From c30ec9ec9de39eff70dfb1b93b7f004a73e5856a Mon Sep 17 00:00:00 2001
From: Ian Streeter <ian@snowplowanalytics.com>
Date: Tue, 10 Sep 2024 22:30:19 +0100
Subject: [PATCH] Http4s Client with configuration appropriate for
 common-streams apps

Common-streams apps require an http4s Client for:

- Iglu resolver
- Webhook monitoring alerts
- Telemetry

This commit provides a Client which is configured appropriately for
these common use cases.
---
 .../src/main/resources/reference.conf         |  6 +++
 .../snowplow/runtime/HttpClient.scala         | 41 +++++++++++++++++++
 project/Dependencies.scala                    |  5 ++-
 3 files changed, 51 insertions(+), 1 deletion(-)
 create mode 100644 modules/runtime-common/src/main/scala/com/snowplowanalytics/snowplow/runtime/HttpClient.scala

diff --git a/modules/runtime-common/src/main/resources/reference.conf b/modules/runtime-common/src/main/resources/reference.conf
index e218bcc..6e1713e 100644
--- a/modules/runtime-common/src/main/resources/reference.conf
+++ b/modules/runtime-common/src/main/resources/reference.conf
@@ -1,4 +1,10 @@
 snowplow.defaults: {
+  http: {
+    client: {
+      maxConnectionsPerServer: 4
+    }
+  }
+
   statsd: {
     port: 8125
     tags: {}
diff --git a/modules/runtime-common/src/main/scala/com/snowplowanalytics/snowplow/runtime/HttpClient.scala b/modules/runtime-common/src/main/scala/com/snowplowanalytics/snowplow/runtime/HttpClient.scala
new file mode 100644
index 0000000..51745e0
--- /dev/null
+++ b/modules/runtime-common/src/main/scala/com/snowplowanalytics/snowplow/runtime/HttpClient.scala
@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2023-present Snowplow Analytics Ltd. All rights reserved.
+ *
+ * This program is licensed to you under the Snowplow Community License Version 1.0,
+ * and you may not use this file except in compliance with the Snowplow Community License Version 1.0.
+ * You may obtain a copy of the Snowplow Community License Version 1.0 at https://docs.snowplow.io/community-license-1.0
+ */
+package com.snowplowanalytics.snowplow.runtime
+
+import cats.effect.{Async, Resource}
+import org.http4s.blaze.client.BlazeClientBuilder
+import org.http4s.client.Client
+import io.circe._
+import io.circe.generic.semiauto._
+
+object HttpClient {
+  case class Config(
+    maxConnectionsPerServer: Int
+  )
+
+  object Config {
+    implicit def telemetryConfigDecoder: Decoder[Config] = deriveDecoder
+  }
+
+  /**
+   * Provides a http4s Client configured appropriately for a snowplow common-streams app
+   *
+   * Blaze option `maxConnectionsPerRequestKey` is set to something small. This is required so we
+   * can traverse over many schemas in parallel without overwhelming any single Iglu server.
+   *
+   * Blaze options `maxTotalConnections` and `maxWaitQueueLimit` are unlimited. This is appropriate
+   * because common-streams apps are already naturally rate limited by the flow of events. We do not
+   * want exceptions for exceeding number of requests allowed in a queue.
+   */
+  def resource[F[_]: Async](config: Config): Resource[F, Client[F]] =
+    BlazeClientBuilder[F]
+      .withMaxConnectionsPerRequestKey(Function.const(config.maxConnectionsPerServer))
+      .withMaxTotalConnections(Int.MaxValue)
+      .withMaxWaitQueueLimit(Int.MaxValue)
+      .resource
+}
diff --git a/project/Dependencies.scala b/project/Dependencies.scala
index f9233a9..69bf274 100644
--- a/project/Dependencies.scala
+++ b/project/Dependencies.scala
@@ -16,7 +16,8 @@ object Dependencies {
     val catsRetry        = "3.1.3"
     val fs2              = "3.10.0"
     val log4cats         = "2.6.0"
-    val http4s           = "0.23.26"
+    val http4s           = "0.23.28"
+    val blaze            = "0.23.16"
     val decline          = "2.4.1"
     val circe            = "0.14.6"
     val circeExtra       = "0.14.3"
@@ -59,6 +60,7 @@ object Dependencies {
   val catsRetry         = "com.github.cb372"       %% "cats-retry"              % V.catsRetry
   val emberServer       = "org.http4s"             %% "http4s-ember-server"     % V.http4s
   val http4sCirce       = "org.http4s"             %% "http4s-circe"            % V.http4s
+  val blazeClient       = "org.http4s"             %% "http4s-blaze-client"     % V.blaze
   val decline           = "com.monovore"           %% "decline-effect"          % V.decline
   val circeConfig       = "io.circe"               %% "circe-config"            % V.circeConfig
   val circeGeneric      = "io.circe"               %% "circe-generic"           % V.circe
@@ -164,6 +166,7 @@ object Dependencies {
   )
 
   val runtimeCommonDependencies = Seq(
+    blazeClient,
     cats,
     catsEffectKernel,
     catsRetry,