proxy: raise UpstreamRegistryError if we can't request upstream (#1220)

requests will either throw a RequestException or a ConnectionError if it
fails to request the given url for whatever reason.
callers are only expected to treat UpstreamRegistryError, so we throw it
instead of the requests related exceptions, adding the original message
to the new exception.

proxy/__init__.py

@@ -6,6 +6,7 @@
 import re
 
 import requests
+from requests.exceptions import RequestException
 
 from app import model_cache
 from data.cache import cache_key
@@ -119,14 +120,20 @@ def head(self, *args, **kwargs) -> requests.Response:
         return self._request(self._session.head, *args, **kwargs)
 
     def _request(self, request_func, *args, **kwargs) -> requests.Response:
-        resp = request_func(*args, **kwargs)
+        resp = self._safe_request(request_func, *args, **kwargs)
         if resp.status_code == 401:
             self._authorize(self._credentials(), force_renewal=True)
-            resp = request_func(*args, **kwargs)
+            resp = self._safe_request(request_func, *args, **kwargs)
         if not resp.ok:
             raise UpstreamRegistryError(resp.status_code)
         return resp
 
+    def _safe_request(self, request_func, *args, **kwargs):
+        try:
+            return request_func(*args, **kwargs)
+        except (RequestException, ConnectionError) as e:
+            raise UpstreamRegistryError(str(e))
+
     def _credentials(self) -> tuple[str, str] | None:
         auth = None
         username = self._config.upstream_registry_username
@@ -174,7 +181,7 @@ def _authorize(self, auth: tuple[str, str] | None = None, force_renewal: bool =
         if auth is not None:
             basic_auth = requests.auth.HTTPBasicAuth(auth[0], auth[1])
 
-        resp = self._session.get(auth_url, auth=basic_auth)
+        resp = self._safe_request(self._session.get, auth_url, auth=basic_auth)
         if not resp.ok:
             raise UpstreamRegistryError(
                 f"Failed to get token from: '{realm}', with status code: {resp.status_code}"