C Programming: Accepting Connections (`accept()`)

Welcome to a comprehensive guide on C Programming! In this lesson, we'll delve into the accept() function, which is crucial for establishing connections in a server-client setup.

Before we dive in, let's ensure you have the prerequisites down:

Basics of C programming (variables, data types, functions, etc.)
Knowledge of socket programming

Understanding `accept()`

The accept() function is used by a server to accept connections from clients. It waits for a connection request from a client, and when it receives one, it creates a new socket that represents the connection.

💡 Pro Tip: accept() is a built-in function in C sockets library.

Data Types

int accept(int sockfd, struct sockaddr *addr, socklen_t *addrlen)
- sockfd: The socket that the server is listening on
- addr: The address of the client requesting a connection
- addrlen: The length of the socket address

Setting Up the Server

Let's create a simple server that listens for incoming connections.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <arpa/inet.h>

#define PORT 8080

int main() {
    int server_fd, client_fd;
    struct sockaddr_in server_addr, client_addr;

    server_fd = socket(AF_INET, SOCK_STREAM, 0);
    if (server_fd == 0) {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }

    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(PORT);
    server_addr.sin_addr.s_addr = INADDR_ANY;

    if (bind(server_fd, (struct sockaddr *)&server_addr, sizeof(server_addr)) < 0) {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }

    if (listen(server_fd, 3) < 0) {
        perror("listen");
        exit(EXIT_FAILURE);
    }

    printf("Server is running on port %d\n", PORT);

    int addr_len = sizeof(client_addr);
    client_fd = accept(server_fd, (struct sockaddr *)&client_addr, &addr_len);
    if (client_fd < 0) {
        perror("accept");
        exit(EXIT_FAILURE);
    }

    // Now we can handle the client here.

    return 0;
}

Now let's create a client to connect to our server.

Setting Up the Client

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <arpa/inet.h>

#define PORT 8080

int main() {
    int sockfd, connfd;
    struct sockaddr_in server_addr;

    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    if (sockfd < 0) {
        perror("socket failed");
        exit(EXIT_FAILURE);
    }

    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(PORT);

    if (inet_pton(AF_INET, "127.0.0.1", &server_addr.sin_addr) <= 0) {
        perror("inet_pton failed");
        exit(EXIT_FAILURE);
    }

    connfd = connect(sockfd, (struct sockaddr *)&server_addr, sizeof(server_addr));
    if (connfd < 0) {
        perror("connect failed");
        exit(EXIT_FAILURE);
    }

    // Now we have connected to the server.

    return 0;
}

Stay tuned for more on C Programming, and remember to practice regularly to master these concepts! 🎯

C Programming: Accepting Connections (`accept()`)

C Programming: Accepting Connections (accept())

Understanding accept()

Data Types

Setting Up the Server

Setting Up the Client

C Programming: Accepting Connections (`accept()`)

Understanding `accept()`