[英]Typelevel Cats.Effect vs Typlevel eff. which and why?
[英]IO.async callback problem with cats.effect in Scala
我試圖通過 Scala 中的 java11 HttpClient
重寫 httpclient
這是我的代碼:
import cats.effect._
import java.net.http._
import java.net.http.HttpResponse._
import java.net.http.HttpClient._
trait HttpClients[F[_]] {
def send(req: HttpRequest)(implicit F: Async[F]): F[HttpResponse[_]]
}
object HttpClients {
val client: HttpClient = HttpClient.newBuilder().followRedirects(Redirect.ALWAYS).build()
def newClient[F[_] : Async](): HttpClients[F] = new HttpClients[F] {
override def send(req: HttpRequest)(implicit F: Async[F]): F[HttpResponse[_]] = F.async { cb =>
val resp = client.sendAsync(req, BodyHandlers.ofString())
val s = resp.handle((res: HttpResponse[String], err: Throwable) => {
if (err == null)
cb(Right(res))
else
cb(Left(err))
})
s // TODO ?
// Type missmatch
// Required: F[Option[F[Unit]]]
// Found: Unit
}
}
}
來自this的句柄回調
我猜錯誤來自這里,但我不知道接下來該怎么寫。
然后我做了一些改變:
def newClient[F[_] : Async](): HttpClients[F] = new HttpClients[F] {
override def send(req: HttpRequest)(implicit F: Async[F]): F[HttpResponse[_]] = F.async[HttpResponse[_]] { cb =>
val s = Sync[F](F: Async[F]).delay {
val resp = client.sendAsync(req, BodyHandlers.ofString())
resp.handle((res: HttpResponse[String], err: Throwable) => {
if (err == null)
cb(Right(res))
else
cb(Left(err))
}).join()
}
F.delay(s.some)
}
}
這一次,沒有錯誤,但我不知道如何獲取響應的正文
感謝您的回復!
@OlegPyzhcov 已經在您使用CE3的情況下提供了見解,這個答案是使用CE2以防您想要什么。
代碼的第一個版本是正確的,這是一個使用Ammonite並進行了一些樣式改進並確保為每次調用和評估newClient
創建一個新客戶端的完整運行示例
// scala 2.13.5
import $ivy.`org.typelevel::cats-effect:2.5.0`
import cats.effect.{Async, IO}
import cats.syntax.all._
import java.net.URI
import java.net.http.{HttpClient, HttpRequest, HttpResponse}
trait HttpClients[F[_]] {
def send(req: HttpRequest): F[HttpResponse[String]]
}
object HttpClients {
def newClient[F[_]](implicit F: Async[F]): F[HttpClients[F]] =
F.delay {
HttpClient
.newBuilder
.followRedirects(HttpClient.Redirect.ALWAYS)
.build()
} map { client =>
new HttpClients[F] {
override def send(req: HttpRequest): F[HttpResponse[String]] =
F.async { cb =>
client.sendAsync(req, HttpResponse.BodyHandlers.ofString).handle {
(res: HttpResponse[String], err: Throwable) =>
if (err == null) cb(Right(res))
else cb(Left(err))
}
}
}
}
}
object Main {
private val request =
HttpRequest
.newBuilder
.GET
.uri(URI.create("https://stackoverflow.com/questions/tagged/scala?tab=Newest"))
.build()
private val program = for {
_ <- IO.delay(println("Hello, World!"))
client <- HttpClients.newClient[IO]
response <- client.send(request)
_ <- IO.delay(println(response))
_ <- IO.delay(println(response.body))
} yield ()
def run(): Unit = {
program.unsafeRunSync()
}
}
@main
def main(): Unit = {
Main.run()
}
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