add tcp_serial_bridge.py
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Brian Harrison
203
bridges/tcp_serial_bridge.py
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203
bridges/tcp_serial_bridge.py
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"""
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tcp_serial_bridge.py — Local TCP-to-serial bridge for bench testing TcpTransport.
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Listens on a TCP port and, when a client connects, opens a serial port and
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bridges bytes bidirectionally. This lets you test the SFM server's TCP
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endpoint (?host=127.0.0.1&tcp_port=12345) against a locally-attached MiniMate
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Plus without needing a field modem.
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The bridge simulates an RV55 cellular modem in transparent TCP passthrough mode:
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- No handshake bytes on connect
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- Raw bytes forwarded in both directions
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- One connection at a time (new connection closes any existing serial session)
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Usage:
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python bridges/tcp_serial_bridge.py --serial COM5 --tcp-port 12345
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Then in another window:
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python -m uvicorn sfm.server:app --port 8200
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curl "http://localhost:8200/device/info?host=127.0.0.1&tcp_port=12345"
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Or just hit http://localhost:8200/device/info?host=127.0.0.1&tcp_port=12345
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in a browser.
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Requirements:
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pip install pyserial
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"""
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from __future__ import annotations
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import argparse
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import logging
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import select
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import socket
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import sys
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import threading
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import time
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try:
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import serial # type: ignore
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except ImportError:
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print("pyserial required: pip install pyserial", file=sys.stderr)
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sys.exit(1)
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logging.basicConfig(
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level=logging.INFO,
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format="%(asctime)s %(levelname)-7s %(message)s",
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datefmt="%H:%M:%S",
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)
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log = logging.getLogger("tcp_serial_bridge")
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# ── Constants ─────────────────────────────────────────────────────────────────
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DEFAULT_BAUD = 38_400
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DEFAULT_TCP_PORT = 12345
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CHUNK = 256 # bytes per read call
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SERIAL_TIMEOUT = 0.02 # serial read timeout (s) — non-blocking in practice
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TCP_TIMEOUT = 0.02 # socket recv timeout (s)
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BOOT_DELAY = 2.0 # seconds to wait after opening serial port before
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# forwarding data — mirrors the unit's startup beep
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# ── Bridge session ─────────────────────────────────────────────────────────────
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def _pipe_tcp_to_serial(sock: socket.socket, ser: serial.Serial, stop: threading.Event) -> None:
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"""Forward bytes from TCP socket → serial port."""
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sock.settimeout(TCP_TIMEOUT)
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while not stop.is_set():
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try:
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data = sock.recv(CHUNK)
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if not data:
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log.info("TCP peer closed connection")
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stop.set()
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break
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log.debug("TCP→SER %d bytes: %s", len(data), data.hex())
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ser.write(data)
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except socket.timeout:
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pass
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except OSError as exc:
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if not stop.is_set():
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log.warning("TCP read error: %s", exc)
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stop.set()
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break
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def _pipe_serial_to_tcp(sock: socket.socket, ser: serial.Serial, stop: threading.Event) -> None:
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"""Forward bytes from serial port → TCP socket."""
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while not stop.is_set():
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try:
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data = ser.read(CHUNK)
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if data:
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log.debug("SER→TCP %d bytes: %s", len(data), data.hex())
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try:
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sock.sendall(data)
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except OSError as exc:
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if not stop.is_set():
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log.warning("TCP send error: %s", exc)
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stop.set()
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break
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except serial.SerialException as exc:
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if not stop.is_set():
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log.warning("Serial read error: %s", exc)
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stop.set()
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break
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def _run_session(conn: socket.socket, addr: tuple, serial_port: str, baud: int, boot_delay: float) -> None:
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"""Handle one TCP client connection."""
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peer = f"{addr[0]}:{addr[1]}"
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log.info("Connection from %s", peer)
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try:
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ser = serial.Serial(
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port = serial_port,
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baudrate = baud,
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bytesize = 8,
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parity = "N",
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stopbits = 1,
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timeout = SERIAL_TIMEOUT,
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)
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except serial.SerialException as exc:
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log.error("Cannot open serial port %s: %s", serial_port, exc)
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conn.close()
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return
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log.info("Opened %s at %d baud — waiting %.1fs for unit boot", serial_port, baud, boot_delay)
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ser.reset_input_buffer()
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ser.reset_output_buffer()
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if boot_delay > 0:
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time.sleep(boot_delay)
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ser.reset_input_buffer() # discard any boot noise
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log.info("Bridge active: TCP %s ↔ %s", peer, serial_port)
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stop = threading.Event()
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t_tcp_to_ser = threading.Thread(
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target=_pipe_tcp_to_serial, args=(conn, ser, stop), daemon=True
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)
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t_ser_to_tcp = threading.Thread(
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target=_pipe_serial_to_tcp, args=(conn, ser, stop), daemon=True
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)
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t_tcp_to_ser.start()
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t_ser_to_tcp.start()
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stop.wait() # block until either thread sets the stop flag
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log.info("Session ended, cleaning up")
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try:
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conn.close()
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except OSError:
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pass
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try:
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ser.close()
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except OSError:
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pass
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t_tcp_to_ser.join(timeout=2.0)
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t_ser_to_tcp.join(timeout=2.0)
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log.info("Session with %s closed", peer)
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# ── Server ────────────────────────────────────────────────────────────────────
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def run_bridge(serial_port: str, baud: int, tcp_port: int, boot_delay: float) -> None:
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"""Accept TCP connections forever and bridge each one to the serial port."""
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srv = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
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srv.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
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srv.bind(("0.0.0.0", tcp_port))
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srv.listen(1)
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log.info(
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"Listening on TCP :%d — will bridge to %s at %d baud",
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tcp_port, serial_port, baud,
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)
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log.info("Send test: curl 'http://localhost:8200/device/info?host=127.0.0.1&tcp_port=%d'", tcp_port)
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try:
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while True:
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conn, addr = srv.accept()
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# Handle one session at a time (synchronous) — matches modem behaviour
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_run_session(conn, addr, serial_port, baud, boot_delay)
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except KeyboardInterrupt:
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log.info("Shutting down")
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finally:
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srv.close()
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# ── Entry point ────────────────────────────────────────────────────────────────
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if __name__ == "__main__":
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ap = argparse.ArgumentParser(description="TCP-to-serial bridge for bench testing TcpTransport")
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ap.add_argument("--serial", default="COM5", help="Serial port (default: COM5)")
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ap.add_argument("--baud", type=int, default=DEFAULT_BAUD, help="Baud rate (default: 38400)")
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ap.add_argument("--tcp-port", type=int, default=DEFAULT_TCP_PORT, help="TCP listen port (default: 12345)")
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ap.add_argument("--boot-delay", type=float, default=BOOT_DELAY,
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help="Seconds to wait after opening serial before forwarding (default: 2.0). "
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"Set to 0 if unit is already powered on.")
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ap.add_argument("--debug", action="store_true", help="Show individual byte transfers")
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args = ap.parse_args()
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if args.debug:
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logging.getLogger().setLevel(logging.DEBUG)
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run_bridge(args.serial, args.baud, args.tcp_port, args.boot_delay)
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