---
title: RestServer Component
description: RESTful API server implementation for ESP32 with WebSocket support
keywords: [REST API, WebSocket, ESP32, Modbus, AsyncWebServer]
---

## RestServer

**Path**: [`src/components/RestServer.h`](../src/components/RestServer.h)

**Revision History**: Initial documentation

The RestServer component implements a RESTful API server that interfaces with the Modbus system. It provides HTTP endpoints for accessing and manipulating Modbus registers and coils, as well as WebSocket functionality for real-time communication with clients.

## REQUIREMENTS

### Hardware
- ESP32 microcontroller
- WiFi connectivity

### Software
- Arduino core for ESP32
- AsyncWebServer library
- AsyncJSON library
- ArduinoJSON library
- AsyncTCP library
- LittleFS for serving static files

## FEATURES

- RESTful API endpoints for Modbus system interaction
- WebSocket support for real-time data updates
- System information retrieval
- Modbus coil and register access and manipulation
- Log level configuration
- File system browsing capabilities
- Static file serving from LittleFS

## DEPENDENCIES

- [Component](../src/Component.h) - Base class for component functionality
- [Bridge](../src/Bridge.h) - Communication interface
- [ModbusTCP](../src/ModbusTCP.h) - Modbus TCP implementation
- [ESPAsyncWebServer](https://github.com/me-no-dev/ESPAsyncWebServer) - Asynchronous web server library
- [ArduinoJSON](https://arduinojson.org/) - JSON parsing and creation library

```mermaid
graph TD
    RestServer --> Component
    RestServer --> Bridge
    RestServer --> ModbusTCP
    RestServer --> AsyncWebServer
    RestServer --> ArduinoJSON
    RestServer --> AsyncTCP
```

## BEHAVIOUR

The RestServer component initializes an AsyncWebServer and sets up various RESTful API endpoints. When WebSocket support is enabled, it also initializes an AsyncWebSocket server for real-time communication.

```mermaid
stateDiagram-v2
    [*] --> Setup
    Setup --> Running: setup()
    Running --> ProcessRequests: loop()
    ProcessRequests --> Running
    Running --> BroadcastUpdates: WebSocket event
    BroadcastUpdates --> Running
    Running --> HandleMessage: onMessage()
    HandleMessage --> Running
```

The component responds to HTTP requests for system information, Modbus coil/register access, and file system operations. When WebSocket is enabled, it broadcasts updates to connected clients in real-time.

## TODOS

### PERFORMANCE

- Consider implementing caching mechanisms for frequently accessed data
- Optimize JSON document size based on actual needs
- Investigate memory usage during peak concurrent connections
- Consider implementing pagination for large data sets

### SECURITY

- Implement authentication for API access
- Consider HTTPS support for secure communication
- Add rate limiting to prevent abuse
- Implement input validation for all API endpoints
- Consider implementing CORS protection

### COMPLIANCE

- Ensure GDPR compliance for any data collected
- Follow RESTful API best practices
- Document API endpoints using OpenAPI/Swagger specification

### RECOMMENDATIONS

- Use environment variables or configuration files for server settings
- Implement proper error handling and logging
- Consider implementing API versioning
- Separate API logic from server implementation for better maintainability
- Provide client-side libraries or SDK for easier integration

## EXAMPLE

The following example shows how to initialize and mount the RestServer component:

```cpp
#ifdef ENABLE_REST_SERVER
  IPAddress localIP = WiFi.localIP();
  restServer = new RESTServer(
      localIP,       // IP address
      80,            // Port
      modbusTCPServer, // ModbusTCP manager
      this           // Owner component
  );
  if (restServer) {
    components.push_back(restServer);
    Log.infoln(F("RESTServer initialized. IP:%s, Port:%d"),
              localIP.toString().c_str(), 80);
  } else {
    Log.errorln(F("RESTServer initialization failed."));
  }
#endif
```

### References

${DOXYGEN_PLACEHOLDER}

${VENDOR_PLACEHOLDER}