retry unknownHost too (#869)

* retry unknownHost too

* small test

* changing exception type

* fmt

* Update src/test/scala/com/cognite/sdk/scala/sttp/RetryingBackendTest.scala

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

* fix test

* fix tests

* Apply suggestion from @dmivankov

Co-authored-by: Dmitry Ivankov <dmitry.ivankov@cognite.com>

* Update src/test/scala/com/cognite/sdk/scala/sttp/RetryingBackendTest.scala

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

* fix test

* fmt

---------

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
Co-authored-by: Dmitry Ivankov <dmitry.ivankov@cognite.com>

Author: 3 people

src/main/scala/com/cognite/sdk/scala/sttp/RetryingBackend.scala

@@ -11,7 +11,7 @@ import sttp.client3.{Request, Response, SttpBackend, SttpClientException}
 import sttp.model.StatusCode
 import sttp.monad.MonadError
 
-import java.net.ConnectException
+import java.net.{ConnectException, UnknownHostException}
 import scala.concurrent.TimeoutException
 import scala.concurrent.duration.{DurationInt, FiniteDuration}
 import scala.util.Random
@@ -54,7 +54,8 @@ class RetryingBackend[F[_], +P](
       case cdpError: CdpApiException => maybeRetry(Some(StatusCode(cdpError.code)), cdpError)
       case sdkException @ SdkException(_, _, _, code @ Some(_)) =>
         maybeRetry(code.map(StatusCode(_)), sdkException)
-      case e @ (_: TimeoutException | _: ConnectException | _: SttpClientException) =>
+      case e @ (_: TimeoutException | _: ConnectException | _: SttpClientException |
+          _: UnknownHostException) =>
         maybeRetry(None, e)
     }
     responseMonad.flatMap(r) { resp =>

src/test/scala/com/cognite/sdk/scala/sttp/RetryingBackendTest.scala

@@ -0,0 +1,65 @@
+package com.cognite.sdk.scala.sttp
+
+import cats.effect.IO
+import cats.effect.unsafe.implicits.global
+import sttp.client3._
+import sttp.monad.MonadError
+import org.scalatest.flatspec.AnyFlatSpec
+import org.scalatest.matchers.should.Matchers
+import sttp.capabilities.Effect
+import sttp.client3.impl.cats.implicits.monadError
+
+import java.net.UnknownHostException
+import java.util.concurrent.atomic.AtomicInteger
+import scala.concurrent.duration.DurationInt
+
+@SuppressWarnings(Array("org.wartremover.warts.AsInstanceOf", "org.wartremover.warts.NonUnitStatements"))
+class FailingRetryingBackend[F[_], +P](val shouldSucceed: Boolean = false)(implicit val responseMonad: MonadError[F]) extends SttpBackend[F, P] {
+  val callCount: AtomicInteger = new java.util.concurrent.atomic.AtomicInteger(0)
+
+  override def send[T, R >: P with Effect[F]](request: Request[T, R]): F[Response[T]] = {
+    callCount.incrementAndGet()
+    if(shouldSucceed)
+      responseMonad.unit(Response.ok(Right("mock success").asInstanceOf[T]))
+    else
+      responseMonad.error(new UnknownHostException("Connection failed"))
+  }
+  override def close(): F[Unit] = responseMonad.unit(())
+}
+
+@SuppressWarnings(Array("org.wartremover.warts.NonUnitStatements"))
+class RetryingBackendTest extends AnyFlatSpec with Matchers {
+  val port: Int = 50000 + (java.lang.Math.random() * 1000).toInt
+
+  "RetryingBackend" should "retry failed requests multiple times" in {
+    val mockBackend = new FailingRetryingBackend[IO, Any]
+    val retryingBackend = new RetryingBackend[IO, Any](mockBackend, maxRetries = 2, initialRetryDelay = 1.millis)
+
+    //request doesn't matter, underlying backend just returns a failure
+    val request = basicRequest
+      .body("test")
+      .post(uri"http://host:$port/string")
+
+    an[UnknownHostException] should be thrownBy {
+      request.send(retryingBackend).unsafeRunSync()
+      ()
+    }
+
+    mockBackend.callCount.get should be(3)
+  }
+
+  it should "not retry successful requests multiple times" in {
+    val mockBackend = new FailingRetryingBackend[IO, Any](shouldSucceed = true)
+    val retryingBackend = new RetryingBackend[IO, Any](mockBackend, maxRetries = 2, initialRetryDelay = 1.millis)
+
+    //request doesn't matter, underlying backend just returns a success
+    val request = basicRequest
+      .body("test")
+      .post(uri"http://host:$port/string")
+
+    request.send(retryingBackend).unsafeRunSync()
+
+
+    mockBackend.callCount.get shouldBe 1
+  }
+}