text/event-stream not supported

[rome-user]

What version of ogen are you using?

$ go list -m github.com/ogen-go/ogen
github.com/ogen-go/ogen v1.8.1

Can this issue be reproduced with the latest version?

Yes

What did you do?

Consider the following schema. Save it as openapi.yaml.

openapi: 3.0.0
info:
  title: Example API
  version: "1.0"
paths:
  /events:
    get:
      summary: SSE example
      responses:
        "200":
          description: OK
          content:
            text/event-stream:
              schema:
                type: string

Run the following terminal commands

$ go mod init repro
$ go get github.com/ogen-go/ogen/cmd/ogen
$ go run github.com/ogen-go/ogen/cmd/ogen --target gen/api -package api --clean openapi.yaml
$ go mod tidy

Create a main.go file with the following contents.

Click to view server implementation

package main

import (
	"context"
	"io"
	"log"
	"net/http"
	"time"

	"repro/api"
)

func main() {
	srv, err := api.NewServer(&service{})
	if err != nil {
		log.Fatal(err)
	}

	if err := http.ListenAndServe(":8080", srv); err != nil {
		log.Fatal(err)
	}
}

type service struct{}

func (s *service) EventsGet(ctx context.Context) (api.EventsGetOK, error) {
	r, w := io.Pipe()

	go func() {
		defer w.Close()
		for ctx.Err() == nil {
			select {
			case <-ctx.Done():
				return
			case <-time.After(1 * time.Second):
				w.Write([]byte("data: ping\n\n"))
			}
		}
	}()

	return api.EventsGetOK{Data: r}, nil
}

Finally, start the server.

$ go run main.go

What did you expect to see?

Client can stream the response. e.g.

$ curl -N http://localhost:8080/events
data: ping
data: ping
...

What did you see instead?

The generated code in oas_response_encoders_gen.go looks like the following.

Click to view generated code

func encodeEventsGetResponse(response EventsGetOK, w http.ResponseWriter, span trace.Span) error {
	w.Header().Set("Content-Type", "text/event-stream")
	w.WriteHeader(200)
	span.SetStatus(codes.Ok, http.StatusText(200))

	writer := w
	if _, err := io.Copy(writer, response); err != nil {
		return errors.Wrap(err, "write")
	}

	return nil
}

The call to io.Copy prevents streaming of response. This results in clients not receiving data.

[gedw99]

Your trying to do sync push ?

I am also doing protocol buffers to open ali for pull and push ( over open api ).

Thee is a thing called asyncapi that is designed for openapi but for async . It’s got many more foot guns though .

Would love to know your use case

[rokf]

I'm personally interested in this functionality so that I could generate boilerplate handler code for https://data-star.dev with ogen.

What I do currently is that I have two OpenAPI specifications for an application - one API that returns HTML for the GUI and one that returns JSON for M2M communication.

With support for text/event-stream I could squeeze in the SSE endpoints for Datastar into my ogen HTML API - currently I need a custom set of handlers next to those managed by ogen and combine them all with a mux.

[rokf]

As a workaround you can use middleware to pass and retrieve the raw request and response objects - #1252.

I've tested this approach with https://github.com/starfederation/datastar/tree/main/sdk/go and it works fine.

The only issue I found was that Ogen writes an error log saying that there's an superfluous header write once the stream is finished - it doesn't seem to break anything though.

[gedw99]

hey @rokf your use case is identical to mine :) I also use datastar