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Creating a server on python

I’m trying to create a server on my raspberry pi using python and then i want to test the server by accessing it from another device using the IP address of the raspberry pi, but the problem is that everytime i type the IP address of my raspberry pi into my webpage, it doesn’t open and i don’t know if there’s a problem in my code or not, i will write below so that anyone could check
import socket
import sys
my_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
host = socket.gethostname()
try:
my_socket.bind((host, 1234))
except socket.error:
print(‘failed’)
sys.exit()
my_socket.listen(5)
While True:
conn, addr = my_socket.accept()
data = conn.recv(1000)
if data:
print(‘got a request’)
my_socket.send(‘Thank you’)
my_socket.close()
conn.close()
after that i tried typing the raspberry pi’s IP address on my laptop’s webpage but it was no use, first i typed ifconfig in the terminal of the raspberry pi to get the IP address and i tried it but it didn’t work, then i added another line in the code which is gethostbyname to the variable host and printed it and it showed different IP address than the one in ifconfig which was confusing to me, but i even tried this another IP address on my webpage and it didn’t work too

Did you check with netstat to see if the code is actually listening? Should list the <IP>:<Port> as LISTENING, i always check that when i do server code.
Sometimes when you try out code and don't terminate it properly, there can be a orphan process still listening to the Interface:Port hogging the port. Been there, done that, got the T-shirt.
Also, try using 0.0.0.0 instead, it tells the socket listener to listen on all interfaces, including loopback.
Got any firewall denying the connection ? Check that.
Also, check try using curl as a debug tool and see if 1) Curl can connect and 2) you get send some HTTP data to the server:
Curl 127.0.0.1:1234/HelloWorld

Connecting between computers with a socket

Is there a way to connect to another computer via their public IP using python sockets, so that you can send data?
In a similar way to which you can connect to a webpage, etc can you do something like this:
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((ip, 6000))
I have seen examples of people using this in DOS scripts but can't seem to recreate it. All I get is timeout errors. The only time it worked was when using port 5000 and connecting to my own IP (but all other ports failed), any idea why this happened as well?

Building a packet sniffer with Python + sockets

So I'm trying to build a packet sniffer in Python to deepen my understanding of networking. Thing is, it has turned out to be a tad bit more confusing than I initially anticipated. The problem is that all resources with thorough explanations cover the scenario of creating sockets for client/server data sending/receiving purposes.
At this point, I've successfully created some classes that handle packet header decoding for IPv4 and ICMP. Now, since my socket code only seemed to capture ICMP packets, I've been trying to configure it so that I can catch all traffic reaching my wifi interface, but I still almost exclusively see ICMP packets (with localhost as both source and destination).
So, I have some questions which I'd like to get answered. But first, my code:
import socket
import sys
from protocols.ipv4 import IPv4
PACKET_SIZE = 65535
sock = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_IP)
sock.bind(("0.0.0.0", 0))
try:
while True:
# read in a packet
raw_buffer = sock.recvfrom(PACKET_SIZE)[0]
# create an IP packet object
ip_header = IPv4(raw_buffer)
# print the packet
print(ip_header)
except KeyboardInterrupt:
print("\nExiting...")
sock.close()
sys.exit(0)
This is how I've understood it:
First I'm creating a socket with socket.socket, where I specify address family, socket type and protocol. In my case, I'm selecting the AF_INET family which I don't really understand very well, but it seems to yield packets from the network layer. The socket type is set to SOCK_RAW meaning that I want the raw sockets as opposed to using SOCK_STREAM for TCP connections and SOCK_DGRAM for UDP. The last argument IPPROTO_IP just indicates that I want IP packets only.
Then, I'm binding the socket to 0.0.0.0 which supposedly means "any address" as described here.
What I don't understand:
Initially, I saw some examples of creating a sniffer socket which used the AF_PACKET address family. I soon found out that this address family is not available on macos (which I'm using). Why is that? What is an address family how does it relate to sockets? Is there an alternative way to catch packets from lower levels? In Wireshark I can see ethernet datagrams, so it seems possible.
As I've stated, I want to sniff all the traffic reaching my wifi interface. How does the socket know which interface I want it to operate on? Also I've learned that network interfaces can be put into different modes like monitor or promiscuous, how does that relate to sockets and my goal of catching packets?
Why am I almost only catching ICMP packets? What is the purpose of these packets with localhost both as destination and source?
I know there are lots of gaps in my current understanding of this. I'm not sure if I'll be able to get this to work, but I'm curious and I'd be grateful for any kind of answer or even just some good resources to check out.
Edit: My main question is where can I find out more about sockets in the context of packet sniffing?

Python socket NAT port address

I have a client socket behind a NAT and I want to get the local port number used by the process.
To illustrate my question, here's a quick example.
Let's say I create a server using the following code:
welcome_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
welcome_socket.bind(("", 1500))
welcome_socket.listen(5)
I then listen for incoming connections:
(client_socket, address) = self.welcome_socket.accept()
I connect from a client (behind a NAT) using the following code:
sock = socket.create_connection(("server_address", 1500))
Here is where I'm a little confused.
The address I get on the server side has the public address of the WiFi network the client is connected to (which I expect) and some port number, which based on my understanding of NATs, should be different from the actual port number used by the client and is used for address translation.
However, if I used the getsockname() function on the client, I get the same port number as the one given by the server.
Returning to the example in code.
On the server:
client_socket.getpeername()
>>> ('WiFi_address', 4551)
On the client:
sock.getsockname()
>>> ('local_address', 4551)
So, both port numbers are the same, even though the client is behind a NAT. How is this the case? Am I misunderstanding how the NAT works? Or is there another command to get the physical address that the client socket is bound to?
Any insight would be appreciated.

It is likely that the Router is using Port Address Translation (or one-to-many NAT). The wiki link further quotes
PAT attempts to preserve the original source port. If this source port
is already used, PAT assigns the first available port number starting
from the beginning of the appropriate port group 0-511, 512-1023, or
1024-65535. When there are no more ports available and there is more
than one external IP address configured, PAT moves to the next IP
address to try to allocate the original source port again. This
process continues until it runs out of available ports and external IP
addresses.
And that should be the reason why you are seeing port 4551 on the server.
(This link should also help to clarify the difference between NAT and PAT)

Trouble initiating a TCP connection in Python--blocking and timing out

For a class project I'm trying to do some socket programming Python but running into a very basic issue. I can't create a TCP connection from my laptop to a lab machine. (Which I'm hoping to use as the "server") Without even getting into the scripts I have written, I've been simply trying interpreter line commands with no success. On the lab machine (kh4250-39.cselabs.umn.edu) I type the following into Python:
from socket import *
sock = socket()
sock.bind(('', 8353))
sock.listen(5)
sock.accept()
And then on my laptop I type:
from socket import *
sock = socket()
sock.connect(('kh4250-39.cselabs.umn.edu', 8353))
At which point both machines block and don't do anything until the client times out or I send a SIGINT. This code is pretty much exactly copied from examples I've found online and from Mark Lutz's book Programming Python (using '' for the server host name apparently uses the OS default and is fairly common). If I run both ends in my computer and use 'localhost' for the hostname it works fine, so I suspect it's some problem with the hostnames I'm using on one or both ends. I'm really not sure what could be going wrong on such a simple example. Does anyone have an idea?

A good way to confirm whether it's a firewall issue or not is to perform a telnet from the command-line to the destination host in question:
% telnet kh4250-39.cselabs.umn.edu 8353
Trying 128.101.38.44...
And then sometime later:
telnet: connect to address 128.101.38.44: Connection timed out
If it just hangs there at Trying and then eventually times out, chances are the connection to the remote host on that specific port is being blocked by a firewall. It could either be at the network layer (e.g. a real firewall or a router access-list) or at the host, such as iptables or other host-based filtering mechanisms.
Access to this lab host might only be available from within the lab or the campus network. Talk with your professor or a network administrator or someone "in the know" on the network to find out for sure.

Try to bind the server to 'kh4250-39.cselabs.umn.edu' instead of '':
sock.bind(('kh4250-39.cselabs.umn.edu', 8353))
If this does not work: Another reason could be a firewall blocking the port 8353....