I am trying to create webapp with http4s that is based on Http4sServlet. The following code does not compile:
import cats.effect._
import org.http4s.servlet.BlockingServletIo
import org.http4s.servlet.Http4sServlet
import scala.concurrent.ExecutionContext.global
import org.http4s.implicits._
class UserSvcServlet
extends Http4sServlet[IO](service = UserSvcServer.start
, servletIo = BlockingServletIo(4096, Blocker.liftExecutionContext(global)))(IOApp)
the error message:
[error] /home/developer/scala/user-svc/src/main/scala/io/databaker/UserSvcServlet.scala:12:54: Cannot find implicit value for ConcurrentEffect[[+A]cats.effect.IO[A]].
[error] Building this implicit value might depend on having an implicit
[error] s.c.ExecutionContext in scope, a Scheduler, a ContextShift[[+A]cats.effect.IO[A]]
[error] or some equivalent type.
[error] extends Http4sServlet[IO]( service = UserSvcServer.stream
[error] ^
[error] /home/developer/scala/user-svc/src/main/scala/io/databaker/UserSvcServlet.scala:13:36: Cannot find an implicit value for ContextShift[[+A]cats.effect.IO[A]]:
[error] * import ContextShift[[+A]cats.effect.IO[A]] from your effects library
[error] * if using IO, use cats.effect.IOApp or build one with cats.effect.IO.contextShift
[error] , servletIo = BlockingServletIo(4096, Blocker.liftExecutionContext(global)))
[error] ^
[error] two errors found
[error] (Compile / compileIncremental) Compilation failed
[error] Total time: 1 s, completed May 29, 2020, 8:45:00 PM
The UserSvcServer
is implemented as follows:
import org.http4s.HttpApp
import cats.effect.{ConcurrentEffect, ContextShift, Timer}
import org.http4s.implicits._
import org.http4s.server.middleware.Logger
object UserSvcServer {
def start[F[_] : ConcurrentEffect](implicit T: Timer[F], C: ContextShift[F]): HttpApp[F] = {
val helloWorldAlg = HelloWorld.impl[F]
val httpApp = UserSvcRoutes.helloWorldRoutes[F](helloWorldAlg).orNotFound
Logger.httpApp(true, true)(httpApp)
}
}
How can I import ContextShift implicitly?