extracted blobSlicer, fixed download cancel tests

app/ece.js

@@ -1,4 +1,5 @@
 import 'buffer';
+import BlobSlicer from './blobSlicer';
 import { transformStream } from './streams';
 
 const NONCE_LENGTH = 12;
@@ -225,40 +226,6 @@ class ECETransformer {
   }
 }
 
-export class BlobSlicer {
-  constructor(blob, rs, mode) {
-    this.blob = blob;
-    this.index = 0;
-    this.mode = mode;
-    this.chunkSize = mode === MODE_ENCRYPT ? rs - 17 : rs;
-  }
-
-  pull(controller) {
-    return new Promise((resolve, reject) => {
-      const bytesLeft = this.blob.size - this.index;
-      if (bytesLeft <= 0) {
-        controller.close();
-        return resolve();
-      }
-      let size = 1;
-      if (this.mode === MODE_DECRYPT && this.index === 0) {
-        size = Math.min(21, bytesLeft);
-      } else {
-        size = Math.min(this.chunkSize, bytesLeft);
-      }
-      const blob = this.blob.slice(this.index, this.index + size);
-      const reader = new FileReader();
-      reader.onload = () => {
-        controller.enqueue(new Uint8Array(reader.result));
-        resolve();
-      };
-      reader.onerror = reject;
-      reader.readAsArrayBuffer(blob);
-      this.index += size;
-    });
-  }
-}
-
 class StreamSlicer {
   constructor(rs, mode) {
     this.mode = mode;
@@ -350,7 +317,7 @@ export default class ECE {
 
     if (this.input instanceof Blob) {
       inputStream = new ReadableStream(
-        new BlobSlicer(this.input, this.rs, this.mode)
+        new BlobSlicer(this.input, this.rs - 17)
       );
     } else {
       inputStream = transformStream(