Introduction
The C programming language is a powerful language commonly used for developing computer programs. In this article, we will explore how to create a basic server and client application using the C programming language. Such an application can help you gain a fundamental understanding of data communication and network programming.
Server Application
First, let’s create the server application. The server will listen for incoming connections and handle data from clients. Here’s a basic template for a C server application:
You can view our server/client article we wrote with Python 😉
- Creating a Socket: First, it creates a socket to listen for incoming connections.
- Configuring the Server Address: It configures the server address, specifying the IP address and port number to bind to.
- Binding the Socket: The server binds the socket to the specified IP address and port number.
- Listening for Connections: It listens for incoming connections from clients.
- Accepting and Handling Connections: When a client connects, the server accepts the connection and processes it.
- Handling Communication: The server handles communication with the client, receiving data and, if necessary, sending a response.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#define PORT 12345
#define MAX_CONNECTIONS 5
#define BUFFER_SIZE 1024
int main() {
// Define socket and other variables
int server_socket, client_socket;
struct sockaddr_in server_addr, client_addr;
socklen_t client_addr_len = sizeof(client_addr);
// Create a socket
server_socket = socket(AF_INET, SOCK_STREAM, 0);
if (server_socket == -1) {
perror("Error: Failed to create socket");
exit(EXIT_FAILURE);
}
// Configure the server address
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(PORT);
server_addr.sin_addr.s_addr = INADDR_ANY;
// Bind the socket
if (bind(server_socket, (struct sockaddr *)&server_addr, sizeof(server_addr)) == -1) {
perror("Error: Bind failed");
close(server_socket);
exit(EXIT_FAILURE);
}
// Listen for incoming connections
if (listen(server_socket, MAX_CONNECTIONS) == -1) {
perror("Error: Listen failed");
close(server_socket);
exit(EXIT_FAILURE);
}
printf("Listening on port %d...\n", PORT);
// Accept incoming connections and process them
while (1) {
client_socket = accept(server_socket, (struct sockaddr *)&client_addr, &client_addr_len);
if (client_socket == -1) {
perror("Error: Accept failed");
continue;
}
printf("Connection accepted from %s:%d\n", inet_ntoa(client_addr.sin_addr), ntohs(client_addr.sin_port));
// Handle communication with the client (you can define your own communication protocol here)
char buffer[BUFFER_SIZE];
ssize_t bytes_received;
while ((bytes_received = recv(client_socket, buffer, BUFFER_SIZE, 0)) > 0) {
buffer[bytes_received] = '\0'; // Null-terminate the received data
printf("Received: %s", buffer);
// Implement your server's response logic here
// For example, you can send a reply to the client using the send() function.
}
close(client_socket);
printf("Connection closed by the client.\n");
}
close(server_socket);
return 0;
}
Client Application
Next, let’s create a client application that will communicate with the server:
For port scanning application with C
- Creating a Socket: It creates a socket for communication.
- Configuring the Server Address: The client configures the server’s IP address and port number.
- Connecting to the Server: It establishes a connection with the server.
- Sending Data: The client can send data to the server using the
send()function. - Receiving Data: It can also receive data from the server using the
recv()function.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#define SERVER_IP "127.0.0.1" // Enter the server's IP address here
#define SERVER_PORT 12345
#define BUFFER_SIZE 1024
int main() {
int client_socket;
struct sockaddr_in server_addr;
// Create a socket
client_socket = socket(AF_INET, SOCK_STREAM, 0);
if (client_socket == -1) {
perror("Error: Failed to create socket");
exit(EXIT_FAILURE);
}
// Configure the server address
server_addr.sin_family = AF_INET;
server_addr.sin_port = htons(SERVER_PORT);
server_addr.sin_addr.s_addr = inet_addr(SERVER_IP);
// Connect to the server
if (connect(client_socket, (struct sockaddr *)&server_addr, sizeof(server_addr)) == -1) {
perror("Error: Failed to connect to the server");
close(client_socket);
exit(EXIT_FAILURE);
}
printf("Connected to the server at %s:%d\n", SERVER_IP, SERVER_PORT);
// You can send data to the server using the send() function.
char message[] = "Hello, server!";
send(client_socket, message, strlen(message), 0);
// You can also receive data from the server using the recv() function.
char buffer[BUFFER_SIZE];
ssize_t bytes_received = recv(client_socket, buffer, BUFFER_SIZE, 0);
if (bytes_received > 0) {
buffer[bytes_received] = '\0'; // Null-terminate the received data
printf("Received from the server: %s\n", buffer);
}
// Close the socket
close(client_socket);
return 0;
}
And The Result
Conclusion
In this article, we’ve covered the basics of creating a server and client application using the C programming language. This application serves as a foundation for understanding network programming and allows you to define your own communication protocols and implement more complex features as needed.