I have to send and recieve data from a limited hardware setup running linux. I thought to use Telnet utility since it was available in the device (No netcat or anything similar available).
The Bash script which I used to send and recieve data looks like this.

#!/bin/bash

# IP address and port of the server
TELNET_SERVER="192.168.0.111"
TELNET_PORT="12345"

while true; do
    # Running command to obtain required data
    data=$(./wrs_dump_shmem -M)
    message="$data"

    # Send message via Telnet to the server and receive response

    response=$(echo "$message" | telnet "$TELNET_SERVER" "$TELNET_PORT" 2>&1 | tail -n 1)

    # Extract adjust and offset values from response
    adjust=$(echo "$response" | awk -F ', ' '{print $1}' | cut -d ':' -f 2)
    offset=$(echo "$response" | awk -F ', ' '{print $2}' | cut -d ':' -f 2)

    # Check if adjust is True
    if [ "$adjust" == "True" ]; then
        # Run ppsi_conf command with offset value
        ./ppsi_conf 4 "$offset"
        echo "PPSI configuration adjusted with offset: $offset"
    elif [ "$adjust" == "False" ]; then
        echo "No adjustment needed. Continuing..."
    else
        echo "Invalid response: $response"
        exit 1
    fi

    #Sleeping for 0.25 Seconds. 
    usleep 250000  
done

I made a Python server to send and recieve data in my machine

import socket
from datetime import datetime

ip0 = "192.168.0.120"
ip1 = "192.168.0.121"
ip2 = "192.168.0.122"
M12 = 0
M21 = 0
M13 = 0
M31 = 0


def save_to_file(ip, message):
    filename = f"{ip}.txt"
    with open(filename, "a") as file:
        timestamp = datetime.now().strftime("[%Y-%m-%d %H:%M:%S]")
        file.write(f"{timestamp} {message}n")

def send_response(client_socket, adjust, offset):
    response = f"Adjust:{adjust},offset:{offset}r"
    client_socket.send(response.encode())
    print(f"Response sent: {response}")

def extract_final_numbers(data):
    # Split the data by newlines
    lines = data.strip().split('n')
    final_numbers = []
    # Iterate over each line
    for line in lines:
        # Split the line by colon
        parts = line.split()
        # Extract the final numbers (excluding the timestamp)
        numbers = [part.split(':')[1] for part in parts if ':' in part]
        final_numbers.extend(numbers)
    return final_numbers

def listen(port):
    offset = 0
    # Create a socket object
    server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
   
    # Bind the socket to a host and port
    server_socket.bind(('0.0.0.0', port))

    # Listen for incoming connections
    server_socket.listen(5)
    print(f"Listening on port {port}...")

    while True:
        # Accept incoming connection
        client_socket, client_address = server_socket.accept()
        print(f"Connection from {client_address}")

        # Receive data from client
        data = client_socket.recv(1024).decode("utf-8").strip()

        
        if data:
           # Save data to file
            save_to_file(client_address[0], data)           
            f=extract_final_numbers(data)
            if(client_address[0]==ip0):
                M12 = int(f[0])
            if(client_address[0]==ip2):
                M13 = int(f[0])
            if(client_address[0]==ip1):
                M31 = int(f[1])
                M21 = int(f[2])
                offset =int( (M21-M12+M31-M13)/6 )
            # Check if adjust should be True or False based on the client IP
            adjust = "True" if client_address[0] == ip1 else "False"

            # Send response
            send_response(client_socket, adjust, offset)

        # Close the connection
        client_socket.close()

if __name__ == "__main__":
    PORT = 12345  # port number
    listen(PORT)

I am able to recieve the data from the client as expected but unable to give a response.
The Bash script doesn’t seems to recieve any response from the server. Can anyone help me point out the problem.
I am not familiar with the Telent or socket programming. The documentations I coudl find in the internet hasn’t been helpful so far. Thank you in advance.

I thought of using telnetlib in python. But I could only find method to establish a client side application. I tried changing the formatting, assuming telnet is not parsing the response properly. I used wireshark to sniff the packets that is being exchanged and I could see that my machine is sending the packets to the remote client.

Wireshark Output:

Frame 975: 87 bytes on wire (696 bits), 87 bytes captured (696 bits) on interface wlp0s20f3, id 0
Ethernet II, Src: IntelCor_ec:0e:be (00:d4:9e:ec:0e:be), Dst: SevenSol_08:67 (64:fb:81:20:08:67)
Internet Protocol Version 4, Src: 192.168.0.111, Dst: 192.168.0.120
Transmission Control Protocol, Src Port: 12345, Dst Port: 49152, Seq: 1, Ack: 10, Len: 21
    Source Port: 12345
    Destination Port: 49152
    [Stream index: 7]
    [Conversation completeness: Complete, WITH_DATA (63)]
    [TCP Segment Len: 21]
    Sequence Number: 1    (relative sequence number)
    Sequence Number (raw): 4022264318
    [Next Sequence Number: 22    (relative sequence number)]
    Acknowledgment Number: 10    (relative ack number)
    Acknowledgment number (raw): 3254986498
    1000 .... = Header Length: 32 bytes (8)
    Flags: 0x018 (PSH, ACK)
    Window: 128
    [Calculated window size: 65536]
    [Window size scaling factor: 512]
    Checksum: 0x8273 [unverified]
    [Checksum Status: Unverified]
    Urgent Pointer: 0
    Options: (12 bytes), No-Operation (NOP), No-Operation (NOP), Timestamps
    [Timestamps]
    [SEQ/ACK analysis]
    TCP payload (21 bytes)
Data (21 bytes)
    Data: 41646a7573743a46616c73652c6f66667365743a30
    [Length: 21]

I hope someone can point out my mistake.