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2023-10-10

Summary

keywords

TODO

HW

Exercise*

Next time

Recap

Socket programming​

Why do we learn this?

If you do not denote the serverPort, it is a loopback, also called localhost.

decode is required to make binary sentences into strings.

Accept will accept the connection requested by client call clientSocket.send().

difference in TCP & UDP​

  • There is connection establishment in TCP. (shown in accept call)

#todo : add System theory practice book, Programmer's Perspective

Multiplexing using Sockets

Let's support multiple clients. How one-process one-server can support multiple clients?

We will focus on...

  • one process
  • sequential manner
  • First-come-first-served manner

Multiplexing​

Many people are sharing a particular media.

all sockets are files.

Three system calls for implementing multiplexing.​

socket(),accept(),select()

socket(), accept()​

  1. Creating Master Socket Socket()
  • *Socket() will create and return Master Socket(Master file Descriptor, like a pointer).
  • serverSocket = socekt(AF_INET,SOCK_STREAM)
  1. Master Socket is responsible for connection request.accept()
  • For each acceptance of request, master socket will create communication socket (Communication file descriptors).
  • *serverSocket.accept() returns client address(IP+port), and the communication socket
  • If second client requests, Master socket will accept, and create another communication socket. with, this socket, further communication is made.
  • accept() is for 3-way handshake.
  1. Each Communication Socket is responsible for Service request(Further communications).
  • Further communication will be handled by each communication socket.

select()​

  • a waiting(blocking) system call.
  • for monitoring all client activity.
  • monitoring all socket File Descriptor list (Master socket, communication sockets)
  • in the argument, list of sockets are requested.
  • monitoring all connection request, service request.
  • select() unblocks when
    • New connection request arrives
    • New Service request from existing client arrives.
  • will return a particular socket that needs an activity.

Example codes: Chat application​

listen 5 connections prepare a list inputs[] of socket FDs. While there is a element in inputs[],

if s is server : if s is a master socket