Fix reloading of the configuration from HTTP(S)

The `HttpWatcher` didn't propagate the observed
last modification time back to the configuration.
As a result, each new configuration was already
deprecated when it started and the reconfiguration
process looped.

Closes #2937

log4j-core-test/src/test/java/org/apache/logging/log4j/core/util/HttpWatcherTest.java

@@ -0,0 +1,161 @@
+/*
+ * 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.logging.log4j.core.util;
+
+import static com.github.tomakehurst.wiremock.client.WireMock.aResponse;
+import static com.github.tomakehurst.wiremock.client.WireMock.get;
+import static com.github.tomakehurst.wiremock.client.WireMock.urlPathEqualTo;
+import static java.util.Collections.singletonList;
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.github.tomakehurst.wiremock.client.WireMock;
+import com.github.tomakehurst.wiremock.junit5.WireMockRuntimeInfo;
+import com.github.tomakehurst.wiremock.junit5.WireMockTest;
+import com.github.tomakehurst.wiremock.stubbing.StubMapping;
+import java.net.URL;
+import java.time.Instant;
+import java.time.ZoneOffset;
+import java.time.format.DateTimeFormatter;
+import java.time.temporal.ChronoUnit;
+import java.util.List;
+import java.util.Queue;
+import java.util.concurrent.BlockingQueue;
+import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.TimeUnit;
+import org.apache.logging.log4j.core.config.AbstractConfiguration;
+import org.apache.logging.log4j.core.config.Configuration;
+import org.apache.logging.log4j.core.config.ConfigurationListener;
+import org.apache.logging.log4j.core.config.ConfigurationSource;
+import org.apache.logging.log4j.core.config.HttpWatcher;
+import org.apache.logging.log4j.core.config.Reconfigurable;
+import org.apache.logging.log4j.core.net.UrlConnectionFactory;
+import org.apache.logging.log4j.test.junit.SetTestProperty;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Test the WatchManager
+ */
+@SetTestProperty(key = UrlConnectionFactory.ALLOWED_PROTOCOLS, value = "http,https")
+@WireMockTest
+class HttpWatcherTest {
+
+    private static final DateTimeFormatter formatter = DateTimeFormatter.RFC_1123_DATE_TIME.withZone(ZoneOffset.UTC);
+    private static final String XML = "application/xml";
+
+    @Test
+    void testModified(final WireMockRuntimeInfo info) throws Exception {
+        final WireMock wireMock = info.getWireMock();
+
+        final BlockingQueue<String> queue = new LinkedBlockingQueue<>();
+        List<ConfigurationListener> listeners = singletonList(new TestConfigurationListener(queue, "log4j-test1.xml"));
+        // HTTP Last-Modified is in seconds
+        Instant now = Instant.now().truncatedTo(ChronoUnit.SECONDS);
+        Instant previous = now.minus(5, ChronoUnit.MINUTES);
+        final URL url = new URL(info.getHttpBaseUrl() + "/log4j-test1.xml");
+        final Configuration configuration = createConfiguration(url);
+
+        final StubMapping stubMapping = wireMock.register(get(urlPathEqualTo("/log4j-test1.xml"))
+                .willReturn(aResponse()
+                        .withBodyFile("log4j-test1.xml")
+                        .withStatus(200)
+                        .withHeader("Last-Modified", formatter.format(previous))
+                        .withHeader("Content-Type", XML)));
+        Watcher watcher = new HttpWatcher(configuration, null, listeners, previous.toEpochMilli());
+        watcher.watching(new Source(url));
+        try {
+            assertThat(watcher.isModified()).as("File was modified").isTrue();
+            assertThat(watcher.getLastModified()).as("File modification time").isEqualTo(previous.toEpochMilli());
+            // Check if listeners are correctly called
+            // Note: listeners are called asynchronously
+            watcher.modified();
+            String str = queue.poll(1, TimeUnit.SECONDS);
+            assertThat(str).isEqualTo("log4j-test1.xml");
+            ConfigurationSource configurationSource = configuration.getConfigurationSource();
+            // Check that the last modified time of the ConfigurationSource was modified as well
+            // See: https://github.com/apache/logging-log4j2/issues/2937
+            assertThat(configurationSource.getLastModified())
+                    .as("Last modification time of current ConfigurationSource")
+                    .isEqualTo(0L);
+            configurationSource = configurationSource.resetInputStream();
+            assertThat(configurationSource.getLastModified())
+                    .as("Last modification time of next ConfigurationSource")
+                    .isEqualTo(previous.toEpochMilli());
+        } finally {
+            wireMock.removeStubMapping(stubMapping);
+        }
+    }
+
+    @Test
+    void testNotModified(final WireMockRuntimeInfo info) throws Exception {
+        final WireMock wireMock = info.getWireMock();
+
+        final BlockingQueue<String> queue = new LinkedBlockingQueue<>();
+        final List<ConfigurationListener> listeners =
+                singletonList(new TestConfigurationListener(queue, "log4j-test2.xml"));
+        // HTTP Last-Modified is in seconds
+        Instant now = Instant.now().truncatedTo(ChronoUnit.SECONDS);
+        Instant previous = now.minus(5, ChronoUnit.MINUTES);
+        final URL url = new URL(info.getHttpBaseUrl() + "/log4j-test2.xml");
+        final Configuration configuration = createConfiguration(url);
+
+        final StubMapping stubMapping = wireMock.register(get(urlPathEqualTo("/log4j-test2.xml"))
+                .willReturn(aResponse()
+                        .withStatus(304)
+                        .withHeader("Last-Modified", formatter.format(now) + " GMT")
+                        .withHeader("Content-Type", XML)));
+        Watcher watcher = new HttpWatcher(configuration, null, listeners, previous.toEpochMilli());
+        watcher.watching(new Source(url));
+        try {
+            assertThat(watcher.isModified()).as("File was modified").isFalse();
+            // If the file was not modified, neither should be the last modification time
+            assertThat(watcher.getLastModified()).isEqualTo(previous.toEpochMilli());
+            // Check that the last modified time of the ConfigurationSource was not modified either
+            ConfigurationSource configurationSource = configuration.getConfigurationSource();
+            assertThat(configurationSource.getLastModified())
+                    .as("Last modification time of current ConfigurationSource")
+                    .isEqualTo(0L);
+            configurationSource = configurationSource.resetInputStream();
+            assertThat(configurationSource.getLastModified())
+                    .as("Last modification time of next ConfigurationSource")
+                    .isEqualTo(0L);
+        } finally {
+            wireMock.removeStubMapping(stubMapping);
+        }
+    }
+
+    // Creates a configuration with a predefined configuration source
+    private static Configuration createConfiguration(URL url) {
+        ConfigurationSource configurationSource = new ConfigurationSource(new Source(url), new byte[0], 0L);
+        return new AbstractConfiguration(null, configurationSource) {};
+    }
+
+    private static class TestConfigurationListener implements ConfigurationListener {
+        private final Queue<String> queue;
+        private final String name;
+
+        public TestConfigurationListener(final Queue<String> queue, final String name) {
+            this.queue = queue;
+            this.name = name;
+        }
+
+        @Override
+        public void onChange(final Reconfigurable reconfigurable) {
+            // System.out.println("Reconfiguration detected for " + name);
+            queue.add(name);
+        }
+    }
+}