kfaraz commented on code in PR #20784: URL: https://github.com/apache/druid/pull/20784#discussion_r4424337991
########## server/src/main/java/org/apache/druid/server/http/AsyncRequest.java: ########## @@ -0,0 +1,301 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one + * or more contributor license agreements. See the NOTICE file + * distributed with this work for additional information + * regarding copyright ownership. The ASF licenses this file + * to you 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.apache.druid.server.http; + +import com.fasterxml.jackson.core.type.TypeReference; +import com.fasterxml.jackson.databind.JavaType; +import com.fasterxml.jackson.databind.ObjectMapper; +import com.fasterxml.jackson.databind.ObjectWriter; +import com.google.common.base.Preconditions; +import com.google.common.util.concurrent.FutureCallback; +import com.google.common.util.concurrent.Futures; +import com.google.common.util.concurrent.ListenableFuture; +import com.google.common.util.concurrent.MoreExecutors; +import org.apache.druid.java.util.common.logger.Logger; + +import javax.annotation.Nullable; +import javax.servlet.AsyncContext; +import javax.servlet.http.HttpServletRequest; +import javax.servlet.http.HttpServletResponse; +import javax.ws.rs.core.MediaType; +import java.lang.reflect.Type; +import java.util.concurrent.atomic.AtomicBoolean; +import java.util.function.Function; + +/** + * Wraps the {@link AsyncContext} of a {@link HttpServletRequest} and ensures that the + * response is completed at most once, guarding against writing to a timed-out or already-completed request. + * Use {@link #completed(HttpServletRequest, ObjectMapper, AsyncResponse)} to complete a request immediately, or + * {@link #create(HttpServletRequest, ListenableFuture, long)} to obtain a {@link Builder} that responds based on + * the outcome of the future; call {@link Builder#contentType} to specify how to write the response entity. + */ +public class AsyncRequest +{ + private static final Logger log = new Logger(AsyncRequest.class); + + private final AtomicBoolean completed = new AtomicBoolean(false); + private final AsyncContext context; + private final ObjectMapper objectMapper; + private final String contentType; + + /** + * Starts async processing of the request and immediately completes it with the given response, writing any + * response entity as JSON using the given {@link ObjectMapper}. + */ + public static <T> AsyncRequest completed(HttpServletRequest request, ObjectMapper jsonMapper, AsyncResponse<T> response) + { + return completed(request, jsonMapper, MediaType.APPLICATION_JSON, response); + } + + /** + * Starts async processing of the request and immediately completes it with the given response, writing any + * response entity using the given {@link ObjectMapper} and content type. + */ + public static <T> AsyncRequest completed(HttpServletRequest request, ObjectMapper objectMapper, String contentType, AsyncResponse<T> response) + { + final AsyncRequest asyncRequest = new AsyncRequest(request, objectMapper, contentType); + asyncRequest.complete(response); + return asyncRequest; + } + + /** + * Creates a {@link Builder} that waits on the given future. Call {@link Builder#contentType} to specify the + * {@link ObjectMapper} and content type to use for writing the response entity. + */ + public static <T> Builder<T> create(HttpServletRequest request, ListenableFuture<T> future, long timeoutMillis) + { + Preconditions.checkArgument(timeoutMillis > 0, "timeoutMillis[%s] must be greater than zero", timeoutMillis); + return new Builder<>(request, future, timeoutMillis); + } + + private AsyncRequest(HttpServletRequest request, ObjectMapper objectMapper, String contentType) + { + this.context = request.startAsync(); + this.objectMapper = objectMapper; + this.contentType = contentType; + } + + /** + * Completes the request as described by the given {@link AsyncResponse}, if it hasn't already been completed. + */ + private <T> void complete(AsyncResponse<T> response) + { + if (!completed.compareAndSet(false, true)) { + log.warn("Request has already been completed"); Review Comment: ```suggestion ``` -- This is an automated message from the Apache Git Service. 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