Socket Programming in C++

Socket programming is a way for two computers or programs to talk to each other over a network (like the internet or a local network).

There are two main types of sockets:

Stream Sockets (TCP)

• Connection-based, reliable communication.
• Guarantees data arrives in order without loss or duplication.
• Used for web browsing, email, and file transfers.

Datagram Sockets (UDP)

• Connectionless, unreliable communication.
• Faster but does not guarantee delivery or order.
• Used for video-streaming, online-gamine, and voice calls.

Note: The headers <netinet/in.h> and <sys/socket.h> are part of POSIX socket APIs and are supported on Unix/Linux-based systems. These libraries are not available on microcontroller platforms like Arduino (e.g., Arduino Uno). For Arduino, networking is typically done using hardware-specific libraries such as WiFi.h or Ethernet.h.

Server-Side Socket Programming Stages

1. Creating the Server Socket

int serverSocket = socket(AF_INET, SOCK_STREAM, 0);

• AF_INET : IPv4 protocol
• SOCK_STREAM: TCP socket

2. Defining Server Address

sockaddr_in serverAddress;
serverAddress.sin_family = AF_INET;
serverAddress.sin_port = htons(8080);
serverAddress.sin_addr.s_addr = INADDR_ANY;

• htons(): Converts port to network byte order.
• INADDR_ANY: Accept connections on any IP.

here,

• sockaddr_in: It is the data type that is used to store the address of the socket.
• htons(): This function is used to convert the unsigned int from machine byte order to network byte order.
• INADDR_ANY: It is used when we don't want to bind our socket to any particular IP and instead make it listen to all the available IPs.

3. Bind Socket to Address

bind(serverSocket, (struct sockaddr*)&serverAddress, sizeof(serverAddress));

4. Listen for Incoming Connections

listen(serverSocket, 5);

5. Accept Client Connection

int clientSocket = accept(serverSocket, nullptr, nullptr);

6. Receive Data from Client

char buffer[1024] = {0};
recv(clientSocket, buffer, sizeof(buffer), 0);
cout << "Message from client: " << buffer << endl;

7. Close Server Socket

close(serverSocket);

Client-Side Socket Programming Stages

Similar to server, we also have to create a socket and specify the address. But instead of accepting request, we send the connection request when we can to sent the data using connect() call.

Then we sent the data using send() call. After all the operations are done, we close the connection using close() call.

1. Create Client Socket

int clientSocket = socket(AF_INET, SOCK_STREAM, 0);

2. Defining Server Address

sockaddr_in serverAddress;
serverAddress.sin_family = AF_INET;
serverAddress.sin_port = htons(8080);
serverAddress.sin_addr.s_addr = INADDR_ANY;

3. Connect to Server

connect(clientSocket, (struct sockaddr*)&serverAddress, sizeof(serverAddress));

4. Send Data to the Server

const char* message = "Hello, server!";
send(clientSocket, message, strlen(message), 0);

5. Close Client Socket

close(clientSocket);

Example of Socket Programming in C++

server.cpp

#include <cstring>
#include <iostream>
#include <netinet/in.h>
#include <sys/socket.h>
#include <unistd.h>

using namespace std;

int main()
{
    // creating socket
    int serverSocket = socket(AF_INET, SOCK_STREAM, 0);

    // specifying the address
    sockaddr_in serverAddress;
    serverAddress.sin_family = AF_INET;
    serverAddress.sin_port = htons(8080);
    serverAddress.sin_addr.s_addr = INADDR_ANY;

    // binding socket.
    bind(serverSocket, (struct sockaddr*)&serverAddress,
         sizeof(serverAddress));

    // listening to the assigned socket
    listen(serverSocket, 5);

    // accepting connection request
    int clientSocket
        = accept(serverSocket, nullptr, nullptr);

    // recieving data
    char buffer[1024] = { 0 };
    recv(clientSocket, buffer, sizeof(buffer), 0);
    cout << "Message from client: " << buffer
              << endl;

    // closing the socket.
    close(serverSocket);

    return 0;
}

client.cpp

#include <cstring>
#include <iostream>
#include <netinet/in.h>
#include <sys/socket.h>
#include <unistd.h>

int main()
{
    // creating socket
    int clientSocket = socket(AF_INET, SOCK_STREAM, 0);

    // specifying address
    sockaddr_in serverAddress;
    serverAddress.sin_family = AF_INET;
    serverAddress.sin_port = htons(8080);
    serverAddress.sin_addr.s_addr = INADDR_ANY;

    // sending connection request
    connect(clientSocket, (struct sockaddr*)&serverAddress,
            sizeof(serverAddress));

    // sending data
    const char* message = "Hello, server!";
    send(clientSocket, message, strlen(message), 0);

    // closing socket
    close(clientSocket);

    return 0;
}

By compiling and running server and client source files, we get the following output.

Output:

As we can see, the message we sent to the server at port 8080 is revived and printed by the server. We can also create a loop where we can keep sending the messages to the server.

Application of Socket Programming

• Web Servers and browsers
• Chat applications
• File transfer protocols (FTP)
• Online gaming platforms
• Distributed Systems

Advantages of Socket Programming

• Language Interoperability
• Efficient Communication
• Multi-user Handling