orbisat-oeiras / backend24

Backend para o dashboard do CanSat. / Backend for the CanSat's dashboard.

Project structure

• Controllers: classes derived from ControlerBase, implementing API endpoints
  • ServerEventsController: responsible for opening an SSE channel and sending tagged data to the client. Provides the following endpoint for subscribing to SSE: api/sse. All data sent will be collected from objects marked with EventFinalizerAttribute, which will be automatically registered at startup.
• Models: classes defining data models for the app to work with
  • GPSCoords: represents GPS coordinates (latitude, longitude, altitude)
  • DataStamp: general metadata attached to all data sent, e.g., timestamp and coordinates
  • EventData: wrapper for data flowing through the app, packs the main data with a DataStamp object
• Services: Modular classes implementing internal functionality
  • DataProviders: classes responsible for emitting data. All data providers must implement IDataProvider. A consumer class can subscribe to a provider's OnDataProvided to be notified whenever new data is available.
    • RandomProvider: provides random floats on a configurable interval.
    • SerialProvider: provides string arrays from a serial port.
  • DataProcessors: classes responsible for transforming data. Notably, every processor both subscribes to a provider to get new data to transform, and is itself a provider, emiting a new event after it has transformed the data.
    • DataExtractors: classes responsible for extracting a specific piece of data from SerialProvider data.
  • EventFinalizers: classes responsible for finalizing an event, i.e., collecting the necessary data and tagging it properly. Finalizers must be IDataProviders (though they'll usually be processors) marked with EventFinalizerAttribute. Each finalizer is responsible for only one tagged events. The following tags are (or will be) provided, along with their respective finalizers.
    • primary/pressure by PressureFinalizer
    • primary/temperature by TemperatureFinalizer
    • primary/altitude by AltitudeFinalizer
    • secondary/raw
    • seconddary/ndvi
    • general/acceleration
    • general/position
    • general/raw

Data flow

• All data is encapsulated in EventData objects, which pack the actual data together with a DataStamp, which in turn contains mandatory information (like timestamp and GPS coordinates)
• IDataProviders emit an event when they get data
• IDataProcessors subscribe to providers, process their data and send a new event
• The main controller finds and subscribes to finalizers and communicates their data to the client through Server Sent Events (SSE)

Notes and useful things

Most browsers have a limit of 6 connections per domain. Since each SSE endpoint represents a connection that stays open indeterminatly, we have to be very careful when subscribing to SSEs. However, response bodies consist of data tags and event tags, so we can have a single endpoint which sends all the data. Thus the endpoints specified above become internal spearations which all write to the same endpoint.