Static Files

On static data and HTTP

Usually, if you fetch a file via HTTP, it ships with an ETag. An ETag specifies a file version. So the next time the browser requests that information, it sends the ETag along, and gets a 304 Not Modified back, so you don’t have to send the data over the wire again.

All of these solutions are most likely slower than the equivalent in nginx or a similar static file hoster, but they’re often fast enough.

Serving static files

Http4s provides a few helpers to handle ETags for you, they’re located in StaticFile.

import cats.effect._
// import cats.effect._

import org.http4s._
// import org.http4s._

import org.http4s.dsl.io._
// import org.http4s.dsl.io._

import java.io.File
// import java.io.File

Prerequisites

Static file support uses a blocking API, so we’ll need a blocking execution context:

import java.util.concurrent._
import scala.concurrent.ExecutionContext

val blockingEc = ExecutionContext.fromExecutorService(Executors.newFixedThreadPool(4))

It also needs a main thread pool to shift back to. This is provided when we’re in IOApp, but you’ll need one if you’re following along in a REPL:

implicit val cs: ContextShift[IO] = IO.contextShift(ExecutionContext.global)
val routes = HttpRoutes.of[IO] {
  case request @ GET -> Root / "index.html" =>
    StaticFile.fromFile(new File("relative/path/to/index.html"), blockingEc, Some(request))
      .getOrElseF(NotFound()) // In case the file doesn't exist
}

Serving from jars

For simple file serving, it’s possible to package resources with the jar and deliver them from there. Append to the List as needed.

def static(file: String, blockingEc: ExecutionContext, request: Request[IO]) =
  StaticFile.fromResource("/" + file, blockingEc, Some(request)).getOrElseF(NotFound())
// static: (file: String, blockingEc: scala.concurrent.ExecutionContext, request: org.http4s.Request[cats.effect.IO])cats.effect.IO[org.http4s.Response[cats.effect.IO]]

val routes = HttpRoutes.of[IO] {
  case request @ GET -> Root / path if List(".js", ".css", ".map", ".html", ".webm").exists(path.endsWith) =>
    static(path, blockingEc, request)
}
// routes: org.http4s.HttpRoutes[cats.effect.IO] = Kleisli(org.http4s.HttpRoutes$$$Lambda$74195/1154140308@6642c092)

Webjars

A special service exists to load files from WebJars. Add your WebJar to the class path, as you usually would:

libraryDependencies ++= Seq(
  "org.webjars" % "jquery" % "3.1.1-1"
)
// <console>:28: error: not found: value libraryDependencies
//        libraryDependencies ++= Seq(
//        ^
// <console>:29: error: value % is not a member of String
//          "org.webjars" % "jquery" % "3.1.1-1"
//                        ^

Then, mount the WebjarService like any other service:

import org.http4s.server.staticcontent.webjarService
// import org.http4s.server.staticcontent.webjarService

import org.http4s.server.staticcontent.WebjarService.{WebjarAsset, Config}
// import org.http4s.server.staticcontent.WebjarService.{WebjarAsset, Config}

// only allow js assets
def isJsAsset(asset: WebjarAsset): Boolean =
  asset.asset.endsWith(".js")
// isJsAsset: (asset: org.http4s.server.staticcontent.WebjarService.WebjarAsset)Boolean

val webjars: HttpRoutes[IO] = webjarService(
  Config(
    filter = isJsAsset,
    blockingExecutionContext = blockingEc
  )
)
// webjars: org.http4s.HttpRoutes[cats.effect.IO] = Kleisli(org.http4s.server.staticcontent.WebjarService$$$Lambda$74265/1144234303@8d66c2d)
blockingEc.shutdown()