better download error exception

teeth_agent/errors.py

@@ -61,3 +61,15 @@ class HeartbeatError(errors.RESTError):
     def __init__(self, details):
         super(HeartbeatError, self).__init__()
         self.details = details
+
+
+class ImageDownloadError(errors.RESTError):
+    """Error raised when an image cannot be downloaded."""
+
+    message = 'Error downloading image.'
+
+    def __init__(self, image_id, image_url):
+        details = 'Image with id {} not found at url {}.'.format(image_id,
+                                                                 image_url)
+        super(ImageDownloadError, self).__init__()
+        self.details = details

teeth_agent/standby.py

@@ -48,10 +48,11 @@ def _write_image(image_info, configdrive='configdrive', device='/dev/sda'):
 
 
 def _download_image(image_info):
-    resp = requests.get(image_info['urls'][0], stream=True)
+    # TODO(jimrollenhagen) try all URLs
+    url = image_info['urls'][0]
+    resp = requests.get(url, stream=True)
     if resp.status_code != 200:
-        # TODO(jimrollenhagen) define a better exception
-        raise Exception
+        raise errors.ImageDownloadError(image_info['id'], url)
     image_location = _image_location(image_info)
     with open(image_location, 'wb') as f:
         for chunk in resp.iter_content(1024 * 1024):

teeth_agent/tests/standby_agent.py

@@ -120,7 +120,9 @@ class TestBaseTeethAgent(unittest.TestCase):
         image_info = self._build_fake_image_info()
         response = requests_mock.return_value
         response.status_code = 404
-        self.assertRaises(Exception, standby._download_image, image_info)
+        self.assertRaises(errors.ImageDownloadError,
+                          standby._download_image,
+                          image_info)
 
     @mock.patch('teeth_agent.standby._verify_image', autospec=True)
     @mock.patch('__builtin__.open', autospec=True)