Fix: Consider event type in data payload when processing model response streams

[JaredConover]

What

Enable the parsing of type property inside of the event.data object for mapping model responses.

Why

Parsing of streamed events from /responses endpoint only looks at the type property of the SSE event itself, and not at the type property inside the events data payload. As a result it is not possible to parse properly formed events.

When attempting to stream events from the /responses api using OpenAI.responses.createResponseStreaming() it seems there is a bug that prevents the events from being processed.

Despite receiving properly formatted events, ie:

data: {"type":"response.output_text.delta","sequence_number":0,"delta":"#", ...}

ModelResponseEventsStreamInterpreter.processEvent for:

Printing description of event:
▿ Event
  - id : nil
  ▿ data : 69 bytes
    - count : 69
    ▿ pointer : 0x000000011450ec90
      - pointerValue : 4635815056
  - decodedData : "{\"type\":\"response.output_text.delta\",\"sequence_number\":0,\"delta\":\"#\"}"
  - eventType : "message"
  - retry : nil

Produces error:

Printing description of error:
▿ InterpreterError
  - unknownEventType : "message"

The "message" event type is not present in the event received and seems to come from line 207 of the ServerSentEventsStreamParser that sets a default event type (for the sse event) to "message" by default if there is no value in the event field of the sse event.

I believe the bug is that ModelResponseEventsStreamInterpreter.processEvent refers to this default value for the SSE event field when attempting to parse a ModelResponseStreamEventType when it should be using the type property inside the SSE event's data object as per the openAI spec. We can see is "response.output_text.delta" in the example above.

Affected Areas

This updates how streamed model responses are parsed and processed.

[JaredConover]

@nezhyborets what do you think?

[nezhyborets]

Hi @JaredConover , I'm looking into the issue. Thanks for the provided solution, but I want to look into parser first. It's strange that it doesn't parse the type if the data is there.

[nezhyborets]

BTW I don't know why but it doesn't happen for me, can't reproduce

[nezhyborets]

Do you use some other server/provider than OpenAI, that doesn't set SSE event type?

[JaredConover]

Yes exactly, the type is not set at the level of the SSE event - just in the data object.

This should still work no? I didn't see anywhere in the OpenAI api spec where specifying the type in two places (ie payload data object and top level of the SSE event) is necessary