[Storage] Give useful error msg when bad URL passed to BlobClient.from_blob_url() (Azure#23996)

Author: pat-hearps

sdk/storage/azure-storage-blob/CHANGELOG.md

@@ -1,5 +1,11 @@
 # Release History
 
+## 12.##.## (Unreleased)
+
+### Bugs Fixed:
+- fixes a bug in `BlobClient.from_blob_url()` such that users will receive a more helpful error
+message if they pass an incorrect URL without a full `/container/blob` path.
+
 ## 12.12.0b1 (2022-04-14)
 
 ### Features Added

sdk/storage/azure-storage-blob/azure/storage/blob/_blob_client.py

@@ -241,23 +241,28 @@ def from_blob_url(cls, blob_url, credential=None, snapshot=None, **kwargs):
         account_path = ""
         if ".core." in parsed_url.netloc:
             # .core. is indicating non-customized url. Blob name with directory info can also be parsed.
-            path_blob = parsed_url.path.lstrip('/').split('/', 1)
+            path_blob = parsed_url.path.lstrip('/').split('/', maxsplit=1)
         elif "localhost" in parsed_url.netloc or "127.0.0.1" in parsed_url.netloc:
-            path_blob = parsed_url.path.lstrip('/').split('/', 2)
+            path_blob = parsed_url.path.lstrip('/').split('/', maxsplit=2)
             account_path += '/' + path_blob[0]
         else:
             # for customized url. blob name that has directory info cannot be parsed.
             path_blob = parsed_url.path.lstrip('/').split('/')
             if len(path_blob) > 2:
                 account_path = "/" + "/".join(path_blob[:-2])
+
         account_url = "{}://{}{}?{}".format(
             parsed_url.scheme,
             parsed_url.netloc.rstrip('/'),
             account_path,
             parsed_url.query)
+
+        msg_invalid_url = "Invalid URL. Provide a blob_url with a valid blob and container name."
+        if len(path_blob) <= 1:
+            raise ValueError(msg_invalid_url)
         container_name, blob_name = unquote(path_blob[-2]), unquote(path_blob[-1])
         if not container_name or not blob_name:
-            raise ValueError("Invalid URL. Provide a blob_url with a valid blob and container name.")
+            raise ValueError(msg_invalid_url)
 
         path_snapshot, _ = parse_query(parsed_url.query)
         if snapshot:

sdk/storage/azure-storage-blob/tests/test_blob_client.py

@@ -480,6 +480,12 @@ def test_create_blob_client_with_sub_directory_path_in_blob_name(self):
         self.assertEqual(blob_client.blob_name, "dir1/sub000/2010_Unit150_Ivan097_img0003.jpg")
         self.assertEqual(blob_client.url, blob_emulator_url)
 
+    def test_from_blob_url_too_short_url(self):
+        """Test that a useful error message is obtained if user gives incorrect URL"""
+        url = "https://testaccount.blob.core.windows.net/containername/"
+        with pytest.raises(ValueError, match="Invalid URL"):
+            _ = BlobClient.from_blob_url(url)
+
     def test_create_client_for_emulator(self):
         container_client = ContainerClient(
             account_url='http://127.0.0.1:1000/devstoreaccount1',