Sending zio http response from callback function - scala

Question

I am trying to play around with ZIO http using their simples hello world example. I have a Java-written service which does some logic, and it expecting a handler function, so it can call it when result is ready. How do I user it together with ZIO http ?
I want something like this:
object HelloWorld extends App {
def app(service: JavaService) = Http.collect[Request] {
case Method.GET -> Root / "text" => {
service.doSomeStuffWIthCallback((s:String) => Response.text(s))
}
}
override def run(args: List[String]): URIO[zio.ZEnv, ExitCode] =
Server.start(8090, app(new JavaService)).exitCode
}
Basically I want to send ZIO HTTP response from the callback function, I am just not sure how to go about that. Thanks.
EDIT:
I coudn't get the right types from your code, so I decided to simplify the whole thing, and arrived to this:
val content: HttpData[Blocking, Throwable] = HttpData.fromStream {
ZStream.fromEffect(doSomeStuffWrapped)
}
def doSomeStuffWrapped = {
UIO.effectAsync[String] { cb =>
cb(
IO.succeed("TEST STRING")
)
}
}
However, the issue here is that types do not match, HttpData.fromStream requires ZStream of byte
Here is the link to my gist:
https://gist.github.com/pmkyl/a37ff8b49e013c4e2e6f8ab5ad83e258

Answer 1

You should wrap your Java service with callback in an effect using effectAsync:
def doSomeStuffWrapped(service: JavaService): Task[String] = {
IO.effectAsync[Throwable, String] { cb =>
service.doSomeStuffWithCallback((s: String) => {
// Success case
cb(IO.succeed(s))
// Optional error case?
// cb(IO.fail(someException))
})
}
}
def app(service: JavaService) = Http.collectM[Request] {
case Method.GET -> Root / "text" => {
doSomeStuffWrapped(service)
.fold(err => {
// Handle errors in some way
Response.text("An error occured")
}, successStr => {
Response.text(successStr)
})
}
}
You might want to see this article presenting different options for wrapping impure code in ZIO: https://medium.com/#ghostdogpr/wrapping-impure-code-with-zio-9265c219e2e

Answer 2

In ZIO-http v1.0.0.0-RC18 HttpData.fromStream can also take ZStream[R, E, String] as input with Http charset which defaults to CharsetUtil.UTF_8 however you can pass any charset to the HttpData.fromStream as its second argument. you can find the solution below
val stream: ZStream[Any, Nothing, String] = ZStream.fromEffect(doSomeStuffWrapped)
val content: HttpData[Any, Nothing] = HttpData.fromStream(stream)
def doSomeStuffWrapped = {
UIO.effectAsync[String] { cb =>
cb(
IO.succeed("TEST STRING"),
)
}
}
// Create HTTP route
val app = Http.collect[Request] {
case Method.GET -> !! / "health" => Response.ok
case Method.GET -> !! / "file" => Response(data = content)
}
// Run it like any simple app
override def run(args: List[String]): URIO[zio.ZEnv, ExitCode] =
Server.start(8090, app.silent).exitCode
However in previous versions you could have done something like given below to make it work
val stream: ZStream[Any, Nothing, Byte] =
ZStream.fromEffect(doSomeStuffWrapped).mapChunks(_.map(x => Chunk.fromArray(x.getBytes(HTTP_CHARSET))).flatten)
val content: HttpData[Any, Nothing] = HttpData.fromStream(stream)
def doSomeStuffWrapped = {
UIO.effectAsync[String] { cb =>
cb(
IO.succeed("TEST STRING"),
)
}
}
// Create HTTP route
val app = Http.collect[Request] {
case Method.GET -> !! / "health" => Response.ok
case Method.GET -> !! / "file" => Response(data = content)
}
// Run it like any simple app
override def run(args: List[String]): URIO[zio.ZEnv, ExitCode] =
Server.start(8090, app.silent).exitCode

Answer 3

Here is also another way of achieving the same result:
case class MyService(name: String) {
def imDone[R, E](s: String => Unit): Unit = s(name)
}
val s: MyService = MyService("test")
val app: Http[Any, Nothing, Request, UResponse] = Http.collectM[Request] { case Method.GET -> Root / "text" =>
ZIO.effectAsync[Any, Nothing, UResponse] { cb =>
s.imDone { b =>
cb(IO.succeed(Response.text(b)))
}
}
}