chat_server.c

// chat_server.c
// Author: Harsh Kukutkar
// Description: Multi-Client Chat Server with Username Support using TCP sockets and pthreads
// Compilation: gcc chat_server.c -o server -lpthread
// Run Command: ./server

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <pthread.h>

#define MAX_USERS 10
#define MSG_LENGTH 1024

int connectedClients[MAX_USERS];
int totalClients = 0;
pthread_mutex_t clientLock = PTHREAD_MUTEX_INITIALIZER;

// Send a message to all connected clients except the sender
void sendToAll(char *message, int senderSocket) {
    pthread_mutex_lock(&clientLock);
    for (int i = 0; i < totalClients; i++) {
        if (connectedClients[i] != senderSocket) {
            send(connectedClients[i], message, strlen(message), 0);
        }
    }
    pthread_mutex_unlock(&clientLock);
}

// Handle communication with a single client
void *handleClient(void *arg) {
    int clientSocket = *(int *)arg;
    free(arg);

    char userName[50];
    char messageBuffer[MSG_LENGTH];
    int msgLength;

    // Receive username from client
    msgLength = recv(clientSocket, userName, sizeof(userName), 0);
    if (msgLength <= 0) {
        close(clientSocket);
        return NULL;
    }
    userName[msgLength] = '\0';
    printf("%s connected.\n", userName);

    // Notify others that this user joined
    char joinMsg[MSG_LENGTH];
    snprintf(joinMsg, sizeof(joinMsg), "%s joined the chat.\n", userName);
    sendToAll(joinMsg, clientSocket);

    // Keep listening for messages from this client
    while ((msgLength = recv(clientSocket, messageBuffer, MSG_LENGTH, 0)) > 0) {
        messageBuffer[msgLength] = '\0';
        printf("%s", messageBuffer);
        sendToAll(messageBuffer, clientSocket);
    }

    // Handle disconnect
    printf("%s disconnected.\n", userName);
    close(clientSocket);

    // Remove this client from list
    pthread_mutex_lock(&clientLock);
    for (int i = 0; i < totalClients; i++) {
        if (connectedClients[i] == clientSocket) {
            for (int j = i; j < totalClients - 1; j++) {
                connectedClients[j] = connectedClients[j + 1];
            }
            totalClients--;
            break;
        }
    }
    pthread_mutex_unlock(&clientLock);

    // Announce that the user left
    snprintf(joinMsg, sizeof(joinMsg), "%s left the chat.\n", userName);
    sendToAll(joinMsg, clientSocket);

    return NULL;
}

int main() {
    int serverSocket, newClientSocket;
    struct sockaddr_in serverAddress, clientAddress;
    socklen_t clientAddrLen = sizeof(clientAddress);

    // Create TCP socket
    serverSocket = socket(AF_INET, SOCK_STREAM, 0);
    if (serverSocket < 0) {
        perror("Socket creation failed");
        exit(1);
    }

    // Set up server details
    serverAddress.sin_family = AF_INET;
    serverAddress.sin_port = htons(8080);
    serverAddress.sin_addr.s_addr = INADDR_ANY;

    // Bind socket to address
    if (bind(serverSocket, (struct sockaddr*)&serverAddress, sizeof(serverAddress)) < 0) {
        perror("Bind failed");
        exit(1);
    }

    // Start listening for clients
    listen(serverSocket, 5);
    printf("Chat Server started on port 8080...\n");

    while (1) {
        newClientSocket = accept(serverSocket, (struct sockaddr*)&clientAddress, &clientAddrLen);
        if (newClientSocket < 0) {
            perror("Accept failed");
            continue;
        }

        pthread_mutex_lock(&clientLock);
        if (totalClients >= MAX_USERS) {
            printf("Maximum clients reached. Connection refused.\n");
            close(newClientSocket);
            pthread_mutex_unlock(&clientLock);
            continue;
        }
        connectedClients[totalClients++] = newClientSocket;
        pthread_mutex_unlock(&clientLock);

        int *clientPtr = malloc(sizeof(int));
        *clientPtr = newClientSocket;

        pthread_t clientThread;
        pthread_create(&clientThread, NULL, handleClient, (void*)clientPtr);
        pthread_detach(clientThread);
    }

    close(serverSocket);
    return 0;
}