Python Tcp disconnect detection

Question

I have a simpletcp example:

import socket
import time


TCP_IP = '127.0.0.1'
TCP_PORT = 81
BUFFER_SIZE = 1024

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((TCP_IP, TCP_PORT))

while True:
    s.send(bytes('hello', 'UTF-8'))
    time.sleep(1)

s.close()

How can I detect, if I lost the connection to the server, and how can I safely reconnect then?

Is it necessary to wait for answer to the server?

UPDATE:

import socket
import time

TCP_IP = '127.0.0.1'
TCP_PORT = 81
BUFFER_SIZE = 1024

def reconnect():
    toBreak = False
    while True:
        s.close()
        try:
            s.connect((TCP_IP, TCP_PORT))
            toBreak = True
        except:
            print ("except")        
        if toBreak:
            break
        time.sleep(1)


s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((TCP_IP, TCP_PORT))

while True:
    try:    
        s.send(bytes('hello', 'UTF-8'))
        print ("sent hello")
    except socket.error as e:
        reconnect()

    time.sleep(1)

s.close()

If I break the connection, it raises an error (does not really matter what), and goes to the reconnect loop. But after I restore the connection, the connect gives back this error:

OSError: [WinError 10038] An operation was attempted on something that is not a socket

If I restart the script, which calls the same s.connect((TCP_IP, TCP_PORT)), it works fine.

Answer 1

You'll get a socket.error:[Errno 104] Connection reset by peer exception (aka ECONNRESET) on any call to send() or recv() if the connection has been lost or disconnected. So to detect that, just catch that exception:

while True:
    try:
        s.send(bytes('hello', 'UTF-8'))
    except socket.error, e:
        if e.errno == errno.ECONNRESET:
            # Handle disconnection -- close & reopen socket etc.
        else:
            # Other error, re-raise
            raise
    time.sleep(1)

Answer 2

Use a new socket when you attempt to reconnect.

def connect():
    while True:
        try:
            s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
            s.connect((host, port))
            return s.makefile('w')
        except socket.error as e:
            log("socket error {} reconnecting".format(e))
            time.sleep(5)

dest = connect()
while True:
    line = p.stdout.readline()
    try:
        dest.write(line)
        dest.flush()
    except socket.error as e:
        log("socket error {} reconnecting".format(e))
        dest = connect()