135 lines
4.1 KiB
Java
135 lines
4.1 KiB
Java
/*
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* Copyright (C) 2014 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package android.media.midi;
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/**
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* This class contains utilities for socket communication between a
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* MidiInputPort and MidiOutputPort
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*/
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/* package */ class MidiPortImpl {
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private static final String TAG = "MidiPort";
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/**
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* Packet type for data packet
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*/
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public static final int PACKET_TYPE_DATA = 1;
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/**
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* Packet type for flush packet
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*/
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public static final int PACKET_TYPE_FLUSH = 2;
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/**
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* Maximum size of a packet that can be passed between processes.
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*/
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public static final int MAX_PACKET_SIZE = 1024;
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/**
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* size of message timestamp in bytes
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*/
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private static final int TIMESTAMP_SIZE = 8;
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/**
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* Data packet overhead is timestamp size plus packet type byte
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*/
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private static final int DATA_PACKET_OVERHEAD = TIMESTAMP_SIZE + 1;
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/**
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* Maximum amount of MIDI data that can be included in a packet
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*/
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public static final int MAX_PACKET_DATA_SIZE = MAX_PACKET_SIZE - DATA_PACKET_OVERHEAD;
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/**
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* Utility function for packing MIDI data to be passed between processes
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*
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* message byte array contains variable length MIDI message.
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* messageSize is size of variable length MIDI message
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* timestamp is message timestamp to pack
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* dest is buffer to pack into
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* returns size of packed message
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*/
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public static int packData(byte[] message, int offset, int size, long timestamp,
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byte[] dest) {
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if (size > MAX_PACKET_DATA_SIZE) {
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size = MAX_PACKET_DATA_SIZE;
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}
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int length = 0;
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// packet type goes first
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dest[length++] = PACKET_TYPE_DATA;
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// data goes next
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System.arraycopy(message, offset, dest, length, size);
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length += size;
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// followed by timestamp
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for (int i = 0; i < TIMESTAMP_SIZE; i++) {
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dest[length++] = (byte)timestamp;
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timestamp >>= 8;
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}
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return length;
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}
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/**
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* Utility function for packing a flush command to be passed between processes
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*/
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public static int packFlush(byte[] dest) {
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dest[0] = PACKET_TYPE_FLUSH;
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return 1;
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}
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/**
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* Returns the packet type (PACKET_TYPE_DATA or PACKET_TYPE_FLUSH)
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*/
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public static int getPacketType(byte[] buffer, int bufferLength) {
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return buffer[0];
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}
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/**
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* Utility function for unpacking MIDI data received from other process
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* returns the offset of the MIDI message in packed buffer
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*/
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public static int getDataOffset(byte[] buffer, int bufferLength) {
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// data follows packet type byte
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return 1;
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}
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/**
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* Utility function for unpacking MIDI data received from other process
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* returns size of MIDI data in packed buffer
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*/
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public static int getDataSize(byte[] buffer, int bufferLength) {
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// message length is total buffer length minus size of the timestamp
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return bufferLength - DATA_PACKET_OVERHEAD;
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}
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/**
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* Utility function for unpacking MIDI data received from other process
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* unpacks timestamp from packed buffer
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*/
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public static long getPacketTimestamp(byte[] buffer, int bufferLength) {
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// timestamp is at end of the packet
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int offset = bufferLength;
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long timestamp = 0;
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for (int i = 0; i < TIMESTAMP_SIZE; i++) {
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int b = (int)buffer[--offset] & 0xFF;
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timestamp = (timestamp << 8) | b;
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}
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return timestamp;
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}
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}
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