More clearly separate concerns for explicitly getting monitored objects.

service/src/main/java/org/whispersystems/textsecuregcm/util/S3ObjectMonitor.java

@@ -12,6 +12,7 @@ import com.amazonaws.services.s3.model.ObjectMetadata;
 import com.amazonaws.services.s3.model.S3Object;
 import com.google.common.annotations.VisibleForTesting;
 import io.dropwizard.lifecycle.Managed;
+import java.io.IOException;
 import java.time.Duration;
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.ScheduledFuture;
@@ -103,12 +104,33 @@ public class S3ObjectMonitor implements Managed {
   }
 
   /**
-   * Polls S3 for object metadata and notifies the listener provided at construction time if and only if the object has
-   * changed. This method blocks until S3 object metadata has been retrieved and, if the object has changed, the
-   * listener returns. Callers may wish to call this method at initialization time if they need data from the monitored
-   * S3 object immediately and don't want to wait for the first scheduled update.
+   * Immediately returns the monitored S3 object regardless of whether it has changed since it was last retrieved.
+   *
+   * @return the current version of the monitored S3 object
+   *
+   * @throws IOException if the retrieved S3 object is larger than the configured maximum size
    */
-  public void refresh() {
+  public S3Object getObject() throws IOException {
+    final S3Object s3Object = s3Client.getObject(s3Bucket, objectKey);
+
+    lastETag.set(s3Object.getObjectMetadata().getETag());
+
+    if (s3Object.getObjectMetadata().getContentLength() <= maxObjectSize) {
+      return s3Object;
+    } else {
+      log.warn("Object at s3://{}/{} has a size of {} bytes, which exceeds the maximum allowed size of {} bytes",
+          s3Bucket, objectKey, s3Object.getObjectMetadata().getContentLength(), maxObjectSize);
+
+      throw new IOException("S3 object too large");
+    }
+  }
+
+  /**
+   * Polls S3 for object metadata and notifies the listener provided at construction time if and only if the object has
+   * changed since the last call to {@link #getObject()} or {@code refresh()}.
+   */
+  @VisibleForTesting
+  void refresh() {
     try {
       final ObjectMetadata objectMetadata = s3Client.getObjectMetadata(s3Bucket, objectKey);
 
@@ -116,17 +138,12 @@ public class S3ObjectMonitor implements Managed {
       final String refreshedETag = objectMetadata.getETag();
 
       if (!StringUtils.equals(initialETag, refreshedETag) && lastETag.compareAndSet(initialETag, refreshedETag)) {
-        final S3Object s3Object = s3Client.getObject(s3Bucket, objectKey);
+        final S3Object s3Object = getObject();
 
         log.info("Object at s3://{}/{} has changed; new eTag is {} and object size is {} bytes",
             s3Bucket, objectKey, s3Object.getObjectMetadata().getETag(), s3Object.getObjectMetadata().getContentLength());
 
-        if (s3Object.getObjectMetadata().getContentLength() <= maxObjectSize) {
-          changeListener.accept(s3Object);
-        } else {
-          log.warn("Object at s3://{}/{} has a size of {} bytes, which exceeds the maximum allowed size of {} bytes",
-              s3Bucket, objectKey, s3Object.getObjectMetadata().getContentLength(), maxObjectSize);
-        }
+        changeListener.accept(s3Object);
       }
     } catch (final Exception e) {
       log.warn("Failed to refresh monitored object", e);

service/src/main/java/org/whispersystems/textsecuregcm/util/TorExitNodeManager.java

@@ -14,6 +14,7 @@ import io.micrometer.core.instrument.Counter;
 import io.micrometer.core.instrument.Metrics;
 import io.micrometer.core.instrument.Timer;
 import java.io.BufferedReader;
+import java.io.IOException;
 import java.io.InputStream;
 import java.io.InputStreamReader;
 import java.util.Collections;
@@ -57,7 +58,12 @@ public class TorExitNodeManager implements Managed {
 
   @Override
   public synchronized void start() {
-    exitListMonitor.refresh();
+    try {
+      handleExitListChanged(exitListMonitor.getObject());
+    } catch (final Exception e) {
+      log.warn("Failed to load initial Tor exit node list", e);
+    }
+
     exitListMonitor.start();
   }
 

service/src/test/java/org/whispersystems/textsecuregcm/util/S3ObjectMonitorTest.java

@@ -5,6 +5,7 @@ import com.amazonaws.services.s3.model.ObjectMetadata;
 import com.amazonaws.services.s3.model.S3Object;
 import org.junit.jupiter.api.Test;
 
+import java.io.IOException;
 import java.time.Duration;
 import java.util.UUID;
 import java.util.concurrent.ScheduledExecutorService;
@@ -50,6 +51,38 @@ class S3ObjectMonitorTest {
     verify(listener).accept(s3Object);
   }
 
+  @Test
+  void refreshAfterGet() throws IOException {
+    final AmazonS3 s3Client = mock(AmazonS3.class);
+    final ObjectMetadata metadata = mock(ObjectMetadata.class);
+    final S3Object s3Object = mock(S3Object.class);
+
+    final String bucket = "s3bucket";
+    final String objectKey = "greatest-smooth-jazz-hits-of-all-time.zip";
+
+    //noinspection unchecked
+    final Consumer<S3Object> listener = mock(Consumer.class);
+
+    final S3ObjectMonitor objectMonitor = new S3ObjectMonitor(
+        s3Client,
+        bucket,
+        objectKey,
+        16 * 1024 * 1024,
+        mock(ScheduledExecutorService.class),
+        Duration.ofMinutes(1),
+        listener);
+
+    when(metadata.getETag()).thenReturn(UUID.randomUUID().toString());
+    when(s3Object.getObjectMetadata()).thenReturn(metadata);
+    when(s3Client.getObjectMetadata(bucket, objectKey)).thenReturn(metadata);
+    when(s3Client.getObject(bucket, objectKey)).thenReturn(s3Object);
+
+    objectMonitor.getObject();
+    objectMonitor.refresh();
+
+    verify(listener, never()).accept(s3Object);
+  }
+
   @Test
   void refreshOversizedObject() {
     final AmazonS3 s3Client = mock(AmazonS3.class);