coap_client.py

import asyncio
from aiocoap import *
import time
import struct

async def fetch_image(uri, output_path):
    context = await Context.create_client_context()
    request = Message(code=GET, uri=uri)

    client_start_time = time.time()

    try:
        response = await context.request(request).response

        client_end_time = time.time()

        # Unpack the server timestamp from the response payload
        server_timestamp, = struct.unpack('d', response.payload[:8])
        image_data = response.payload[8:]

        with open(output_path, 'wb') as file:
            file.write(image_data)

        print(f"Image successfully saved to {output_path}")

        # Calculate times
        rtt = client_end_time - client_start_time
        transmission_time = client_end_time - server_timestamp

        print(f"Round-trip time (RTT): {rtt:.6f} seconds")
        print(f"Time taken for image transmission: {transmission_time:.6f} seconds")

    except Exception as e:
        print(f"An error occurred: {e}")

async def main():
    coap_server_uri = "coap://192.168.137.106:5683/image"
    output_file_path = r"C:\Users\anant\OneDrive\Pictures\received_image_by_coap.png"
    await fetch_image(coap_server_uri, output_file_path)

# Check if there's an existing event loop
loop = asyncio.get_event_loop()

if loop.is_running():
    # If the event loop is already running, just create a task for the main function
    asyncio.ensure_future(main())
else:
    # Otherwise, run the main function in a new event loop
    asyncio.run(main())