Fix s3 download for folders

src/anemoi/utils/remote/__init__.py

@@ -138,6 +138,8 @@ def copy(self, source, target, **kwargs):
         raise NotImplementedError
 
     def get_temporary_target(self, target, pattern):
+        if pattern is None:
+            return target
         dirname, basename = os.path.split(target)
         return pattern.format(dirname=dirname, basename=basename)
 
@@ -199,13 +201,13 @@ def __init__(
             target = os.path.basename(source)
 
         temporary_target = {
-            False: "{dirname}/{basename}",
+            False: None,
             True: "{dirname}-downloading/{basename}",
             "-tmp/*": "{dirname}-tmp/{basename}",
             "*-tmp": "{dirname}/{basename}-tmp",
             "tmp-*": "{dirname}/tmp-{basename}",
         }.get(temporary_target, temporary_target)
-        assert isinstance(temporary_target, str), (type(temporary_target), temporary_target)
+        assert temporary_target is None or isinstance(temporary_target, str), (type(temporary_target), temporary_target)
 
         self.source = source
         self.target = target

src/anemoi/utils/remote/s3.py

@@ -192,6 +192,9 @@ def _transfer_file(self, source, target, overwrite, resume, verbosity, threads,
         _, _, bucket, key = source.split("/", 3)
         s3 = s3_client(bucket)
 
+        if key.endswith("/"):
+            return 0
+
         try:
             response = s3.head_object(Bucket=bucket, Key=key)
         except s3.exceptions.ClientError as e: