TCP Client-Server Program to Check if a Given String is Palindrome

Last Updated : 02 Aug, 2019

Prerequisites:

This article describes a Client and Server setup where a Client connects, sends a string to the server and the server shows the original string and sends confirmation whether the string is a palindrome or not, to the client using socket connection. Examples:

Input: naman
Output: Palindrome

Input: geek
Output: Not Palindrome

Approach:

In this, first set up a client-server connection.
When the connection will setup, the client will send the user input string to the server by the send system call.
At the server-side, the server will wait for a string sent by the client.
Server reads the string by the reading system call.
After this, the server will check if the string is a palindrome or not and sends the confirmation back to the client.

Compiling:

First, run the server program as
```
gcc server.c -o server
./server
```
Run the client program on another terminal
```
gcc client.c -o client
./client
```
Server program is waiting for the string sent by the client.
Input the string in client-side.
Server program will print original string.
Client program will print result.

Below is the implementation of the above approach:

TCP Server

// defines in_addr structure
#include <arpa/inet.h>

// contains constants and structures
// needed for internet domain addresses
#include <netinet/in.h>

// standard input and output library
#include <stdio.h>

// contains string functions
#include <string.h>

// for socket creation
#include <sys/socket.h>

// contains constructs that facilitate getting
// information about files attributes.
#include <sys/stat.h>

// contains a number of basic derived types
// that should be used whenever appropriate
#include <sys/types.h>

main()
{
    struct sockaddr_in client, server;
    int s, n, sock, g, j, left, right, flag;
    char b1[20], b2[10], b3[10], b4[10];

    // creating socket
    s = socket(AF_INET, SOCK_STREAM, 0);

    // assign IP, PORT
    server.sin_family = AF_INET;

    // this is the port number of running server
    server.sin_port = 2000;
    server.sin_addr.s_addr = inet_addr("127.0.0.1");

    // Binding newly created socket
    // to given IP and verification
    bind(s, (struct sockaddr*)&server, sizeof server);
    listen(s, 1);
    n = sizeof client;

    sock = accept(s, (struct sockaddr*)&client, &n);
    for (;;) {
        recv(sock, b1, sizeof(b1), 0);

        // whenever a request from a client came.
        // It will be processed here.
        printf("\nThe string received is:%s\n", b1);
        if (strlen(b1) == 0)
            flag = 1;
        else {
            left = 0;
            right = strlen(b1) - 1;
            flag = 1;
            while (left < right && flag) {
                if (b1[left] != b1[right])
                    flag = 0;
                else {
                    left++;
                    right--;
                }
            }
        }
        send(sock, &flag, sizeof(int), 0);
        break;
    }
    close(sock);

    // close the socket
    close(s);
}

TCP Client

// defines in_addr structure
#include <arpa/inet.h>

// contains constants and structures
// needed for internet domain addresses
#include <netinet/in.h>

// standard input and output library
#include <stdio.h>

// contains string functions
#include <string.h>

// for socket creation
#include <sys/socket.h>

// contains constructs that facilitate getting
// information about files attributes.
#include <sys/stat.h>

// contains a number of basic derived types
// that should be used whenever appropriate
#include <sys/types.h>

main()
{
    struct sockaddr_in client;
    int s, flag;
    char buffer[20];

    // socket create
    s = socket(AF_INET, SOCK_STREAM, 0);

    // assign IP, PORT
    client.sin_family = AF_INET;
    client.sin_port = 2000;
    client.sin_addr.s_addr = inet_addr("127.0.0.1");

    // connect the client socket to server socket
    connect(s, (struct sockaddr*)&client, sizeof client);

    for (;;) {
        printf("\nEnter a string to check palindrome: ");
        scanf("%s", buffer);

        printf("\nClient: %s", buffer);
        send(s, buffer, sizeof(buffer), 0);
        recv(s, &flag, sizeof(int), 0);

        if (flag == 1) {
            printf("\nServer: The string is a Palindrome.\n");
            break;
        }
        else {
            printf("\nServer: The string is not a palindrome.\n");
            break;
        }
    }

    // close the socket
    close(s);
}