Learn socket programming in C by building a simple TCP client and server on Debian 12. This tutorial covers creating sockets, connecting, sending, and receiving data with clear code examples using Vim.

Socket Programming in C: TCP Client and Server

Socket programming lets your C programs communicate over networks. This tutorial shows how to create a TCP client and server using sockets on Debian 12.

TCP Server

The server creates a socket, binds to a port, listens for connections, and accepts one client. It then receives a message and replies back.

Server Code Example

// tcp_server.c
#include 
#include 
#include 
#include 
#include 

#define PORT 8080
#define BUFFER_SIZE 1024

int main() 
    int server_fd, new_socket;
    struct sockaddr_in address;
    int addrlen = sizeof(address);
    char buffer[BUFFER_SIZE] = 0;
    char *hello = \\"Hello from server\\";

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

    address.sin_family = AF_INET;
    address.sin_addr.s_addr = INADDR_ANY;
    address.sin_port = htons(PORT);

    if (bind(server_fd, (struct sockaddr *)&address, sizeof(address))<0) 
        perror(\\"bind failed\\");
        exit(EXIT_FAILURE);
    

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

    printf(\\"Waiting for a connection...\\\
\\");
    if ((new_socket = accept(server_fd, (struct sockaddr *)&address, (socklen_t*)&addrlen))<0) 
        perror(\\"accept\\");
        exit(EXIT_FAILURE);
    

    read(new_socket, buffer, BUFFER_SIZE);
    printf(\\"Message from client: %s\\\
\\", buffer);
    send(new_socket, hello, strlen(hello), 0);
    printf(\\"Hello message sent\\\
\\");

    close(new_socket);
    close(server_fd);

    return 0;

TCP Client

The client creates a socket, connects to the server, sends a message, and waits for a response.

Client Code Example

// tcp_client.c
#include 
#include 
#include 
#include 
#include 

#define PORT 8080
#define BUFFER_SIZE 1024

int main() 
    int sock = 0;
    struct sockaddr_in serv_addr;
    char *hello = \\"Hello from client\\";
    char buffer[BUFFER_SIZE] = 0;

    if ((sock = socket(AF_INET, SOCK_STREAM, 0)) < 0) 
        printf(\\"Socket creation error\\\
\\");
        return -1;
    

    serv_addr.sin_family = AF_INET;
    serv_addr.sin_port = htons(PORT);

    if(inet_pton(AF_INET, \\"127.0.0.1\\", &serv_addr.sin_addr)<=0) 
        printf(\\"Invalid address / Address not supported\\\
\\");
        return -1;
    

    if (connect(sock, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0) 
        printf(\\"Connection Failed\\\
\\");
        return -1;
    

    send(sock, hello, strlen(hello), 0);
    printf(\\"Hello message sent\\\
\\");
    int valread = read(sock, buffer, BUFFER_SIZE);
    printf(\\"Message from server: %s\\\
\\", buffer);

    close(sock);
    return 0;

Compile and Run

Open two terminals. In the first, compile and run the server:

gcc tcp_server.c -o tcp_server
./tcp_server

In the second, compile and run the client:

gcc tcp_client.c -o tcp_client
./tcp_client

Expected Output

Server terminal:

Waiting for a connection...
Message from client: Hello from client
Hello message sent

Client terminal:

Hello message sent
Message from server: Hello from server

Conclusion

With socket programming, your C programs can communicate over networks, enabling powerful distributed applications.

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