Add route to download app backups

src/routes/apps.js

@@ -56,6 +56,7 @@ exports = module.exports = {
     downloadFile,
 
     updateBackup,
+    downloadBackup,
 
     getLimits,
     getGraphs,
@@ -852,6 +853,17 @@ async function updateBackup(req, res, next) {
     next(new HttpSuccess(200, {}));
 }
 
+async function downloadBackup(req, res, next) {
+    assert.strictEqual(typeof req.app, 'object');
+    assert.strictEqual(typeof req.params.backupId, 'string');
+
+    const [error, result] = await safe(apps.getBackupDownloadStream(req.app, req.params.backupId));
+    if (error) return next(BoxError.toHttpError(error));
+
+    res.attachment(`${req.params.backupId}.tgz`);
+    result.pipe(res);
+}
+
 async function uploadFile(req, res, next) {
     assert.strictEqual(typeof req.app, 'object');