[TOSFS #18] Override fssepc#exists default implementation to optimize…

… performance

tosfs/core.py

@@ -46,6 +46,9 @@ def setup_logging() -> None:
     "The tosfs's log level is set to be %s", logging.getLevelName(logger.level)
 )
 
+# constants
+SERVER_RESPONSE_CODE_NOT_FOUND = 404
+
 
 class TosFileSystem(AbstractFileSystem):
     """Tos file system.
@@ -124,6 +127,53 @@ def ls(
 
         return files if detail else sorted([o["name"] for o in files])
 
+    def exists(self, path: str, **kwargs: Union[str, bool, float, None]) -> bool:
+        """Is there a file at the given path."""
+        bucket, key, _ = self._split_path(path)
+        if not key:
+            return self._exists_bucket(bucket)
+
+        object_exists = self._exists_object(bucket, key)
+        if not object_exists:
+            return self._exists_object(bucket, key + "/")
+        return object_exists
+
+    def _exists_bucket(self, bucket: str) -> bool:
+        """Check the bucket exist."""
+        try:
+            self.tos_client.head_bucket(bucket)
+            return True
+        except tos.exceptions.TosClientError as e:
+            logger.error("Tosfs failed with client error: %s", e)
+            raise e
+        except tos.exceptions.TosServerError as e:
+            if e.status_code == SERVER_RESPONSE_CODE_NOT_FOUND:
+                return False
+            else:
+                logger.error("Tosfs failed with server error: %s", e)
+                raise e
+        except Exception as e:
+            logger.error("Tosfs failed with unknown error: %s", e)
+            raise TosfsError(f"Tosfs failed with unknown error: {e}") from e
+
+    def _exists_object(self, bucket: str, key: str) -> bool:
+        """Check the object exist."""
+        try:
+            self.tos_client.head_object(bucket, key)
+            return True
+        except tos.exceptions.TosClientError as e:
+            logger.error("Tosfs failed with client error: %s", e)
+            raise e
+        except tos.exceptions.TosServerError as e:
+            if e.status_code == SERVER_RESPONSE_CODE_NOT_FOUND:
+                return False
+            else:
+                logger.error("Tosfs failed with server error: %s", e)
+                raise e
+        except Exception as e:
+            logger.error("Tosfs failed with unknown error: %s", e)
+            raise TosfsError(f"Tosfs failed with unknown error: {e}") from e
+
     def _lsbuckets(self, refresh: bool = False) -> List[dict]:
         """List all buckets in the account.
 

tosfs/tests/test_tosfs.py

@@ -83,3 +83,23 @@ def test_inner_rm(tosfs: TosFileSystem, bucket: str, temporary_workspace: str) -
     assert tosfs.ls(f"{bucket}/{temporary_workspace}", detail=False) == []
 
     tosfs._rm(f"{bucket}/{temporary_workspace}/{file_name}")
+
+
+def test_exists_bucket(
+    tosfs: TosFileSystem, bucket: str, temporary_workspace: str
+) -> None:
+    assert tosfs.exists(bucket)
+    assert not tosfs.exists("nonexistent")
+
+
+def test_exists_object(
+    tosfs: TosFileSystem, bucket: str, temporary_workspace: str
+) -> None:
+    file_name = random_path()
+    tosfs.tos_client.put_object(bucket=bucket, key=f"{temporary_workspace}/{file_name}")
+    assert tosfs.exists(f"{bucket}/{temporary_workspace}")
+    assert tosfs.exists(f"{bucket}/{temporary_workspace}/")
+    assert tosfs.exists(f"{bucket}/{temporary_workspace}/{file_name}")
+    assert not tosfs.exists(f"{bucket}/{temporary_workspace}/nonexistent")
+    assert not tosfs.exists(f"{bucket}/nonexistent")
+    assert not tosfs.exists(f"{bucket}/{temporary_workspace}/nonexistent")