We Keep Coding

Connect to a server using public IPv4 address in python

I'm experimenting with socket server-client communication using python 3 socket module. Just to test if an eventual connection can be made, I've tried to program the simplest scenario possible. Thus the server code has the only purpose to print new connections; its code is:
import socket
server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server.bind(("0.0.0.0", 30000))
while True:
server.listen()
print("listening...")
conn, addr = server.accept()
print(f"{addr} connected")
while the client only tries to connect to the server using the public IPv4 address of my computer:
import socket
client = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
print("Trying to connect...")
client.connect(("99.99.99.99", 30000))
client.close()
When I try to run the server and then the client nothing happens: the server just waits for conections, while the client displays nothing. After a while on the client side it is displayed the socket timeout error. I've tried to establish the connection even running the server and the client on the same computer, I've tried changing the ip of the server to "localhost" or "127.0.0.1", but nothing happens. Have you got any ideas on how this issue can be solved?
P.S. Thank you in advance for eventual answers and excuse my poor English, I'm still practising it!

"Connection Refused" running a server externally , although working locally

Trying to get into sockets and networking.
I wrote some simple server and client scripts and ran them,
which was working when connected locally and client-server communicated just fine, yet when my client script tries to connect to my_external_ip:open_port it gets a "Connection Refused" [WinError 10061]
I've opened a port (5234 in this case) and checked it using those port-scanning sites, what the server seems to react to and even accept connections.
Yet when I run my client script, it throws an exception, and the server doesn't seem to respond or even be aware of the connection attempt.
I've shut down my firewall temporarily and made sure I'm listening on 0.0.0.0:5234 (which to my understanding should be what I'm doing).
Am I missing something? doesn't make sense to me that the script runs locally, the server takes incoming external connections, yet this doesn't work.
Maybe the problem is that the client's outbound connection attempt is somehow blocked?
I cleaned up some unrelated code, but that's about it:
SERVER:
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server = "" #Also tried socket.gethostname() and 0.0.0.0
port = 5234
s.bind((server,port))
s.listen()
connection, address = s.accept()
CLIENT:
def __init__(self):
self.client = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
self.server = my_public_ip
self.port = 5234
self.client.connect((self.server,self.port)

Connect to python server in different network

My port forward rule
I've created a python TCP server and client which is working fine when I launch both server and client on my computer and when I launch the server and the client on different computers on the same network, however I wanted to make it work when computers are in different networks. I have forwarded my router port 8080 to convert to 8888 in my computer, in fact I have also a rule for the port 80 on my router converting to 8080 on my PC which is the Wamp server, and as the python server is not working I guessed it was from the code but I can't figure it out:
Server:
import socket
sck = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sck.bind(("127.0.0.1", 8888))
sck.listen(1)
conn, adr = sck.accept()
print('Connected to ', adr)
while 1:
data = conn.recv(1024).decode()
if data and ('over' not in data):
conn.send(data.encode())
continue
break
conn.close()
Client:
import socket
sck = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sck.connect(('<my_external_ip>', 8888))
while True:
data = input('Say something: ')
if 'Shut up' in data:
sck.send('over'.encode())
sck.close
break
sck.send(data.encode())
I've made this test:
Started Wamp server and tried to access it by my external ip with chrome (working)
Opened my Python TCP Client and connected to the Wamp server (working)
Turned Wamp off and started my python server with the same port as Wamp, then tried to acess with the python client (not working)
If there's nothing wrong with the TCP Server code why does Wamp work and he don't? Please check the following - Whats the logic behind binding 127.0.0.1 I couldn't understand... Won't that make it only be accessible by my PC?
If that part is ok than at least is something related to the Server code I guess...

Python client can not communicate with ruby server. I get [Errno 10061] No connection could be made because the target machine actively refused it

I have the intention of running machine learning algorithms written in Python on data in a database of a Ruby on Rails app. After some research I have discovered sockets and therefore created a Ruby server and Python client. I am running them both on two different command prompt terminals.
Here is the Ruby server code:
require "socket"
server = TCPServer.open(2000)
loop {
client = server.accept
client.puts(Time.now.ctime)
client.puts "Closing the connection. Bye!"
client.close
}
Here is the Python client code:
import socket
s = socket.socket()
host = "localhost"
port = 2000
s.connect((host , port))
I do not understand where the problem is. Kindly assist.

Given insightful answers to my question above the code Ruby server and Python client should be as below.
For the Ruby server:
require "socket" # Get sockets from stdlib
server = TCPServer.open("127.0.0.1" , 2000) # Socket to listen on port 2000
loop { # Server runs forever
client = server.accept # Wait for a client to connect
client.puts(Time.now.ctime) # Send the time to the client
client.puts "Closing the connection. Bye!"
client.close # Disconnect from the client
}
For the Python client:
import socket # Import socket module
s = socket.socket() # Create a socket object
host = "127.0.0.1"
port = 2000 # Reserve a port for your service.
s.connect((host , port))
print s.recv(1024)
s.close() # Close the socket when done
The open() method of the TCPServer class in Ruby takes two parameters. The first being the host name and the second the port i.e
TCPServer.open(hostname , port)

Socket programming in Python -- actual remote port

I've been doing a bit of network programming these days in Python and would like to confirm the flow I think happens between the client and the server:
The servers listens to a given
advertised port (9999)
The client connects to the server by creating a new socket (e.g. 1111)
The servers accepts the client request and automatically spawns a new socket (????) which would now handle the communication between the client and the server
As you can see, in the above flow there are 3 sockets involved:
The server socket which listens to clients
The socket spawned by the client
The socket spawned by the server to handle client
I'm aware of getting the ports for the first two sockets (9999 and 1111) but don't know how to get the "real" port which communicates with the client on the server side.The snippet I'm using right now is:
def sock_request(t):
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect(('localhost', 9999))
print('local sock name: ' + str(s.getsockname()))
print('peer sock name: ' + str(s.getpeername()))
s.send('a' * 1024 * int(t))
s.close()
Any help on getting the "port" number on the server which actually communicates with the client would be much appreciated. TIA.

The new socket is on the same port. A TCP connection is identified by 4 pieces of information: the source IP and port, and the destination IP and port. So the fact that your server has two sockets on the same port (i.e. the listening socket and the accepted socket) is not a problem.