Include support to parse ElasticSearch time units

[aochsner]

This is a pretty small start but the goal is to parse http://www.elastic.co/guide/en/elasticsearch/reference/current/common-options.html#time-units into a TimeSpan.

I started down this path when I realized that if I set Timeout("20m") on a request (/_cluster/health for example) that I also have to set the RequestConfiguration.RequestTimeout(). Longer term, might be nice to do that be default, but not sure the right place to put that.

Not sure the right place for this but for my tests to work better, it ended up in Elasticsearch.Net instead of NEST.

Also not quite sure what to do about things bigger than a week. They start to become dependent on DateTime.Now (months aren't always 31 days, years aren't always 365 days). Even days are a bit incorrect wrt timezones. But it's a start...

[gmarz]

@aochsner thanks for opening this! You raise a very a good point, it makes sense that RequesTimeout always be the same as Timeout().

Before sending the request, we could probably look for a timeout query param and set RequesTimeout if it's present.

As far as parsing the time values, might make sense to mimic the logic in Elasticsearch: https://github.com/elastic/elasticsearch/blob/master/src/main/java/org/elasticsearch/common/unit/TimeValue.java#L228

[aochsner]

Yeah I had seen the TimeValue code. Wasn't completely sure if that's what's used so stuck w/ the time-units doc from above. But I can easily change that logic and add the additional units. Is it OK to just return null or do you want to have the signature look the same?

Also, any pointer on where to do that inspection for timeout query param just before it goes out?

[gmarz]

I think returning null is fine if the value passed in is null/empty. But if parsing fails then I think it's more appropriate to throw the exception.

Also, any pointer on where to do that inspection for timeout query param just before it goes out?

I think the best place is in HttpConnection.GetRequestTimeout(). You'll just need to add the request URL as another parameter.

Also, thinking about this a bit more, I think it makes more sense to only set the request timeout to the timeout query param if it's > the current request timeout.

@Mpdreamz thoughts?