Add RemovableDriveManager method.

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/file/RemovableDriveManager.java

@@ -1,6 +1,7 @@
 package org.briarproject.bramble.api.plugin.file;
 
 import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.properties.TransportProperties;
 
@@ -37,4 +38,9 @@ public interface RemovableDriveManager {
 	 * ignored.
 	 */
 	RemovableDriveTask startWriterTask(ContactId c, TransportProperties p);
+
+	/**
+	 * Returns true if there is anything to send to the given contact.
+	 */
+	boolean isWriterTaskNeeded(ContactId c) throws DbException;
 }

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/RemovableDriveManagerImpl.java

@@ -1,6 +1,8 @@
 package org.briarproject.bramble.plugin.file;
 
 import org.briarproject.bramble.api.contact.ContactId;
+import org.briarproject.bramble.api.db.DatabaseComponent;
+import org.briarproject.bramble.api.db.DbException;
 import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.file.RemovableDriveManager;
@@ -14,12 +16,15 @@ import javax.annotation.concurrent.GuardedBy;
 import javax.annotation.concurrent.ThreadSafe;
 import javax.inject.Inject;
 
+import static org.briarproject.bramble.plugin.file.RemovableDrivePluginFactory.MAX_LATENCY;
+
 @ThreadSafe
 @NotNullByDefault
 class RemovableDriveManagerImpl
 		implements RemovableDriveManager, RemovableDriveTaskRegistry {
 
 	private final Executor ioExecutor;
+	private final DatabaseComponent db;
 	private final RemovableDriveTaskFactory taskFactory;
 	private final Object lock = new Object();
 
@@ -30,8 +35,9 @@ class RemovableDriveManagerImpl
 
 	@Inject
 	RemovableDriveManagerImpl(@IoExecutor Executor ioExecutor,
-			RemovableDriveTaskFactory taskFactory) {
+			DatabaseComponent db, RemovableDriveTaskFactory taskFactory) {
 		this.ioExecutor = ioExecutor;
+		this.db = db;
 		this.taskFactory = taskFactory;
 	}
 
@@ -74,6 +80,12 @@ class RemovableDriveManagerImpl
 		return created;
 	}
 
+	@Override
+	public boolean isWriterTaskNeeded(ContactId c) throws DbException {
+		return db.transactionWithResult(true, txn ->
+				db.containsAnythingToSend(txn, c, MAX_LATENCY, true));
+	}
+
 	@Override
 	public void removeReader(RemovableDriveTask task) {
 		synchronized (lock) {

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/RemovableDrivePluginFactory.java

@@ -17,7 +17,7 @@ import static org.briarproject.bramble.api.plugin.file.RemovableDriveConstants.I
 @NotNullByDefault
 public class RemovableDrivePluginFactory implements SimplexPluginFactory {
 
-	private static final int MAX_LATENCY = (int) DAYS.toMillis(14);
+	static final int MAX_LATENCY = (int) DAYS.toMillis(14);
 
 	@Inject
 	RemovableDrivePluginFactory() {