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