add error detail handling to DrBotzoBackend

written for expecting a JSON with detail in an error response, but might
also decently handle the other cases

hitomi/backends.py

@@ -9,13 +9,36 @@ import hitomi.config as config
 logger = logging.getLogger(__name__)
 
 
+class DrBotzoError(requests.HTTPError):
+    """Wrap HTTPError with the error detail from the dr.botzo API, if available."""
+
+    def __init__(self, *args, **kwargs):
+        """Initialize DrBotzoError."""
+        detail = kwargs.pop('detail', None)
+        self.detail = detail
+        super(DrBotzoError, self).__init__(*args, **kwargs)
+
+
 class DrBotzoBackend(object):
     """Basic HTTP requests API, wrapped with some authentication and config stuff."""
 
     def post(self, url, **kwargs):
         """Wrap requests.post with authentication and hostname settings."""
-        return requests.post(urljoin(config.DR_BOTZO_BACKEND_HOST, url),
-                             auth=(config.DR_BOTZO_BACKEND_USER, config.DR_BOTZO_BACKEND_PASS), **kwargs)
+        try:
+            response = requests.post(urljoin(config.DR_BOTZO_BACKEND_HOST, url),
+                                     auth=(config.DR_BOTZO_BACKEND_USER, config.DR_BOTZO_BACKEND_PASS), **kwargs)
+            response.raise_for_status()
+            return response
+        except requests.ConnectionError as cex:
+            logger.exception("received a connection error during POST %s", url)
+            raise DrBotzoError(cex, detail="A connection error occurred.")
+        except requests.HTTPError as httpex:
+            logger.exception("received an HTTP error during POST %s", url)
+            try:
+                detail = httpex.response.json()['detail']
+                raise DrBotzoError(httpex, detail=detail)
+            except (ValueError, KeyError):
+                raise DrBotzoError(httpex, detail="An unexpected error occurred.")
 
 
 dr_botzo = DrBotzoBackend()