PhotonVision hit an array out of bound exception with 2026.2.2

[trc492]

Console log and stack dump below. It looks like an off-by-one error (i.e. length instead of length - 1).

Error at org.photonvision.common.dataflow.structures.Packet.decodeByte(Packet.java:297): Unhandled exception: java.lang.ArrayIndexOutOfBoundsException: Index 34 out of bounds for length 34
The robot program quit unexpectedly. This is usually due to a code error.
The above stacktrace can help determine where the error occurred.
See https://wpilib.org/stacktrace for more information.
   from: edu.wpi.first.wpilibj.RobotBase.runRobot(RobotBase.java:450)

The startCompetition() method (or methods called by it) should have handled the exception above.
at org.photonvision.common.dataflow.structures.Packet.decodeByte(Packet.java:297)
at org.photonvision.common.dataflow.structures.Packet.decodeList(Packet.java:413)
at org.photonvision.struct.PhotonPipelineResultSerde.unpack(PhotonPipelineResultSerde.java:78)
at org.photonvision.struct.PhotonPipelineResultSerde.unpack(PhotonPipelineResultSerde.java:43)
at org.photonvision.common.networktables.PacketSubscriber.parse(PacketSubscriber.java:66)
at org.photonvision.common.networktables.PacketSubscriber.getAllChanges(PacketSubscriber.java:110)
at org.photonvision.PhotonCamera.getAllUnreadResults(PhotonCamera.java:262)
at frclib.vision.FrcPhotonVision.getRobotEstimatedInfo(FrcPhotonVision.java:746)
at frclib.drivebase.FrcSwerveDrive.visionUpdate(FrcSwerveDrive.java:171)
at teamcode.Robot.robotPeriodic(Robot.java:400)
at frclib.robotcore.FrcRobot.startCompetition(FrcRobot.java:581)
at edu.wpi.first.wpilibj.RobotBase.runRobot(RobotBase.java:436)
at edu.wpi.first.wpilibj.RobotBase.startRobot(RobotBase.java:527)
at teamcode.Main.main(Main.java:33)
Warning at edu.wpi.first.wpilibj.RobotBase.runRobot(RobotBase.java:450): The robot program quit unexpectedly. This is usually due to a code error.
The above stacktrace can help determine where the error occurred.
See https://wpilib.org/stacktrace for more information.
Error at edu.wpi.first.wpilibj.RobotBase.runRobot(RobotBase.java:457): The startCompetition() method (or methods called by it) should have handled the exception above.```

[crschardt]

Can you share the code that triggered this crash?

[trc492]

In the file: https://github.com/PhotonVision/photonvision/blob/main/photon-targeting/src/main/java/org/photonvision/common/dataflow/structures/Packet.java
The comparison should be:
if (readPos >= packetData.length)

With the current code, if readPos is exactly packetData.length, it will blow up with array out of bound.

/**
* Returns a decoded byte from the packet.
*
* @return A decoded byte from the packet.
*/
public byte decodeByte() {
if (packetData.length < readPos) {
return '\0';
}
return packetData[readPos++];
}

[Gold856]

at org.photonvision.struct.PhotonPipelineResultSerde.unpack(PhotonPipelineResultSerde.java:43) is highly sus. That's just the beginning of the class...