295 lines
7.7 KiB
Kotlin
295 lines
7.7 KiB
Kotlin
/**
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* Protocol.kt
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* SkyLink 多平台实时视频传输 - Kotlin 协议定义
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*
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* 这是对应 protocol.h 的 Kotlin 实现版本，用于 Android 端解析 UDP 数据包。
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* 使用 ByteBuffer 进行二进制数据的解析和序列化。
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*
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* @author SkyLink Team
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* @date 2026-01-19
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*/
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package com.skylink.protocol
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import java.nio.ByteBuffer
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import java.nio.ByteOrder
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/**
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* SkyLink 协议版本号
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*/
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const val SKYLINK_VERSION = "1.0"
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/**
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* 数据包魔数
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*/
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const val SKYLINK_MAGIC: Short = 0xAA55.toShort()
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/**
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* UDP 最大包大小 (MTU - IP - UDP)
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*/
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const val MAX_UDP_PACKET_SIZE = 1472
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/**
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* 最大载荷大小
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*/
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const val MAX_PAYLOAD_SIZE = MAX_UDP_PACKET_SIZE - PacketHeaderSize
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/**
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* 包头大小 (字节)
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*/
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const val PacketHeaderSize = 50
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/**
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* UDP 接收缓冲区大小
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*/
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const val RX_BUFFER_SIZE = 65536
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/**
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* 最大分片数
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*/
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const val MAX_CHUNKS = 1000
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/**
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* 帧超时时间 (毫秒)
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*/
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const val FRAME_TIMEOUT_MS = 5000L
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/**
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* JPEG 图像格式 ID
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*/
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const val IMAGE_FORMAT_JPEG: Byte = 0x01
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/**
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* JPEG 最大质量
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*/
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const val JPEG_MAX_QUALITY = 100
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/**
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* JPEG 最小质量
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*/
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const val JPEG_MIN_QUALITY = 10
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// ============================================================================
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// 数据类定义
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// ============================================================================
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/**
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* SkyLink 数据包头结构
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*
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* 完整映射 C++ protocol.h 的 PacketHeader：
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* - Magic (2 bytes)
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* - FrameID (4 bytes)
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* - TotalChunks (2 bytes)
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* - ChunkIndex (2 bytes)
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* - DataLen (2 bytes)
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* - Timestamp (8 bytes)
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* - Latitude (8 bytes)
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* - Longitude (8 bytes)
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* - Altitude (8 bytes)
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* - CRC16 (2 bytes)
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* - Reserve (4 bytes)
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* 总计: 50 字节
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*/
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data class SkyLinkPacketHeader(
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val magic: Short, // 0xAA55
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val frameId: Int, // 帧ID
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val totalChunks: Short, // 总分片数
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val chunkIndex: Short, // 当前分片索引
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val dataLen: Short, // 载荷长度
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val timestamp: Double, // 时间戳
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val lat: Double, // 纬度
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val lon: Double, // 经度
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val alt: Double, // 海拔
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val crc16: Short, // 校验码
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val reserve: Int // 预留字段
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) {
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companion object {
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/**
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* 从 ByteArray 中解析包头
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* @param data 字节数组
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* @return 解析成功返回 SkyLinkPacketHeader，否则返回 null
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*/
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fun fromByteArray(data: ByteArray): SkyLinkPacketHeader? {
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if (data.size < PacketHeaderSize) {
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return null
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}
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val buffer = ByteBuffer.wrap(data, 0, PacketHeaderSize)
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buffer.order(ByteOrder.LITTLE_ENDIAN) // ARM 平台使用小端序
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return try {
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val magic = buffer.short
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val frameId = buffer.int
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val totalChunks = buffer.short
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val chunkIndex = buffer.short
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val dataLen = buffer.short
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val timestamp = buffer.double
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val lat = buffer.double
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val lon = buffer.double
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val alt = buffer.double
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val crc16 = buffer.short
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val reserve = buffer.int
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SkyLinkPacketHeader(
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magic = magic,
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frameId = frameId,
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totalChunks = totalChunks,
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chunkIndex = chunkIndex,
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dataLen = dataLen,
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timestamp = timestamp,
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lat = lat,
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lon = lon,
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alt = alt,
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crc16 = crc16,
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reserve = reserve
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)
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} catch (e: Exception) {
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e.printStackTrace()
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null
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}
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}
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/**
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* 将包头序列化为 ByteArray
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*/
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fun toByteArray(header: SkyLinkPacketHeader): ByteArray {
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val buffer = ByteBuffer.allocate(PacketHeaderSize)
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buffer.order(ByteOrder.LITTLE_ENDIAN)
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buffer.putShort(header.magic)
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buffer.putInt(header.frameId)
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buffer.putShort(header.totalChunks)
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buffer.putShort(header.chunkIndex)
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buffer.putShort(header.dataLen)
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buffer.putDouble(header.timestamp)
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buffer.putDouble(header.lat)
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buffer.putDouble(header.lon)
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buffer.putDouble(header.alt)
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buffer.putShort(header.crc16)
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buffer.putInt(header.reserve)
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return buffer.array()
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}
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}
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/**
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* 验证包头魔数是否有效
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*/
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fun isValid(): Boolean {
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return magic == SKYLINK_MAGIC
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}
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/**
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* 获取此包头对应的载荷部分
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*/
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fun getPayloadSize(): Int {
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return dataLen.toInt()
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}
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}
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/**
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* 完整的 SkyLink 数据包
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*/
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data class SkyLinkPacket(
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val header: SkyLinkPacketHeader,
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val payload: ByteArray // 实际的图像数据
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) {
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override fun equals(other: Any?): Boolean {
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if (this === other) return true
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if (javaClass != other?.javaClass) return false
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other as SkyLinkPacket
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if (header != other.header) return false
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if (!payload.contentEquals(other.payload)) return false
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return true
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}
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override fun hashCode(): Int {
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var result = header.hashCode()
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result = 31 * result + payload.contentHashCode()
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return result
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}
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/**
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* 获取总的包大小
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*/
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fun getTotalSize(): Int {
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return PacketHeaderSize + payload.size
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}
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}
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/**
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* 图像帧的组装结果
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*/
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data class DecodedFrame(
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val frameId: Int,
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val imageData: ByteArray, // JPEG 图像数据
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val timestamp: Double,
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val lat: Double,
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val lon: Double,
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val alt: Double,
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val receivedTime: Long = System.currentTimeMillis() // 接收时刻
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) {
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override fun equals(other: Any?): Boolean {
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if (this === other) return true
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if (javaClass != other?.javaClass) return false
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other as DecodedFrame
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if (frameId != other.frameId) return false
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if (!imageData.contentEquals(other.imageData)) return false
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if (timestamp != other.timestamp) return false
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if (lat != other.lat) return false
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if (lon != other.lon) return false
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if (alt != other.alt) return false
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if (receivedTime != other.receivedTime) return false
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return true
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}
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override fun hashCode(): Int {
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var result = frameId
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result = 31 * result + imageData.contentHashCode()
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result = 31 * result + timestamp.hashCode()
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result = 31 * result + lat.hashCode()
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result = 31 * result + lon.hashCode()
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result = 31 * result + alt.hashCode()
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result = 31 * result + receivedTime.hashCode()
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return result
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}
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}
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// ============================================================================
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// 辅助函数
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// ============================================================================
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/**
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* 验证 CRC16 校验 (CCITT 多项式)
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*/
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fun calculateCrc16(data: ByteArray): Short {
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var crc: Int = 0xFFFF
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for (byte in data) {
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crc = crc xor ((byte.toInt() and 0xFF) shl 8)
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for (j in 0 until 8) {
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crc = if (crc and 0x8000 != 0) {
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((crc shl 1) xor 0x1021) and 0xFFFF
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} else {
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(crc shl 1) and 0xFFFF
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}
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}
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}
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return crc.toShort()
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}
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/**
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* 验证包头合法性
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*/
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fun isValidSkyLinkPacket(header: SkyLinkPacketHeader): Boolean {
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return header.isValid() &&
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header.chunkIndex < header.totalChunks &&
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header.dataLen > 0 &&
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header.dataLen <= MAX_PAYLOAD_SIZE
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}
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