Network Programming - Server & Client B : File Transfer

In this chapter, we're going to extend Python Network Programming I - Basic Server / Client A, and try to file transfer from a server to numerous clients. The main purpose is to check the performance of the server from which clients download files.

Here is the code to send a file from a local server to a local client.

# server.py
import socket # Import socket module
port = 60000 # Reserve a port for your service.
s = socket.socket() # Create a socket object
host = socket.gethostname() # Get local machine name
s.bind((host, port)) # Bind to the port
s.listen(5) # Now wait for client connection.
print 'Server listening....'
while True:
 conn, addr = s.accept() # Establish connection with client.
 print 'Got connection from', addr
 data = conn.recv(1024)
 print('Server received', repr(data))
 filename='mytext.txt'
 f = open(filename,'rb')
 l = f.read(1024)
 while (l):
 conn.send(l)
 print('Sent ',repr(l))
 l = f.read(1024)
 f.close()
 print('Done sending')
 conn.send('Thank you for connecting')
 conn.close()
# client.py
import socket # Import socket module
s = socket.socket() # Create a socket object
host = socket.gethostname() # Get local machine name
port = 60000 # Reserve a port for your service.
s.connect((host, port))
s.send("Hello server!")
with open('received_file', 'wb') as f:
 print 'file opened'
 while True:
 print('receiving data...')
 data = s.recv(1024)
 print('data=%s', (data))
 if not data:
 break
 # write data to a file
 f.write(data)
f.close()
print('Successfully get the file')
s.close()
print('connection closed')

Output on a local server:

Server listening....
Got connection from ('192.168.56.10', 62854)
('Server received', "'Hello server!'")
('Sent ', "'1 1234567890\\n
...
('Sent ', "'4567890\\n105
...
('Sent ', "'300 1234567890\\n'")
Done sending

Output on a local client:

file opened
receiving data...
data=1 1234567890
2 1234567890
...
103 1234567890
104 123
receiving data...
data=4567890
105 1234567890
106 1234567890
...
299 1234567890
receiving data...
data=300 1234567890
Thank you for connecting
receiving data...
data=
Successfully get the file
connection closed

Our server code above can only interact with one client. If we try to connect with a second client, however, it simply won't reply to the new client. To let the server interact with multiple clients, we need to use multi-threading. Here is the new server script to accept multiple client connections:

# server2.py
import socket
from threading import Thread
from SocketServer import ThreadingMixIn
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='mytext.txt'
 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()
# client2.py
#!/usr/bin/env python
import socket
TCP_IP = 'localhost'
TCP_PORT = 9001
BUFFER_SIZE = 1024
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((TCP_IP, TCP_PORT))
with open('received_file', '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')

Below is the output from the server console when we run two clients simultaneously:

$ python server2.py
Waiting for incoming connections...
Got connection from ('127.0.0.1', 55184)
 New thread started for 127.0.0.1:55184
Waiting for incoming connections...
Got connection from ('127.0.0.1', 55185)
 New thread started for 127.0.0.1:55185
Waiting for incoming connections...

In the following codes, we made two changes:

1. ip switched to amazon ec2 ip
2. To calculate the time to take download a file, we import time module.

# server3.py on EC2 instance
import socket
from threading import Thread
from SocketServer import ThreadingMixIn
# TCP_IP = 'localhost'
TCP_IP = socket.gethostbyaddr("your-ec2-public_ip")[0]
TCP_PORT = 60001
BUFFER_SIZE = 1024
print 'TCP_IP=',TCP_IP
print 'TCP_PORT=',TCP_PORT
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='mytext.txt'
 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()
# client3.py on local machine
#!/usr/bin/env python
#!/usr/bin/env python
import socket
import time
#TCP_IP = 'localhost'
TCP_IP = 'ip-ec2-instance'
TCP_PORT = 60001
BUFFER_SIZE = 1024
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((TCP_IP, TCP_PORT))
clock_start = time.clock()
time_start = time.time()
with open('received_file', 'wb') as f:
 print 'file opened'
 while True:
 #print('receiving data...')
 data = s.recv(1024)
 #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')
clock_end = time.clock()
time_end = time.time()
duration_clock = clock_end - clock_start
print 'clock: start = ',clock_start, ' end = ',clock_end
print 'clock: duration_clock = ', duration_clock
duration_time = time_end - time_start
print 'time: start = ',time_start, ' end = ',time_end
print 'time: duration_time = ', duration_time

Server console shows the following output after a connection from my local home machine:

$ python server3.py
TCP_IP= ec2-...
TCP_PORT= 60001
Waiting for incoming connections...
Got connection from ('108.239.135.40', 56742)
 New thread started for 108.239.135.40:56742

The ip is isp's:

On my local mac:

$ python client3.py
file opened
file close()
Successfully get the file
connection closed
clock: start = 0.018806 end = 0.038608
clock: duration_clock = 0.019802
time: start = 1434991840.37 end = 1434991840.42
time: duration_time = 0.0457620620728

File downloaded from EC2, received_file is simple, and it looks like this:

From EC2
1
2
3
4
5
6
7
8
9

Here is the output showing the wall-clock time depending on the number of concurrent connections:

Our server is located in California, and the following picture compares the download speed between US and Japan:

Python Network Programming