Return url for file in GCP public bucket instead of error (#748)

src/datachain/client/gcs.py

@@ -32,6 +32,15 @@ def create_fs(cls, **kwargs) -> GCSFileSystem:
 
         return cast(GCSFileSystem, super().create_fs(**kwargs))
 
+    def url(self, path: str, expires: int = 3600, **kwargs) -> str:
+        try:
+            return self.fs.sign(self.get_full_path(path), expiration=expires, **kwargs)
+        except AttributeError as exc:
+            is_anon = self.fs.storage_options.get("token") == "anon"
+            if is_anon and "you need a private key to sign credentials" in str(exc):
+                return f"https://storage.googleapis.com/{self.name}/{path}"
+            raise
+
     @staticmethod
     def parse_timestamp(timestamp: str) -> datetime:
         """

tests/unit/test_client_gcs.py

@@ -0,0 +1,17 @@
+from datachain.client import Client
+
+
+def test_anon_url(mocker):
+    def sign(*args, **kwargs):
+        raise AttributeError(
+            "you need a private key to sign credentials."
+            "the credentials you are currently using"
+            " <class 'google.oauth2.credentials.Credentials'> just contains a token."
+            " see https://googleapis.dev/python/google-api-core/latest/auth.html"
+            "#setting-up-a-service-account for more details."
+        )
+
+    mocker.patch("gcsfs.GCSFileSystem.sign", side_effect=sign)
+
+    client = Client.get_client("gs://foo", None, anon=True)
+    assert client.url("bar") == "https://storage.googleapis.com/foo/bar"