C Programming: Working with struct sockaddr 🎯

Welcome to this comprehensive guide on struct sockaddr in C programming! This tutorial is designed for both beginners and intermediates, and we'll cover the topic from the ground up. Let's get started!

Understanding struct sockaddr 📝

struct sockaddr is a fundamental structure in C programming, used for sockets communication. It provides a common format for different types of sockets, allowing for versatility in network programming.

struct sockaddr {
    sa_family_t sa_family;  // Address family (AF_INET, AF_INET6, etc.)
    char sa_data[14];       // Actual address data
};

💡 Pro Tip: sa_family_t is a type that represents the address family.

Creating a socket address 📝

To create a socket address, we first need to define the address family and then fill the address data.

#include <arpa/inet.h>

struct sockaddr_in serv_addr; // Define a socket address for IPv4
serv_addr.sin_family = AF_INET;
serv_addr.sin_addr.s_addr = inet_addr("127.0.0.1");
serv_addr.sin_port = htons(8080);

💡 Pro Tip: inet_addr() converts a string representation of an IP address to a binary format, and htons() converts the port number to network byte order.

Example: Server and Client Communication 📝

Let's create a simple server-client example using struct sockaddr.

Server Code 📝

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

#define PORT 8080

int main() {
    int server_fd, new_socket, valread;
    struct sockaddr_in address;
    int opt = 1;
    int addrlen = sizeof(address);
    char buffer[1024] = {0};
    char *hello = "Hello from server";

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

    // Set options on the socket
    if (setsockopt(server_fd, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT, &opt, sizeof(opt))) {
        perror("setsockopt");
        exit(EXIT_FAILURE);
    }

    // Prepare the sockaddr_in structure
    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY;
    address.sin_port = htons(PORT);

    // Bind the socket to the specified address and port
    if (bind(server_fd, (struct sockaddr *)&address, sizeof(address)) < 0) {
        perror("bind failed");
        exit(EXIT_FAILURE);
    }

    // Listen for incoming connections
    if (listen(server_fd, 3) < 0) {
        perror("listen");
        exit(EXIT_FAILURE);
    }

    // Accept a connection from a client
    if ((new_socket = accept(server_fd, (struct sockaddr *)&address, (socklen_t*)&addrlen)) < 0) {
        perror("accept");
        exit(EXIT_FAILURE);
    }

    // Read and print the message from the client
    valread = read(new_socket, buffer, 1024);
    printf("Message received: %s\n", buffer);

    // Send the response to the client
    send(new_socket, hello, strlen(hello), 0);
    printf("Hello sent to client\n");

    return 0;
}

Client Code 📝

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

#define PORT 8080

int main() {
    int sock = 0;
    struct sockaddr_in serv_addr;
    char *message = "Hello from client";

    // Create a socket
    if ((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
        perror("socket creation error");
        exit(EXIT_FAILURE);
    }

    // Prepare the sockaddr_in structure
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(PORT);

    // Convert IPv4 address from text to binary form
    if (inet_pton(AF_INET, "127.0.0.1", &serv_addr.sin_addr) <= 0) {
        perror("Invalid address/ Address not supported");
        exit(EXIT_FAILURE);
    }

    // Connect to the server
    if (connect(sock, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) {
        perror("Connection failed");
        exit(EXIT_FAILURE);
    }

    // Send the message to the server
    send(sock, message, strlen(message), 0);
    printf("Message sent to server\n");

    // Receive the response from the server
    char response[1024] = {0};
    recv(sock, response, 1024, 0);
    printf("Server response: %s\n", response);

    return 0;
}

Quiz 🎯

That's it for this tutorial! We've covered the basics of working with struct sockaddr in C programming, including creating a socket address and a simple server-client example. Happy coding! 🚀