# Bridge

**Path**: [src/modbus/Bridge.h](../../../src/modbus/Bridge.h)

**Revision History**:
- Initial documentation

A Bridge component that enables inter-component messaging and remote method invocation in an ESP32-based system. It allows components to register member functions that can be called via a message passing mechanism, typically triggered by Modbus commands.

## REQUIREMENTS

- No specific hardware pins required
- Software dependencies for messaging and component management

## PROVIDES

- `SComponentInfo`: A structure that stores information about registered component methods
  - Stores component key, instance pointer, method name, and function pointer
- `Bridge`: Main class that manages component method registration and message handling
  - Inherits from `Component` base class

## FEATURES

- Register component member functions for remote invocation
- Message routing between components
- Method lookup by component ID and method name
- Debug support for listing registered methods
- Support for component discovery for Modbus management

## DEPENDENCIES

- [Component](./Component.md): Base class for all components
- [WString](https://github.com/espressif/arduino-esp32): String manipulation
- [xtypes](./xtypes.md): Type definitions
- [enums](./enums.md): Enumeration definitions
- [macros](./macros.md): Macro definitions
- [Vector](./Vector.md): Container for storing component information
- [Streaming](./Streaming.md): Stream output utilities

```mermaid
graph TD
    Bridge --> Component
    Bridge --> WString
    Bridge --> xtypes
    Bridge --> enums
    Bridge --> macros
    Bridge --> Vector
    Bridge --> Streaming
```

## BEHAVIOUR

The Bridge acts as a message router between components. It maintains a registry of component methods and handles method invocation based on message parameters.

```mermaid
sequenceDiagram
    participant Caller
    participant Bridge
    participant Component

    Caller->>Bridge: onMessage(id, verb, flags, user, src)
    alt EC_METHOD verb
        Bridge->>Bridge: Parse method parameters
        Bridge->>Bridge: hasMethod(id, methodName)
        alt Method found
            Bridge->>Component: Invoke method
            Component-->>Bridge: Return result
            Bridge-->>Caller: Return result
        else Method not found
            Bridge-->>Caller: Return E_NOT_FOUND
        end
    else Other verbs
        Bridge-->>Caller: Return E_OK
    end
```

## TODOS

### PERFORMANCE

- The current implementation uses dynamic memory allocation for component registration which could lead to heap fragmentation. Consider using a fixed-size pool for `SComponentInfo` objects.
- Message parsing could be optimized for cases with large numbers of registered components.

### SECURITY

- There is no authentication mechanism for method invocation. Consider adding a permission system.
- Method invocation through Modbus should be validated to prevent buffer overflows and other security issues.

### COMPLIANCE

- Ensure proper memory management to comply with embedded system best practices.
- Test for compliance with industrial communication standards when used with Modbus.

### RECOMMENDATIONS

- Use descriptive method names and consistent component IDs to make debugging easier.
- Keep registered method count below the `MAX_COMPONENTS` limit (defined in configuration).
- When adding new components, always register their methods during initialization.
- Consider implementing an unregister mechanism for dynamically loaded/unloaded components.