Develop Reference

How to know packet type in sockets?

I am writing a simple client server program using Sockets in python. In my example, 1st I want to send a simple "text" in a packet for example, 2nd I will send an image for example.
In the client I want that if I receive a text, I print it on my console. But, if I receive a file (like an image), I save it on my hard drive.
How can I differentiate between the packets I receive on the client side?
#Server Code
import socket
host = socket.gethostname()
s_client=socket.socket()
port_server = 8081
s_client.bind((host, port_server))
s_client.listen(1)
print("Waiting for any incoming connections from clients ...")
conn_client, addr_client = s_client.accept()
#Send a text
conn_client.send("text".encode())
#Send a file (image for example)
f = open("image", "rb")
l = f.read(1024)
while (l):
conn_client.send(l)
l = f.read(1024)
#Client code
import socket
s = socket.socket()
host = socket.gethostname()
port_server = 8081
s.connect((host, port_server))
print("Connected...")
while True:
data = s.recv(1024)
#I WANT TO DIFFERENTIATE HERE
if data:
print(data)

Python's socket object is designed for low-level network communication. In other words, you can use it to send some raw data from one communication endpoint to another one. The socket object itself does not have any means to differentiate between data types or content. This typically takes place on a higher protocol layer.
For example, when a browser receives some data from a server via http, usually the content type is transmitted so the browser knows how to handle the data.
For your purpose, it might be perfectly sufficient if the server would in a similar way send some kind of prefix before the actual data - for example the string 'TXT' if the subsequent data is a text, and 'IMG' if the subsequent data is an image. The client could then evaluate these first three characters and interpret the data appropriately.

How to use a Python 3 socket client/server setup over the internet (not locally)?

I am trying to implement a simple chat program that uses sockets to transmit data via a UDP connection. However, I can't figure out how to correctly set it up so that people from outside my local network can access it if I am hosting it on my laptop. I am utilizing port 5000, and have port-forwarded that port on my router for my laptop. The port-forwarding doesn't seem to be the issue; at least the "Port Forward Network Utilities" from portforward.com seems to detect it as properly forwarded. Maybe I am mixing up the IP addresses I need to host from and connect with? The code in question is below:
import socket
import threading
import sys
class Server:
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
connections = []
def __init__(self):
self.sock.bind(('192.168.1.5', 5000))
self.sock.listen(1)
def handler(self, c, a):
while True:
data = c.recv(1024)
for connection in self.connections:
print(data.decode())
connection.send(data)
if not data:
break
def run(self):
while True:
c, a = self.sock.accept()
cThread = threading.Thread(target=self.handler, args=(c, a))
cThread.daemon = True
cThread.start()
self.connections.append(c)
print(self.connections)
class Client:
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
usr_name = ""
def sendMsg(self):
while True:
self.sock.send(bytes(self.usr_name + ": " + input("-> "), 'utf-8'))
def __init__(self, address):
self.sock.connect((address, 5000))
self.usr_name = input("Enter a username: ")
iThread = threading.Thread(target=self.sendMsg)
iThread.daemon = True
iThread.start()
while True:
data = self.sock.recv(1024)
if not data:
break
print(data.decode())
if len(sys.argv) > 1:
client = Client(sys.argv[1])
else:
server = Server()
server.run()
As you can see, I have my current local IP address inputted for hosting the server, while the client asks for an IP to connect to. I'm not sure what to do now for hosting this over the internet, but I have tried every IP combination I can think of and it returns a number of errors.
Thanks in advance.
Edit:
The two main errors I was getting are:
Timeout Error [WinError 10060]
My friend received this when trying to connect from another network
[WinError 10061]
I would receive this when trying to connect using my public IP from the same computer
I'm sorry that I can't be more detailed in my errors and provide a full printout, and I will try to update this if I'm able to replicate them.
Edit:
I was able to rewrite it and get it to work, I don't need anymore help with this.
Thanks.

You're port-forwarding UDP port 5000 to 5000.
But you're opening TCP streams, not UDP. That's what SOCK_STREAM means. If you want UDP, you need to use SOCK_DGRAM.
So, you need to make these two consistent. The only problem is, I'm not sure which one you actually want here.
On the one hand, your code is doing connection-oriented recv, and seems to be assuming reliable transmission, which means you probably want TCP.
On the other hand, your code seems to be assuming that each recv(1024) is going to get exactly one send from the other side, which is only true for UDP; TCP sockets are byte streams, not message streams. When you do a recv(1024), you could easily get just the first 12 bytes of an 80-byte line, which means it could end in the middle of a UTF-8 character, which means decode will throw an exception.
I think you want TCP, but with a framing protocol on top of it. The simplest protocol that would probably make sense here is lines of text. Which is pretty easy to do on your own, but even easier to do with socket.makefile, given that you're dedicating a thread to each connection.

Python TCP sockets headers

I need to create a communication between a client and a server with TCP. But I'd like to send and work with "headers". So from the client I'd like to send a header "COMMAND1" and the server returns me something.
I have the following code:
Server
import socket
import threading
bind_ip = '0.0.0.0'
bind_port = 9998
server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server.bind((bind_ip, bind_port))
server.listen(5) # max backlog of connections
print ('Listening on {}:{}'.format(bind_ip, bind_port))
def handle_client_connection(client_socket):
request = client_socket.recv(1024)
print ('Received {}'.format(request))
client_socket.send('Response1!'.encode('utf-8'))
client_socket.close()
while True:
client_sock, address = server.accept()
print ('Accepted connection from {}:{}'.format(address[0], address[1]))
client_handler = threading.Thread(
target=handle_client_connection,
args=(client_sock,) # without comma you'd get a... TypeError: handle_client_connection() argument after * must be a sequence, not _socketobject
)
client_handler.start()
Client
import socket
hostname, sld, tld, port = 'www', 'integralist', 'co.uk', 80
target = '{}.{}.{}'.format(hostname, sld, tld)
# create an ipv4 (AF_INET) socket object using the tcp protocol (SOCK_STREAM)
client = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
# connect the client
# client.connect((target, port))
client.connect(('0.0.0.0', 9998))
# send some data (in this case a HTTP GET request)
client.send('hi'.encode('utf-8'))
# receive the response data (4096 is recommended buffer size)
response = client.recv(4096)
print (response)
Anyone knows the best way to return "Response1!" when the header is "COMMAND1" and "Response2!" when the header is "COMMAND2"?
I can't find examples on how to use headers
EDIT: It doesn't have to be "COMMAND1" or "COMMAND2" it can be a "0" or "1", or anything else.

If you want to add your own header, you just have to:
Make sure your programm finds the start of your message (like, every message beginns "!?&")
Send your own header-data just after the start-symbol of your message.
Maybe mark the end of your message with something or pass a length in your header.
Since TCP will give you a stream of data, it might come to a case, where it just gives you 2 or 3 messages at once. You have to separate these messages by yourself (e.g. by using "?!&" as start of every message).
You can always create your own protocoll as payload of another protocoll. Just as TCP is just payload from the ethernet point of view.

You can do something i have done with my program to accept such headers
Use pickle library to encode a dict headers and send it through socket.
Code will look something like this.
import pickle
def handleSocket(headers:dict):
message = pickle.dumps(headers)
socket.send(message)
For server side, you will be handling it
Gonna initialise the socket recv to 100 kb
def handleReceivedSocket(socket):
message:dict = pickle.loads(socket.recv(102400))
Another way to do this. Is sending a raw json string to the server (just change pickle.dumps,pickle.loads by json.dumps,json.loads
But it will be in raw and less secure.
Last way you can do it is uri encoding. Check w3schools

Simple Python Web Server trouble

I'm trying to write a python web server using the socket library. I've been through several sources and can't figure out why the code I've written doesn't work. Others have run very similar code and claim it works. I'm new to python so I might be missing something simple.
The only way it will work now is I send the data variable back to the client. The browser prints the original GET request. When I try to send an HTTP response, the connection times out.
import socket
##Creates several variables, including the host name, the port to use
##the size of a transmission, and how many requests can be handled at once
host = ''
port = 8080
backlog = 5
size = 1024
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((host,port))
s.listen(backlog)
while 1:
client, address = s.accept()
data = client.recv(16)
if data:
client.send('HTTP/1.0 200 OK\r\n')
client.send("Content-Type: text/html\r\n\r\n")
client.send('<html><body><h1>Hello World</body></html>')
client.close()
s.close()

You need to consume the input before responding, and you shouldn't close the socket in your while loop:
Replace client.recv(16) with client.recv(size), to consume the request.
Move your last line, s.close() back one indent, so that it is not in your while loop. At the moment you are closing the connection, then trying to accept from it again, so your server will crash after the first request.
Unless you are doing this as an exercise, you should extend SimpleHTTPServer instead of using sockets directly.
Also, adding this line after your create the socket (before bind) fixes any "Address already in use" errors you might be getting.
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
Good luck!

python icmp raw socket implementation

i am relatively new to python, so please be considerate...
i'm implementing a server and a client via raw_sockets.
i have the necessary privileges.
now, the server i defined so:
host = socket.gethostbyname(socket.gethostname())
address = (host, 22224)
sockSer = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_ICMP)
sockSer.bind(address)
sockSer.ioctl(socket.SIO_RCVALL, socket.RCVALL_ON)
packet, addr = sockSer .recvfrom(4096) # wait for packet from client
Q1) why can't i simply type: hosts = 'localhost'.
if i do so, it doesn't allow me to write the line: sockSer.ioctl(socket.SIO_RCVALL, socket.RCVALL_ON). and then the server doesn't receive my client's messages.
only when doing gethostbyname(socket.gethostname()) i get 192.168.1.101
and then it works.
in a different class:
the client socket:
host = socket.gethostbyname(socket.gethostname())
address = (host, 22224)
sockCli = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_ICMP)
Q2) do i also need to type: sockCli.ioctl(socket.SIO_RCVALL, socket.RCVALL_ON)
or maybe sockCli.connect(address)? seems that it works without the connect command.
for the client socket?
now, the problems arise when i do the following:
1) send a packet from client to server:
header=...
payload='a'
sockCli.sendto(header + payload, address)
2) receive packet in server and send something back to client:
while(true):
data, addr = sockSer.recvfrom(4096)
header2=...
payload2='b'
sockSer.sendto(header2 + payload2, addr)
now, my important question is:
Q3) the server sent only 1 packet to client, with payload 'b'.
what happens is, my client actually receives 2 packets in the while loop:
first packet is what the client itself sent to server, and the other packet is what the client got from the server.
hence my output is 'ab' instead of simply 'b'
why is this happening???
NOTE: i didn't type the entire code, but i think my syntax,parsing,header composition etc.. are correct.
is there an obvious problem in my code?
if necessary i'll upload the entire code.
thanks

I got this too.
my solution is add a judge in the receive code,such as if I send Ping package so I only want ECHO　Reply( type 0 code 0), I write
if type != 0:
continue
and you also can write as
if addr == my_ip:
continue
It seems not has any smooth solution

Q1: I was able to bind to localhost and call IOCTL with both parameters just fine. Assuming your client is also running on the same system, ensure the client is sending to "localhost", otherwise your server will never receive the packets. If your client is on another system, obviously your server will never receive the packets.
Q2: You do not need IOCTL for sending the packet. Just send it via sendto().
Q3: The reason you're seeing two replies is, the kernel is also processing the echo request, in addition to your own user-space code.
Although you can use ICMP for arbitrary message passing, as someone else pointed out this isn't its intended design. You may find that your data portion is truncated out in message replies. For example, when sending echo requests, your reply likely will contain everything you sent; however, a reply that is type 3 code 3 may not include your data, but only the first 8 bytes of the ICMP header.