Server-sent events support

[madeddie]

We're hosting some containers making use of server-sent events EventSource and noticed this doesn't work with Fabio.

If you're unfamiliar with SSE, it's comparable to long polling and is a form of HTTP server push.

The problem is that the default ReverseProxy implementation of Go doesn't flush its buffer while the request is still open.

I'm somewhat sure this is not all to it, but if I simply add a FlushInterval to the ReverseProxy instance, the application starts working as expected.

I've made a quick hack here, please let me know if this is something you might want to add Fabio.

master...madeddie:server_sent_events

[madeddie]

I didn't actually intend to, but seem to have accidentally opened a pull-request (#130) nonetheless.

[magiconair]

:) no worries. Contributions are very welcome.

SSE vaguely rings a bell but very, very far in the back of my head. This looks simple enough but I just need to figure out how to expose this. Let me read up on SSE and determine whether I can make this automatic by detecting it through the Accept header (like Websockets) or whether there is some other mechanism. I'll add this to the list of things that need to be configured through #111

[magiconair]

@madeddie: Since github doesn't allow me to make changes to your PR I've created a new one which makes the option configurable and just extends the existing HTTP handler. Could you please test this by checking out this branch and running go install? It should behave the same way as your patch as long as you configure the proxy.flushinterval to a value > 0s.

OTOH, I'm not sure if for SSE requests there should always be a non-zero flush interval since it otherwise doesn't seem to work. Need to think about that.

[magiconair]

Added attribution to your PR.

[madeddie]

Awesome, looks like what I need! Thanks. I've closed my PR.
Ow and will test in the morning and report.

[madeddie]

It works like expected. There might be more situations where people want in-between flushes as well as configurable keepalive etc, so I think it's a good idea to keep it in the scope of #111

[magiconair]

I think I'm going to change the behavior which makes SSE work out-of-the box, e.g. set a default flush interval for auto-detected SSE connections. fabio's goal is to be zero-conf. Will do a bit more digging if a 1s flush interval for SSE connections is a sane default. Opinions are welcome.

[madeddie]

I've set it to 1s in our env (we use Fabio both outside to container as well as container to container, so the time adds up sometimes) to keep the connection fast. We don't have a lot of users, so, no idea about any potential problems with load or anything.

The idea of SSE is that any event is separated from others by an empty line (so 2 line returns). So the strictest way of doing this is by flushing buffer on empty line, but I have no clue how to do that :) (it'll probably mean rewriting some basis net/http methods, so; non-trivial).

In short, as long as there are no obvious performance penalties, 1s for SSE buffer flush is an ok default, as long as it's specifically mentioned in the docs somewhere.

[magiconair]

I've set the default to 1s and merged it to master.