A gzip filter.

This filter may gzip the responses for any requests that aren't HEAD requests and specify an accept encoding of gzip.

It won't gzip under the following conditions:

- The response code is 204 or 304 (these codes MUST NOT contain a body, and an empty gzipped response is 20 bytes long) - The response already defines a Content-Encoding header - The size of the response body is equal or smaller than a given threshold. If the body size cannot be determined, then it is assumed the response is over the threshold - A custom shouldGzip function is supplied and it returns false

Since gzipping changes the content length of the response, this filter may do some buffering - it will buffer any streamed responses that define a content length less than the configured chunked threshold. Responses that are greater in length, or that don't define a content length, will not be buffered, but will be sent as chunked responses.