SseEmitter cannot use "send(SseEventBuilder builder)" method with custom SseEventBuilder implementation [SPR-13591]

[spring-projects-issues]

Maksym Shalak opened SPR-13591 and commented

SseEmitter class contains method "send(SseEventBuilder builder)" which is supposed to be used for custom messages. But the first line of this method contains code

Set<DataWithMediaType> dataToSend = ((SseEventBuilderImpl) builder).build();

That means if we pass SseEventBuilder to the method we receive a ClassCastException since we cannot cast our implementation of interface SseEventBuilder to built-in implementation SseEventBuilderImpl. And SseEventBuilderImpl is a private class, so we will not be able to override it. So basically that means we cannot create our custom messages at all.

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Affects: 4.2.1

Attachments:

• private class.PNG (19.19 kB)
• wrong class cast.PNG (14.07 kB)

Referenced from: commits https://github.com/spring-projects/spring-framework/commit/1c382be00e39060a0a4005d80098365f2bee45d4

[spring-projects-issues]

Rossen Stoyanchev commented

I've removed the class cast and added a build method to SseEventBuilder.

By the way I'd interested to hear more about your use case with creating a custom message, i.e. the underlying reason for wanting to extend SseEventBuilder.

[spring-projects-issues]

Maksym Shalak commented

We just wanted to get rid of the "data:" prefix and pass pure JSON into the stream.

[spring-projects-issues]

Rossen Stoyanchev commented

Is this for Server-Sent Events you mean? According to the spec the field name should be: event, data, id, retry, or otherwise should be ignored. Or if you just want to stream data to the response (not necessarily SSE-formatted) why not use ResponseBodyEmitter instead of SseEmitter?

[spring-projects-issues]

Maksym Shalak commented

Yep, looks like ResponseBodyEmitter better suites my needs, thanks.