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      1 /*
      2  * Copyright (C) 2014 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package android.media.midi;
     18 
     19 import java.io.IOException;
     20 
     21 /**
     22  * Interface for sending and receiving data to and from a MIDI device.
     23  */
     24 abstract public class MidiReceiver {
     25 
     26     private final int mMaxMessageSize;
     27 
     28     /**
     29      * Default MidiReceiver constructor. Maximum message size is set to
     30      * {@link java.lang.Integer#MAX_VALUE}
     31      */
     32     public MidiReceiver() {
     33         mMaxMessageSize = Integer.MAX_VALUE;
     34     }
     35 
     36     /**
     37      * MidiReceiver constructor.
     38      * @param maxMessageSize the maximum size of a message this receiver can receive
     39      */
     40     public MidiReceiver(int maxMessageSize) {
     41         mMaxMessageSize = maxMessageSize;
     42     }
     43 
     44     /**
     45      * Called whenever the receiver is passed new MIDI data.
     46      * Subclasses override this method to receive MIDI data.
     47      * May fail if count exceeds {@link #getMaxMessageSize}.
     48      *
     49      * NOTE: the msg array parameter is only valid within the context of this call.
     50      * The msg bytes should be copied by the receiver rather than retaining a reference
     51      * to this parameter.
     52      * Also, modifying the contents of the msg array parameter may result in other receivers
     53      * in the same application receiving incorrect values in their {link #onSend} method.
     54      *
     55      * @param msg a byte array containing the MIDI data
     56      * @param offset the offset of the first byte of the data in the array to be processed
     57      * @param count the number of bytes of MIDI data in the array to be processed
     58      * @param timestamp the timestamp of the message (based on {@link java.lang.System#nanoTime}
     59      * @throws IOException
     60      */
     61     abstract public void onSend(byte[] msg, int offset, int count, long timestamp)
     62             throws IOException;
     63 
     64     /**
     65      * Instructs the receiver to discard all pending MIDI data.
     66      * @throws IOException
     67      */
     68     public void flush() throws IOException {
     69         onFlush();
     70     }
     71 
     72     /**
     73      * Called when the receiver is instructed to discard all pending MIDI data.
     74      * Subclasses should override this method if they maintain a list or queue of MIDI data
     75      * to be processed in the future.
     76      * @throws IOException
     77      */
     78     public void onFlush() throws IOException {
     79     }
     80 
     81     /**
     82      * Returns the maximum size of a message this receiver can receive.
     83      * @return maximum message size
     84      */
     85     public final int getMaxMessageSize() {
     86         return mMaxMessageSize;
     87     }
     88 
     89     /**
     90      * Called to send MIDI data to the receiver without a timestamp.
     91      * Data will be processed by receiver in the order sent.
     92      * Data will get split into multiple calls to {@link #onSend} if count exceeds
     93      * {@link #getMaxMessageSize}.  Blocks until all the data is sent or an exception occurs.
     94      * In the latter case, the amount of data sent prior to the exception is not provided to caller.
     95      * The communication should be considered corrupt.  The sender should reestablish
     96      * communication, reset all controllers and send all notes off.
     97      *
     98      * @param msg a byte array containing the MIDI data
     99      * @param offset the offset of the first byte of the data in the array to be sent
    100      * @param count the number of bytes of MIDI data in the array to be sent
    101      * @throws IOException if the data could not be sent in entirety
    102      */
    103     public void send(byte[] msg, int offset, int count) throws IOException {
    104         // TODO add public static final TIMESTAMP_NONE = 0L
    105         send(msg, offset, count, 0L);
    106     }
    107 
    108     /**
    109      * Called to send MIDI data to the receiver with a specified timestamp.
    110      * Data will be processed by receiver in order first by timestamp, then in the order sent.
    111      * Data will get split into multiple calls to {@link #onSend} if count exceeds
    112      * {@link #getMaxMessageSize}.  Blocks until all the data is sent or an exception occurs.
    113      * In the latter case, the amount of data sent prior to the exception is not provided to caller.
    114      * The communication should be considered corrupt.  The sender should reestablish
    115      * communication, reset all controllers and send all notes off.
    116      *
    117      * @param msg a byte array containing the MIDI data
    118      * @param offset the offset of the first byte of the data in the array to be sent
    119      * @param count the number of bytes of MIDI data in the array to be sent
    120      * @param timestamp the timestamp of the message, based on {@link java.lang.System#nanoTime}
    121      * @throws IOException if the data could not be sent in entirety
    122      */
    123     public void send(byte[] msg, int offset, int count, long timestamp)
    124             throws IOException {
    125         int messageSize = getMaxMessageSize();
    126         while (count > 0) {
    127             int length = (count > messageSize ? messageSize : count);
    128             onSend(msg, offset, length, timestamp);
    129             offset += length;
    130             count -= length;
    131         }
    132     }
    133 }
    134