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

A Palindrome is a word, phrase, or sequence that reads the same backward as forward, such as "madam", "racecar", or "level". This article demonstrates a TCP client-server program where the client sends a string to the server, and the server checks if it's a palindrome and returns the result.

How It Works

The TCP client-server palindrome checker follows this communication pattern:

• Connection establishment − The server listens on a specific port, and the client connects to it using TCP sockets.

• Data transmission − The client uses the send() system call to transmit the input string to the server.

• Palindrome checking − The server receives the string using recv() and checks if it reads the same forwards and backwards.

• Result communication − The server sends back a flag indicating whether the string is a palindrome or not.

Example Input/Output

Input: "WOW" ? Output: Palindrome

Input: "soap" ? Output: Not Palindrome

Compilation and Execution

To run this program, compile both server and client files separately:

gcc -o server server.c
gcc -o client client.c

Run the server first, then the client in a separate terminal:

./server
./client

TCP Server Code

#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>

main(){
    struct sockaddr_in client, server;
    int s1, n, sock, left, right, flag;
    char buffer[20];

    s1 = socket(AF_INET, SOCK_STREAM, 0);
    server.sin_family = AF_INET;
    server.sin_port = 20000;
    server.sin_addr.s_addr = inet_addr("127.0.0.1");
    bind(s1, (struct sockaddr*)&server, sizeof server);
    listen(s1, 1);
    n = sizeof client;
    sock = accept(s1, (struct sockaddr*)&client, &n);
    
    for (;;) {
        recv(sock, buffer, sizeof(buffer), 0);
        printf("\nThe string received is: %s
", buffer);
        
        if (strlen(buffer) == 0)
            flag = 1;
        else {
            left = 0;
            right = strlen(buffer) - 1;
            flag = 1;
            while (left < right && flag) {
                if (buffer[left] != buffer[right])
                    flag = 0;
                else {
                    left++;
                    right--;
                }
            }
        }
        send(sock, &flag, sizeof(int), 0);
        break;
    }
    close(sock);
    close(s1);
}

TCP Client Code

#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>

main(){
    struct sockaddr_in client;
    int s, flag;
    char buffer[20];
    
    s = socket(AF_INET, SOCK_STREAM, 0);
    client.sin_family = AF_INET;
    client.sin_port = 20000;
    client.sin_addr.s_addr = inet_addr("127.0.0.1");
    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 Palindrome.
");
            break;
        }
        else {
            printf("\nServer: The string isn't a palindrome.
");
            break;
        }
    }
    close(s);
}

Key Features

• Socket programming − Uses TCP sockets for reliable client-server communication

• String comparison − Implements palindrome checking using two-pointer technique

• Bidirectional communication − Client sends string, server responds with result

Conclusion

This TCP client-server program demonstrates network programming concepts by implementing a palindrome checker. The server receives strings from clients, performs palindrome validation using character comparison, and returns the result over a reliable TCP connection.