Send a file through sockets in Python

Question

I'm trying to make a program in python that implements sockets. Each client sends a PDF file and the server receives it and the title is changed to "file_(number).pdf" (e.g.: file_1.pdf). The problem presented is that only a client can send a file successfully. When a second client tries to send the file, the program crashes. What am I doing wrong and how can I solve my code to allow N clients (with N < 20) to connect to the server and transfer files?

Here's the server code:

import socket
import sys
s = socket.socket()
s.bind(("localhost",9999))
s.listen(10) # Accepts up to 10 incoming connections..
sc, address = s.accept()

print address
i=1
f = open('file_'+ str(i)+".pdf",'wb') # Open in binary
i=i+1
while (True):

    # We receive and write to the file.
    l = sc.recv(1024)
    while (l):
        f.write(l)
        l = sc.recv(1024)
f.close()

sc.close()
s.close()

Here's the client code:

import socket
import sys

s = socket.socket()
s.connect(("localhost",9999))
f = open ("libroR.pdf", "rb")
l = f.read(1024)
while (l):
    s.send(l)
    l = f.read(1024)
s.close()

To simplify my code, I always use a book with file name "libroR.pdf", but in the full code it is chosen by a GUI.

Answer 1

You must put all the code from sc, address = s.accept() upto sc.close() into another loop or the server simply terminates after receiving the first file. It doesn't crash, the script is just finished.

[EDIT] Here is the revised code:

import socket
import sys
s = socket.socket()
s.bind(("localhost",9999))
s.listen(10) # Accepts up to 10 connections.

while True:
    sc, address = s.accept()

    print address
    i=1
    f = open('file_'+ str(i)+".pdf",'wb') #open in binary
    i=i+1
    while (True):       
    # receive data and write it to file
        l = sc.recv(1024)
        while (l):
                f.write(l)
                l = sc.recv(1024)
    f.close()


    sc.close()

s.close()

Note that s.listen(10) means "set maximum accept rate to 10 connections", not "stop after 10 connections".

Answer 2

Your code is getting stuck in the second while loop.

See:

import socket
import sys
s = socket.socket()
s.bind(("localhost",9999))
s.listen(10)

i=1

while True:
    sc, address = s.accept()

    print address

    f = open('file_'+str(i)+".pdf",'wb') #open in binary
    i=i+1
    print(i)
    l = 1
    while(l):
        l = sc.recv(1024)
        while (l):
            f.write(l)
            l = sc.recv(1024)
        f.close()


    sc.close()

s.close()

Answer 3

Server:

import socket
from threading import Thread

TCP_IP = 'localhost'
TCP_PORT = 9001
BUFFER_SIZE = 1024


class ClientThread(Thread):

    def __init__(self, ip, port, sock):
        Thread.__init__(self)
        self.ip = ip
        self.port = port
        self.sock = sock
        print(" New thread started for "+ip+":"+str(port))

    def run(self):
        filename = 'anon234.jpeg'
        f = open(filename, 'rb')
        while True:
            l = f.read(BUFFER_SIZE)
            while (l):
                self.sock.send(l)
                #print('Sent ',repr(l))
                l = f.read(BUFFER_SIZE)
            if not l:
                f.close()
                self.sock.close()
                break


tcpsock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
tcpsock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
tcpsock.bind((TCP_IP, TCP_PORT))
threads = []

while True:
    tcpsock.listen(5)
    print("Waiting for incoming connections...")
    (conn, (ip, port)) = tcpsock.accept()
    print('Got connection from ', (ip, port))
    newthread = ClientThread(ip, port, conn)
    newthread.start()
    threads.append(newthread)

for t in threads:
    t.join()

Client:

import socket
import time

TCP_IP = 'localhost'
TCP_PORT = 9001
BUFFER_SIZE = 1024

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((TCP_IP, TCP_PORT))
recived_f = 'imgt_thread'+str(time.time()).split('.')[0]+'.jpeg'
with open(recived_f, 'wb') as f:
    print('file opened')
    while True:
        #print('receiving data...')
        data = s.recv(BUFFER_SIZE)
        print('data=%s', (data))
        if not data:
            f.close()
            print('file close()')
            break
        # write data to a file
        f.write(data)

print('Successfully get the file')
s.close()
print('connection closed')

Answer 4

You are closing the server socket (s in your code) after handling the first client connection. Thus only one client is ever handled by your server. Make a loop around accept and reading from the sc.

Answer 5

Using this code you can send files multiple time using the same client.py

Server.py

import socket
import sys
s = socket.socket()
s.bind(("localhost",9999))
s.listen(10) # Acepta hasta 10 conexiones entrantes.

i = 1
while True:
    sc, address = s.accept()

    print address
    f = open('file_'+ str(i)+".wav",'wb') #open in binary
    i=i+1
    while (True):
        # recibimos y escribimos en el fichero
        l = sc.recv(1024)
        f.write(l)

        if not l:
            break

    f.close()
    sc.close()
    print('copied the file.')

s.close()