Added gzip decompression support to elastic4s-http

[ilyshav]

Resolves #1472

[sksamuel]

👍

[yanns]

Any documentation on how to activate this?

[ilyshav]

@yanns You have to add Accept-Encoding: gzip header.
I did it with httpClientConfigCallback:

import scala.collection.JavaConverters._

RestClient
      .builder(new HttpHost("localhost", 9200))
      .setHttpClientConfigCallback((httpClientBuilder: HttpAsyncClientBuilder) => {
        httpClientBuilder.setDefaultHeaders(List(new BasicHeader("Accept-Encoding", "gzip")).asJava)
      }).build

Also gzip compression must be enabled in Elastic config:
http.compression: true

[yanns]

Thx a lot.
Should we consider activating that per default?
It will only be used the elastic config enables that, right?

[ilyshav]

Should we consider activating that per default?

I think we should not enable gzip by default, because this give some profit only is some cases - when Elastic's responses are huge or network perfomance isn't good, but when responses are small, compression will only waste CPU resources , as far as I know.

It will only be used the elastic config enables that, right?

I think if Elastic compression will be disabled and we pass accept-encoding header, Elastic will just send plain text responses, so it will work anyway, but this is only my assumption, I'm not checked it.