Support POST requests for Server-Sent Events

[MurrayFurtado]

Can you please add support for POST requests returning SSEs?

msw/src/core/sse.ts

Line 91 in 41f725d

super('GET', path, async (info) => {

[kettanaito]

Hi, @MurrayFurtado. Can you please tell me more about your use case? A reproduction repo of what you are trying to achieve would be best.

The sse API in MSW is modeled closely after EventSource that produces GET requests:

new EventSource('https://example.com')
// GET https://example.com

I haven't found any actual requirement in the WHATWG HTML spec that would limit EventSource to GET requests though. Would like to learn more from you first.

The GET request limitation can be derived from the spec though: a request instance you do not control (apart from withCredentials), which always produces a GET request. Sending a body to a SSE request is also rather unconventional.

[MurrayFurtado]

I am using the urql library (https://github.com/urql-graphql/urql) to send graphql queries to the server rather than using an EventSource and this uses POST as queries could exceed the length of 2,048 characters of a GET request. Our requests are returning SSEs which we want to mock.

[kettanaito]

I see, thanks for the clarification! Your use case falls outside of SSE on the web. I recommend you use http.post(url, resolver) and handle the response stream directly by queuing chunks from the resolver.

I wonder if we could expose ServerSentEventClient and ServerSentEventServer primitives so you could construct them in any resolver, like your http.post() and get the same ergonomics as when using sse() directly.

http.post('/endpoint', ({ request }) => {
  const client = new ServerSentEventClient()
  const server = new ServerSentEventServer({ request, client })

  client.send({ data: 'hello world' })

  return new Response(stream, sseInit)
})

Would make more sense to wrap them in a utility that returns { client, server, stream }. Let me know what you think about this.

[kettanaito]

Maybe something like this: #2718

[kettanaito]

@MurrayFurtado, by the way, how are you consuming that request? Do you manually parse the SSE messages? You cannot use EventSource since it's hard-coded to a GET request. That part is really something I can't quite understand.

[MurrayFurtado]

So we are using the Netflix domain graph service framework in spring boot - https://github.com/netflix/dgs-framework
This provides a set of annotations which make it easy to consume graphql post requests. Please refer here to how it deals with SSE - https://netflix.github.io/dgs/advanced/subscriptions/