I just started with socket in python. I set up a basic client-server arrangement in localhost using the following:
for server:
from socket import *
s = socket(AF_INET, SOCK_STREAM)
s.bind(('', 6969))
s.listen(10)
c, a = s.accept()
while c.recv(100000) != '':
print c.recv(100000)
for client:
from socket import *
s = socket(AF_INET, SOCK_STREAM)
s.connect(('localhost', 6969))
while True:
say = raw_input('Input Text: ')
s.send(say)
Now, some data (50 %) is lost when I send it, which means it's not received by the server.
Screenshot :
Why is is so?
Can I do anything to improve the efficiency?
In the server you are calling recv() twice: first in the while loop condition, and then in the body of the loop. Each recv() consumes up to 100000 bytes from the socket, so you are effectively discarding the data from every second read.
Try this instead:
from socket import *
s = socket(AF_INET, SOCK_STREAM)
s.bind(('', 6969))
s.listen(10)
c, a = s.accept()
while True:
data = c.recv(100000)
if data:
print data
else:
print "Client closed connection"
break
Related
so basically I have multiple conn.send(data) functions one after another in my server, problem is that when client receives that it puts it in one line, this is my server code:
server = "0.0.0.0"
port = 5851
s = socket(AF_INET, SOCK_STREAM)
s.setsockopt(SOL_SOCKET, SO_REUSEADDR, 1)
s.bind((server, port))
s.listen(10)
try:
conn, addr = s.accept()
print(addr)
conn.send("chr Room_1")
conn.send("cr Room_1")
conn.send("cr Room_2")
s.close()
exit()
except KeyboardInterrupt:
print("\nexiting")
s.close()
So when client receives this data it puts it in one line instead of 3 separate data variables.
So, I have a server sending responses to a client with the socket.send() method. From time to time testing the code on localhost, the socket.recv() method, used by the client to receive the server responses, gets two different messages in one, when the server uses socket.send() twice in a row.
For example:
Server:
from socket import *
serverSocket = socket(AF_INET, SOCK_STREAM)
serverPort = 13005
serverSocket.bind(('', serverPort))
serverSocket.listen(1)
connection_socket, client_ip = serverSocket.accept()
connection_socket.send('Message one')
connection_socket.send('Message two')
Client:
from socket import *
serverName = 'localhost'
serverPort = 13005
clientSocket = socket(AF_INET, SOCK_STREAM)
clientSocket.connect((serverName, serverPort))
print clientSocket.recv(1024)
print clientSocket.recv(1024)
The result from running the client, at random times, is
Message oneMessage two
unless I put a sleep(0.1) between the two send(). Is there a way to avoid using sleep? Do I need to put the exact number of bytes to receive in the recv() method?
TCP is a stream oriented protocol and don't send message one by one. A easy way to split the messages that you can set a split string in the end of message like \r\n
Example:
Client:
#!/usr/bin/env python
import socket
TCP_IP = '127.0.0.1'
TCP_PORT = 13005
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((TCP_IP, TCP_PORT))
s.send('Message one\r\n')
s.send('Message two\r\n')
s.close()
Server:
#!/usr/bin/env python
import socket
TCP_IP = '127.0.0.1'
TCP_PORT = 13005
BUFFER_SIZE = 20 # Normally 1024, but we want test
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((TCP_IP, TCP_PORT))
s.listen(1)
conn, addr = s.accept()
data = ''
while 1:
data += conn.recv(BUFFER_SIZE)
if not data: break
if not data.endswith('\r\n'):
continue
lines = data.split('\r\n')
for line in lines:
print line
data = ''
conn.close()
If your message is complicated and long, you can see: Python Socket Receive Large Amount of Data
I copied the echo server example from the python documentation and it's working fine. But when I edit the code, so it wont send the data back to the client, the socket.recv() method doesn't return when it's called the second time.
import socket
HOST = ''
PORT = 50007
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((HOST, PORT))
s.listen(1)
conn, addr = s.accept()
print('Connected by', addr)
while True:
data = conn.recv(1024)
if not data: break
conn.sendall(b'ok')
conn.close()
In the original version from the python documentation the while loop is slightly different:
while True:
data = conn.recv(1024)
if not data: break
conn.sendall(data)
Client's code:
import socket
HOST = 'localhost'
PORT = 50007
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((HOST, PORT))
s.sendall(b'Hello, world')
data = s.recv(1024)
s.close()
print('Received', repr(data))
TCP sockets are streams of data. There is no one-to-one correlation between send calls on one side and receive calls on the other. There is a higher level correlation based on the protocol you implement. In the original code, the rule was that the server would send exactly what it received until the client closed the incoming side of the connection. Then the server closed the socket.
With your change, the rules changed. Now the server keeps receiving and discarding data until the client closes the incoming side of the connection. Then the server sends "ok" and closes the socket.
A client using the first rule hangs because its expecting data before it closes the socket. If it wants to work with this new server rule, it has to close its outgoing side of the socket to tell the server its done, and then it can get the return data.
I've updated the client and server to shutdown parts of the connection and also have the client do multiple recv's in case the incoming data is fragmented. Less complete implementations seem to work for small payloads because you are unlikely to get fragmentation, but break horribly in real production code.
server
import socket
HOST = ''
PORT = 50007
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.bind((HOST, PORT))
s.listen(1)
conn, addr = s.accept()
print('Connected by', addr)
while True:
data = conn.recv(1024)
if not data: break
conn.sendall(b'ok')
conn.shutdown(socket.SHUT_WR)
conn.close()
client
import socket
HOST = 'localhost'
PORT = 50007
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((HOST, PORT))
s.sendall(b'Hello, world')
s.shutdown(socket.SHUT_WR)
data = b''
while True:
buf = s.recv(1024)
if not buf:
break
data += buf
s.close()
print('Received', repr(data))
The number of receive and send operations have to match because they are blocking. This is the flow diagram for your code:
Server listen
Client connect
Server receive (this waits until a message arrives at the server) [1]
Client send 'Hello world' (received by [1])
Server receive (because there was data received) [2]
Client receive [3]
Because the server and the client are blocked now, no program can continue any further.
The fix would be to remove the client's receive call because you removed the server's send call.
I have started to make my own TCP server and client. I was able to get the server and the client to connect over my LAN network. But when I try to have another client connect to make a three way connection, it does not work. What will happen is only when the first connected client has terminated the connection between, the server and the client, can the other client connect and start the chat session. I do not understand why this happens. I have tried threading, loops, and everything else I can think of. I would appreciate any advice. I feel like there is just one small thing i am missing and I can not figure out what it is.
Here is my server:
import socket
from threading import Thread
def whatBeip():
s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
s.connect(('8.8.8.8', 0))
local_ip_address = s.getsockname()[0]
print('Current Local ip: ' + str(local_ip_address))
def clietConnect():
conn, addr = s.accept()
print 'Connection address:', addr
i = True
while i == True:
data = conn.recv(BUFFER_SIZE)
if not data:
break
print('IM Recieved: ' + data)
conn.sendall(data) # echo
whatBeip()
TCP_IP = ''
TCP_PORT = 5005
BUFFER_SIZE = 1024
peopleIn = 4
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((TCP_IP, TCP_PORT))
s.listen(peopleIn)
for client in range(peopleIn):
Thread(target=clietConnect()).start()
conn.close()
Here is my client
import socket
TCP_IP = '10.255.255.3'
TCP_PORT = 5005
BUFFER_SIZE = 1024
MESSAGE = "Hello, World!"
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((TCP_IP, TCP_PORT))
i = True
while i == True:
s.sendall(raw_input('Type IM: '))
data = s.recv(BUFFER_SIZE)
s.close()
This is your main problem: Thread(target=clietConnect()).start() executes the function clientConnect and uses it's return value as the Thread function (which is None, so the Thread does nothing)
Also have a look at:
1) You should wait for all connections to close instead of conn.close() in the end of the server:
threads = list()
for client in range(peopleIn):
t = Thread(target=clietConnect)
t.start()
threads.append(t)
for t in threads: t.join()
and to close the connection when no data is received:
if not data:
conn.close()
return
2) You probably want to use SO_REUSEADDR [ Socket options SO_REUSEADDR and SO_REUSEPORT, how do they differ? Do they mean the same across all major operating systems? , Python: Binding Socket: "Address already in use" ]
3) And have a look at asyncio for python
A simple demo of socket programming in python:
server.py
import socket
host = '127.0.0.1'
port = 8000
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((host, port))
s.listen(1)
conn, addr = s.accept()
while True:
data = conn.recv(1024)
print 'Received:', data
if not data:
break
conn.sendall(data)
print 'Sent:', data
conn.close()
client.py
import socket
host = '127.0.0.1'
port = 8000
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((host, port))
s.sendall('Hel')
s.sendall('lo world!')
print 'Received:', s.recv(1024)
s.close()
Now code work well. However, the client may not know if server will always send back every time. I tried symmetric code of while-loop in server.py
client_2.py
import socket
host = '127.0.0.1'
port = 8000
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((host, port))
s.sendall('Hel')
s.sendall('lo world!')
while True:
data = s.recv(1024)
if not data:
break
print 'Received:', data
s.close()
This code will block at
data = s.recv(1024)
But in server.py, if no data received, it will be blank string, and break from while-loop
Why it does not work for client? How can I do for same functionality without using timeout?
You can set a socket to non-blocking operation via socket.setblocking(false), which is equivalent to socket.settimeout(0). Solving this "without using timeout" is impossible.