0.2.4

src/main/kotlin/com/wire/bots/polls/setup/HttpClient.kt

@@ -1,5 +1,6 @@
 package com.wire.bots.polls.setup
 
+import com.wire.bots.polls.utils.ClientRequestMetric
 import com.wire.bots.polls.utils.createLogger
 import com.wire.bots.polls.utils.httpCall
 import io.ktor.client.HttpClient
@@ -9,7 +10,6 @@ import io.ktor.client.features.json.JsonFeature
 import io.ktor.client.features.logging.LogLevel
 import io.ktor.client.features.logging.Logger
 import io.ktor.client.features.logging.Logging
-import io.ktor.client.features.observer.ResponseObserver
 import io.micrometer.core.instrument.MeterRegistry
 
 
@@ -22,14 +22,8 @@ fun createHttpClient(meterRegistry: MeterRegistry) =
             serializer = JacksonSerializer()
         }
 
-        // TODO check https://github.com/ktorio/ktor/issues/1813
-        @Suppress("ConstantConditionIf") // temporary disabled until https://github.com/ktorio/ktor/issues/1813 is resolved
-        if (false) {
-            install(ResponseObserver) {
-                onResponse {
-                    meterRegistry.httpCall(it)
-                }
-            }
+        install(ClientRequestMetric) {
+            onResponse { meterRegistry.httpCall(it) }
         }
 
         install(Logging) {

src/main/kotlin/com/wire/bots/polls/utils/ClientRequestMetric.kt

@@ -0,0 +1,72 @@
+package com.wire.bots.polls.utils
+
+import io.ktor.client.HttpClient
+import io.ktor.client.features.HttpClientFeature
+import io.ktor.client.statement.HttpReceivePipeline
+import io.ktor.client.statement.HttpResponse
+import io.ktor.client.statement.request
+import io.ktor.util.AttributeKey
+import mu.KLogging
+
+/**
+ * [ClientRequestMetric] callback.
+ */
+typealias RequestMetricHandler = suspend (RequestMetric) -> Unit
+
+
+/**
+ * Enables callback after HttpClient sends a request with [RequestMetric].
+ */
+class ClientRequestMetric(private val metricHandler: RequestMetricHandler) {
+
+    class Config {
+        internal var metricHandler: RequestMetricHandler = {}
+
+        /**
+         * Set [RequestMetricHandler] called at the end of the request.
+         */
+        fun onResponse(block: RequestMetricHandler) {
+            metricHandler = block
+        }
+    }
+
+    companion object Feature : HttpClientFeature<Config, ClientRequestMetric>, KLogging() {
+
+        override val key: AttributeKey<ClientRequestMetric> =
+            AttributeKey("ClientRequestMetric")
+
+        override fun prepare(block: Config.() -> Unit) =
+            ClientRequestMetric(Config().apply(block).metricHandler)
+
+        override fun install(feature: ClientRequestMetric, scope: HttpClient) {
+            // synchronous response pipeline hook
+            // instead of ResponseObserver - which spawns a new coroutine
+            scope.receivePipeline.intercept(HttpReceivePipeline.After) { response ->
+                // WARNING: Do not consume HttpResponse.content here,
+                // or you will corrupt the client response.
+                runCatching { feature.metricHandler(response.toRequestMetric()) }
+                    .onFailure { logger.error(it) { "Error during metering!" } }
+            }
+        }
+
+        // does not touch the content
+        private fun HttpResponse.toRequestMetric() = RequestMetric(
+            requestTime = requestTime.timestamp,
+            responseTime = responseTime.timestamp,
+            method = request.method.value,
+            url = request.url.toString(),
+            responseCode = status.value
+        )
+    }
+}
+
+
+data class RequestMetric(
+    // number of epoch milliseconds
+    val requestTime: Long,
+    val responseTime: Long,
+    val method: String,
+    val url: String,
+    val responseCode: Int
+)
+

src/main/kotlin/com/wire/bots/polls/utils/PrometheusExtensions.kt

@@ -1,7 +1,5 @@
 package com.wire.bots.polls.utils
 
-import io.ktor.client.statement.HttpResponse
-import io.ktor.client.statement.request
 import io.micrometer.core.instrument.MeterRegistry
 import io.micrometer.core.instrument.Tag
 import java.util.concurrent.TimeUnit
@@ -18,18 +16,17 @@ fun MeterRegistry.countException(exception: Throwable, additionalTags: Map<Strin
     counter("exceptions", tags).increment()
 }
 
+
 /**
  * Register http call.
+ *
  */
-fun MeterRegistry.httpCall(response: HttpResponse) {
-    val startTime = response.requestTime.timestamp
-    val endTime = response.responseTime.timestamp
-
-    val duration = endTime - startTime
+fun MeterRegistry.httpCall(requestMetric: RequestMetric) {
+    val duration = requestMetric.responseTime - requestMetric.requestTime
     val tags = mapOf(
-        "method" to response.request.method.value,
-        "url" to response.request.url.toString(),
-        "response_code" to response.status.value.toString()
+        "method" to requestMetric.method,
+        "url" to requestMetric.url,
+        "response_code" to requestMetric.responseCode.toString()
     ).toTags()
 
     timer("http_calls", tags).record(duration, TimeUnit.MILLISECONDS)