How connect my Kivy client to a server (TCP, Sockets)

Question

So as part of my project (2D Multiplayer Card Game), I've figured out how to host and run a server script online. My plan is to have two separate kivy clients connect to the server (which will just be a script with commands).

However I'm somewhat confused about the order of operations because I think the client connection is potentially in conflict with the message loop so I'm wondering if someone could basically tell me what I should be doing:

I'm going to be using this as my serverscript:

import socket

serversocket = socket.socket()

host = 'INSERTIPHERE'
port = PORTHERE


serversocket.bind(('', port))

serversocket.listen(1)

while True:
    clientsocket,addr = serversocket.accept()
    print("got a connection from %s" % str(addr))

    msg = 'Thank you for connecting' + "\r\n"
    clientsocket.send(msg.encode('ascii'))
    clientsocket.close()

This is my client connection function

def Main():
    host = 'INSERTIPHERE'
    port = PORTHERE

   mySocket = socket.socket()
   mySocket.connect((host, port))

   message = input(' -> ')

   while message != 'q':
           mySocket.send(message.encode())
           data = mySocket.recv(1024).decode()
           print('Received from server: ' + data)
           message = input(' -> ')

  mySocket.close()

Note: I understand that the server and client aren't perfectly aligned in functions but provided I can at least a connection confirmation for now, I can work from there.

I'm basically wondering how do I put this code into a simple kivy app like this:

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout

class BoxWidget(BoxLayout):
    pass

class BoxApp(App):

     def build(self):
        return BoxWidget()

if __name__ == '__main__':
     BoxApp().run()

My best guess is that you want to:

• Establish the connection before opening the client
• Passing the server connection to the primary widget (in this case the Box Widget) as you're running an instance of the client (ie BoxApp(server).run()?)
• Use that connection in a message loop function of the BoxWidget

I also understand that Kivy has built in solutions with Twisted but I'm having trouble with the python 2-3 differences.

Thank you for reading.

Just to clarify: All I want to do right now is open a blank window and also have a confirmation message sent to the command line (or failing that a label in the window).

Answer 1

You can use threading so you don't interrupt the main thread in kivy.
I rewrote your example a bit, so what you send from the server, will be the text of a label.

server.py

import socket


serversocket = socket.socket()

host = 'localhost'
port = 54545


serversocket.bind(('', port))

serversocket.listen(1)

clientsocket,addr = serversocket.accept()
print("got a connection from %s" % str(addr))

while True:
    msg = input("> ") + "\r\n"
    clientsocket.send(msg.encode('ascii'))

client.py

import socket

class MySocket:

    def __init__(self,host="localhost",port=54545):

        self.sock = socket.socket()
        self.sock.connect((host, port))


    def get_data(self):
        return self.sock.recv(1024)

main.py

from kivy.app import App
from kivy.uix.label import Label
from client import *
from threading import Thread


class MyLabel(Label):

    def __init__(self, **kwargs):
        super(MyLabel,self).__init__(**kwargs)

        self.sock = MySocket()
        Thread(target=self.get_data).start()

    def get_data(self):
        while True:
            self.text = self.sock.get_data()


class BoxApp(App):

     def build(self):
        return MyLabel()


if __name__ == '__main__':
     BoxApp().run()

Now just run server.py in one terminal, then main.py from another

Answer 2

I got a basic version of it working with buttons. Both on local machine and online. This Solution is likely not viable for many real time apps or even a chat server since the reply has to be initiated. However for my goal of a multiplayer card game it should more than suffice with proper conditionals.

video of test on local machine

EDIT: In the video I talk about double clicking. I have just realized this is because the first click is putting the window back in focus.

EDIT 2: Using TextInput in kv file instead of input in Python file.

server script:

import socket

def Main():
    host = '127.0.0.1'
    port = 7000

    mySocket = socket.socket()
    mySocket.bind((host,port))

    mySocket.listen(1)
    conn, addr = mySocket.accept()
    print ("Connection from: " + str(addr))
    message = 'Thank you connecting'
    conn.send(message.encode())

    while True:
        data = conn.recv(1024).decode()
        strdata = str(data)
        print(strdata)
        reply = 'confirmed'
        conn.send(reply.encode())

    mySocket.close()

if __name__ == '__main__':
    Main()

This is a pretty simple server. Listen for a single client, confirm connection, open a send and receive message loop.

This is the client script which isn't hugely complicated really:

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.properties import ObjectProperty
import socket

class BoxWidget(BoxLayout):
    s = socket.socket()
    host = '127.0.0.1'
    port = 7000
    display = ObjectProperty()


    def connect_to_server(self):
        # called by a Button press

        # Connects to the server
        self.s.connect((self.host, self.port)) 

        # Receives confirmation from Server
        data = self.s.recv(1024).decode()      

        # Converts confirmation to string
        strdata = str(data)                     

        # Prints confirmation
        print(strdata)                                   

    def send_message(self):    
        # Is called by the function below
        # Encodes and sends the message variable                  
        self.s.send(self.message.encode()) 

        # Waits for a reply   
        self.receive_message()                     

    def message_to_send(self):  
        # Defines Message to send                 
        self.message = self.display.text
        # Calls function to send the message                
        self.send_message()     

    # Note
    # When I used message = input directly in send_message,
    # the app would crash. So I defined message input 
    # in its own function which then calls the 
    # send function  

    # message_to_send is the function actually
    # called by a button press which then
    # starts the chain of events
    # Define Message, Send Message, get Reply

    def receive_message(self):
        # Decodes a reply                    
         reply = self.s.recv(1024).decode()

        # Converts reply to a str
        strreply = str(reply)

        # prints reply
        print(strreply)

class ServerApp(App):    
     def build(self):
          box = BoxWidget()
          return box

if __name__ == '__main__':
    ServerApp().run()    

Edit: Forgot to include the kv file

<BoxWidget>:
     display: display
     Button:
        text: 'Hello'
        on_press: root.message_to_send()
    Button:
        text: 'Connect'
        on_press: root.connect_to_server()
    TextInput:
        id: display

In future iterations, I'll be replacing print statements with conditionals (ie did client one draw a card? if so client 2's opponent draws a face-down card etc).

Relatively rudimentary as it is now but there is a lot you could do from here.