Automatic gzip compression of responses.

This Middleware adds gzip encoding to an application. Its use is pretty straightforward, but it's good to know how and when it decides to encode the response body.

A few things to keep in mind when using this middleware:

• It is advised to put any Middlewares that change the response behind this one, because it bases a lot of its decisions on the returned response.
• Enabling compression may counteract zero-copy response optimizations on some platforms.
• This middleware is applied to every response by default. If it should only encode certain paths, Network.Wai.Middleware.Routed might be helpful.

There are a good amount of requirements that should be fulfilled before a response will actually be gzip encoded by this Middleware, so here's a short summary.

Request requirements:

• The request needs to accept "gzip" in the "Accept-Encoding" header.
• Requests from Internet Explorer 6 will not be encoded. (i.e. if the request's "User-Agent" header contains "MSIE 6")

Response requirements:

• The response isn't already encoded. (i.e. shouldn't already have a "Content-Encoding" header)
• The response isn't a 206 Partial Content (partial content should never be compressed)
• If the response contains a "Content-Length" header, it should be larger than the gzipSizeThreshold.
• The "Content-Type" response header's value should evaluate to True when applied to gzipCheckMime (though GzipPreCompressed will use the ".gz" file regardless of MIME type on any ResponseFile response)

If you would like to use the default settings, use defaultGzipSettings. The default settings don't compress file responses, only builder and stream responses, and only if the response passes the MIME and length checks. (cf. defaultCheckMime and gzipSizeThreshold)

To customize your own settings, use defaultGzipSettings and set the fields you would like to change as follows:

myGzipSettings :: GzipSettings
myGzipSettings =
  defaultGzipSettings
    { gzipFiles = GzipCompress
    , gzipCheckMime = myMimeCheckFunction
    , gzipSizeThreshold = 860
    }

defaultCheckMime is exported in case anyone wants to use it in defining their own gzipCheckMime function. def has been re-exported for convenience sake, but its use is now heavily discouraged. Please use the explicit defaultGzipSettings.