TCP Server Using Via

Example Path: examples/TCP/TcpServerVia

TCP Server Via Example

Overview

This application demonstrates a TCP server implementation for multi-interface NetBurner devices using the listenvia() function. The server creates multiple listening sockets - one that listens on all network interfaces and additional sockets that listen on specific network interfaces.

Features

• Multi-Interface Support: Creates listening sockets for each available network interface
• Multiple Concurrent Connections: Supports up to 10 simultaneous TCP connections
• Port Management: Uses incrementing port numbers starting from port 23
• Single-Task Architecture: Uses select() to handle multiple sockets within one task
• Connection Monitoring: Provides detailed logging of connections and interface information
• Live Web View: A built-in web page shows the listening sockets and connected clients in real time

Technical Details

Configuration

• Base Port: 23 (Telnet)
• Maximum Connections: 10 concurrent connections
• Read Buffer Size: 1,024 bytes
• Connection Queue: Up to 5 pending connection requests per listening socket

Socket Architecture

The application creates the following listening sockets:

1. One socket listening on all interfaces (port 23)
2. For each available network interface:
   • One socket on port 24 (listenPort + 1)
   • One socket on port 24 + interface_number

Network Interface Handling

• Automatically detects available network interfaces using GetInterfaceBlock()
• Creates dedicated listening sockets for each interface using listenvia()
• Provides interface-specific connection information to clients

Web Interface

Point a browser at http://<device_ip>/ to see a live dashboard of the server. The page is a self-contained static HTML file (plain CSS, no framework or CDN) with two device-rendered tables:

• Listening Sockets – one row per entry in the listeners[] array, showing the file descriptor, the interface it is bound to, and its local port. The all-interfaces listen() socket and the per-interface listenvia() sockets appear together so you can see the "via" layout at a glance. The bound interface is taken from the socket's slot in listeners[] (slot 0 is the all-interfaces listener; the two listenvia() sockets for interface N occupy slots N*2 and N*2+1), because TcpGetSocketInterface() only reports a bound interface on an accepted socket, not a listening one.
• Connected Clients – one row per fdArray[] slot. For each active client it shows the local port (which listener accepted it – 23 for all-interfaces, 24 and up for a listenvia() socket), the physical interface the connection arrived on (from TcpGetSocketInterface()), and the client IP:port. This table refreshes itself: a small script polls connections.html – the same callback served on its own – every 1.5 seconds, so it stays live without a full-page reload. With scripting disabled the table still renders once when the page loads.

Both tables are produced on the device by <!--CPPCALL --> tags that hand the HTTP socket to ShowListenersWeb() / ShowConnectionsWeb() in main.cpp, which walk the same arrays the server loop uses and print each row with fdprintf(). Open Telnet sessions to the different ports and watch the slots fill in.

Usage

Building and Running

1. Compile the application for your NetBurner device
2. Deploy to the target hardware
3. The application will automatically start listening on configured ports

Testing Connections

Use Telnet to test connections from the command line:

telnet <ip_address> <port>

Examples:

• telnet 192.168.1.100 23 - Connect to the all-interfaces socket
• telnet 192.168.1.100 24 - Connect to interface 1, port 24
• telnet 192.168.1.100 25 - Connect to interface 1, port 25

Client Interaction

• Upon connection, clients receive a welcome message
• Interface information is displayed showing which interface accepted the connection
• Type 'Q' to quit and close the connection
• Server echoes received data and provides connection status

Code Structure

Main Components

Initialization**

• System diagnostics enabled
• Waits for active network (10-second timeout)
• Displays IP addresses for all interfaces

• Starts the web server (StartHttp()) so the live dashboard is reachable at http://<device_ip>/

  Socket Management**

• listeners[] array stores all listening socket file descriptors
• fdArray[] manages active client connections

• Automatic socket recovery on errors

  Event Loop**

• Uses select() for efficient I/O multiplexing
• Processes new connections, data reception, and errors
• Automatic cleanup of closed connections

Key Functions Used

• listen() - Creates socket listening on all interfaces
• listenvia() - Creates socket listening on specific interface
• accept() - Accepts incoming connections
• select() - Monitors multiple sockets for I/O events
• TcpGetSocketInterface() - Retrieves interface information

Error Handling

• Connection Limit: When server is full, new connections are rejected with a message
• Socket Errors: Automatic detection and recovery of failed listening sockets
• Read Errors: Proper cleanup of corrupted client connections
• Interface Failures: Continues operation even if some interfaces fail

Application Output

The application provides detailed console output including:

• Network interface discovery and socket creation status
• Connection acceptance with client IP and port information
• Interface identification for each connection
• Data reception logging
• Connection closure notifications
• Error condition reporting

Requirements

• NetBurner hardware platform
• NetBurner SDK with TCP networking support
• Multi-interface network configuration (optional for full functionality)

Notes

• System diagnostics are enabled by default (should be disabled for production)
• Socket file descriptors are automatically managed and cleaned up
• The server continues running indefinitely until manually stopped