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

Author: catap

core/.js/src/main/scala/io/udash/utils/FileService.scala

@@ -0,0 +1,158 @@
+package io.udash.utils
+
+import java.io.{IOException, InputStream}
+
+import org.scalajs.dom._
+import org.scalajs.dom.raw.Blob
+
+import scala.scalajs.js
+import scala.concurrent.{Future, Promise}
+import scala.scalajs.js.annotation.JSGlobal
+import scala.scalajs.js.typedarray.ArrayBuffer
+import scala.util.Try
+
+@js.native
+@JSGlobal
+sealed class FileReaderSync() extends js.Object {
+ def readAsArrayBuffer(blob: Blob): ArrayBuffer = js.native
+}
+
+final class FileBufferedInputStream(file: File, bufferSize: Int) extends InputStream {
+ val fileReaderSync = new FileReaderSync()
+
+ var filePos: Int = 0
+ var pos: Int = 0
+
+ var buffer: Array[Byte] = Array.empty
+
+ override def available(): Int = {
+ val res = file.size.toInt - filePos
+ if (res < 0) 0 else res
+ }
+
+ override def read(): Int = {
+ if (pos >= buffer.length) {
+ import js.typedarray._
+
+ if (filePos >= file.size)
+ return -1
+
+ val len = math.min(filePos + bufferSize, file.size.toInt)
+ val slice = file.slice(filePos, len)
+ buffer = new Int8Array(fileReaderSync.readAsArrayBuffer(slice)).toArray
+ filePos += buffer.length
+ pos = 0
+ }
+ val r = buffer(pos).toInt & 0xff
+ pos += 1
+ r
+ }
+
+ override def close(): Unit = filePos = file.size.toInt
+
+ override def markSupported(): Boolean = true
+
+ var markPos: Option[Int] = None
+
+ override def mark(readlimit: Int): Unit =
+ markPos = Some(pos + filePos - buffer.length)
+
+ override def reset(): Unit = markPos match {
+ case Some(p) =>
+ filePos = p
+ pos = 0
+ buffer = Array.empty
+ markPos = None
+
+ case _ =>
+ // do nothing
+ }
+}
+
+final case class CloseableUrl(value: String) extends AutoCloseable {
+ override def close(): Unit = {
+ URL.revokeObjectURL(value)
+ }
+}
+
+object FileService {
+
+ final val OctetStreamType = "application/octet-stream"
+
+ /**
+ * Converts specified bytes arrays to string that contains URL
+ * that representing the array given in the parameter with specified mime-type.
+ *
+ * Keep in mind that returned URL should be closed.
+ */
+ def createURL(bytesArrays: Seq[Array[Byte]], mimeType: String): CloseableUrl = {
+ import js.typedarray._
+
+ val jsBytesArrays = js.Array[js.Any](bytesArrays.map(_.toTypedArray) :_ *)
+ val blob = new Blob(jsBytesArrays, BlobPropertyBag(mimeType))
+ CloseableUrl(URL.createObjectURL(blob))
+ }
+
+ /**
+ * Converts specified bytes arrays to string that contains URL
+ * that representing the array given in the parameter with `application/octet-stream` mime-type.
+ *
+ * Keep in mind that returned URL should be closed.
+ */
+ def createURL(bytesArrays: Seq[Array[Byte]]): CloseableUrl =
+ createURL(bytesArrays, OctetStreamType)
+
+ /**
+ * Converts specified bytes array to string that contains URL
+ * that representing the array given in the parameter with specified mime-type.
+ *
+ * Keep in mind that returned URL should be closed.
+ */
+ def createURL(byteArray: Array[Byte], mimeType: String): CloseableUrl =
+ createURL(Seq(byteArray), mimeType)
+
+ /**
+ * Converts specified bytes array to string that contains URL
+ * that representing the array given in the parameter with `application/octet-stream` mime-type.
+ *
+ * Keep in mind that returned URL should be closed.
+ */
+ def createURL(byteArray: Array[Byte]): CloseableUrl =
+ createURL(Seq(byteArray), OctetStreamType)
+
+ /**
+ * Asynchronously convert specified file to bytes array.
+ */
+ def asBytesArray(file: File): Future[Array[Byte]] = {
+ import js.typedarray._
+
+ val fileReader = new FileReader()
+ val promise = Promise[Array[Byte]]()
+
+ fileReader.onerror = (e: Event) =>
+ promise.failure(new IOException(e.toString))
+
+ fileReader.onabort = (e: Event) =>
+ promise.failure(new IOException(e.toString))
+
+ fileReader.onload = (_: UIEvent) =>
+ promise.complete(Try(
+ new Int8Array(fileReader.result.asInstanceOf[ArrayBuffer]).toArray
+ ))
+
+ fileReader.readAsArrayBuffer(file)
+
+ promise.future
+ }
+
+ /**
+ * Convert specified file to InputStream with blocking I/O
+ *
+ * Because it is using synchronous I/O that could potentially this API can be used only inside worker.
+ *
+ * This method is using FileReaderSync that is part of Working Draft File API.
+ * Anyway it is supported for majority of modern browsers
+ */
+ def asInputStream(file: File, bufferSize: Int = 1024): InputStream =
+ new FileBufferedInputStream(file, bufferSize)
+}

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

@@ -24,6 +24,8 @@ class FrontendFilesView extends View {
  ),
  p("You can find a working demo application in the ", a(href := References.UdashFilesDemoRepo, target := "_blank")("Udash Demos"), " repositiory."),
  h3("Frontend forms"),
+ p(i("FileService"), " is an object that allows to convert ", i("Array[Byte]")," to URL, save it as file from frontend ",
+ " and asynchronously convert ", i("File"), " to ", i("Array[Byte]"), "."),
  p(i("FileInput"), " is the file HTML input wrapper providing a property containing selected files. "),
  fileInputSnippet,
  p("Take a look at the following live demo:"),

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

@@ -1,6 +1,7 @@
 package io.udash.web.guide.views.frontend.demos
 
 import io.udash.css.CssView
+import io.udash.utils.FileService
 import io.udash.web.guide.demos.AutoDemo
 import io.udash.web.guide.styles.partials.GuideStyles
 import scalatags.JsDom.all._
@@ -9,8 +10,11 @@ object FileInputDemo extends AutoDemo with CssView {
 
  private val (rendered, source) = {
  import io.udash._
- import org.scalajs.dom.File
+ import org.scalajs.dom.{File, URL}
  import scalatags.JsDom.all._
+ import org.scalajs.dom.window
+
+ import scala.concurrent.ExecutionContext.Implicits.global
 
  val acceptMultipleFiles = Property(true)
  val selectedFiles = SeqProperty.blank[File]
@@ -19,7 +23,26 @@ object FileInputDemo extends AutoDemo with CssView {
  FileInput(selectedFiles, acceptMultipleFiles)("files"),
  h4("Selected files"),
  ul(repeat(selectedFiles)(file => {
- li(file.get.name).render
+ val content = Property(Array.empty[Byte])
+
+ FileService.asBytesArray(file.get) foreach { bytes =>
+ content.set(bytes)
+ }
+
+ val name = file.get.name
+ li(showIfElse(content.transform(_.isEmpty))(
+ span(name).render,
+ {
+ val url = FileService.createURL(content.get)
+ val download = a(href := url.value, attr("download") := name)(name)
+ val revoke = a(href := "#", onclick := { () =>
+ content.set(Array.empty[Byte])
+ url.close()
+ })("revoke")
+
+ Seq(download, span(" or "), revoke).render
+ }
+ )).render
  }))
  )
  }.withSourceCode