FileTransfer.kt

package com.github.antweb.donkey

import android.bluetooth.BluetoothGatt
import android.bluetooth.BluetoothGattCharacteristic
import android.bluetooth.BluetoothGattDescriptor
import android.os.Environment
import android.util.Log
import java.io.BufferedInputStream
import java.io.File
import java.io.FileInputStream
import java.nio.ByteBuffer
import java.util.*
import java.util.zip.CRC32

private const val TAG = "FileTransfer"

class FileTransfer(
    private val gatt: BluetoothGatt,
    private val tx: BluetoothGattCharacteristic,
    private val rx: BluetoothGattCharacteristic,
    private val mtu: Int
) {
    private val filePath = "/Download/SEND.txt"

    private val iterator = openFile().iterator()
    private var offset: Int = 0

    private var lastCrc: Long = 0


    private fun openFile(): ByteArray {
        // TODO: Don't listen to Android Docs, use stuff that is not deprecated
        val file = File(
            Environment.getExternalStorageDirectory()
                .absolutePath, filePath
        )

        val size = file.length()
        val bytes = ByteArray(size.toInt())
        val buf = BufferedInputStream(FileInputStream(file))
        buf.read(bytes, 0, bytes.size)
        buf.close()

        return bytes
    }

    fun sendFile() {
        // Send first chunk
        sendNext()
    }

    fun sendNext() {
        Log.d(TAG, "Sending next chunk: $offset")

        if (!iterator.hasNext()) {
            return
        }

        val chunk = mutableListOf<Byte>()
//        for (i in 0 until (mtu - 5)) {
        for (i in 0 until (10)) {
            chunk.add(iterator.next())
        }

        // Our packet:
        // 4 byte header + chunk
        val header = offset
        offset += chunk.size

        val sendBuffer = ByteBuffer.allocate(chunk.size + 4)
        sendBuffer.putInt(header)
        sendBuffer.put(chunk.toByteArray())
        val bytes = sendBuffer.array()

        val crc = CRC32()
        crc.update(bytes)
        lastCrc = crc.value

//        gatt?.beginReliableWrite()
        tx?.value = bytes
        val status = gatt?.writeCharacteristic(tx)

        if (!status) {
            Log.d(TAG, "Write status: $status")
        }
    }
}