Web Socket Echo

WebSocket Echo Application

Overview

The WebSocket Echo Application is a real-time communication server that implements a WebSocket endpoint capable of echoing messages back to connected clients. Built for embedded systems or microcontroller environments, this application demonstrates basic WebSocket server functionality using a network stack framework.

Application Details

Application Name:** WebsocketEcho

Features

• WebSocket Server: Implements a WebSocket endpoint at the pattern "echo*"
• Real-time Echo: Receives messages from WebSocket clients and echoes them back
• Network Stack Integration: Built on top of a custom network initialization framework
• HTTP Server: Includes web server functionality on default port 80
• Connection Management: Handles WebSocket connection lifecycle with proper cleanup
• System Diagnostics: Optional diagnostic capabilities for development

Architecture

Core Components

1. WebSocket Endpoint Handler: CallBackWSEndPoint wsep("echo*", WSStart)
   • Registers a WebSocket endpoint that matches URLs starting with "echo"
   • Calls WSStart() callback when new connections are established
2. Connection Management:
   • Global WebSocket file descriptor (ws_fd)
   • Semaphore-based synchronization (waitingForWS)
   • Select-based I/O multiplexing for non-blocking operations
3. Echo Logic:
   • Reads incoming WebSocket data
   • Writes data to stdout (for logging/debugging)
   • Echoes the same data back to the WebSocket client
   • Flushes WebSocket buffers to ensure immediate transmission

Application Flow

1. Initialization Phase:
   • Initialize network stack
   • Enable system diagnostics (development feature)
   • Start HTTP server on port 80
   • Wait for active network connection (5-second timeout)
   • Initialize file descriptor sets for select() operations
2. Main Loop:
   • Wait for WebSocket connection using semaphore
   • Monitor WebSocket file descriptor for read/error events
   • Handle incoming data by echoing it back to the client
   • Manage connection cleanup on errors or disconnections
   • Implement 1-second delay between connection attempts

Technical Implementation

Key Functions

• WSStart(int rv): Callback function for new WebSocket connections
• UserMain(void *pd): Main application entry point and event loop

System Dependencies

• Custom network initialization framework (init.h)
• WebSocket implementation (websockets.h)
• POSIX-style socket operations (select, read, write, close)
• Real-time operating system primitives (semaphores, timing)

Buffer Management

• Uses SMPoolPtr for memory pool management
• Buffer size defined by ETHER_BUFFER_SIZE
• Automatic buffer cleanup and reuse

Usage

Starting the Application

The application automatically starts when deployed to the target system:

1. Network stack initializes
2. HTTP server starts on port 80
3. WebSocket endpoint becomes available at URLs matching "echo*"
4. Application waits for WebSocket connections

Connecting Clients

WebSocket clients can connect to endpoints such as:

• ws://[device-ip]/echo
• ws://[device-ip]/echo-test
• ws://[device-ip]/echo-anything

Message Flow

1. Client sends WebSocket message
2. Server receives and logs message to stdout
3. Server immediately echoes message back to client
4. Client receives the echoed message

Development Notes

Production Considerations

• System diagnostics should be disabled in production builds
• Consider implementing authentication for WebSocket endpoints
• Add error handling for memory allocation failures
• Implement rate limiting for DoS protection

Debugging Features

• Real-time message logging to stdout
• Connection status messages
• Socket close notifications

Error Handling

The application includes error handling:

• Automatic connection cleanup on socket errors
• Graceful handling of multiple connection attempts
• Resource management with proper file descriptor cleanup
• Timeout handling for network operations