In SSE mode, loading may end too early

[Fabilin]

When using Server-Sent Events to transmit messages, the tock-react-kit assumes all messages in a response have been processed by the time the POST response is received. However, because TOCK's server-sent events are sent concurrently to the POST response, there is no guarantee of that being the case. This is especially an issue for custom user interfaces that need a way to tell whether the chat is expecting more messages.

Diagnosis: Sequence diagram

sequenceDiagram
    actor user
    participant TRK as tock-react-kit
    participant TOCK as TOCK Backend
    user->>TRK: message
    TRK-->>user: <loading starts>
    TRK->>TOCK: <send message>
    par
      TOCK->>TRK: POST answer
      TRK-->>user: <loading ends>
    and
      TOCK->>TRK: SSE answer
      TRK->>user: Display answer
    end

Proposed Solution

We could make it so when the POST response is received before the first SSE message for that response, it gets processed immediately and the late SSE messages are discarded. This would also have the benefit of ensuring messages do not get lost when the SSE connection is lost at the same time a user sends a message.

This would however require an update to the TOCK backend, to allow linking responses from SSE and POST.