How do I use "writeOutputStream" with an fs2 Stream[IO, Byte]

Question

I am trying to use fs2.io.writeOutputStream for the output to a Java AWS lambda fn. I don't know how to provide the implicit parameter it's looking for:

"no implicits found for parameter cs: ContextShift[IO]"

I found some documentation for creating my own implicit ContextShift object but that seems like overkill for what I'm trying to do.

final def handleRequest(in: InputStream, out: OutputStream, context: Context): Unit = (for {
  bytes <- in.compile.toList
  str   =  getString(bytes)
  args  <- decode(str).raiseIO
  _     <- produce(args).to(writeOutputStream(IO(out), global)).compile.drain
} yield Unit).unsafeRunAsyncAndForget() // throws exception in the case of Failure
// ------------------------------------------------
// produce(args: MyCaseClass): fs2.Stream[IO, Byte]

Answer 1

"By default, Cats Effect can provide instance of ContextShift[IO] that manages thread-pools, but only if there’s an ExecutionContext in scope or if IOApp is used."

-- Cats-effect documentation.

From an ExecutionContext.

import cats.effect.{IO, ContextShift}
import scala.concurrent.ExecutionContext.Implicits.global

val contextShift = IO.contextShift(global)

Using IOApp.

import cats.effect.{IO, IOApp, ContextShift}

object Main extends IOApp {
  override def run(args: List[String]): IO[ExitCode] = {
     val cs = implicitly[ContextShift[IO]]
  }
}