Echo-back HTTP server to demonstrate MicroPython uasyncio

uasyncio_http_echo_server.py

# Example of using uasyncio to run a web server.
# The server does nothing but echo back what was sent to it.
# But the point here is to demonstrate the use of uasyncio, callbacks,
# and the mixing of async and regular (synchronous) functions.

import uasyncio

# This is a synchronous function that gets called from inside the async function.
def create_http_response(body):
    res_lines = []
    res_lines.append('HTTP/1.1 200 OK')
    res_lines.append(f'Content-Length: {len(body)}')
    res_lines.append('Content-Type: text/plain')
    res_lines.append('Server: uasyncio (MicroPython)')
    res_lines.append('Connection: close')
    res_lines.append('')
    res_lines.append(f'{body}')
    return '\r\n'.join(res_lines)

# This is the callback function that gets executed when there's a new connection.
async def on_connect(reader, writer):
    print("Client connected.")
    req_buffer = await reader.read(1024)
    print("Input read.")
    print(req_buffer)
    body = req_buffer.decode('utf8')
    res = create_http_response(body)
    writer.write(res)
    print("Response sent.")
    await writer.drain()
    reader.close()
    await reader.wait_closed()
    writer.close()
    print("Connection closed.")

# Here, the server is created and inserted into the event loop as a task.
print("Server starting...")
server = uasyncio.start_server(on_connect, '0.0.0.0', 80, 5)
loop = uasyncio.get_event_loop()
loop.create_task(server)
loop.run_forever()