05-client-server-interaction

See also

examples/05-client-server-interaction/main.cpp

This guide will introduce you to the basics of client-server communication in the irsol system, even if you have never worked with irsol or network programming before. We will cover:

• What sockets are and why they're important
• How the irsol server uses sockets to communicate
• How to build a simple C++ client to connect, send, and receive messages

1. What Are Sockets?

A socket is an endpoint for sending or receiving data across a computer network. Think of it as a virtual "plug" that allows two programs (often on different computers) to talk to each other.

• Server socket: Listens for incoming connections.
• Client socket: Connects to a server and exchanges data.

Note: communication through the socket is bidirectional and asynchronous. This is very different from other communication strategies like the "request-response" model.

[Server] <--- socket ---> [Client]

Note: a single server can have connections to multiple clients at the same time. Every connection is independently handled. In irsol every client is server by a dedicated thread that manages the communication with the client.

See also

server_architecture

2. How irsol Uses Sockets

The irsol server uses sockets to allow clients to connect and exchange protocol messages. Under the hood, irsol uses the sockpp C++ library to manage sockets in a cross-platform way.

• The server app creates a listening socket (TCP) on a specified port.
• Each client connects to this port using its own socket.
• Messages are exchanged using a defined protocol (see irsol::protocol).

**irsol Server App Flow:**

1. Start server, bind to a port (e.g., 5555).
2. Wait for client connections.
3. For each client:
   • Accept connection.
   • Read messages, process, and send responses.

3. Example: Building a Simple C++ Client

Let's walk through a minimal C++ client that connects to an irsol server, sends a message, and receives a response.

Prerequisites

• C++17 or later
• sockpp library installed

Example Client Code

#include <sockpp/tcp_connector.h>
#include <iostream>
 
int main() {
    // Connect to server at localhost:5555
    sockpp::tcp_connector conn({"127.0.0.1", 5555});
    if (!conn) {
        std::cerr << "Error connecting to server\n";
        return 1;
    }
 
    // Send a message (for example, a simple string)
    std::string msg = "Hello, `irsol` server!";
    if (conn.write(msg) != msg.size()) {
        std::cerr << "Error sending message\n";
        return 1;
    }
 
    // Receive a response
    char buf[256];
    ssize_t n = conn.read(buf, sizeof(buf));
    if (n > 0) {
        std::cout << "Received: " << std::string(buf, n) << std::endl;
    } else {
        std::cerr << "Error receiving response\n";
    }
 
    return 0;
}

Note: In a real irsol system, you would use the irsol protocol to format messages, not just plain strings.

See also

irsol::protocol

4. How the irsol Server Handles Clients

When you run the irsol server app, it:

• Listens for incoming TCP connections.
• For each client, creates a session and processes messages using registered handlers in a client-dedicate thread.
• Sends responses back to the client, either as an immediate action triggered from the incoming message (e.g. a irsol::protocol::Inquiry), or asynchronously (e.g. processing the gis command).

+-------------------+      +-------------------+
| IRSOL Client 1    | ---> |                   |
+-------------------+      |                   |
                           |                   |
+-------------------+      |                   |
| IRSOL Client 2    | ---> |   IRSOL Server    |
+-------------------+      |                   |
                           |                   |
+-------------------+      |                   |
| IRSOL Client N    | ---> |                   |
+-------------------+      +-------------------+

5. Next Steps

See also

examples/05-client-server-interaction/main.cpp

Explore the example server and client code in this folder. Try running the server and connecting with multiple clients. Experiment with sending different messages and handling responses. For more details on the irsol protocol and message handlers, see the other examples and the API documentation.