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ConcurrentRequests.scala
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ConcurrentRequests.scala
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/*
* Copyright 2014 http4s.org
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.http4s.server.middleware
import cats.data._
import cats.effect._
import cats.implicits._
import org.http4s._
import org.http4s.server._
/** Middlewares for tracking the quantity of concurrent requests.
*
* These are generalized middlewares and can be used to implement metrics,
* logging, max concurrent requests, etc.
*
* @note The concurrent request count is decremented on the completion of the
* Response body, or in the event of any error, and is guaranteed to
* only occur once.
*/
object ConcurrentRequests {
/** Run a side effect each time the concurrent request count increments and
* decrements.
*
* @note Each side effect is given the current number of concurrent
* requests as an argument.
*
* @note `onIncrement` should never be < 1 and `onDecrement` should never
* be value < 0.
*
* @note This is the same as [[route]], but allows for the inner and outer
* effect types to differ.
*/
def route2[F[_]: Sync, G[_]: Async]( // TODO (ce3-ra): Sync + MonadCancel
onIncrement: Long => G[Unit],
onDecrement: Long => G[Unit],
): F[ContextMiddleware[G, Long]] =
Ref
.in[F, G, Long](0L)
.map(ref =>
BracketRequestResponse.bracketRequestResponseRoutes[G, Long](
ref.updateAndGet(_ + 1L).flatTap(onIncrement)
)(Function.const(ref.updateAndGet(_ - 1L).flatMap(onDecrement)))
)
/** Run a side effect each time the concurrent request count increments and
* decrements.
*
* @note Each side effect is given the current number of concurrent
* requests as an argument.
*
* @note `onIncrement` should never be < 1 and `onDecrement` should never
* be value < 0.
*/
def route[F[_]: Async](
onIncrement: Long => F[Unit],
onDecrement: Long => F[Unit],
): F[ContextMiddleware[F, Long]] =
route2[F, F](onIncrement, onDecrement)
/** As [[route]], but runs the same effect on increment and decrement of the concurrent request count. */
def onChangeRoute[F[_]: Async](onChange: Long => F[Unit]): F[ContextMiddleware[F, Long]] =
route[F](onChange, onChange)
/** Run a side effect each time the concurrent request count increments and
* decrements.
*
* @note Each side effect is given the current number of concurrent
* requests as an argument.
*
* @note `onIncrement` should never be < 1 and `onDecrement` should never
* be value < 0.
*
* @note This is the same as [[app]], but allows for the inner and outer
* effect types to differ.
*/
def app2[F[_]: Sync, G[_]: Async](
onIncrement: Long => G[Unit],
onDecrement: Long => G[Unit],
): F[Kleisli[G, ContextRequest[G, Long], Response[G]] => Kleisli[G, Request[G], Response[G]]] =
Ref
.in[F, G, Long](0L)
.map(ref =>
BracketRequestResponse.bracketRequestResponseApp[G, Long](
ref.updateAndGet(_ + 1L).flatTap(onIncrement)
)(Function.const(ref.updateAndGet(_ - 1L).flatMap(onDecrement)))
)
/** Run a side effect each time the concurrent request count increments and
* decrements.
*
* @note Each side effect is given the current number of concurrent
* requests as an argument.
*
* @note `onIncrement` should never be < 1 and `onDecrement` should never
* be value < 0.
*/
def app[F[_]: Async](
onIncrement: Long => F[Unit],
onDecrement: Long => F[Unit],
): F[Kleisli[F, ContextRequest[F, Long], Response[F]] => Kleisli[F, Request[F], Response[F]]] =
app2[F, F](onIncrement, onDecrement)
/** As [[app]], but runs the same effect on increment and decrement of the concurrent request count. */
def onChangeApp[F[_]: Async](
onChange: Long => F[Unit]
): F[Kleisli[F, ContextRequest[F, Long], Response[F]] => Kleisli[F, Request[F], Response[F]]] =
app[F](onChange, onChange)
}