How to send a message from the server to a client using sockets

Question

Server

import socket
import sys
HOST = ''
PORT = 9000
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
print 'Socket created'
try:
    s.bind((HOST, PORT))
except socket.error , msg:
    print 'Bind failed. Error Code : ' + str(msg[0]) + ' Message ' + msg[1]
    sys.exit()
print 'Socket bind complete'
s.listen(10)
print 'Socket now listening'
conn, addr = s.accept()
print 'Connecting from: ' + addr[0] + ':' + str(addr[1])
while 1:
    message=raw_input(">")
    s.sendto(message, (addr[0], addr[1]))
    print(s.recv(1024))

How do I make this send a message to the client? I can make it reply to a string the client sends to the server, but in this case I want the server to send the first message... Can anyone help me, The solutions on google don't seem to work properly and I'm not sure what I'm doing wrong.

Solution 1

Since this is the 1st Google Stack Overflow result for this, I'll post a complete, working example for both a client and a server. You can start either 1st. Verified working on Ubuntu 18.04 w/ Python 3.6.9

text_send_server.py:

# text_send_server.py

import socket
import select
import time

HOST = 'localhost'
PORT = 65439

ACK_TEXT = 'text_received'


def main():
    # instantiate a socket object
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    print('socket instantiated')

    # bind the socket
    sock.bind((HOST, PORT))
    print('socket binded')

    # start the socket listening
    sock.listen()
    print('socket now listening')

    # accept the socket response from the client, and get the connection object
    conn, addr = sock.accept()      # Note: execution waits here until the client calls sock.connect()
    print('socket accepted, got connection object')

    myCounter = 0
    while True:
        message = 'message ' + str(myCounter)
        print('sending: ' + message)
        sendTextViaSocket(message, conn)
        myCounter += 1
        time.sleep(1)
    # end while
# end function

def sendTextViaSocket(message, sock):
    # encode the text message
    encodedMessage = bytes(message, 'utf-8')

    # send the data via the socket to the server
    sock.sendall(encodedMessage)

    # receive acknowledgment from the server
    encodedAckText = sock.recv(1024)
    ackText = encodedAckText.decode('utf-8')

    # log if acknowledgment was successful
    if ackText == ACK_TEXT:
        print('server acknowledged reception of text')
    else:
        print('error: server has sent back ' + ackText)
    # end if
# end function

if __name__ == '__main__':
    main()

text_receive_client.py

# text_receive_client.py

import socket
import select
import time

HOST = 'localhost'
PORT = 65439

ACK_TEXT = 'text_received'


def main():
    # instantiate a socket object
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    print('socket instantiated')

    # connect the socket
    connectionSuccessful = False
    while not connectionSuccessful:
        try:
            sock.connect((HOST, PORT))    # Note: if execution gets here before the server starts up, this line will cause an error, hence the try-except
            print('socket connected')
            connectionSuccessful = True
        except:
            pass
        # end try
    # end while

    socks = [sock]
    while True:
        readySocks, _, _ = select.select(socks, [], [], 5)
        for sock in readySocks:
            message = receiveTextViaSocket(sock)
            print('received: ' + str(message))
        # end for
    # end while
# end function

def receiveTextViaSocket(sock):
    # get the text via the scoket
    encodedMessage = sock.recv(1024)

    # if we didn't get anything, log an error and bail
    if not encodedMessage:
        print('error: encodedMessage was received as None')
        return None
    # end if

    # decode the received text message
    message = encodedMessage.decode('utf-8')

    # now time to send the acknowledgement
    # encode the acknowledgement text
    encodedAckText = bytes(ACK_TEXT, 'utf-8')
    # send the encoded acknowledgement text
    sock.sendall(encodedAckText)

    return message
# end function

if __name__ == '__main__':
    main()

Solution 2

Use the returned socket object from 'accept' for sending and receiving data from a connected client:

while 1:
    message=raw_input(">")
    conn.send(message)
    print conn.recv(1024)