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Socket Programming Tutorial

Learn about sockets, virtual connections between processes, bi-directional transmission, ports, and socket programming concepts.

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Socket Programming Tutorial

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  1. Socket Programming Tutorial CS447 - Socket Programming Tutorial Department of Computer Science Southern Illinois University Edwardsville Fall, 2019 Dr. Hiroshi Fujinoki E-mail: hfujino@siue.edu Socket.ppt/001

  2. What is “socket”? CS447 - Socket Programming Tutorial • A socket is a virtual connection between two applications • Using a socket, two processes can communicate with each other • The socket is the major communication tool for Internet applications • A socket is bi-directional (full-duplex) transmission • A socket can be created dynamically Socket.ppt/001

  3. Socket + NW protocol Socket connection (virtual connection) Network Adapter Card CS447 - Socket Programming Tutorial Socket as a virtual connection between two processes Host A Host B Process 1 Process 2 Information Hiding Network (physical connection) Socket.ppt/002

  4. How can we distinguish two connections? The server should always be waiting for requests from the clients. A client makes a request, then the server responds. Host C Client 2 socket socket Host A Server Client 3 Host B Request Reply Socket “PORT #” Client 1 CS447 - Socket Programming Tutorial Socket as a client/server model Socket.ppt/003

  5. Concept of “ports” It’s a logical connecting point at the transport-layer protocol. Connect to process B Process A Process B Client Host X Request Request Request (1) Response Response Response with tag (2) Request (3) Server Host Internet Internet Response (4) 146.163.147.81 IP Address 146.163.147.81 Internet Client Host Y CS447 - Socket Programming Tutorial What is “port”? If we do not have “ports”, what would happen? 146.163.147.81 Socket.ppt/004

  6. Concept of “ports” (2) If we use only IP address, we can’t select a destination process at the destination host Connect to process B Only one network application program Can exist at a time Process A Process B Client Host X Request Request Request (1) Response Response Response with tag (2) Request (3) Server Host Internet Internet Response (4) 146.163.147.81 IP Address 146.163.147.81 Internet Client Host Y CS447 - Socket Programming Tutorial 146.163.147.81 Socket.ppt/005

  7. Host Computer Concept of “ports” (3) 6055 9133 12133 1045 Transport Layer (TCP Layer) ports Process D Process C Process B Process A Network Layer (IP Layer) LLC Layer Physical Layer Datalink Layer MAC Layer IP Address CS447 - Socket Programming Tutorial Socket.ppt/006

  8. API Client/Server Process Organization “*” indicates a blocking function call. 1: Connection Request * * Request Acknowledge * 2. Send a request * 3. Receive the result CS447 - Socket Programming Tutorial Application Programming Interface SERVER socket() CLIENT socket() bind() listen() connect() accept() write() read() read() write() close() close() Socket.ppt/007

  9. CS447 - Socket Programming Tutorial Functions and parameter format (for server side) (1) create socket: socket_id = socket (AF_INET, SOCK_STREM, DEFAULT_PROTOCOL); (2) bind socket: bind (socket_id, server_addr, server_len); (3) listen to socket: listen (socket_id, number_of_connection); (4) accept a connection: accept (socket_id, &client_addr, &client_len); (5) read (receive) data: read (socket_id, buffer, buffer_len); (6) write (send) data: write (socket_id, buffer, buffer_len); (7) close socket: close(socket_id); Socket.ppt/008

  10. CS447 - Socket Programming Tutorial Functions and parameter format (for client side) (1) create socket: same as server socket_id = socket (AF_INET, SOCK_STREM, DEFAULT_PROTOCOL); (2) connect socket: connect (socket_id, serverINETaddress, server_len); (3) write (send) data: write (socket_id, buffer, buffer_len); (4) read (receive) data: read (socket_id, buffer, buffer_len); (5) close socket: same as server close(socket_id); Socket.ppt/009

  11. write() 4. END close() CS447 - Socket Programming Tutorial SERVER “*” indicates a blocking function call. socket() CLIENT We are not doing this... socket() bind() 1: Connection Request * listen() connect() * accept() write() * read() 2. Send a command * read() 3. Receive the result Socket.ppt/010

  12. Step 1: socket( ) call • Prepare data structure to • manage socket • OS is responsible for this Server Server Host Computer CS447 - Socket Programming Tutorial After socket(_) call: It declares a socket to be used. Socket.ppt/011

  13. Step 2: bind( ) call Port Port = A logical connecting point at a host for two communicating processes using socket 6500 Server CS447 - Socket Programming Tutorial After bind(_) call: Port Numbers: 0~1023: System Reserved Port 21: FTP Port 23: telnet Port 80: HTTP 1024 and above: available to users It connects a process to a specific port Socket.ppt/012

  14. Step 3: listen( ) call listen( ) system call: prepare memory buffer for incoming connections Buffer Client request Server We need to specify how many connection requests should be held in the buffer when SERVER is busy (can’t accept a request). CS447 - Socket Programming Tutorial After listen(_) call: 6500 listen (socket_id, number_of_connection); Socket.ppt/013

  15. accept ( ) function is a blocking function Client Server The server process accepts a request from a client CS447 - Socket Programming Tutorial Step 4 - Part 1: accept( ) call After accept(_) call: 6500 Socket.ppt/014

  16. Step 4 - Part 2: accept( ) call  Server needs to close the first Server  OS duplicates the socket connection  A new port is assigned by OS CS447 - Socket Programming Tutorial The accept(_) call returns another port number and establish another connection 6500 Client 7100 Socket.ppt/015

  17. write (or send) read (or recv) Server Data transmission The server and client communicate using the second socket CS447 - Socket Programming Tutorial Step 5: read( ) and write( ) call 6500 Client 7100 Socket.ppt/016

  18. Close the second socket and leave the first socket for next client CS447 - Socket Programming Tutorial Step 6: close( ) call 6500 Client 7100 Server Socket.ppt/017

  19. The server process goes back to the accept call CS447 - Socket Programming Tutorial Step 7: Go back to accept( ) call 6500 Client Server Socket.ppt/018

  20. CS447 - Socket Programming Tutorial Winsock Programming Technical Details Socket.ppt/019

  21. Initialize Winsock Step 1: Define your socket Winsock version 1.1      Step 2: Initialize your socket /* This stuff initializes winsock */ WSAStartup(wVersionRequested, &wsaData); /* Create a socket */ My_SocketID = socket ( ….. ); Step 3: Start using it CS447 - Socket Programming Tutorial void main (void) { /* The following two lines needed for Window's socket */ WORD wVersionRequested = MAKEWORD(1,1); /* Stuff for WSA functions */ WSADATA wsaData; /* Stuff for WSA functions */ Socket.ppt/020

  22. Returns socket ID on success “AF_INET” = Use IP protocol socket ( ) function “SOCK_STREAM” = Use TCP Always 0 CS447 - Socket Programming Tutorial unsigned int socket_id = socket (AF_INET, SOCK_STREAM, 0); Socket.ppt/021

  23. bind ( ) function Return code (< 0 if error) Socket ID returned by socket function The sockaddr_in structure to specify port # and IP address of this machine (server machine) The byte size of the Sockaddr_in structure CS447 - Socket Programming Tutorial int status = bind (socket_id, (struct sockaddr_in *) my_addr, sizeof(my_addr)); Socket.ppt/022

  24. The “sock_addr” structure Step 1: You instantiate the structure    /* Set My(client's) IP Address ---------------------------------------- */ my_addr.sin_family= AF_INET; /* Address Family To Be Used */ my_addr.sin_port = htons (MY_PORT_NUM); /* Port number to use */ my_addr.sin_addr.s_addr = htonl (INADDR_ANY); /* My IP address */ Step 2: Fill up the components CS447 - Socket Programming Tutorial struct sockaddr_in my_addr; /* My (client) Internet address */ Socket.ppt/023

  25. listen ( ) function Return code (< 0 if error) Socket ID returned by socket function The size of the connection request buffer CS447 - Socket Programming Tutorial int status = listen (socket_id, 3); Socket.ppt/024

  26. accept ( ) function duplicated socket ID (< 0 if error) Socket ID returned by socket function The sockaddr_in structure for a connecting client The size of the sockaddr_in structure for connecting client CS447 - Socket Programming Tutorial unsingned int child_sock = accept (socket_id, (struct sockaddr_in *) client_addr, sizeof (client_addr); Socket.ppt/025

  27. recv ( ) function Return code (< 0 if error) Socket ID returned by socket function The input (receive) buffer as a character string The maximum buffer size Always 0 CS447 - Socket Programming Tutorial On success, the number of bytes received int status = recv (child_sock, in_buffer, MAX_BUFFER_SIZE, 0); Example: char in_buffer [MAX_BUFFER] Socket.ppt/026

  28. send ( ) function Return code (< 0 if error) Socket ID returned by socket function The output (send) buffer as a character string The maximum buffer size Always 0 CS447 - Socket Programming Tutorial On success, the number of bytes actually sent int status = send (child_sock, out_buffer, MAX_BUFFER_SIZE, 0); Socket.ppt/027

  29. closesocket ( ) function Return code (< 0 if error) Socket ID returned by socket function CS447 - Socket Programming Tutorial int status = closesocket (child_sock); Socket.ppt/028

  30. Clear winsock CS447 - Socket Programming Tutorial After you call “closesocket” function but before your program is terminated /* This stuff cleans-up winsock */ WSACleanup( ); Socket.ppt/029

  31. 1 digit integer write() close() Format of time stamp: “HH:MM:SS” CS447 - Socket Programming Tutorial SERVER “*” indicates a blocking function call. socket() CLIENT socket() bind() 1: Connection Request * listen() connect() * accept() Client ID# write() * read() 2. Send a command * read() 3. Receive the result Socket.ppt/030

  32. How to specify your destination in socket? Each destination for a socket connection is determined by < IP address + Port# > Port # Client Host X Server Host IP Address Server Process CS447 - Socket Programming Tutorial < IP Address + Port# > Socket.ppt/031

  33. sockaddr_in structure is used to define your destination How to specify your destination in our socket program source code? struct sockaddr_in { u_char sin_len; /* Length of this structure */ u_char sin_family; /* Network protocol used*/ u_short sin_port; /* Port number */ struct in_addr sin_addr; /* Pointer to an IP address */ char sin_zero[8]; /* Extra information */ }; Pointer struct in_addr { u_long s_addr; /* Actual IP address */ }; CS447 - Socket Programming Tutorial • The sockaddr_instructure is defined in C/C++ struct • The sockaddr_in structure is defined in windows.h header file Socket.ppt/032

  34. How to specify your destination in our socket program source code (part 2)? An instance of sockaddr_in structure in memory Structure length (in bytes) An instance of in_addr structure in memory Network-layer protocol IP address as a binary number (32 bits) Port number Pointer to in_addr structure Extra information CS447 - Socket Programming Tutorial Socket.ppt/033

  35. How to specify your destination in our socket program source code (part 3)? CS447 - Socket Programming Tutorial An instance of sockaddr_in structure in memory An instance of in_addr structure in memory 128 IP protocol 146 163 147 59 1050 Extra information Socket.ppt/034

  36. How to specify your destination in our socket program source code (part 4)? IP Address Case 1: by “32-bit IP address” Host Name “INADDR_ANY” keyword Case 2: by a host name Case 3: by a system-defined parameter CS447 - Socket Programming Tutorial How can I set the IP address and the port number of my destination? STEP #1: Instantiate a sockaddr_in structure: structsockaddr_in server_address; STEP #2: Set your destination IP address: server_address.sin_addr.s_addr = inet_addr(“146.163.147.59”); server_address.sin_addr.s_addr = inet_aton(“cougar.siue.edu”); server_address.sin_addr.s_addr = htonl(INADDR_ANY); Socket.ppt/035

  37. How to specify your destination in our socket program source code (part 4)? You are connecting to port #80! CS447 - Socket Programming Tutorial How can I set the IP address and the port number of my destination? STEP #3: Set your destination port number: server_address.sin_port = htons(80); Socket.ppt/036

  38. Example of setting IP address and port number #define SERVER_IP "146.163.144.99“ /* Server IP address */ #define SERVER_PORT 8050 /* Server-side port # */ structsockaddr_in server_addr; /* Server Internet address */ /* Set Server's IP Address --------------------------------------------- */ server_addr.sin_family = AF_INET; /* Address Family to be Used */ server_addr.sin_addr.s_addr = inet_addr(SERVER_IP); /* IP address */ server_addr.sin_port = htons(int(SERVER_PORT));/* Port num to use */ CS447 - Socket Programming Tutorial Socket.ppt/037

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