Android BLE file transfer manager with folder-based protocol

article-bleftp-android-gatt-manager.kt

private val advertiseCallback = object : AdvertiseCallback() {
    override fun onStartSuccess(settingsInEffect: AdvertiseSettings) {
        pendingStart = false
        log("Advertising started for service $SERVICE_UUID")
    }

    override fun onStartFailure(errorCode: Int) {
        pendingStart = false
        log("Advertising failed: ${advertiseFailureMessage(errorCode)}")
        stopServer()
    }
}

@RequiresPermission(Manifest.permission.BLUETOOTH_CONNECT)
private fun startAdvertising() {
    val currentAdvertiser = advertiser ?: run {
        pendingStart = false
        stopServer()
        return
    }

    val settings = AdvertiseSettings.Builder()
        .setAdvertiseMode(AdvertiseSettings.ADVERTISE_MODE_LOW_LATENCY)
        .setConnectable(true)
        .setTimeout(0)
        .setTxPowerLevel(AdvertiseSettings.ADVERTISE_TX_POWER_HIGH)
        .build()

    val data = AdvertiseData.Builder()
        .addServiceUuid(ParcelUuid(SERVICE_UUID))
        .build()

    val scanResponse = AdvertiseData.Builder()
        .setIncludeDeviceName(true)
        .build()

    currentAdvertiser.startAdvertising(settings, data, scanResponse, advertiseCallback)
}

private fun sendStatus() {
    val payload = JSONObject()
        .put("type", "status")
        .put("chunkSize", mtuPayloadSize)
        .put("sharedFolder", outgoingTreeName ?: JSONObject.NULL)
        .put("incomingFolderConfigured", incomingTreeUri != null)
        .put("sharedFolderConfigured", outgoingTreeUri != null)
        .put("commands", JSONArray().put("status").put("list").put("put").put("get").put("cancel"))
    sendControl(payload)
}

private fun listDirectory(message: JSONObject) {
    val outgoingRoot = outgoingTreeUri?.let { DocumentFile.fromTreeUri(context, it) }
        ?: run {
            sendError("Select a shared folder in Android first")
            return
        }

    val pathParts = parseRelativePath(message.optString("path")) ?: run {
        sendError("Invalid list path")
        return
    }

    val target = resolvePath(outgoingRoot, pathParts) ?: run {
        sendError("Path not found")
        return
    }

    if (!target.isDirectory) {
        sendError("Requested path is not a directory")
        return
    }

    sendControl(JSONObject().put("type", "list_begin").put("path", buildRelativePath(pathParts)))

    for (child in target.listFiles().sortedBy { it.name.orEmpty().lowercase(Locale.US) }) {
        val childName = child.name ?: continue
        sendControl(
            JSONObject()
                .put("type", "list_entry")
                .put("name", childName)
                .put("path", buildRelativePath(pathParts, childName))
                .put("directory", child.isDirectory)
                .put("size", if (child.isFile) child.length() else JSONObject.NULL)
        )
    }

    sendControl(
        JSONObject()
            .put("type", "list_complete")
            .put("path", buildRelativePath(pathParts))
    )
}