Group Chatting with P2P File Transfer

Overview

• Term project in Embedded OS course (Undergraduate)
• Chatting program that have with P2P file transfer function
• If you want to know more information about its source code, visit my Github

Idea

• Design Server-Client architecture with socket programming (Developed with C language)
• Using TCP/IP protocol (Transfer layer in OSI 7 layers) in communication
• Based in Ubuntu server, so need to know Linux command and vim code editor

Description

• This project is required port assignment to build up server and client
  • In this project, it needs 1 server and 2 clients (Server ↔ Client#1, Client#2)
• To implement this program, it should be followed step by step process
  • Server-Client Model
  • Group Chatting
  • P2P File Transfer

Server-Client Model

• Properties
  • A user accesses the server
  • Each user has to log-in the server with ID/PW
  • Background for implementing group chatting

• Model structure

  

  Server-Client Model structure

• Key Idea

  • How much know about fork() method

  • fork()

    • Create child process from parent process (Copy-Paste form)

• Result

  

  Result of Server-Client Model

Group Chatting

• Properties
  • 1 server, 2 more clients architecture based on Server-Client Model
  • In this part, several fork() calls are required

• Model structure

  

  Group Chatting Model structure

• Key Idea

  • There are many other methods to implement Group Chatting, Client#1 ↔ Server ↔ Client#2

  • For me, I used pipe() method. Refer more about pipe()

  • pipe()

    • Connection between two processes, useful for communication between related processes
    • Parent and child sharing a pipe

  • My Group Chatting architecture using pipe() method

    

    Group Chatting architecture - pipe()

• Result

  • Server

    

    Group Chatting Model-Server result

  • Client 1

    

    Group Chatting Model-Client1 result

  • Client 2

    

    Group Chatting Model-Client2 result

P2P File Transfer

• Properties

  • When log in, make clients are sending their P2P IP/Port#
  • If a special msg(e.g., “[FILE]”) is received, a P2P file transfer process is starting
  • P2P file transfer process - when Client#1 require file transfer to Client#2
    • Client#1 receive file lists from Client#2
    • Client#1 choose file, and send file’s number to Client#2
    • Client#1 receive file successfully
  • P2P Server-Client is newly generated with P2P IP/Port#. (additional fork() calls are required)
  • In P2P network, there are no master-slave relationship
    • So original communication(Server) need to be disconnected and direct communication between client1,2 should be established

• Model Structure

  

  P2P File Transfer Model structure

• Key Idea

  • There are many other methods to implement file transfer

  • For me, I used dirent.h header file to show file lists of Client

  • dirent.h

    • Header file that can handle directory files

    • Structure

      • struct dirent {
          long d_ino; 	//l-노드 번호
        	  off_t	d_off;		//offset
        	  unsigned short d_reclen;	//파일 이름 길이
        	  char d_name[NAME_MAX+1];		//파일 이름
        }
        

    • Usage function (In this project)

      • opendir()
      • readdir()
      • closedir()

  • About file transfer between Client#1 and Client#2, I devised some trick(?) solution

    • When Client#2 send file lists, send its content additionally to Client#1
    • So if Client#1 select one file, then it can be reasonable to create requested file in Client#1 itself

• Result

  • Server - User1(client1) request [FILE]

    

    P2P File Transfer Model result - Server

  • Client#1 - Change P2P network and Select ‘a-2.txt’ file that is third in file list

    

    P2P File Transfer Model result - Client#1

  • Client#2 - Change P2P network in IP/Port#1 of client#1 and Send file list

    

    P2P File Transfer Model result - Client#2

Development Environment

• Putty - Ubuntu Server (OS : Linux)
• WinSCP
• Vim - Code Editor (Used C language)

Reference

• Socket Programming
  • http://beej.us/guide/bgnet/
  • http://www.stanford.edu/class/cs244a/socket-links.html
  • http://www.tenouk.com/cnlinuxsockettutorials.html
• Linux/Unix Programming Environment
  • http://www.unix-ag.uni-siegen.de/docs/unix/unix.html
• Vi Editor
  • http://www.cs.rit.edu/~cslab/vi.html