GZip Compression

Http4s provides Middleware, named GZip, for allowing for the compression of the Response body using GZip.

Examples in this document have the following dependencies.

libraryDependencies ++= Seq(
  "org.http4s" %% "http4s-dsl" % http4sVersion,
  "org.http4s" %% "http4s-server" % http4sVersion
)

And we need some imports.

import cats.effect._
import org.http4s._
import org.http4s.dsl.io._
import org.http4s.implicits._

Let’s start by making a simple service that returns a (relatively) large string in its body. We’ll use as[String] to examine the body.

val service = HttpRoutes.of[IO] {
  case _ =>
    Ok("I repeat myself when I'm under stress. " * 3)
}
// service: HttpRoutes[IO] = Kleisli(
//   org.http4s.HttpRoutes$$$Lambda$12274/406817917@1dd0cc3b
// )

val request = Request[IO](Method.GET, uri"/")
// request: Request[IO] = (
//   Method("GET"),
//   Uri(None, None, "/", , None),
//   HttpVersion(1, 1),
//   Headers(),
//   Stream(..),
//   io.chrisdavenport.vault.Vault@54d7b6f2
// )

// Do not call 'unsafeRun' in your code - see note at bottom.
val response = service.orNotFound(request).unsafeRunSync()
// response: Response[IO] = Response(
//   Status(200),
//   HttpVersion(1, 1),
//   Headers(Content-Type: text/plain; charset=UTF-8, Content-Length: 117),
//   Stream(..),
//   io.chrisdavenport.vault.Vault@6840e9bc
// )
val body = response.as[String].unsafeRunSync()
// body: String = "I repeat myself when I'm under stress. I repeat myself when I'm under stress. I repeat myself when I'm under stress. "
body.length
// res0: Int = 117

Now we can wrap the service in the GZip middleware.

import org.http4s.server.middleware._
val zipService = GZip(service)
// zipService: Http[cats.data.OptionT[IO, A], IO] = Kleisli(
//   org.http4s.server.middleware.GZip$$$Lambda$13188/1241156866@487d1bce
// )

// Do not call 'unsafeRun' in your code - see note at bottom.
val response = zipService.orNotFound(request).unsafeRunSync()
// response: Response[IO] = Response(
//   Status(200),
//   HttpVersion(1, 1),
//   Headers(Content-Type: text/plain; charset=UTF-8, Content-Length: 117),
//   Stream(..),
//   io.chrisdavenport.vault.Vault@5357b7ee
// )
val body = response.as[String].unsafeRunSync()
// body: String = "I repeat myself when I'm under stress. I repeat myself when I'm under stress. I repeat myself when I'm under stress. "
body.length
// res1: Int = 117

So far, there was no change. That’s because the caller needs to inform us that they will accept GZipped responses via an Accept-Encoding header. Acceptable values for the Accept-Encoding header are “gzip”, “x-gzip”, and “*”.

val acceptHeader = Header("Accept-Encoding", "gzip")
// acceptHeader: Header.Raw = Raw(Accept-Encoding, "gzip")
val zipRequest = request.putHeaders(acceptHeader)
// zipRequest: request.Self = (
//   Method("GET"),
//   Uri(None, None, "/", , None),
//   HttpVersion(1, 1),
//   Headers(Accept-Encoding: gzip),
//   Stream(..),
//   io.chrisdavenport.vault.Vault@54d7b6f2
// )

// Do not call 'unsafeRun' in your code - see note at bottom.
val response = zipService.orNotFound(zipRequest).unsafeRunSync()
// response: Response[IO] = Response(
//   Status(200),
//   HttpVersion(1, 1),
//   Headers(Content-Type: text/plain; charset=UTF-8, Content-Encoding: gzip),
//   Stream(..),
//   io.chrisdavenport.vault.Vault@3a5eeb50
// )
val body = response.as[String].unsafeRunSync()
// body: String = "\u001f\ufffd\b\u0000\u0000\u0000\u0000\u0000\u0000\u0000\ufffdT(J-HM,Q\u022d,N\ufffdIS(\ufffdH\ufffdS\ufffdT\ufffdU(\ufffdKI-R(.)J-.\ufffdS\ufffd2\u0000UX\ufffd<u\u0000\u0000\u0000"
body.length
// res2: Int = 59

Notice how the response no longer looks very String-like and it’s shorter in length. Also, there is a Content-Encoding header in the response with a value of “gzip”.

As described in Middleware, services and middleware can be composed such that only some of your endpoints are GZip enabled.

NOTE: In this documentation, we are calling unsafeRunSync to extract values out of a service or middleware code. You can work with values while keeping them inside the F using map, flatMap and/or for. Remember, your service returns an F[Response].