MidiPortImpl.java revision eebc98ff18c1ee92dff3fcd505158ea161d552be 
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
17package android.media.midi;
18
19/**
20 * This class contains utilities for socket communication between a
21 * MidiInputPort and MidiOutputPort
22 */
23/* package */ class MidiPortImpl {
24    private static final String TAG = "MidiPort";
25
26    /**
27     * Maximum size of a packet that can pass through our ParcelFileDescriptor.
28     */
29    public static final int MAX_PACKET_SIZE = 1024;
30
31    /**
32     * size of message timestamp in bytes
33     */
34    private static final int TIMESTAMP_SIZE = 8;
35
36    /**
37     * Maximum amount of MIDI data that can be included in a packet
38     */
39    public static final int MAX_PACKET_DATA_SIZE = MAX_PACKET_SIZE - TIMESTAMP_SIZE;
40
41    /**
42     * Utility function for packing a MIDI message to be sent through our ParcelFileDescriptor
43     *
44     * message byte array contains variable length MIDI message.
45     * messageSize is size of variable length MIDI message
46     * timestamp is message timestamp to pack
47     * dest is buffer to pack into
48     * returns size of packed message
49     */
50    public static int packMessage(byte[] message, int offset, int size, long timestamp,
51            byte[] dest) {
52        if (size + TIMESTAMP_SIZE > MAX_PACKET_SIZE) {
53            size = MAX_PACKET_SIZE - TIMESTAMP_SIZE;
54        }
55        // message data goes first
56        System.arraycopy(message, offset, dest, 0, size);
57
58        // followed by timestamp
59        for (int i = 0; i < TIMESTAMP_SIZE; i++) {
60            dest[size++] = (byte)timestamp;
61            timestamp >>= 8;
62        }
63
64        return size;
65    }
66
67    /**
68     * Utility function for unpacking a MIDI message received from our ParcelFileDescriptor
69     * returns the offset of the MIDI message in packed buffer
70     */
71    public static int getMessageOffset(byte[] buffer, int bufferLength) {
72        // message is at the beginning
73        return 0;
74    }
75
76    /**
77     * Utility function for unpacking a MIDI message received from our ParcelFileDescriptor
78     * returns size of MIDI data in packed buffer
79     */
80    public static int getMessageSize(byte[] buffer, int bufferLength) {
81        // message length is total buffer length minus size of the timestamp
82        return bufferLength - TIMESTAMP_SIZE;
83    }
84
85    /**
86     * Utility function for unpacking a MIDI message received from our ParcelFileDescriptor
87     * unpacks timestamp from packed buffer
88     */
89    public static long getMessageTimeStamp(byte[] buffer, int bufferLength) {
90        // timestamp is at end of the packet
91        int offset = bufferLength;
92        long timestamp = 0;
93
94        for (int i = 0; i < TIMESTAMP_SIZE; i++) {
95            int b = (int)buffer[--offset] & 0xFF;
96            timestamp = (timestamp << 8) | b;
97        }
98        return timestamp;
99    }
100}
101