Fixed 500 reported for client disconnection

[coufalja]

What does this PR do?

Fix an issue with random 500s reported in Traefik metrics middleware. Issue: traefik/traefik#1926

Motivation

By default oxy middleware reports 500 for Context cancel error, which does not make much sense as in this case the 500 won't be received by the client and further HttpHandlers down the line (like Traefik metrics middleware) can go nuts because of it. I originally had this issue in Traefik so if it doesn't make sense to fix it in oxy I need to find a way how to fix it in Traefik only.

More

Fixes: traefik/traefik#1926

[coufalja]

@juliens Any feedback on this? I am not sure if this is a right direction but I am really keen on getting some fix for those 500s into traefik 1.7 otherwise we need to run from our fork. The issue might be bigger for us as most of our clients access our servers over unreliable networks where disconnections are not uncommon.

[juliens]

I think, it's a good idea to catch the context.Canceled, but like this, in the access logs we got a 200, and I'm not sure it's a good idea to have 200 WDYT?

[coufalja]

Hmm true, I would be for not outputting this request into access log at all. I think this is how apache/nginx access log handles the situation as well (while putting the line just into error log). TBH I am not sure how to achieve this in Traefik architecture. The second option would be to use some custom code, e.g. 599/499 or something. In that case, it would end up in both metrics and access log but it could be distinguished from regular 500

[juliens]

I prefer a solution with a specific status code, but I think this is more a 4x than a 5x.

[coufalja]

Thanks, I have picked 499 the same as nginx does.
https://httpstatuses.com/499

[juliens]

It's better like this ;) thx
Just one little thing

[juliens]

WDYT about create

func statusText(statusCode int) string {
    if statusCode == StatusClientClosedRequest {
        return StatusClientClosedRequestText
    }
    return http.StatusText(statusCode)
}

and use this new func in the Write?

[coufalja]

Yep good idea

[juliens]

👏 LGTM