Github user pnowojski commented on a diff in the pull request: https://github.com/apache/flink/pull/5193#discussion_r159220879 --- Diff: flink-streaming-java/src/test/java/org/apache/flink/streaming/api/functions/sink/ContentDump.java --- @@ -0,0 +1,134 @@ +/* + * 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.flink.streaming.api.functions.sink; + +import java.util.ArrayList; +import java.util.Collection; +import java.util.HashMap; +import java.util.List; +import java.util.Map; +import java.util.Set; + +import static org.apache.flink.util.Preconditions.checkArgument; +import static org.apache.flink.util.Preconditions.checkNotNull; +import static org.apache.flink.util.Preconditions.checkState; + +/** + * Utility class to simulate in memory file like writes, flushes and closing. + */ +public class ContentDump { + private boolean writable = true; + private Map<String, List<String>> filesContent = new HashMap<>(); + + public Set<String> listFiles() { + return filesContent.keySet(); + } + + public void setWritable(boolean writable) { + this.writable = writable; + } + + /** + * Creates an empty file. + */ + public ContentWriter createWriter(String name) { + checkArgument(!filesContent.containsKey(name), "File [%s] already exists", name); + filesContent.put(name, new ArrayList<>()); + return new ContentWriter(name, this); + } + + public static void move(String name, ContentDump source, ContentDump target) { + Collection<String> content = source.read(name); + try (ContentWriter contentWriter = target.createWriter(name)) { + contentWriter.write(content).flush(); + } + source.delete(name); + } + + public void delete(String name) { + filesContent.remove(name); + } + + public Collection<String> read(String name) { + List<String> content = filesContent.get(name); + checkState(content != null, "Unknown file [%s]", name); + List<String> result = new ArrayList<>(content); + content.clear(); --- End diff -- Hmm, I was thinking more in a manner of reading from a file descriptor, where subsequent reads return only new data. But now when I think about it, that would be more expected behaviour for some `ContentReader` class and dropping `content.clear()` here makes more sense.
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