820-users-manual.pdf. If this isn't true, the answer is useless

2. According to above doc, EthernetScanner_GetConnectStatus's possible return statuses are (emphasis is mine):

   Status is a unsigned integer used as a buffer to contain the status code when the function returns.
   The status codes are:

   • 0: Disconnected
   • 1: Disconnecting
   • 2: Connecting
   • 3: Connected

   
   

   Based on the above, and the fact that the connect timeout is 0, I assumed (nothing in the doc to support it, though) that it tries to connect in non blocking mode:

   • EthernetScanner_Connect returns immediately (meaning that before attempting to connect - it "schedules" a connection operation if you will) a non NULL pointer. For a non blocking (async) IO example, check [MS.Docs]: connect function
   • The (above) pointer should be queried (periodically) using EthernetScanner_GetConnectStatus. That's why it makes sense for the pointer to be non NULL (as when EthernetScanner_Connect returns, the connection attempt result is not yet known)

Here's a piece of code that is supposed to deal with the problem (needless to say that it's blind coding - meaning that I didn't actually test it).
As a consequence of the 2 assumption, if passing a timeout greater than 0, EthernetScanner_Connect should return NULL.

code.py:

#!/usr/bin/env python3

import sys
import ctypes
import time


DLL_NAME = "c:\\EthernetScanner.dll"

CONNECT_STATUS_DISCONNECTED = 0
CONNECT_STATUS_DISCONNECTING = 1
CONNECT_STATUS_CONNECTING = 2
CONNECT_STATUS_CONNECTED = 3

CONNECT_STATUSES_PENDING = [
    CONNECT_STATUS_CONNECTING,
    CONNECT_STATUS_DISCONNECTING,
]

def main():

    connect_timeout_msec = 0
    nb_mode = connect_timeout_msec == 0

    dll = ctypes.WinDLL(DLL_NAME)

    EthernetScanner_Connect = dll.EthernetScanner_Connect
    EthernetScanner_Connect.argtypes = [ctypes.c_char_p, ctypes.c_char_p, ctypes.c_uint32]
    EthernetScanner_Connect.restype = ctypes.c_void_p

    EthernetScanner_GetConnectStatus = dll.EthernetScanner_GetConnectStatus
    EthernetScanner_GetConnectStatus.argtypes = [ctypes.c_void_p, ctypes.POINTER(ctypes.c_uint32)]

    EthernetScanner_Disconnect = dll.EthernetScanner_Disconnect
    EthernetScanner_Disconnect.argtypes = [ctypes.c_void_p]
    EthernetScanner_Disconnect.restype = ctypes.c_uint32

    ptr = EthernetScanner_Connect(b"192.168.100.1", b"32001", connect_timeout_msec)
    if nb_mode:
        print("Non blocking mode: EthernetScanner_Connect returned {:}".format(ptr))
        poll_timeout_sec = 0.5
        connect_status = ctypes.c_int(CONNECT_STATUS_CONNECTING)
        while connect_status.value in CONNECT_STATUSES_PENDING:
            time.sleep(poll_timeout_sec)
            EthernetScanner_GetConnectStatus(ptr, ctypes.byref(connect_status))
        if connect_status.value != CONNECT_STATUS_CONNECTED:
            print("Couldn't connect (status: {:})!".format(connect_status.value))
            return
    else:
        print("Blocking mode: EthernetScanner_Connect returned {:}".format(ptr))
        if not ptr:
            print("Couldn't connect!")
            return

    # Do something with the sensor (pointer)

    EthernetScanner_Disconnect(ptr)


if __name__ == "__main__":
    print("Python {:s} on {:s}\n".format(sys.version, sys.platform))
    main()
    print("Done.")