Fix http server startup

Closes: #2358

modules/common/src/main/scala/docspell/common/util/ResourceUse.scala

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2020 Eike K. & Contributors
+ *
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+package docspell.common.util
+
+import cats.effect._
+import cats.syntax.all._
+import fs2._
+import fs2.concurrent.{Signal, SignallingRef}
+
+object ResourceUse {
+  def apply[F[_]: Concurrent, A](
+      resource: Resource[F, A]
+  ): Implicits.UseSyntax[F, A] =
+    new Implicits.UseSyntax(resource)
+
+  object Implicits {
+    implicit final class UseSyntax[F[_]: Concurrent, A](resource: Resource[F, A]) {
+
+      /** Evaluates `resource` endlessly or until the signal turns `true`. */
+      def useUntil(
+          signal: Signal[F, Boolean],
+          returnValue: Ref[F, ExitCode]
+      ): F[ExitCode] = {
+        val server = Stream.resource(resource)
+        val blockUntilTrue = signal.discrete.takeWhile(_ == false).drain
+        val exit = fs2.Stream.eval(returnValue.get)
+        (server *> (blockUntilTrue ++ exit)).compile.lastOrError
+      }
+
+      def useForever(implicit ev: Async[F]): F[ExitCode] = for {
+        termSignal <- SignallingRef.of[F, Boolean](false)
+        exitValue <- Ref.of(ExitCode.Success)
+        rc <- useUntil(termSignal, exitValue)
+      } yield rc
+    }
+  }
+}