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package com.softwaremill.sttp.prometheus
import java.util.concurrent.ConcurrentHashMap
import com.softwaremill.sttp.{FollowRedirectsBackend, MonadError, Request, Response, SttpBackend}
import io.prometheus.client.Histogram
import scala.collection.mutable
import scala.language.higherKinds
import scala.collection.JavaConverters._
class PrometheusBackend[R[_], S] private (delegate: SttpBackend[R, S],
requestToHistogramNameMapper: Option[Request[_, S] => String])
extends SttpBackend[R, S] {
import PrometheusBackend._
private[this] val histograms: mutable.Map[String, Histogram] = new ConcurrentHashMap[String, Histogram]().asScala
override def send[T](request: Request[T, S]): R[Response[T]] = {
val histogramName = getHistogramName(request)
val histogram = histograms.getOrElseUpdate(histogramName, createNewHistogram(histogramName))
val requestTimer = histogram.startTimer()
responseMonad.handleError(
responseMonad.map(delegate.send(request)) { response =>
requestTimer.observeDuration()
response
}
) {
case e: Exception =>
requestTimer.observeDuration()
responseMonad.error(e)
}
}
override def close(): Unit = delegate.close()
override def responseMonad: MonadError[R] = delegate.responseMonad
private[this] def getHistogramName(request: Request[_, S]): String =
requestToHistogramNameMapper.map(_.apply(request)).getOrElse(DefaultHistogramName)
private[this] def createNewHistogram(name: String): Histogram = Histogram.build().name(name).help(name).register()
}
object PrometheusBackend {
val DefaultHistogramName = "sttp_request_latency"
def apply[R[_], S](delegate: SttpBackend[R, S],
requestToHistogramNameMapper: Option[Request[_, S] => String] = None): SttpBackend[R, S] = {
// redirects should be handled before brave tracing, hence adding the follow-redirects backend on top
new FollowRedirectsBackend(new PrometheusBackend(delegate, requestToHistogramNameMapper))
}
}
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