Coding Corner Networking Edition

1
Coding Corner Networking Edition

• with Luke Wagner

• Your mom circulates like a public key,Servicing
  more requests than HTTP.She keeps all her ports
  open like Windows ME,Oh, there's so much drama
  in the PhD
• So Much Drama in the PhD by Monzy

2
Overview

• Goal
• send Hello, World! from one computer to another
• Communication protocols
• Socket abstraction
• WinSock2 API
• NetUtil abstraction
• HelloWorld.exe

3
Connections and protocol

• Need a protocol both computers understand
• In the field of telecommunications, a
  communications protocol is the set of standard
  rules for data representation, signalling,
  authentication, and error detection required to
  send information over a communications channel.
• Communications protocol, Wikipedia
• We could reinvent the wheel
• So many protocols
• Null modem
• IPX
• TCP/IP
• HTTP
• What is the difference?

4
The OSI Stack

• The ISO (International Organization for
  Standardization) developed the OSI (Open Systems
  Interconnection) abstraction

HelloWorld.exe
WAN, connection, errors from Network
WAN, single packet
LAN, catch/correct Physical errors
On the wire
5
The OSI Stack
abstracted below the line
Hello, World!
Hello, World!
Hello, World!
2 packets 1Hello, 2World!
127.0.0.12 packets 127.0.0.11Hello,
127.0.0.12World!
0011ff127.0.0.12 packets 111ccf127.0.0.11Hello
, ffcc100127.0.0.12World!
raise voltage, wait 10 nanoseconds, lower
voltage...
6
TCP/IP with sockets

• Socket abstraction
• Connection metaphor
• Create/destroy steps
• Succeed 100 or fail
• String of bytes go in, string of bytes come out
• WinSock2
• Microsoft Windows network stack C API
• implements Berkeley Socket API (1983), with
  non-standard extensions of course

7
Creating a connection

• (1969-2005) Make the internet
• main() run A and B, create a socket on each

A
B
internet
8
Creating a connection

• (1969-2005) Make the internet
• main() run A and B, create a socket on each
• B binds its socket to a port, and listens on it

listening
A
B
internet
1
9
Creating a connection

• (1969-2005) Make the internet
• main() run A and B, create a socket on each
• B binds its socket to a port, and listens on it
• A connects, using Bs address, and the same port

connecting
listening
A
B
internet
1
10
Creating a connection

• (1969-2005) Make the internet
• main() run A and B, create a socket on each
• B binds its socket to a port, and listens on it
• A connects, using Bs address, and the same port
• B observes a pending connection and accepts.This
  creates a new socket on B.The listening socket
  keeps listening for new connections.

connected
listening
B
A
internet
1
connected
11
Using a connection

• Send a sequence of bytes
• send(SOCKET, const char send_buf, int len,
  int flags)
• Receive a sequence of bytes
• recv(SOCKET, char recv_buf, int len, int
  flags)
• Receive in packets, not entire send() message.

12
Berkeley Sockets / WinSock2

• 11 mapping from socket conceptual operation to
  function call
• socket(), bind(), listen(), connect()
• accept(), send(), recv()
• C API
• Direct memory manipulation, seg faults abound
• Every function has like 10 error return values

13
NetUtil toolkit

• Object oriented socket wrapper
• http//students.cs.tamu.edu/edu/law1521/StuffFolde
  r/Libraries/NetUtil
• 3 classes
• ListenerSocket
• MessageSocket
• Message

14
Server, part 1

• include "NetUtil.h"
• include ltiostreamgt
• int main() try
• // bind a socket on port 10001, and start
  listening
• NetUtilListenerSocket listener(10001)
• catch(stdexception e)
• // catch any errors that may occur (e.g. someone
  already listening)
• stdcout ltlt e.what() ltlt "\nProgram exiting" ltlt
  stdendl

15
Client, part 1

• include "NetUtil.h"
• include ltiostreamgt
• int main() try
• stdcout ltlt "Enter address (form x.x.x.x
  port) "
• stdstring addr
• int port 0
• stdcin gtgt addr gtgt port
• // connect to addrport and wait until accepted
• NetUtilMessageSocket sock(addr, port, true)
• catch(stdexception e)
• stdcout ltlt e.what() ltlt "\nProgram exiting" ltlt
  stdendl

16
Server, part 2

• include "NetUtil.h"
• include ltiostreamgt
• int main() try
• NetUtilListenerSocket listener(10001)
• // create a socket ready to receive the incoming
  connection
• NetUtilMessageSocket sock
• // wait for the connection to arrive, and then
  accept it
• listener.accept_connection(sock, true)
• // wait for a message to arrive
• while(!sock.message_remain())
• sock.process()
• Sleep(100)
• catch(stdexception e)

17
Client, part 2

• include "NetUtil.h"
• include ltiostreamgt
• int main() try
• stdcout ltlt "Enter IP address (form x.x.x.x)
  "
• string s
• stdcin gtgt s
• NetUtilMessageSocket sock(s.c_str(), 10001,
  true)
• // create message to send
• NetUtilMessage outgoing
• outgoing.msg() ltlt Hello, World!"
• // place it in the outgoing queue
• sock.send_message(outgoing)
• // perform send/receive
• sock.process()
• catch(stdexception e)

18
Server, part 3

• include "NetUtil.h"
• include ltiostreamgt
• int main() try
• NetUtilListenerSocket listener(10001)
• NetUtilMessageSocket sock
• listener.accept_connection(sock, true)
• while(!sock.message_remain())
• sock.process()
• Sleep(100)
• // create an empty message
• NetUtilMessage incoming
• // fill the message with whatever we just
  received
• sock.take_message(incoming)
• stdcout ltlt incoming.msg().str()

19
Moving forward

• Blocking vs. Non-blocking
• Connectionless UDP
• Good for low latency, high bandwidth games
• Beejs Guide to Network Programming
• http//beej.us/guide/bgnet/
• Lightly funny. fork() takes no arguments, and
  CreateProcess() takes about 48 billion arguments