storage: make copy async

src/storage/gcs.js

@@ -31,7 +31,6 @@ const assert = require('assert'),
     constants = require('../constants.js'),
     DataLayout = require('../datalayout.js'),
     debug = require('debug')('box:storage/gcs'),
-    EventEmitter = require('events'),
     PassThrough = require('stream').PassThrough,
     path = require('path'),
     safe = require('safetydance'),
@@ -184,12 +183,11 @@ function listDir(apiConfig, backupFilePath, batchSize, iteratorCallback, callbac
     }, callback);
 }
 
-function copy(apiConfig, oldFilePath, newFilePath) {
+async function copy(apiConfig, oldFilePath, newFilePath, progressCallback) {
     assert.strictEqual(typeof apiConfig, 'object');
     assert.strictEqual(typeof oldFilePath, 'string');
     assert.strictEqual(typeof newFilePath, 'string');
-
-    var events = new EventEmitter();
+    assert.strictEqual(typeof progressCallback, 'function');
 
     function copyFile(entry, iteratorCallback) {
         var relativePath = path.relative(oldFilePath, entry.fullPath);
@@ -206,20 +204,19 @@ function copy(apiConfig, oldFilePath, newFilePath) {
 
     const batchSize = 1000;
     const concurrency = apiConfig.copyConcurrency || 10;
-    var total = 0;
+    let total = 0;
 
-    listDir(apiConfig, oldFilePath, batchSize, function (entries, done) {
+    const listDirAsync = util.promisify(listDir);
+
+    const [copyError] = await safe(listDirAsync(apiConfig, oldFilePath, batchSize, function (entries, done) {
         total += entries.length;
 
-        events.emit('progress', `Copying ${entries.length} files from ${entries[0].fullPath} to ${entries[entries.length-1].fullPath}. total: ${total}`);
+        progressCallback({ message: `Copying ${entries.length} files from ${entries[0].fullPath} to ${entries[entries.length-1].fullPath}. total: ${total}` });
 
         async.eachLimit(entries, concurrency, copyFile, done);
-    }, function (error) {
-        events.emit('progress', `Copied ${total} files`);
-        process.nextTick(() => events.emit('done', error));
-    });
+    }));
 
-    return events;
+    progressCallback({ message: `Copied ${total} files with error: ${copyError}` });
 }
 
 async function remove(apiConfig, filename) {