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Add struct packing/unpacking utility class
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3 files changed

+281
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‎app/src/main/java/io/github/cloudcutter/work/common/ByteStruct.kt‎

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/*
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* Copyright (c) Kuba Szczodrzyński 2022-12-19.
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*/
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package io.github.cloudcutter.work.common
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abstract class ByteStruct {
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abstract fun getValues(): List<Any>
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fun getFormat(): String =
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this::class.java.getAnnotation(ByteStructFormat::class.java)!!.format
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companion object {
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inline fun <reified T : ByteStruct> unpack(data: ByteArray, mode: Int = 0) =
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unpackImpl(data, T::class.java, mode)
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fun pack(data: ByteStruct, mode: Int = 0): ByteArray {
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val cls = data::class.java
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// retrieve child type annotations
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val childTypeMap = cls.getAnnotation(ByteStructChildMap::class.java)?.map?.filter {
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it.mode == mode
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}
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// retrieve format string and get struct values
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val formatString = cls.getAnnotation(ByteStructFormat::class.java)!!.format
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val values = data.getValues().toMutableList()
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// update child type fields
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for ((index, value) in values.withIndex()) {
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if (value is String) {
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values[index] = value.toByteArray()
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continue
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}
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if (value !is ByteStruct)
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continue
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values[index] = pack(value)
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val annotation = childTypeMap?.firstOrNull {
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index == it.dataFieldIndex && value::class == it.dataFieldClass
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} ?: continue
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values[annotation.typeFieldIndex] = annotation.typeFieldValue
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}
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return Struct.pack(formatString, values)
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}
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fun <T : ByteStruct> unpackImpl(data: ByteArray, cls: Class<T>, mode: Int = 0): T {
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// retrieve child type annotations
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val childTypeMap = cls.getAnnotation(ByteStructChildMap::class.java)?.map?.filter {
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it.mode == mode
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}
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// retrieve format string and unpack the struct
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val formatString = cls.getAnnotation(ByteStructFormat::class.java)!!.format
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val values = Struct.unpack(formatString, data).toMutableList()
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// deserialize all child ByteStruct fields
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val constructor = cls.constructors.first()
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for ((index, type) in constructor.parameterTypes.withIndex()) {
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if (String::class.java.isAssignableFrom(type)) {
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values[index] = (values[index] as ByteArray).decodeToString()
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continue
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}
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if (!ByteStruct::class.java.isAssignableFrom(type))
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continue
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val annotation = childTypeMap?.firstOrNull {
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index == it.dataFieldIndex && values[it.typeFieldIndex] == it.typeFieldValue
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}
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val childType = annotation?.dataFieldClass?.java ?: type
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values[index] = unpackImpl(values[index] as ByteArray, childType as Class<T>)
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}
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return constructor.newInstance(*values.toTypedArray()) as T
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}
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}
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}

‎app/src/main/java/io/github/cloudcutter/work/common/ByteStructUtils.kt‎

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/*
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* Copyright (c) Kuba Szczodrzyński 2022-12-19.
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*/
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package io.github.cloudcutter.work.common
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import kotlin.reflect.KClass
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annotation class ByteStructFormat(
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val format: String,
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)
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annotation class ByteStructChild(
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val typeFieldIndex: Int,
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val typeFieldValue: Int,
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val dataFieldIndex: Int,
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val dataFieldClass: KClass<out ByteStruct>,
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val mode: Int = 0,
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)
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annotation class ByteStructChildMap(
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vararg val map: ByteStructChild,
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)

‎app/src/main/java/io/github/cloudcutter/work/common/Struct.kt‎

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/*
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* Copyright (c) Kuba Szczodrzyński 2022-12-19.
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*/
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package io.github.cloudcutter.work.common
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import java.nio.ByteBuffer
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import java.nio.ByteOrder
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object Struct {
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private fun String.getEndianness() = when (this[0]) {
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'<' -> ByteOrder.LITTLE_ENDIAN
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'>', '!' -> ByteOrder.BIG_ENDIAN
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else -> ByteOrder.nativeOrder()
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}
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private fun String.getFormatList() = this
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.replace(" ", "")
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.replace("""(\d+[^s\d])""".toRegex()) {
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it.value
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.last()
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.toString()
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.repeat(it.value.dropLast(1).toInt())
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}
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.replace("""\$\d+s|\d+s""".toRegex()) { " ${it.value} " }
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.split(" ")
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.filter { it.isNotBlank() }
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.flatMap { if (it.last() == 's') listOf(it) else it.split("") }
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.map { if (it == "s") "1s" else it }
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.filter { it.isNotBlank() }
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.dropWhile { it[0] in "@=<>!" }
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private fun getLengthFields(format: List<String>): Map<Int, Int> {
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// Map<length field, data field>
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val lengthFields = mutableMapOf<Int, Int>()
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// find all dynamically-sized strings
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var nullCount = 0
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for ((index, field) in format.withIndex()) {
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if (field == "x") {
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nullCount++
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continue
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}
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if (!field.startsWith("$"))
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continue
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val fieldIndex = field.drop(1).dropLast(1).toInt()
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lengthFields[fieldIndex] = index - nullCount
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}
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return lengthFields
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}
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fun pack(formatString: String, valuesRaw: List<Any>): ByteArray {
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val endianness = formatString.getEndianness()
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val format = formatString.getFormatList()
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val lengthFields = getLengthFields(format)
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// replace 'length fields' with actual length
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val values = valuesRaw.mapIndexed { index, value ->
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if (index in lengthFields)
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(valuesRaw[lengthFields[index] ?: 0] as ByteArray).size
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else
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value
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}
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var nullCount = 0
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val totalLength = format.mapIndexed { index, field ->
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if (field == "x")
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nullCount++
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when (field.last()) {
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'x' -> 1
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'c', 'b', 'B' -> 1
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'?' -> 1
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'h', 'H' -> 2
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'i', 'I' -> 4
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'l', 'L' -> 4
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'q', 'Q' -> 8
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'f' -> 4
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'd' -> 8
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's' -> if (field[0] == '$')
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(values[index - nullCount] as ByteArray).size
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else
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field.dropLast(1).toInt()
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'S' -> (values[index - nullCount] as ByteArray).size
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else -> throw UnsupportedOperationException("Format specifier $field not supported")
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}
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}.sum()
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val buf = ByteBuffer.allocate(totalLength).order(endianness)
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nullCount = 0
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for ((index, field) in format.withIndex()) {
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val spec = field.last()
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if (spec == 'x') {
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nullCount++
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buf.put(0)
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continue
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}
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val value = values[index - nullCount]
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println("Packing field $index - $field($spec) - $value")
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when (spec) {
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'c' -> buf.putChar(value as Char)
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'b', 'B' -> buf.put((value as Number).toByte())
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'?' -> buf.put(if (value == true) 1 else 0)
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'h', 'H' -> buf.putShort((value as Number).toShort())
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'i', 'I' -> buf.putInt((value as Number).toInt())
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'l', 'L' -> buf.putInt((value as Number).toInt())
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'q', 'Q' -> buf.putLong((value as Number).toLong())
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'f' -> buf.putFloat((value as Number).toFloat())
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'd' -> buf.putDouble((value as Number).toDouble())
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's' -> {
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val size = (value as ByteArray).size
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if (field[0] == '$') {
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buf.put(value)
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} else {
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val fieldSize = field.dropLast(1).toInt()
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when {
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size > fieldSize -> buf.put(value.take(fieldSize).toByteArray())
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size < fieldSize -> {
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buf.put(value)
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buf.put(ByteArray(fieldSize - size) { 0 })
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}
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else -> buf.put(value)
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}
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}
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}
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'S' -> buf.put(value as ByteArray)
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else -> throw UnsupportedOperationException("Format specifier $field not supported")
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}
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}
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return buf.array()
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}
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fun unpack(formatString: String, data: ByteArray): List<Any> {
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val endianness = formatString.getEndianness()
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val format = formatString.getFormatList()
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val values = mutableListOf<Any>()
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val buf = ByteBuffer.wrap(data).order(endianness)
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for ((index, field) in format.withIndex()) {
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val spec = field.last()
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print("Unpacking field $index - $field($spec) - ")
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@Suppress("UsePropertyAccessSyntax")
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val value = when (spec) {
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'x' -> buf.get()
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'c' -> buf.getChar()
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'b' -> buf.get().toInt()
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'B' -> buf.get().toUByte().toInt()
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'?' -> buf.get().toInt() == 1
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'h' -> buf.getShort().toInt()
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'H' -> buf.getShort().toUShort().toInt()
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'i' -> buf.getInt()
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'I' -> buf.getInt().toUInt().toInt()
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'l' -> buf.getInt().toLong()
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'L' -> buf.getInt().toUInt().toLong()
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'q' -> buf.getLong()
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'Q' -> buf.getLong().toULong().toLong()
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'f' -> buf.getFloat()
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'd' -> buf.getDouble()
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's' -> {
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val size = if (field[0] == '$') {
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val fieldIndex = field.drop(1).dropLast(1).toInt()
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(values[fieldIndex] as Number).toInt()
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} else {
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field.dropLast(1).toInt()
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}
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val byteArray = ByteArray(size)
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buf.get(byteArray)
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byteArray
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}
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'S' -> data.sliceArray(buf.position() until data.size)
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else -> throw UnsupportedOperationException("Format specifier $field not supported")
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}
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println(value)
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if (spec == 'x')
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continue
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values.add(value)
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}
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return values
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}
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}

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