Default ResponseHandler for Server Sent Event (SSE)

[galileilei]

If I want to userequests on http endpoint that returns Server Sent Event (SSE) (for example on OpenAI chat completion streaming endpoint), a workaround is implementing a SSE parser (specification here) on bufio.Scanner.

This functionality (SSE parser) may be outside of the scope of requests, it is frequent enough that I think a requests/sse sub-package would be a great addition.

[earthboundkid]

That's an interesting idea. I'm not sure how good of a fit requests would be since the idea in requests is that the requests is that each request is handled in a single function call. For SSE, I imagine you would want to open a loop of some sort. What kind of API were you imagining?

[galileilei]

Something like this:

es := sse.NewEventSource(ctx) // (1)
err := requests.URL("").BodyJSON(&body).Handle(es.Recv).Fetch(ctx) // (2)
for event in es.All() { // (3)
     // process the event
}

A few thoughts:

1. Existing packages I found are ssereader and go-sse. Have not looked into integrating them with requests package though.
2. es.Recv does not block and return immediately. Here I use the generic Handle() function; having a dedicated ToSSE() can be an option too.
3. Use iterator style, instead of callback style in Javascript EventSource example or go-sse example. The iterator can either a method with pointer receiver es, or a function on es.

[earthboundkid]

Maybe there could be a magic handler that is blest to leave the connection open at the end of the request. Something like

var rc io.ReadCloser
err := requests.
    URL("http://example.com/sse").
    BodyJSON(&body).
    CheckContentType("text/event-stream").
    Handle(requests.KeepOpen(&rc)).
    Fetch(ctx)
if err !=nil { /**/ }
defer rc.Close()
for event, err := sse.ReadEvents(rc) {
    // ...
}

[earthboundkid]

The go-sse client already does a lot of the validation and backoff stuff you might want to use requests for. I think the solution might be to just use it with requests as a simple request builder. From their example:

client := sse.Client{
    Backoff: sse.Backoff{
        MaxRetries: -1,
    },
    // other settings...
}

body := whatever()
req, err := requests.URL("https://api.openai.com/...").BodyJSON(&body).Request(ctx)
if err != nil { /**/ }
conn := client.NewConnection(req)

conn.SubscribeMessages(/* callback */)

if err := conn.Connect(); !errors.Is(err, io.EOF) {
    // handle error
}

[galileilei]

Did not know there is Request() API. will try this out!