SignalR

We use SignalR for real-time communication between Frontend and Backend. SignalR is an open-source framework that abstracts multiple ways of implementing real-time communication via Web Sockets or Long-Pulling. It also supports authentication and connection grouping.

To lean more about SignalR, we recommend the following resources:

SignalR Hubs

The backend offers SignalR hubs to connect with. A client can connect to these Hubs (mostly via WebSockets) by calling their URLs.

Client library

SignalR offers client libraries for a wide set of frameworks and programming languages. We highly recommend to use on of these libraries.

With the SignalR client library for JavaScript for example, a connection looks like this:

// Prepare SignalR connection to the Streaming Backend
const connection = new HubConnectionBuilder()
  .withUrl('https://example.com/something?property=test', { accessTokenFactory: async () => return 'YOUR_ACCESS_TOKEN' })
  .build();

// Subscribe to events from stream
this.streamConnection.on('SomeEvent', (object) => {
  // ...
});

// Start the connection
await connection.start();

Connection Endpoints

We currently offer connection endpoints in form of SignalR Hubs for the following use-cases:

Recorder: Sends recorded sentences for a specific event to the backend to distribute them to other clients
Corrector: Receives sentences for a specific event for correction, before they get sent to the listeners
Listener: Receives all sentences for a specific event to display them

Each event contains a set of endpoints for these use-cases that you can use to connect to the SignalR Hubs for these specific event. When receiving an event form the REST API, it contains these connection information.

{
  "id": "1",
  "name": "Lorem Ispum",
  // ...
  "endpoints": {
    // ...
    "signalR": {
      "recorder": "https://something.com/recorder/...",
      "corrector": "https://something.com/corrector/...",
      "listener": "https://something.com/listener/..."
    }
  }
}

The backend offers the following hubs to connect with:

Recorder

/recorder?eventId=xxx

A client can connect to the Recorder Hub, to send transcribed sentences to the backend. Depending on the event configuration, these sentences will either be sent to the Listeners or the Moderators of an event.

Subscriptions

A client can subscribe to the following events:

Event Id	Description
`ReceivedSentence`	Gets called by the backend, when a sentence has been processed and gets sent back to the recorder. A `Sentence` object will be passed.
`ReceivedMessage`	Gets called, when something happens in the backend, that the recorder should get notified about. The type of that message is defined in the `BackendMessage` enum, so that the frontend clients can react on it. A `BackendMessage` object will be passed.
`ChangedLanguage`	Gets called, when the recording language should get changed. A `Language` object will be passed.
`StartedRecording`	Notifies the client that the Hub is ready to receive sentences. The `StartRecording` method has to be called before.

Methods

A client can call the following methods:

Method Id	Description
`StartRecording`	Starts a recording session on the server. This call is mandatory to send sentences. If this has not been called, all sentences will be rejected.
`StopRecording`	Stops the recording on the server.
`SendSentence`	Sends a recorded `Sentence` object to the server. A `Sentence` object needs to be passed.

Corrector

/corrector?eventId=xxx

A client can connect to the Correcor Hub, to correct transcribed sentences and send them back to the backend. These corrected sentences will be sent to the Listeners of an event.

Subscriptions

A client can subscribe to the following events:

Event Id	Description
`ReceivedSentence`	Gets called by the backend, when a sentence has been processed and gets sent to the corrector for correction. A `Sentence` object will be passed.

Methods

A client can call the following methods:

Method Id	Description
`ApproveSentence`	Sends a corrected or uncorrected sentence back to the server to send it further to all listeners. Please pass a `Sentence` object.
`ChangeLanguage`	Changes the recording language remotely to another language. A `Language` object needs to be passed.
`SendSentence`	Sends a recorded `Sentence` object to the server. A `Sentence` object needs to be passed.

Listener

/corrector?eventId=xxx

A client can connect to the Listener Hub, to receive transcribed sentences and display them.

Subscriptions

A client can subscribe to the following events:

Event Id	Description
`ReceivedSentence`	Gets called by the backend, when a sentence has been processed and gets sent to the listener for display. A `Sentence` object will be passed.
`ReceivedMessage`	Gets called, when something happens in the backend, that the recorder should get notified about. The type of that message is defined in the `BackendMessage` enum, so that the frontend clients can react on it. A `BackendMessage` object will be passed.

Methods

A client can call the following methods:

Method Id	Description
`ValidateEventPassword`	Unlocks a password protected event by sending the password to the server. A `string` object needs to be passed.