nk3: Improve error message for fetch-update

This patch makes the error message that is shown if the firmware file
already exists less intimidating by introducing a custom exception and
disabling the support hint.

Fixes #189

pynitrokey/cli/nk3/__init__.py

@@ -30,6 +30,7 @@
 from pynitrokey.nk3.exceptions import TimeoutException
 from pynitrokey.nk3.updates import get_repo
 from pynitrokey.nk3.utils import Version
+from pynitrokey.updates import OverwriteError
 
 T = TypeVar("T", bound=Nitrokey3Base)
 
@@ -250,15 +251,18 @@ def fetch_update(path: str, force: bool, version: Optional[str]) -> None:
             path = update.download_to_dir(path, overwrite=force, callback=bar.update)
         else:
             if not force and os.path.exists(path):
-                raise CliException(
-                    f"{path} already exists.  Use --force to overwrite the file."
-                )
+                raise OverwriteError(path)
             with open(path, "wb") as f:
                 update.download(f, callback=bar.update)
 
         bar.close()
 
         local_print(f"Successfully downloaded firmware release {update.tag} to {path}")
+    except OverwriteError as e:
+        raise CliException(
+            f"{e.path} already exists.  Use --force to overwrite the file.",
+            support_hint=False,
+        )
     except Exception as e:
         raise CliException(f"Failed to download firmware update {update.tag}", e)
 

pynitrokey/updates.py

@@ -19,6 +19,17 @@
 ProgressCallback = Callable[[int, int], None]
 
 
+class DownloadError(Exception):
+    def __init__(self, msg: str) -> None:
+        super().__init__("Cannot download firmware: " + msg)
+
+
+class OverwriteError(Exception):
+    def __init__(self, path: str) -> None:
+        super().__init__(f"File {path} already exists and may not be overwritten")
+        self.path = path
+
+
 class FirmwareUpdate:
     def __init__(self, tag: str, url: str) -> None:
         self.tag = tag
@@ -37,14 +48,14 @@ def download_to_dir(
         callback: Optional[ProgressCallback] = None,
     ) -> str:
         if not os.path.exists(d):
-            raise Exception(f"Cannot download firmware: {d} does not exist")
+            raise DownloadError(f"Directory {d} does not exist")
         if not os.path.isdir(d):
-            raise Exception(f"Cannot download firmware: {d} is not a directory")
+            raise DownloadError(f"{d} is not a directory")
         url = urllib.parse.urlparse(self.url)
         filename = os.path.basename(url.path)
         path = os.path.join(d, filename)
         if os.path.exists(path) and not overwrite:
-            raise Exception(f"File {path} already exists and may not be overwritten")
+            raise OverwriteError(path)
         with open(path, "wb") as f:
             self.download(f, callback=callback)
         return path