Replace Supplier<Boolean> with more legible ApiCall interface.

bramble-api/src/main/java/org/briarproject/bramble/api/Supplier.java

@@ -1,9 +0,0 @@
-package org.briarproject.bramble.api;
-
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-
-@NotNullByDefault
-public interface Supplier<T> {
-
-	T get();
-}

bramble-core/src/main/java/org/briarproject/bramble/mailbox/ApiCall.java

@@ -0,0 +1,21 @@
+package org.briarproject.bramble.mailbox;
+
+import org.briarproject.bramble.api.lifecycle.IoExecutor;
+import org.briarproject.bramble.mailbox.MailboxApi.TolerableFailureException;
+
+/**
+ * An interface for calling an API endpoint with the option to retry the call.
+ */
+interface ApiCall {
+
+	/**
+	 * This method makes a synchronous call to an API endpoint and returns
+	 * true if the call should be retried, in which case the method may be
+	 * called again on the same {@link ApiCall} instance after a delay.
+	 *
+	 * @return True if the API call needs to be retried, or false if the API
+	 * call succeeded or {@link TolerableFailureException failed tolerably}.
+	 */
+	@IoExecutor
+	boolean callApi();
+}

bramble-core/src/main/java/org/briarproject/bramble/mailbox/MailboxApiCaller.java

@@ -1,10 +1,8 @@
 package org.briarproject.bramble.mailbox;
 
 import org.briarproject.bramble.api.Cancellable;
-import org.briarproject.bramble.api.Supplier;
 import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.mailbox.MailboxApi.TolerableFailureException;
 
 import static java.util.concurrent.TimeUnit.DAYS;
 import static java.util.concurrent.TimeUnit.MINUTES;
@@ -23,15 +21,12 @@ interface MailboxApiCaller {
 	long MAX_RETRY_INTERVAL_MS = DAYS.toMillis(1);
 
 	/**
-	 * Asynchronously calls the given supplier, automatically retrying at
+	 * Asynchronously calls the given API call on the {@link IoExecutor},
-	 * increasing intervals until the supplier returns false. The returned
+	 * automatically retrying at increasing intervals until the API call
-	 * {@link Cancellable} can be used to cancel any future retries.
+	 * returns false or retries are cancelled.
 	 *
-	 * @param supplier A wrapper for an API call. The supplier's
+	 * @return A {@link Cancellable} that can be used to cancel any future
-	 * {@link Supplier#get() get()} method will be called on the
+	 * retries.
-	 * {@link IoExecutor}. It should return true if the API call needs to be
-	 * retried, or false if the API call succeeded or
-	 * {@link TolerableFailureException failed tolerably}.
 	 */
-	Cancellable retryWithBackoff(Supplier<Boolean> supplier);
+	Cancellable retryWithBackoff(ApiCall apiCall);
 }

bramble-core/src/main/java/org/briarproject/bramble/mailbox/MailboxApiCallerImpl.java

@@ -1,7 +1,6 @@
 package org.briarproject.bramble.mailbox;
 
 import org.briarproject.bramble.api.Cancellable;
-import org.briarproject.bramble.api.Supplier;
 import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.system.TaskScheduler;
@@ -31,15 +30,15 @@ class MailboxApiCallerImpl implements MailboxApiCaller {
 	}
 
 	@Override
-	public Cancellable retryWithBackoff(Supplier<Boolean> supplier) {
+	public Cancellable retryWithBackoff(ApiCall apiCall) {
-		Task task = new Task(supplier);
+		Task task = new Task(apiCall);
 		task.start();
 		return task;
 	}
 
 	private class Task implements Cancellable {
 
-		private final Supplier<Boolean> supplier;
+		private final ApiCall apiCall;
 		private final Object lock = new Object();
 
 		@GuardedBy("lock")
@@ -52,8 +51,8 @@ class MailboxApiCallerImpl implements MailboxApiCaller {
 		@GuardedBy("lock")
 		private long retryIntervalMs = MIN_RETRY_INTERVAL_MS;
 
-		private Task(Supplier<Boolean> supplier) {
+		private Task(ApiCall apiCall) {
-			this.supplier = supplier;
+			this.apiCall = apiCall;
 		}
 
 		private void start() {
@@ -68,8 +67,8 @@ class MailboxApiCallerImpl implements MailboxApiCaller {
 			synchronized (lock) {
 				if (cancelled) return;
 			}
-			// The supplier returns true if we should retry
+			// The call returns true if we should retry
-			if (supplier.get()) {
+			if (apiCall.callApi()) {
 				synchronized (lock) {
 					if (cancelled) return;
 					scheduledTask = taskScheduler.schedule(this::callApi,

bramble-core/src/main/java/org/briarproject/bramble/mailbox/SimpleApiCall.java

@@ -1,6 +1,5 @@
 package org.briarproject.bramble.mailbox;
 
-import org.briarproject.bramble.api.Supplier;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.mailbox.MailboxApi.ApiException;
 import org.briarproject.bramble.mailbox.MailboxApi.TolerableFailureException;
@@ -17,17 +16,17 @@ import static org.briarproject.bramble.util.LogUtils.logException;
  * Convenience class for making simple API calls that don't return values.
  */
 @NotNullByDefault
-public abstract class SimpleApiCall implements Supplier<Boolean> {
+public abstract class SimpleApiCall implements ApiCall {
 
 	private static final Logger LOG = getLogger(SimpleApiCall.class.getName());
 
-	abstract void callApi()
+	abstract void tryToCallApi()
 			throws IOException, ApiException, TolerableFailureException;
 
 	@Override
-	public Boolean get() {
+	public boolean callApi() {
 		try {
-			callApi();
+			tryToCallApi();
 			return false; // Succeeded, don't retry
 		} catch (IOException | ApiException e) {
 			logException(LOG, WARNING, e);

bramble-core/src/test/java/org/briarproject/bramble/mailbox/MailboxApiCallerImplTest.java

@@ -1,7 +1,6 @@
 package org.briarproject.bramble.mailbox;
 
 import org.briarproject.bramble.api.Cancellable;
-import org.briarproject.bramble.api.Supplier;
 import org.briarproject.bramble.api.system.TaskScheduler;
 import org.briarproject.bramble.test.BrambleMockTestCase;
 import org.briarproject.bramble.test.CaptureArgumentAction;
@@ -23,8 +22,7 @@ public class MailboxApiCallerImplTest extends BrambleMockTestCase {
 	private final TaskScheduler taskScheduler =
 			context.mock(TaskScheduler.class);
 	private final Executor ioExecutor = context.mock(Executor.class);
-	private final BooleanSupplier supplier =
+	private final ApiCall apiCall = context.mock(ApiCall.class);
-			context.mock(BooleanSupplier.class);
 	private final Cancellable scheduledTask = context.mock(Cancellable.class);
 
 	private final MailboxApiCallerImpl caller =
@@ -39,12 +37,12 @@ public class MailboxApiCallerImplTest extends BrambleMockTestCase {
 			will(new CaptureArgumentAction<>(runnable, Runnable.class, 0));
 		}});
 
-		caller.retryWithBackoff(supplier);
+		caller.retryWithBackoff(apiCall);
 
-		// When the task runs, the supplier should be called. The supplier
+		// When the task runs, the API call should be called. The call
 		// returns false, so no retries should be scheduled
 		context.checking(new Expectations() {{
-			oneOf(supplier).get();
+			oneOf(apiCall).callApi();
 			will(returnValue(false));
 		}});
 
@@ -60,12 +58,12 @@ public class MailboxApiCallerImplTest extends BrambleMockTestCase {
 			will(new CaptureArgumentAction<>(runnable, Runnable.class, 0));
 		}});
 
-		Cancellable returned = caller.retryWithBackoff(supplier);
+		Cancellable returned = caller.retryWithBackoff(apiCall);
 
-		// When the task runs, the supplier should be called. The supplier
+		// When the task runs, the API call should be called. The call
 		// returns true, so a retry should be scheduled
 		context.checking(new Expectations() {{
-			oneOf(supplier).get();
+			oneOf(apiCall).callApi();
 			will(returnValue(true));
 			oneOf(taskScheduler).schedule(with(any(Runnable.class)),
 					with(ioExecutor), with(MIN_RETRY_INTERVAL_MS),
@@ -90,7 +88,7 @@ public class MailboxApiCallerImplTest extends BrambleMockTestCase {
 		returned.cancel();
 
 		// If the scheduled task runs anyway (cancellation came too late),
-		// the supplier should not be called and no further tries should be
+		// the API call should not be called and no further tries should be
 		// scheduled
 		runnable.get().run();
 	}
@@ -114,13 +112,13 @@ public class MailboxApiCallerImplTest extends BrambleMockTestCase {
 			will(new CaptureArgumentAction<>(runnable, Runnable.class, 0));
 		}});
 
-		caller.retryWithBackoff(supplier);
+		caller.retryWithBackoff(apiCall);
 
-		// Each time the task runs, the supplier returns true, so a retry
+		// Each time the task runs, the API call returns true, so a retry
 		// should be scheduled with a longer interval
 		for (long interval : expectedIntervals) {
 			context.checking(new Expectations() {{
-				oneOf(supplier).get();
+				oneOf(apiCall).callApi();
 				will(returnValue(true));
 				oneOf(taskScheduler).schedule(with(any(Runnable.class)),
 						with(ioExecutor), with(interval), with(MILLISECONDS));
@@ -134,8 +132,4 @@ public class MailboxApiCallerImplTest extends BrambleMockTestCase {
 			runnable.get().run();
 		}
 	}
-
-	// Reify the generic type to mollify jMock
-	private interface BooleanSupplier extends Supplier<Boolean> {
-	}
 }