Simple TCP server script using Python to serve IQ samples to an rtl_tcp client

rtl_tcp_serve.py

'''Simple TCP server implementation to serve IQ samples to an rtl_tcp client'''
import mmap
import socket
import time

TUNERS = {
    'RTLSDR_TUNER_UNKNOWN': 0,
    'E4000': 1,
    'FC0012': 2,
    'FC0013': 3,
    'FC2580': 4,
    'R820T': 5,
    'R828D': 6,
}

GAINS = {
    'RTLSDR_TUNER_UNKNOWN': 0,
    'E4000': 14,
    'FC0012': 5,
    'FC0013': 23,
    'FC2580': 1,
    'R820T': 29,
    'R828D': 29,
}

IQFILE = 'capture.raw'
MAGIC = 'RTL0'
TUNER = 'FC0013'
TUNERID = TUNERS[TUNER]
NUMGAINS = GAINS[TUNER]
HEADER = MAGIC.encode('ascii')
HEADER += TUNERID.to_bytes(4, 'big')
HEADER += NUMGAINS.to_bytes(4, 'big')
BLOCKSIZE = 1024
DATARATE = 2048000 * 2

with open(IQFILE, 'r+b') as file:
    mm = mmap.mmap(file.fileno(), 0)
    
    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
        sock.bind(('localhost', 1234))
        sock.listen()
        
        print("listening...")
        conn, addr = sock.accept()

        with conn:
            print(f"connection from {addr}")
            
            msgs = [conn.recv(255) for _ in range(2)]
            for msg in msgs:
                cmd = int.from_bytes(msg[:1], byteorder='big')
                arg = int.from_bytes(msg[1:], byteorder='big')
                if cmd == 1:
                    print(f"received command to tune to {arg} Hz")
                elif cmd == 2:
                    print(f"received command to set iq sample rate to {arg} sps")
                else:
                    print(f"unknown command {cmd} with argument {arg}")

            print(f"sending header...")
            conn.send(HEADER)

            bytesahead = 0
            prevtime = None

            print("starting to stream samples...")
            while True:
                now = time.perf_counter()
                if (prevtime != None):
                    bytesahead -= (now - prevtime) * DATARATE
                prevtime = now

                samples = mm.read(BLOCKSIZE)
                if mm.tell() == mm.size():
                    print("end of file reached, restarting")
                    mm.seek(0, 0)
                try:
                    bytessent = conn.send(samples)
                except ConnectionResetError:
                    print("client connection closed, exiting")
                    break
                
                if (bytessent > 0):
                    bytesahead += bytessent
                    if (bytesahead > 0):
                        time.sleep(bytesahead / DATARATE)
                else:
                    print("error sending data, exiting")
                    break          
    
    mm.close()