Hi,

If a SSE message arrive without data field, it is silently ignored.

I guess this is due to this rule (cf. https://html.spec.whatwg.org/multipage/server-sent-events.html#dispatchMessage):

If the data buffer is an empty string, set the data buffer and the event type buffer to the empty string and return.

However it is also specified:

When the user agent is required to dispatch the event, the user agent must process the data buffer, the event type buffer, and the last event ID buffer using steps appropriate for the user agent.

For web browsers, the appropriate steps to dispatch the event are as follows:

So my understanding is this behavior is not mandatory in the spec, on the other hand it is error prone:

• when implementing retry on server-side, it is tempting to just send a retry:1000\n\n message
• when implementing custom event on sever-side, the obvious way is to return them without data if they don't need it. For instance event:missed_events\n\n to signify to the client it Last-Event-ID header was too old and hasn't been respected.

I don't think modifying the behavior of this lib is needed though (as it would make it incompatible with what does regular web browsers). This is more like a poor decision when the SSE specification has been written resulting in a footgun.

However I think it's relevant to document this quirk (being in the project's documentation, or just by having this issue) to save time for everybody ;-)

When trying to listen for eventsource from couchdb changes feed , it fails to parse event withh error invalid field.
`data: {"seq":"1-g1AAAAFHeJy1TssKwjAQXK0gfkwXFRGP_QE_YrO7EsuaSNt4bf88Rqk3j3qZYQbmYQCw9JXAmWNiL66Zub53UeqP2OE3G0UvlGzA_sHIlvpBO7TIZPaqJXBjzrn1FcGtGOsTER3dQWCTQoleg8qfpsOqIEyF8vxg8X4gxFvd66832yeC93F0","id":"f48b4a4a-d449-409e-9e2f-adc79ac3db4f","changes":[{"rev":"1-8751ebdb500d588544dda38a6f9f317a"}]}
id: "1-g1AAAAFHeJy1TssKwjAQXK0gfkwXFRGP_QE_YrO7EsuaSNt4bf88Rqk3j3qZYQbmYQCw9JXAmWNiL66Zub53UeqP2OE3G0UvlGzA_sHIlvpBO7TIZPaqJXBjzrn1FcGtGOsTER3dQWCTQoleg8qfpsOqIEyF8vxg8X4gxFvd66832yeC93F0"

data: {"seq":"2-g1AAAAFHeJy1TssKwjAQXFpB_JguKiIe_YF-xGZ3JZY1kbbxav88jVJvHvUywwzMwwCg8rVAyzGxF3deuLn3UZqP2OE3G0UvlGzE4cHIloZRe7TIZPaqJXDPnHPna4JbMdYnIjq6g8AmhRK9BpU_TYdVQZgK5eVB9X4gxFvd6683uxmDVXF1","id":"07ebd855-81cf-4737-8034-6a200a5041b8","changes":[{"rev":"1-0194907cb383fe7e9e32c7874bff16dd"}]}
id: "2-g1AAAAFHeJy1TssKwjAQXFpB_JguKiIe_YF-xGZ3JZY1kbbxav88jVJvHvUywwzMwwCg8rVAyzGxF3deuLn3UZqP2OE3G0UvlGzE4cHIloZRe7TIZPaqJXDPnHPna4JbMdYnIjq6g8AmhRK9BpU_TYdVQZgK5eVB9X4gxFvd6683uxmDVXF1"
`