Lecture 16
Sockets III: Internet Domain Sockets in Python
Outline
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Internet Domain Sockets
Sockets in Python
Threads in Python
Live Coding
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Internet Domain Sockets
• Internet domain socket address = IP address + port number
• Internet domain stream sockets implemented on top of TCP
• Internet domain datagram sockets implemented on UDP
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Data Representation
• Computers on network may have different architectures
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big vs. little endian
16 vs. 32 bit integers
16, 32, 64 bit doubles
etc.
• How to share data between heterogeneous host computers?
• “marshal” the data: put into standard format before transmitting
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Data Representation
Simpler approach: encode data in text form
• Use ASCII representations e.g., “15” instead of binary 0xFF
• Separate data items (messages) with delimiter (e.g., ‘\n’)
• Receiver application buffers incoming data until delimiter
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telnet
UNIX> telnet host port
• Useful tool for debugging programs
• Use telnet to connect to / test your server...
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Outline
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Internet Domain Sockets
Sockets in Python
Threads in Python
Live Coding
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Sockets in Python
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socket()
bind()
listen()
connect()
accept()
send()
recv()
close()
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socket()
s = socket.socket( domain, type );
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import socket
domain := socket.AF_INET
type := socket.SOCK_STREAM
Returns a socket object (e.g., s )
For error checking, put socket() in a try-except block
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bind()
s.bind( (host, port) );
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import socket
s := socket object
host := ip address to bind (e.g., ‘127.0.0.1’)
port := port number to bind (e.g., 50000)
Note: (host, port) is a “tuple”, bind() takes a tuple argument
For error checking, put bind() in a try-except block
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listen()
s.listen( backlog );
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import socket
Listen for incoming connections on the socket object
s := socket object
backlog := maximum number of queued connections
For error checking, put listen() in a try-except block
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connect()
s.connect( (host, port) );
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import socket
s := socket object
(host, port) := tuple specifying host and port to connect to
For error checking, put connect() in a try-except block
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accept()
(conn, addr) = s.accept()
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import socket
Accepts an incoming socket connection
s := socket object
Returns (conn, addr) tuple:
• conn := new socket object to be used for transmissions
• addr := address of socket on other end
• For error checking, put accept() in a try-except block
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send()
s.send( str )
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import socket
s := socket object
str := text message to send
For error checking, put send() in a try-except block
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recv()
str = s.recv( buffer_size );
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import socket
s := socket object
buffer_size := amount of data to be received at once
str := message received
For error checking, put recv() in a try-except block
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close()
s.close();
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import socket
s := socket object
Close the socket s
For error checking, put close() in a try-except block
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server
socket()
bind()
listen()
client
socket()
accept()
connect()
recv()
send()
blocks until
client
connects
send()
close()
multiple
communications
recv()
close()
Outline
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Internet Domain Sockets
Sockets in Python
Threads in Python
Live Coding
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Python threading Module
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Thread()
start()
join()
Lock()
acquire()
release()
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Thread()
t = threading.Thread( target=run, args=(a,) )
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import threading
Creates a Thread object (t)
target=run := defines the function to execute (e.g., run() )
args=(a,) := tuple argument to function
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start()
t.start()
• import threading
• Begins executing run() function of Thread object t
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join()
t.join();
• import threading
• Blocks and waits for thread object t to terminate
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Lock()
mutex = threading.Lock()
• import threading
• Creates and returns a Lock object (e.g., mutex)
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acquire()
mutex.acquire()
• import threading
• Blocks, waiting to acquire (lock) the Lock object mutex
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release()
mutex.release()
• import threading
• Releases (unlocks) the Lock object mutex
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Outline
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Internet Domain Sockets
Sockets in Python
Threads in Python
Live Coding
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Live Coding (Python)
• Client – server “echo”
• Threading
• Spawn N threads
• Use a mutex
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