Ubuntu: Pipe raw unbuffered data to TCP port - linux

Question

My overall goal:
I have a hardware device that streams sensor data to a Ubuntu laptop running a Python script. Data comes in chunks of 240 samples (one per line with \n) every 2 seconds and prints to stdout. I start the Python script on the Ubuntu laptop and pipe its output to a TCP port using netcat. I connect to that TCP port from any other device on the network and get the live data stream - without first loading all previous samples.
My Setup:
Two laptops.
1: Ubuntu collects readings from a sensor, and pipes those readings to TCP port 1234.(This is working.) $ py read_sensors.py | nc -lk 1234
2: Windows 10, has WSL, Python, and existing scripts for processing data streamed from the first laptop. (This is working in WSL) $ nc 10.10.10.01 1234
My Problem:
I begin streaming sensor data on the Ubuntu laptop.
10 min later I connect to that stream from my windows laptop...
I expect to receive the most recent sample at the time the connection was established, and all subsequent samples in (pseudo) real-time.
Instead, as soon as I connect I am flooded with all samples collected since I began the streaming pipeline on the Ubuntu laptop, and once it catches up, I start seeing real-time data.
I have tried: Searching led me to try stdbuf. Lack of results led me to try various combinations of $ stdbuf -oL py read_sensors.py | nc -lk 1234 $ py read_sensors.py | stdbuf -oL nc -lk 1234 but every time I wait a little bit then connect to the port from my windows laptop, it loads all samples from the time I started streaming on the Ubuntu laptop.
I assume: This is a buffering issue and that it will have to be fixed on the Ubuntu machine - but the various combinations of stdbuf has not had any effect on the behavior of the system. So, I turn to the SO gods for insight and grace :)
-Nick

Answer 1

Something like this might meet the overall goal. Based on https://docs.python.org/3/library/socketserver.html#socketserver-tcpserver-example
import socketserver
class MyHandler(socketserver.BaseRequestHandler):
def handle(self):
bytes = read_sensor_data() # call the code that reads the sensors
self.request.sendall(bytes)
if __name__ == "__main__":
with socketserver.TCPServer(("localhost", 1234), MyHandler) as server:
server.serve_forever()

Answer 2

Disable netcat buffering:
Force netcat to send messages immediately (without buffering)
Alternately, I believe if you use bash’s built in tcp connections bypassing netcat, it will work. E.g. read_sensors.py > /dev/tcp/10.10.10.1/1234
EDIT: Added sample code that shows how to send and receive.
Example code:
To send:
#!/bin/bash
while true
do
date > /dev/tcp/localhost/1234 || true # replace date command with read_sensors.py
sleep 1
done
to receive:
ubuntu#ubuntu:~$ nc -lk 1234
Output:
Tue Mar 2 20:40:24 UTC 2021
Tue Mar 2 20:40:25 UTC 2021
Tue Mar 2 20:40:26 UTC 2021
Tue Mar 2 20:40:27 UTC 2021
^C
ubuntu#ubuntu:~$ nc -lk 1234
Tue Mar 2 20:40:40 UTC 2021
Tue Mar 2 20:40:41 UTC 2021
Notice 13 second gap while I hit control C, no data sent or buffered up.