The primary app to handle the client socket interface to the rover server.

rover_client.py

#!/usr/bin/env python3
# rover-client.py is the Rover client app to receive ping from Remote and respond with ACK

import sys, socket, selectors, traceback, time
import rover_libclient
from datetime import datetime

sel = selectors.DefaultSelector()

#	Connection startup - Socket and Message Object Creation

def start_connection(host, port, device, request):
    global sock, events, message
    addr = (host, port)
    print("rover-client starting connection to", addr)
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sock.setblocking(False)
    sock.connect_ex(addr)
    events = selectors.EVENT_READ | selectors.EVENT_WRITE
    message = rover_libclient.Message(sel, sock, addr, device, request)
    sel.register(sock, events, data=message)
    print("rover-client completed connection to Rover Server socket at", addr)

#	Open port to local rover comm server and receive Connected before entering receive mode from remote 

host, port, device = '127.0.0.1',33000,'rover'
request = dict(encoding="utf-8", content=dict(device=device, action='connect'))
start_connection(host, port, device, request)	# Sends rover name and connect request

#	Connection Startup (receive json field message) ---> Connected
result = ''
try:
    while True:
        events = sel.select(timeout=1)
#        print("\nrover-client startup events triggered ******")
        for key, mask in events:
            message.request = {'device': 'rover', 'action': 'connect'}
            try:
                message.process_events(mask)
                content = message.json_content
                if len(content) != 0:
#                    print('rover-client len(content) != 0')
                    result = content["result"]
            except Exception:
                print("rover-client startup error: exception for", f"{message.addr}:\n{traceback.format_exc()}")
                message.close()
        if result == 'Connected': 
            break
        # Check for a socket being monitored to continue.
        if not sel.get_map():
            break
except:
	print("Failed to receive Connected response at startup. Attempting to poll.")
	pass

#	Enter receive mode for remote to send ping to respond with ACK

content = {}
#print('\nEntering main loop **********')
events = selectors.EVENT_READ
message._jsonheader_len = None		# clear json values for read
message.jsonheader = None
message.response = None
message.request = None
#mask = 1
try:
    while True:
        events = sel.select(timeout=1)
        for key, mask in events:
            message = key.data
            try:
#                print("rover-client main loop process_events(mask):", str(mask))
                message.process_events(mask)
            except Exception:
                print("rover-client main loop error: exception for", f"{message.addr}:\n{traceback.format_exc()}")
                message.close()
#            print("rover-client main loop message.json_content:", str(message.json_content))
            content = message.json_content
            if len(content) != 0:
                device = content['device']
                if device == 'rover':		# If this command is for me, rover, send ACK for tests.
                    command = content['action']
                else:
                    command = content['result']
                    print('rover-client response to ping: ', command + ' at ' + str(datetime.now())[0:19])
                if device == 'rover' and command == 'ping':	# Send ACK in response to ping
#                    print('\nCreating ACK message in response to ping from remote.')
                    message.request = {'device':'remote','result':'ACK'}
                    message.queue_request()
                    message.json_content = {}
        # Check for a socket being monitored to continue.
        if not sel.get_map():
            break
except KeyboardInterrupt:
    print("\ncaught keyboard interrupt, exiting\n\n")
finally:
	sel.close()