MIDI Manager: Remove message packetization from MIDI transport

Instead of attempting to package exactly one MIDI message in each call to
MidiReceiver.onPost(), we now pass messages as a raw stream of bytes.
This means we may now receive multiple MIDI messages in MidiReceiver.onPost().

We make this change to avoid the complexity of taking the single message approach
with SysEx and realtime messages. This shifts some of the burden of parsing
MIDI messages to the client application. But the parsing is best handled in the
application anyway, rather than having the framework impose its own policy
on how the messages are parsed.

Change-Id: Idb6c200037f827cc618bc7d9455a7aa864b494a7

1 files changed, 7 insertions, 24 deletions

diff --git a/services/usb/java/com/android/server/usb/UsbMidiDevice.java b/services/usb/java/com/android/server/usb/UsbMidiDevice.java
index 01b2df9..0ca52f6 100644
--- a/services/usb/java/com/android/server/usb/UsbMidiDevice.java
+++ b/services/usb/java/com/android/server/usb/UsbMidiDevice.java
@@ -21,9 +21,9 @@ import android.hardware.usb.UsbDevice;
 import android.midi.MidiDeviceInfo;
 import android.midi.MidiDeviceServer;
 import android.midi.MidiManager;
+import android.midi.MidiPort;
 import android.midi.MidiReceiver;
 import android.midi.MidiSender;
-import android.midi.MidiUtils;
 import android.os.Bundle;
 import android.system.ErrnoException;
 import android.system.Os;
@@ -45,7 +45,9 @@ public final class UsbMidiDevice implements Closeable {
 
     // for polling multiple FileDescriptors for MIDI events
     private final StructPollfd[] mPollFDs;
+    // streams for reading from ALSA driver
     private final FileInputStream[] mInputStreams;
+    // streams for writing to ALSA driver
     private final FileOutputStream[] mOutputStreams;
 
     public static UsbMidiDevice create(Context context, UsbDevice usbDevice, int card, int device) {
@@ -131,7 +133,7 @@ public final class UsbMidiDevice implements Closeable {
         new Thread() {
             @Override
             public void run() {
-                byte[] buffer = new byte[3];
+                byte[] buffer = new byte[MidiPort.MAX_PACKET_DATA_SIZE];
                 try {
                     boolean done = false;
                     while (!done) {
@@ -141,7 +143,8 @@ public final class UsbMidiDevice implements Closeable {
                             if ((pfd.revents & OsConstants.POLLIN) != 0) {
                                 // clear readable flag
                                 pfd.revents = 0;
-                                int count = readMessage(buffer, index);
+
+                                int count = mInputStreams[index].read(buffer);
                                 mOutputPortReceivers[index].onPost(buffer, 0, count,
                                         System.nanoTime());
                             } else if ((pfd.revents & (OsConstants.POLLERR
@@ -150,7 +153,7 @@ public final class UsbMidiDevice implements Closeable {
                             }
                         }
 
-                        // poll if none are readable
+                        // wait until we have a readable port
                         Os.poll(mPollFDs, -1 /* infinite timeout */);
                      }
                 } catch (IOException e) {
@@ -174,26 +177,6 @@ public final class UsbMidiDevice implements Closeable {
         }
     }
 
-    private int readMessage(byte[] buffer, int index) throws IOException {
-        FileInputStream inputStream = mInputStreams[index];
-
-        if (inputStream.read(buffer, 0, 1) != 1) {
-            Log.e(TAG, "could not read command byte");
-            return -1;
-        }
-        int dataSize = MidiUtils.getMessageDataSize(buffer[0]);
-        if (dataSize < 0) {
-            return -1;
-        }
-        if (dataSize > 0) {
-            if (inputStream.read(buffer, 1, dataSize) != dataSize) {
-                Log.e(TAG, "could not read command data");
-                return -1;
-            }
-        }
-        return dataSize + 1;
-    }
-
     private static native int nativeGetSubdeviceCount(int card, int device);
     private static native FileDescriptor[] nativeOpen(int card, int device, int subdeviceCount);
 }