RFR: 8074211: javax.sound.midi: Error with send System Exclusive messages of different length

[Florian Bomers]

Interesting!
I've reviewed this fix, it looks good to me.

For drivers that send Sys-Ex asynchronously, the dwBufferLength field 
/might /be read after the code sets it back to the temporary variable 
bufferLength. Trying to account for that would be much more work... 
But this fix will improve matters in any case.

Florian


On 27.10.2023 13:51, null wrote:
> JVM attempts to reuse the buffer for sending MIDI out data when the buffer size is enough. It use `dwBytesRecorded` in `MIDIHDR` structure to indicate the actual size of the data. However, `midiOutLongMsg()` ignores `dwBytesRecorded`, although it did not mentioned in the documentation. I've tested on Windows 7, 10 and 11. All of them have the same behavior.
>
> The bug cannot be easily reproduced because some MIDI drivers filter out any malformed MIDI data. The example code below create a special case to make sure all MIDI data are legally when the bug is triggered.
>
>
> import javax.sound.midi.*;
>
> public class MidiTest {
>      public static class RawMidiMessage extends MidiMessage {
>          public RawMidiMessage(byte[] data) {
>              super(data);
>          }
>
>          @Override
>          public Object clone() {
>              return new RawMidiMessage(this.getMessage());
>          }
>      }
>
>      public static void main(String[] args) {
>          var deviceInfos = MidiSystem.getMidiDeviceInfo();
>          for (var info : deviceInfos) {
>              try (MidiDevice device = MidiSystem.getMidiDevice(info)) {
>                  if (device.getMaxReceivers() != 0) {
>                      System.out.println("Open MIDI port: " + info.getName());
>                      device.open();
>                      Receiver receiver = device.getReceiver();
>                      // Send two sysex messages at once
>                      receiver.send(new RawMidiMessage(new byte[]{
>                              (byte) 0xF0, 0x7D, 0x01, (byte) 0xF7,
>                              (byte) 0xF0, 0x7D, 0x02, (byte) 0xF7
>                          }), -1);
>                      // Send another sysex message
>                      receiver.send(new RawMidiMessage(new byte[]{(byte) 0xF0, 0x7D, 0x03, (byte) 0xF7}), -1);
>                  }
>              } catch (MidiUnavailableException e) {
>                  e.printStackTrace();
>              }
>          }
>      }
> }
>
>
> The expected messages received should be the following three messages
>
> F0 7D 01 F7
> F0 7D 02 F7
> F0 7D 03 F7
>
>
> But acually four messages was received with the second message repeated twice.
>
> F0 7D 01 F7
> F0 7D 02 F7
> F0 7D 03 F7
> F0 7D 02 F7
>
>
> To resolve the issue, I add a new variable to backup the actual buffer size and set `dwBufferLength` of `MIDIHDR` structure to the size of MIDI data. After calling `midiOutLongMsg()`, I restore the original buffer size if the buffer hasn't been freed due to an error.
>
> It seems that the patch may also resolve JDK-8250667. The extra bytes in the second sysex message is the same issue as JDK-8074211. I didn't figure out how the scrambled data generated in the third sysex message, but all the messages are correct after applying the patch.
>
> -------------
>
> Commit messages:
>   - Resolve the message size issue when sending SysexMessage on Windows
>
> Changes:https://git.openjdk.org/jdk/pull/16399/files
>   Webrev:https://webrevs.openjdk.org/?repo=jdk&pr=16399&range=00
>    Issue:https://bugs.openjdk.org/browse/JDK-8074211
>    Stats: 7 lines in 1 file changed: 6 ins; 0 del; 1 mod
>    Patch:https://git.openjdk.org/jdk/pull/16399.diff
>    Fetch: git fetchhttps://git.openjdk.org/jdk.git  pull/16399/head:pull/16399
>
> PR:https://git.openjdk.org/jdk/pull/16399

-- 
Florian Bomers
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