Handshake error with WebSocket python server and JS client

Question

I am trying to setup a communication between a python script (that will do a lot of computation on data that cannot be done in javascript and send send that data as a json) and a javascript client.

I have the following code for my python server:

import socket
import sys
from thread import *

HOST = ''   # Symbolic name meaning all available interfaces
PORT = 9888 # Arbitrary non-privileged port

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
print 'Socket created'

#Bind socket to local host and port
try:
    s.bind((HOST, PORT))
except socket.error as msg:
    print 'Bind failed. Error Code : ' + str(msg[0]) + ' Message ' + msg[1]
    sys.exit()

print 'Socket bind complete'

#Start listening on socket
s.listen(10)
print 'Socket now listening'

#Function for handling connections. This will be used to create threads
def clientthread(conn):
    #Sending message to connected client
    conn.send('Welcome to the server. Type something and hit enter\n') #send only takes string

    #infinite loop so that function do not terminate and thread do not end.
    while True:

        #Receiving from client
        data = conn.recv(1024)
        reply = 'OK...' + data
        if not data: 
            break

        conn.sendall(reply)

    #came out of loop
    conn.close()

#now keep talking with the client
while 1:
    #wait to accept a connection - blocking call
    conn, addr = s.accept()
    print 'Connected with ' + addr[0] + ':' + str(addr[1])

    #start new thread takes 1st argument as a function name to be run, second is the tuple of arguments to the function.
    start_new_thread(clientthread ,(conn,))

s.close()

And the following code for my javascript client:

var connection = new WebSocket('ws://127.0.0.1:8999');
connection.onopen = function () {
  connection.send('Hello'); // Send the message to the server
};

I get the following error from my javascript client:

Error during WebSocket handshake: net::ERR_INVALID_HTTP_RESPONSE

And the following output from my python server

Socket created
Socket bind complete
Socket now listening
Connected with 127.0.0.1:53956
Unhandled exception in thread started by <function clientthread at 0x10abac578>
Traceback (most recent call last):
  File "server.py", line 71, in clientthread
    data = conn.recv(1024)
socket.error: [Errno 54] Connection reset by peer

Would anyone know what is wrong?

Edit: forgot to mention that I have seen this SO Post before, but my problem is not the same, or rather should I say that the error encountered by OP is not the same as mine.

Community · Accepted Answer · 2021-10-07 11:04:35Z

2

A WebSocket is a not the same as a plain TCP socket you create. WebSocket is a protocol on top of TCP instead which starts with a HTTP handshake and then continues with a framing based protocol. If you want to implement a WebSocket server in Python you need to implement this protocol as specified in RFC 6455 or use existing WebSocket libraries.

An example server-side python code using WebSocket is:

import asyncio
import websockets

async def handle_message(message):
    print(message)

async def consumer_handler(websocket, path):
    while True:
        message = await websocket.recv()
        await handle_message(message)

start_server = websockets.serve(consumer_handler, 'localhost', 8765)

asyncio.get_event_loop().run_until_complete(start_server)
asyncio.get_event_loop().run_forever()

edited Oct 7, 2021 at 11:04

CommunityBot

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answered Sep 17, 2018 at 4:39

Steffen Ullrich

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1 Comment

LBes Over a year ago

Thanks for the pointers. I accepted your answer and added an example code here to make it more complete.

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