Question

Write and run an algorithm for a TCP client and a TCP server with the following specifications: (i) The server should be able to handle at least 5 clients concurrently (ii) A client program sends a string to a server. (iii) The server program converts lower case latters to upper case letters and vice versa. (iv) The converted string is returned to the client. (v) The client program prints the result.

Answer 1

TCP Server – 

1. using create(), Create TCP socket.
2. using bind(), Bind the socket to server address.
3. using listen(), put the server socket in a passive mode, where it waits for the client to approach the server to make a connection
4. using accept(), At this point, connection is established between client and server, and they are ready to transfer data.
5. Go back to Step 3.

TCP Client – 

1. Create TCP socket.
2. connect newly created client socket to server.

TCP Server:

• C

#include <stdio.h>

#include <netdb.h>

#include <netinet/in.h>

#include <stdlib.h>

#include <string.h>

#include <sys/socket.h>

#include <sys/types.h>

#define MAX 80

#define PORT 8080

#define SA struct sockaddr

   

// Function designed for chat between client and server.

void func(int sockfd)

{

    char buff[MAX];

    int n;

    // infinite loop for chat

    for (;;) {

        bzero(buff, MAX);

   

        // read the message from client and copy it in buffer

        read(sockfd, buff, sizeof(buff));

        // print buffer which contains the client contents

        printf("From client: %s\t To client : ", buff);

        bzero(buff, MAX);

        n = 0;

        // copy server message in the buffer

        while ((buff[n++] = getchar()) != '\n')

            ;

   

        // and send that buffer to client

        write(sockfd, buff, sizeof(buff));

   

        // if msg contains "Exit" then server exit and chat ended.

        if (strncmp("exit", buff, 4) == 0) {

            printf("Server Exit...\n");

            break;

        }

    }

}

   

// Driver function

int main()

{

    int sockfd, connfd, len;

    struct sockaddr_in servaddr, cli;

   

    // socket create and verification

    sockfd = socket(AF_INET, SOCK_STREAM, 0);

    if (sockfd == -1) {

        printf("socket creation failed...\n");

        exit(0);

    }

    else

        printf("Socket successfully created..\n");

    bzero(&servaddr, sizeof(servaddr));

   

    // assign IP, PORT

    servaddr.sin_family = AF_INET;

    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);

    servaddr.sin_port = htons(PORT);

   

    // Binding newly created socket to given IP and verification

    if ((bind(sockfd, (SA*)&servaddr, sizeof(servaddr))) != 0) {

        printf("socket bind failed...\n");

        exit(0);

    }

    else

        printf("Socket successfully binded..\n");

   

    // Now server is ready to listen and verification

    if ((listen(sockfd, 5)) != 0) {

        printf("Listen failed...\n");

        exit(0);

    }

    else

        printf("Server listening..\n");

    len = sizeof(cli);

   

    // Accept the data packet from client and verification

    connfd = accept(sockfd, (SA*)&cli, &len);

    if (connfd < 0) {

        printf("server accept failed...\n");

        exit(0);

    }

    else

        printf("server accept the client...\n");

   

    // Function for chatting between client and server

    func(connfd);

   

    // After chatting close the socket

    close(sockfd);

}

TCP Client:

• C

#include <netdb.h>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <sys/socket.h>

#define MAX 80

#define PORT 8080

#define SA struct sockaddr

void func(int sockfd)

{

    char buff[MAX];

    int n;

    for (;;) {

        bzero(buff, sizeof(buff));

        printf("Enter the string : ");

        n = 0;

        while ((buff[n++] = getchar()) != '\n')

            ;

        write(sockfd, buff, sizeof(buff));

        bzero(buff, sizeof(buff));

        read(sockfd, buff, sizeof(buff));

        printf("From Server : %s", buff);

        if ((strncmp(buff, "exit", 4)) == 0) {

            printf("Client Exit...\n");

            break;

        }

    }

}

   

int main()

{

    int sockfd, connfd;

    struct sockaddr_in servaddr, cli;

   

    // socket create and varification

    sockfd = socket(AF_INET, SOCK_STREAM, 0);

    if (sockfd == -1) {

        printf("socket creation failed...\n");

        exit(0);

    }

    else

        printf("Socket successfully created..\n");

    bzero(&servaddr, sizeof(servaddr));

   

    // assign IP, PORT

    servaddr.sin_family = AF_INET;

    servaddr.sin_addr.s_addr = inet_addr("127.0.0.1");

    servaddr.sin_port = htons(PORT);

   

    // connect the client socket to server socket

    if (connect(sockfd, (SA*)&servaddr, sizeof(servaddr)) != 0) {

        printf("connection with the server failed...\n");

        exit(0);

    }

    else

        printf("connected to the server..\n");

   

    // function for chat

    func(sockfd);

   

    // close the socket

    close(sockfd);

}

Compilation – 

Server side: 

gcc server.c -o server 

./server

Client side: 

gcc client.c -o client 

./client

Output – 

Server side: 

Socket successfully created..
Socket successfully binded..
Server listening..
server accept the client...
From client: hi
     To client : hello
From client: exit
     To client : exit
Server Exit... 

Client side: 

Socket successfully created..
connected to the server..
Enter the string : hi
From Server : hello
Enter the string : exit
From Server : exit
Client Exit...