Validate input args before trying image download

Currently client is contacting glance service even if the
caller has niether specified any redirection nor '--file'
option. This unnecessary request although isn't causing
any critical issues but can be avoided by simply doing
input validation first.

TrivialFix

Change-Id: I841bebeda38814235079429eca0b1e5fd2f04dae

2 files changed, 22 insertions, 7 deletions

diff --git a/glanceclient/tests/unit/v2/test_shell_v2.py b/glanceclient/tests/unit/v2/test_shell_v2.py
index fed1f72..4ac8c17 100644
--- a/glanceclient/tests/unit/v2/test_shell_v2.py
+++ b/glanceclient/tests/unit/v2/test_shell_v2.py
@@ -590,6 +590,20 @@ class ShellV2Test(testtools.TestCase):
             test_shell.do_image_download(self.gc, args)
             mocked_data.assert_called_once_with('IMG-01')
 
+    @mock.patch.object(utils, 'exit')
+    @mock.patch('sys.stdout', autospec=True)
+    def test_image_download_no_file_arg(self, mocked_stdout,
+                                        mocked_utils_exit):
+        # Indicate that no file name was given as command line argument
+        args = self._make_args({'id': '1234', 'file': None, 'progress': False})
+        # Indicate that no file is specified for output redirection
+        mocked_stdout.isatty = lambda: True
+        test_shell.do_image_download(self.gc, args)
+        mocked_utils_exit.assert_called_once_with(
+            'No redirection or local file specified for downloaded image'
+            ' data. Please specify a local file with --file to save'
+            ' downloaded image or redirect output to another source.')
+
     def test_do_image_delete(self):
         args = argparse.Namespace(id=['image1', 'image2'])
         with mock.patch.object(self.gc.images, 'delete') as mocked_delete:
diff --git a/glanceclient/v2/shell.py b/glanceclient/v2/shell.py
index 5354db4..9ce6f96 100644
--- a/glanceclient/v2/shell.py
+++ b/glanceclient/v2/shell.py
@@ -278,6 +278,12 @@ def do_explain(gc, args):
            help=_('Show download progress bar.'))
 def do_image_download(gc, args):
     """Download a specific image."""
+    if sys.stdout.isatty() and (args.file is None):
+        msg = ('No redirection or local file specified for downloaded image '
+               'data. Please specify a local file with --file to save '
+               'downloaded image or redirect output to another source.')
+        utils.exit(msg)
+
     try:
         body = gc.images.data(args.id)
     except (exc.HTTPForbidden, exc.HTTPException) as e:
@@ -290,13 +296,8 @@ def do_image_download(gc, args):
 
     if args.progress:
         body = progressbar.VerboseIteratorWrapper(body, len(body))
-    if not (sys.stdout.isatty() and args.file is None):
-        utils.save_image(body, args.file)
-    else:
-        msg = ('No redirection or local file specified for downloaded image '
-               'data. Please specify a local file with --file to save '
-               'downloaded image or redirect output to another source.')
-        utils.exit(msg)
+
+    utils.save_image(body, args.file)
 
 
 @utils.arg('--file', metavar='<FILE>',