Avoid mutating upload options (#676)

Closes #607

addon/system/upload.js

@@ -5,22 +5,26 @@ import { buildWaiter } from '@ember/test-waiters';
 
 const uploadWaiter = buildWaiter('ember-file-upload:upload');
 
+function clone(object) {
+  return object ? { ...object } : {};
+}
+
 function normalizeOptions(file, url, options) {
   if (typeof url === 'object') {
     options = url;
     url = null;
   }
 
-  options = options || {};
+  options = clone(options);
 
   options.url = options.url || url;
   options.method = options.method || 'POST';
   options.accepts = options.accepts || ['application/json', 'text/javascript'];
   if (!Object.prototype.hasOwnProperty.call(options, 'contentType')) {
     options.contentType = file.type;
   }
-  options.headers = options.headers || {};
-  options.data = options.data || {};
+  options.headers = clone(options.headers);
+  options.data = clone(options.data);
   options.fileKey = options.fileKey || 'file';
 
   if (options.headers.Accept == null) {

tests/unit/upload-file-test.js

@@ -34,4 +34,34 @@ module('Unit | UploadFile', function (hooks) {
 
     await file.upload('/image');
   });
+
+  test('it does not mutate the provided options', async function (assert) {
+    this.server.post('/image', () => {});
+
+    const file = UploadFile.fromBlob(
+      new Blob(['My Test File'], { type: 'text' })
+    );
+
+    const options = {
+      accepts: ['foo'],
+      data: {
+        bar: 'bar',
+      },
+      headers: {
+        baz: 'baz',
+      },
+    };
+
+    await file.upload('/image', options);
+
+    assert.deepEqual(options, {
+      accepts: ['foo'],
+      data: {
+        bar: 'bar',
+      },
+      headers: {
+        baz: 'baz',
+      },
+    });
+  });
 });