shell/platform/android/io/flutter/plugin/common/BinaryMessenger.java

// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

package io.flutter.plugin.common;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.annotation.UiThread;
import java.nio.ByteBuffer;

/**
 * Facility for communicating with Flutter using asynchronous message passing with binary messages.
 * The Flutter Dart code should use <a
 * href="https://docs.flutter.io/flutter/services/BinaryMessages-class.html">BinaryMessages</a> to
 * participate.
 *
 * <p>{@code BinaryMessenger} is expected to be utilized from a single thread throughout the
 * duration of its existence. If created on the main thread, then all invocations should take place
 * on the main thread. If created on a background thread, then all invocations should take place on
 * that background thread.
 *
 * @see BasicMessageChannel , which supports message passing with Strings and semi-structured
 *     messages.
 * @see MethodChannel , which supports communication using asynchronous method invocation.
 * @see EventChannel , which supports communication using event streams.
 */
public interface BinaryMessenger {
  /**
   * Sends a binary message to the Flutter application.
   *
   * @param channel the name {@link String} of the logical channel used for the message.
   * @param message the message payload, a direct-allocated {@link ByteBuffer} with the message
   *     bytes between position zero and current position, or null.
   */
  @UiThread
  void send(@NonNull String channel, @Nullable ByteBuffer message);

  /**
   * Sends a binary message to the Flutter application, optionally expecting a reply.
   *
   * <p>Any uncaught exception thrown by the reply callback will be caught and logged.
   *
   * @param channel the name {@link String} of the logical channel used for the message.
   * @param message the message payload, a direct-allocated {@link ByteBuffer} with the message
   *     bytes between position zero and current position, or null.
   * @param callback a {@link BinaryReply} callback invoked when the Flutter application responds to
   *     the message, possibly null.
   */
  @UiThread
  void send(@NonNull String channel, @Nullable ByteBuffer message, @Nullable BinaryReply callback);

  /**
   * Registers a handler to be invoked when the Flutter application sends a message to its host
   * platform.
   *
   * <p>Registration overwrites any previous registration for the same channel name. Use a null
   * handler to deregister.
   *
   * <p>If no handler has been registered for a particular channel, any incoming message on that
   * channel will be handled silently by sending a null reply.
   *
   * @param channel the name {@link String} of the channel.
   * @param handler a {@link BinaryMessageHandler} to be invoked on incoming messages, or null.
   */
  @UiThread
  void setMessageHandler(@NonNull String channel, @Nullable BinaryMessageHandler handler);

  /** Handler for incoming binary messages from Flutter. */
  interface BinaryMessageHandler {
    /**
     * Handles the specified message.
     *
     * <p>Handler implementations must reply to all incoming messages, by submitting a single reply
     * message to the given {@link BinaryReply}. Failure to do so will result in lingering Flutter
     * reply handlers. The reply may be submitted asynchronously.
     *
     * <p>Any uncaught exception thrown by this method will be caught by the messenger
     * implementation and logged, and a null reply message will be sent back to Flutter.
     *
     * @param message the message {@link ByteBuffer} payload, possibly null.
     * @param reply A {@link BinaryReply} used for submitting a reply back to Flutter.
     */
    @UiThread
    void onMessage(@Nullable ByteBuffer message, @NonNull BinaryReply reply);
  }

  /**
   * Binary message reply callback. Used to submit a reply to an incoming message from Flutter. Also
   * used in the dual capacity to handle a reply received from Flutter after sending a message.
   */
  interface BinaryReply {
    /**
     * Handles the specified reply.
     *
     * @param reply the reply payload, a direct-allocated {@link ByteBuffer} or null. Senders of
     *     outgoing replies must place the reply bytes between position zero and current position.
     *     Reply receivers can read from the buffer directly.
     */
    @UiThread
    void reply(@Nullable ByteBuffer reply);
  }
}