a few changes to make A/B testing easier

app/fileReceiver.js

@@ -0,0 +1,100 @@
+import Nanobus from 'nanobus';
+import { hexToArray, bytes } from './utils';
+
+export default class FileReceiver extends Nanobus {
+  constructor(url, k) {
+    super('FileReceiver');
+    this.key = window.crypto.subtle.importKey(
+      'jwk',
+      {
+        k,
+        kty: 'oct',
+        alg: 'A128GCM',
+        ext: true
+      },
+      {
+        name: 'AES-GCM'
+      },
+      false,
+      ['decrypt']
+    );
+    this.url = url;
+    this.msg = 'fileSizeProgress';
+    this.progress = [0, 1];
+  }
+
+  get progressRatio() {
+    return this.progress[0] / this.progress[1];
+  }
+
+  get sizes() {
+    return {
+      partialSize: bytes(this.progress[0]),
+      totalSize: bytes(this.progress[1])
+    };
+  }
+
+  cancel() {
+    // TODO
+  }
+
+  downloadFile() {
+    return new Promise((resolve, reject) => {
+      const xhr = new XMLHttpRequest();
+
+      xhr.onprogress = event => {
+        if (event.lengthComputable && event.target.status !== 404) {
+          this.progress = [event.loaded, event.total];
+          this.emit('progress', this.progress);
+        }
+      };
+
+      xhr.onload = function(event) {
+        if (xhr.status === 404) {
+          reject(new Error('notfound'));
+          return;
+        }
+
+        const blob = new Blob([this.response]);
+        const meta = JSON.parse(xhr.getResponseHeader('X-File-Metadata'));
+        const fileReader = new FileReader();
+        fileReader.onload = function() {
+          resolve({
+            data: this.result,
+            name: meta.filename,
+            type: meta.mimeType,
+            iv: meta.id
+          });
+        };
+
+        fileReader.readAsArrayBuffer(blob);
+      };
+
+      xhr.open('get', this.url);
+      xhr.responseType = 'blob';
+      xhr.send();
+    });
+  }
+
+  async download() {
+    const key = await this.key;
+    const file = await this.downloadFile();
+    this.msg = 'decryptingFile';
+    this.emit('decrypting');
+    const plaintext = await window.crypto.subtle.decrypt(
+      {
+        name: 'AES-GCM',
+        iv: hexToArray(file.iv),
+        tagLength: 128
+      },
+      key,
+      file.data
+    );
+    this.msg = 'downloadFinish';
+    return {
+      plaintext,
+      name: decodeURIComponent(file.name),
+      type: file.type
+    };
+  }
+}