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FileService: a way to work with file at frontend
The usecase of this code is something like this: let image that user is making a protonmail or any another application where content inside frontend (=browser storage) some secret user's data that shouldn't be exposed to backend. Secret key for example or anything like that. This code allows to developer to convert any `Seq[Array[Byte]]` from frontend to URL as simple call `FileService.createURL`, asynchronously convert any uploaded `File` to `Array[Byte]` as `FileService.asBytesArray`, or to `InputStream` via `FileService.asInputStream` inside worker. Unfortunately scalatags doesn't support `download` attribute and I need to make it by hand. I've opened a PR[^1] to introduce it, but it might be a while until it is included to release. `FileService.asInputStream` is using `FileReaderSync` that is also missed inside scala-js-dom. I've opened a PR[^2] but it might be a while. Also, this draft API but it is supported by majority of modern browsers[^3]. [^1]: com-lihaoyi/scalatags#212 [^2]: scala-js/scala-js-dom#424 [^3]: https://caniuse.com/?search=FileReaderSync
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‎core/.js/src/main/scala/io/udash/utils/FileService.scala

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package io.udash.utils
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import java.io.{IOException, InputStream}
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import org.scalajs.dom._
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import org.scalajs.dom.html.Anchor
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import org.scalajs.dom.raw.Blob
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import scalatags.JsDom
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import scala.scalajs.js
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import scala.concurrent.{Future, Promise}
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import scala.scalajs.js.annotation.JSGlobal
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import scala.scalajs.js.typedarray.ArrayBuffer
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import scala.util.Try
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@js.native
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@JSGlobal
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sealed class FileReaderSync() extends js.Object {
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def readAsArrayBuffer(blob: Blob): ArrayBuffer = js.native
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}
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final class FileBufferedInputStream(file: File, bufferSize: Int) extends InputStream {
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val fileReaderSync = new FileReaderSync()
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var filePos: Int = 0
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var pos: Int = 0
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var buffer: Array[Byte] = Array.empty
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override def available(): Int = {
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val res = file.size.toInt - filePos
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if (res < 0) 0 else res
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}
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override def read(): Int = {
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if (pos >= buffer.length) {
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import js.typedarray._
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if (filePos >= file.size)
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return -1
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val len = math.min(filePos + bufferSize, file.size.toInt)
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val slice = file.slice(filePos, len)
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buffer = new Int8Array(fileReaderSync.readAsArrayBuffer(slice)).toArray
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filePos += buffer.length
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pos = 0
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}
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val r = buffer(pos).toInt & 0xff
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pos += 1
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r
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}
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override def close(): Unit = filePos = file.size.toInt
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override def markSupported(): Boolean = true
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var markPos: Option[Int] = None
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override def mark(readlimit: Int): Unit =
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markPos = Some(pos + filePos - buffer.length)
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override def reset(): Unit = markPos match {
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case Some(p) =>
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filePos = p
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pos = 0
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buffer = Array.empty
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markPos = None
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case _ =>
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// do nothing
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}
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}
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object FileService {
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final val OctetStreamType = "application/octet-stream"
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/**
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* Converts specified bytes arrays to string that contains URL
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* that representing the array given in the parameter with specified mime-type.
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*
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* Keep in mind that returned URL should be revoked via `org.scalajs.dom.revokeObjectURL(url)`.
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*/
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def createURL(bytesArrays: Seq[Array[Byte]], mimeType: String): String = {
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import js.typedarray._
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val jsBytesArrays = js.Array[js.Any](bytesArrays.map(_.toTypedArray) :_ *)
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val blob = new Blob(jsBytesArrays, BlobPropertyBag(mimeType))
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URL.createObjectURL(blob)
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}
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/**
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* Converts specified bytes arrays to string that contains URL
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* that representing the array given in the parameter with `application/octet-stream` mime-type.
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*
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* Keep in mind that returned URL should be revoked via `org.scalajs.dom.revokeObjectURL(url)`.
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*/
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def createURL(bytesArrays: Seq[Array[Byte]]): String =
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createURL(bytesArrays, OctetStreamType)
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/**
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* Converts specified bytes array to string that contains URL
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* that representing the array given in the parameter with specified mime-type.
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*
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* Keep in mind that returned URL should be revoked via `org.scalajs.dom.revokeObjectURL(url)`.
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*/
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def createURL(byteArray: Array[Byte], mimeType: String): String =
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createURL(Seq(byteArray), mimeType)
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/**
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* Converts specified bytes array to string that contains URL
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* that representing the array given in the parameter with `application/octet-stream` mime-type.
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*
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* Keep in mind that returned URL should be revoked via `org.scalajs.dom.revokeObjectURL(url)`.
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*/
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def createURL(byteArray: Array[Byte]): String =
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createURL(Seq(byteArray), OctetStreamType)
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/**
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* Asynchronously convert specified file to bytes array.
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*/
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def asBytesArray(file: File): Future[Array[Byte]] = {
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import js.typedarray._
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val fileReader = new FileReader()
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val promise = Promise[Array[Byte]]()
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fileReader.onerror = (e: Event) =>
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promise.failure(new IOException(e.toString))
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fileReader.onabort = (e: Event) =>
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promise.failure(new IOException(e.toString))
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fileReader.onload = (_: UIEvent) =>
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promise.complete(Try(
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new Int8Array(fileReader.result.asInstanceOf[ArrayBuffer]).toArray
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))
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fileReader.readAsArrayBuffer(file)
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promise.future
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}
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/**
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* Convert specified file to InputStream with blocking I/O
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*
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* Because it is using synchronous I/O that could potentially this API can be used only inside worker.
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*
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* This method is using FileReaderSync that is part of Working Draft File API.
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* Anyway it is supported for majority of modern browsers
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*/
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def asInputStream(file: File, bufferSize: Int = 1024): InputStream =
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new FileBufferedInputStream(file, bufferSize)
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}

‎guide/guide/.js/src/main/scala/io/udash/web/guide/views/frontend/FrontendFilesView.scala

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),
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p("You can find a working demo application in the ", a(href := References.UdashFilesDemoRepo, target := "_blank")("Udash Demos"), " repositiory."),
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h3("Frontend forms"),
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p(i("FileService"), " is an object that allows to convert ", i("Array[Byte]")," to URL, save it as file from frontend ",
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" and asynchronously convert ", i("File"), " to ", i("Array[Byte]"), "."),
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p(i("FileInput"), " is the file HTML input wrapper providing a property containing selected files. "),
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fileInputSnippet,
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p("Take a look at the following live demo:"),

‎guide/guide/.js/src/main/scala/io/udash/web/guide/views/frontend/demos/FileInputDemo.scala

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package io.udash.web.guide.views.frontend.demos
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import io.udash.css.CssView
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import io.udash.utils.FileService
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import io.udash.web.guide.demos.AutoDemo
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import io.udash.web.guide.styles.partials.GuideStyles
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import scalatags.JsDom.all._
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private val (rendered, source) = {
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import io.udash._
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import org.scalajs.dom.File
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import org.scalajs.dom.{File, URL}
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import scalatags.JsDom.all._
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import org.scalajs.dom.window
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import scala.concurrent.ExecutionContext.Implicits.global
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val acceptMultipleFiles = Property(true)
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val selectedFiles = SeqProperty.blank[File]
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FileInput(selectedFiles, acceptMultipleFiles)("files"),
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h4("Selected files"),
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ul(repeat(selectedFiles)(file => {
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li(file.get.name).render
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val content = Property(Array.empty[Byte])
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FileService.asBytesArray(file.get) foreach { bytes =>
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content.set(bytes)
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}
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val name = file.get.name
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li(showIfElse(content.transform(_.isEmpty))(
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span(name).render,
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{
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val url = FileService.createURL(content.get)
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val download = a(href := url, attr("download") := name)(name)
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val revoke = a(onclick := { () =>
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content.set(Array.empty[Byte])
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URL.revokeObjectURL(url)
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})("revoke")
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Seq(download, revoke).render
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}
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)).render
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}))
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)
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}.withSourceCode

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