Example Path: examples/Web/SerialWeb

Serial Webserver

A NetBurner RTOS application that bridges serial communication with HTTP web services, allowing HTTP requests to be received and processed over a serial port connection.

Overview

The Serial Webserver demonstrates how to create a bidirectional communication bridge between a serial port and TCP/HTTP connections. This application enables HTTP requests to be sent over a serial connection and receive corresponding web responses back through the same serial interface.

It will receive and reply to HTTP requests over a serial port, using the NetBurner web server implementation. The example will display a Hello World message on the device's index page index.html.

Key Features

Serial-to-HTTP Bridge: Receives HTTP requests via serial port and forwards them to the built-in web server
Bidirectional Communication: Splices data between serial and TCP connections in both directions
Automatic Connection Management: Opens a TCP connection to the local web server on demand and closes it when the response completes, so each serial request is served on a fresh connection
Error Recovery: Reopens the serial port on error, and drops the TCP connection if the peer closes or resets it
Built-in Web Server: Serves static content including HTML, CSS, and images

Technical Specifications

Serial Port: Port 1 at 115200 baud
HTTP Port: Standard port 80
Buffer Size: Uses Ethernet buffer size for data transfer
Network Stack: NetBurner RTOS with TCP/IP support

Application Architecture

The application follows a simple event-driven architecture:

Initialization: Sets up network stack, enables diagnostics, and starts HTTP server
Serial Monitoring: Waits for incoming serial data
Connection Creation: Establishes TCP connection to local web server when data arrives
Data Splicing: Uses select() to monitor both serial and TCP file descriptors
Bidirectional Transfer: Forwards data between serial and TCP connections
Connection Teardown: Closes the TCP connection when the web server finishes its response (a read of 0 bytes) or on error, so it is ready to open a fresh connection for the next request

HTTP Request Format

The application expects standard HTTP requests over the serial connection. A typical request format:

GET /INDEX.HTML HTTP/1.1\r\n\r\n

Important**: The web server requires a double carriage return line feed (\r\n\r\n) to properly parse HTTP requests.

Expected Response

A successful request to the index page returns:

HTTP/1.0 200 OK
Pragma: no-cache
MIME-version: 1.0
Content-Type: text/html
Content-length: <length of the page>
 
<!DOCTYPE html>
<html lang="en">
<head>
    ...
    <title>NetBurner Serial Web Example</title>
    <link rel="stylesheet" href="style.css">
</head>
<body>
    <!-- The branded Serial Web example page: header, an overview of the
         serial<->HTTP bridge, a welcome card, and the footer. -->
</body>
</html>

Web Content

The application serves the following static files:

index.html: Branded example page (header, an overview of the serial<->HTTP bridge, a welcome card, and footer)
style.css: NetBurner Design System stylesheet
logo.png: NetBurner logo (white-knockout wordmark sized for the dark header)

Usage

Flash the application to your NetBurner device
Connect to the device's serial port (Port 1, 115200 baud)
Send HTTP requests through the serial connection
Receive HTTP responses back through the same serial connection

Development Notes

System diagnostics are enabled for development (consider removing for production)
The application uses blocking I/O operations
Memory allocation uses FAST_USER_VAR for the splice buffer

Use Cases

This application is ideal for:

Testing HTTP communication through serial interfaces
Bridging legacy serial devices to modern web services
Remote web server access through serial connections

Build Requirements

NetBurner NBRTOS development environment
Standard NetBurner libraries (init, system, iosys, serial, tcp, netinterface)
Compatible NetBurner hardware platform