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feat(reactor netty): adding reactor-netty based backend service, http host client, and related components
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‎components/client/pom.xml

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<classifier>linux-aarch_64</classifier>
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</dependency>
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<dependency>
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<groupId>io.projectreactor.netty</groupId>
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<artifactId>reactor-netty</artifactId>
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</dependency>
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<dependency>
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<groupId>com.hotels.styx</groupId>
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<artifactId>styx-api</artifactId>
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<dependency>
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<groupId>org.hamcrest</groupId>
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<artifactId>hamcrest</artifactId>
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<scope>test</scope>
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</dependency>
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<dependency>
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<groupId>org.scalatest</groupId>
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<artifactId>scalatest_${scala.version}</artifactId>
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<scope>test</scope>
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</dependency>
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<dependency>
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<groupId>org.mockito</groupId>
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<artifactId>mockito-core</artifactId>
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<scope>test</scope>
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</dependency>
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<dependency>
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<scope>test</scope>
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</dependency>
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<dependency>
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<groupId>io.mockk</groupId>
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<artifactId>mockk-jvm</artifactId>
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<scope>test</scope>
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</dependency>
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<dependency>
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<groupId>com.squareup.okhttp3</groupId>
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<artifactId>mockwebserver</artifactId>
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<scope>test</scope>
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</dependency>
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<dependency>
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<groupId>com.squareup.okhttp3</groupId>
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<artifactId>okhttp-tls</artifactId>
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<scope>test</scope>
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</dependency>
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</dependencies>
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<build>

‎components/client/src/main/kotlin/com/hotels/styx/client/ReactorBackendServiceClient.kt

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/*
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Copyright (C) 2013-2024 Expedia Inc.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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package com.hotels.styx.client
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import com.hotels.styx.api.HttpHeaderNames.CONTENT_LENGTH
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import com.hotels.styx.api.HttpHeaderNames.HOST
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import com.hotels.styx.api.HttpHeaderNames.TRANSFER_ENCODING
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import com.hotels.styx.api.HttpInterceptor
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import com.hotels.styx.api.HttpMethod
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import com.hotels.styx.api.Id
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import com.hotels.styx.api.LiveHttpRequest
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import com.hotels.styx.api.LiveHttpResponse
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import com.hotels.styx.api.exceptions.NoAvailableHostsException
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import com.hotels.styx.api.extension.Origin
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import com.hotels.styx.api.extension.RemoteHost
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import com.hotels.styx.api.extension.loadbalancing.spi.LoadBalancer
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import com.hotels.styx.api.extension.retrypolicy.spi.RetryPolicy
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import com.hotels.styx.api.extension.service.StickySessionConfig
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import com.hotels.styx.client.stickysession.StickySessionCookie.newStickySessionCookie
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import com.hotels.styx.client.stickysession.StickySessionLoadBalancingStrategy
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import com.hotels.styx.ext.newRequest
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import com.hotels.styx.ext.newResponse
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import com.hotels.styx.metrics.CentralisedMetrics
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import org.reactivestreams.Publisher
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import reactor.core.publisher.Mono
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import java.util.Objects.nonNull
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import java.util.Optional
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/**
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* A configurable HTTP client with integration of Reactor Netty client
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*/
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class ReactorBackendServiceClient(
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private val id: Id,
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private val rewriteRuleset: RewriteRuleset,
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private val originsRestrictionCookieName: String?,
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private val stickySessionConfig: StickySessionConfig,
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private val originIdHeader: CharSequence,
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private val loadBalancer: LoadBalancer,
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private val retryPolicy: RetryPolicy,
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private val metrics: CentralisedMetrics,
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private val overrideHostHeader: Boolean,
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) : BackendServiceClient {
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override fun sendRequest(
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request: LiveHttpRequest,
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context: HttpInterceptor.Context,
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): Publisher<LiveHttpResponse> = sendRequest(rewriteUrl(request), emptyList(), 0, context)
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private fun sendRequest(
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request: LiveHttpRequest,
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previousOrigins: List<RemoteHost>,
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attempt: Int,
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context: HttpInterceptor.Context,
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): Publisher<LiveHttpResponse> {
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if (attempt >= MAX_RETRY_ATTEMPTS) {
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return Mono.error(NoAvailableHostsException(id))
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}
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val remoteHost = selectOrigin(request)
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return if (remoteHost.isPresent) {
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val host = remoteHost.get()
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val updatedRequest = shouldOverrideHostHeader(host, request)
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val newPreviousOrigins = previousOrigins.toMutableList()
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newPreviousOrigins.add(host)
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Mono.from(host.hostClient().handle(updatedRequest, context))
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.doOnNext { recordErrorStatusMetrics(it) }
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.map { response ->
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response.addStickySessionIdentifier(host.origin())
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.removeUnexpectedResponseBody(updatedRequest)
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.removeRedundantContentLengthHeader()
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.addOriginId(host.id())
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.let { LiveHttpResponse.Builder(it).request(updatedRequest).build() }
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}
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.onErrorResume { cause ->
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val retryContext = RetryPolicyContext(id, attempt + 1, cause, updatedRequest, previousOrigins)
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retry(updatedRequest, retryContext, newPreviousOrigins, attempt + 1, cause, context)
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}
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} else {
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val retryContext = RetryPolicyContext(id, attempt + 1, null, request, previousOrigins)
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retry(request, retryContext, previousOrigins, attempt + 1, NoAvailableHostsException(id), context)
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}
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}
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private fun recordErrorStatusMetrics(response: LiveHttpResponse) {
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val statusCode = response.status().code()
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if (statusCode.isErrorStatus()) {
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metrics.proxy.client.errorResponseFromOriginByStatus(statusCode).increment()
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}
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}
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private fun Int.isErrorStatus() = this >= 400
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private fun bodyNeedsToBeRemoved(
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request: LiveHttpRequest,
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response: LiveHttpResponse,
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) = isHeadRequest(request) || isBodilessResponse(response)
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private fun responseWithoutBody(response: LiveHttpResponse) =
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response.newResponse {
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header(CONTENT_LENGTH, 0)
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removeHeader(TRANSFER_ENCODING)
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removeBody()
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}
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private fun isBodilessResponse(response: LiveHttpResponse): Boolean =
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when (val code = response.status().code()) {
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204, 304 -> true
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else -> code / 100 == 1
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}
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private fun isHeadRequest(request: LiveHttpRequest): Boolean = request.method() == HttpMethod.HEAD
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private fun shouldOverrideHostHeader(
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host: RemoteHost,
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request: LiveHttpRequest,
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): LiveHttpRequest =
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if (overrideHostHeader && !host.origin().host().isNullOrBlank()) {
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request.newRequest { header(HOST, host.origin().host()) }
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} else {
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request
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}
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private fun LiveHttpResponse.addOriginId(originId: Id): LiveHttpResponse =
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newResponse {
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header(originIdHeader, originId)
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}
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private fun retry(
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request: LiveHttpRequest,
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retryContext: RetryPolicyContext,
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previousOrigins: List<RemoteHost>,
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attempt: Int,
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cause: Throwable,
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context: HttpInterceptor.Context,
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): Mono<LiveHttpResponse> {
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val lbContext: LoadBalancer.Preferences =
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object : LoadBalancer.Preferences {
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override fun preferredOrigins(): Optional<String> = Optional.empty()
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override fun avoidOrigins(): List<Origin> = previousOrigins.map { it.origin() }
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}
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return if (retryPolicy.evaluate(retryContext, loadBalancer, lbContext).shouldRetry()) {
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Mono.from(sendRequest(request, previousOrigins, attempt, context))
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} else {
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Mono.error(cause)
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}
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}
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private fun LiveHttpResponse.removeUnexpectedResponseBody(request: LiveHttpRequest) =
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if (bodyNeedsToBeRemoved(request, this)) {
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responseWithoutBody(this)
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} else {
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this
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}
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private fun LiveHttpResponse.removeRedundantContentLengthHeader() =
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if (contentLength().isPresent && chunked()) {
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newResponse {
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removeHeader(CONTENT_LENGTH)
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}
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} else {
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this
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}
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private fun selectOrigin(rewrittenRequest: LiveHttpRequest): Optional<RemoteHost> {
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val preferences =
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object : LoadBalancer.Preferences {
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override fun preferredOrigins(): Optional<String> {
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return if (nonNull(originsRestrictionCookieName)) {
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rewrittenRequest.cookie(originsRestrictionCookieName)
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.map { it.value() }
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.or { rewrittenRequest.cookie("styx_origin_$id").map { it.value() } }
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} else {
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rewrittenRequest.cookie("styx_origin_$id").map { it.value() }
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}
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}
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override fun avoidOrigins(): List<Origin> = emptyList()
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}
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return loadBalancer.choose(preferences)
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}
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private fun LiveHttpResponse.addStickySessionIdentifier(origin: Origin): LiveHttpResponse =
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if (loadBalancer is StickySessionLoadBalancingStrategy) {
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val maxAge = stickySessionConfig.stickySessionTimeoutSeconds()
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newResponse {
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addCookies(newStickySessionCookie(id, origin.id(), maxAge))
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}
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} else {
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this
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}
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private fun rewriteUrl(request: LiveHttpRequest): LiveHttpRequest = rewriteRuleset.rewrite(request)
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private class RetryPolicyContext(
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private val appId: Id,
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private val retryCount: Int,
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private val lastException: Throwable?,
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private val request: LiveHttpRequest,
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private val previouslyUsedOrigins: Iterable<RemoteHost>,
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) : RetryPolicy.Context {
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override fun appId(): Id = appId
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override fun currentRetryCount(): Int = retryCount
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override fun lastException(): Optional<Throwable> = Optional.ofNullable(lastException)
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override fun currentRequest(): LiveHttpRequest = request
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override fun previousOrigins(): Iterable<RemoteHost> = previouslyUsedOrigins
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override fun toString(): String =
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buildString {
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append("appId", appId)
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append(", retryCount", retryCount)
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append(", lastException", lastException)
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append(", request", request.url())
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append(", previouslyUsedOrigins", previouslyUsedOrigins)
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}
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fun hosts(): String = hosts(previouslyUsedOrigins)
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companion object {
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private fun hosts(origins: Iterable<RemoteHost>): String =
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origins.asSequence().map { it.origin().hostAndPortString() }.joinToString(", ")
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}
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}
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override fun toString(): String =
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buildString {
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append("id", id)
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append(", stickySessionConfig", stickySessionConfig)
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append(", retryPolicy", retryPolicy)
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append(", rewriteRuleset", rewriteRuleset)
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append(", loadBalancingStrategy", loadBalancer)
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append(", overrideHostHeader", overrideHostHeader)
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}
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companion object {
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private const val MAX_RETRY_ATTEMPTS = 3
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}
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}

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