Add a manager class for checking "liveness" of client versions

service/src/main/java/org/whispersystems/textsecuregcm/storage/ClientReleaseManager.java

@@ -0,0 +1,80 @@
+/*
+ * Copyright 2023 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.whispersystems.textsecuregcm.storage;
+
+import com.vdurmont.semver4j.Semver;
+import java.time.Clock;
+import java.time.Duration;
+import java.util.Collections;
+import java.util.Map;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.ScheduledFuture;
+import java.util.concurrent.TimeUnit;
+import io.dropwizard.lifecycle.Managed;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.whispersystems.textsecuregcm.util.ua.ClientPlatform;
+import javax.annotation.Nullable;
+
+public class ClientReleaseManager implements Managed {
+
+  private final ClientReleases clientReleases;
+  private final ScheduledExecutorService scheduledExecutorService;
+  private final Duration refreshInterval;
+  private final Clock clock;
+
+  @Nullable
+  private ScheduledFuture<?> refreshClientReleasesFuture;
+
+  private volatile Map<ClientPlatform, Map<Semver, ClientRelease>> clientReleasesByPlatform = Collections.emptyMap();
+
+  private static final Logger logger = LoggerFactory.getLogger(ClientReleaseManager.class);
+
+  public ClientReleaseManager(final ClientReleases clientReleases,
+      final ScheduledExecutorService scheduledExecutorService,
+      final Duration refreshInterval,
+      final Clock clock) {
+
+    this.clientReleases = clientReleases;
+    this.scheduledExecutorService = scheduledExecutorService;
+    this.refreshInterval = refreshInterval;
+    this.clock = clock;
+  }
+
+  public boolean isVersionActive(final ClientPlatform platform, final Semver version) {
+    final Map<Semver, ClientRelease> releasesByVersion = clientReleasesByPlatform.get(platform);
+
+    return releasesByVersion != null &&
+        releasesByVersion.containsKey(version) &&
+        releasesByVersion.get(version).expiration().isAfter(clock.instant());
+  }
+
+  @Override
+  public void start() throws Exception {
+    refreshClientVersions();
+
+    refreshClientReleasesFuture =
+        scheduledExecutorService.scheduleWithFixedDelay(this::refreshClientVersions,
+            refreshInterval.toMillis(),
+            refreshInterval.toMillis(),
+            TimeUnit.MILLISECONDS);
+  }
+
+  @Override
+  public void stop() throws Exception {
+    if (refreshClientReleasesFuture != null) {
+      refreshClientReleasesFuture.cancel(true);
+    }
+  }
+
+  void refreshClientVersions() {
+    try {
+      clientReleasesByPlatform = clientReleases.getClientReleases();
+    } catch (final Exception e) {
+      logger.warn("Failed to refresh client releases", e);
+    }
+  }
+}