Re: [PR] AIP-58: Add object storage backend for xcom [airflow]

["dirrao (via GitHub)" <gi...@apache.org>]

dirrao commented on code in PR #37058:
URL: https://github.com/apache/airflow/pull/37058#discussion_r1473833512


##########
airflow/providers/common/io/xcom/backend.py:
##########
@@ -0,0 +1,166 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+from __future__ import annotations
+
+import json
+import uuid
+from typing import TYPE_CHECKING, Any, TypeVar
+from urllib.parse import urlsplit
+
+import fsspec.utils
+
+from airflow.configuration import conf
+from airflow.io.path import ObjectStoragePath
+from airflow.models.xcom import BaseXCom
+from airflow.utils.json import XComDecoder, XComEncoder
+
+if TYPE_CHECKING:
+    from sqlalchemy.orm import Session
+
+    from airflow.models import XCom
+
+T = TypeVar("T")
+
+SECTION = "common.io"
+
+
+def _is_relative_to(o: ObjectStoragePath, other: ObjectStoragePath) -> bool:
+    """This is a port of the pathlib.Path.is_relative_to method. It is not available in python 3.8."""
+    if hasattr(o, "is_relative_to"):
+        return o.is_relative_to(other)
+
+    try:
+        o.relative_to(other)
+        return True
+    except ValueError:
+        return False
+
+
+def _get_compression_suffix(compression: str) -> str:
+    """This returns the compression suffix for the given compression.
+
+    :raises ValueError: if the compression is not supported
+    """
+    for suffix, c in fsspec.utils.compressions.items():
+        if c == compression:
+            return suffix
+
+    raise ValueError(f"Compression {compression} is not supported. Make sure it is installed.")
+
+
+class XComObjectStoreBackend(BaseXCom):
+    """XCom backend that stores data in an object store or database depending on the size of the data.
+
+    If the value is larger than the configured threshold, it will be stored in an object store.
+    Otherwise, it will be stored in the database. If it is stored in an object store, the path
+    to the object in the store will be returned and saved in the database (by BaseXCom). Otherwise, the value
+    itself will be returned and thus saved in the database.
+    """
+
+    @staticmethod
+    def _get_key(data: str) -> str:
+        """This gets the key from the url and normalizes it to be relative to the configured path.
+
+        :raises ValueError: if the key is not relative to the configured path
+        :raises TypeError: if the url is not a valid url or cannot be split
+        """
+        path = conf.get(SECTION, "xcom_objectstore_path", fallback="")
+        p = ObjectStoragePath(path)
+
+        try:
+            url = urlsplit(data)
+        except AttributeError:
+            raise TypeError(f"Not a valid url: {data}")
+
+        if url.scheme:
+            k = ObjectStoragePath(data)
+
+            if _is_relative_to(k, p) is False:
+                raise ValueError(f"Invalid key: {data}")
+            else:
+                return data.replace(path, "", 1).lstrip("/")
+
+        raise ValueError(f"Not a valid url: {data}")
+
+    @staticmethod
+    def serialize_value(
+        value: T,
+        *,
+        key: str | None = None,
+        task_id: str | None = None,
+        dag_id: str | None = None,
+        run_id: str | None = None,
+        map_index: int | None = None,
+    ) -> bytes | str:
+        s_val = json.dumps(value, cls=XComEncoder).encode("utf-8")
+        path = conf.get(SECTION, "xcom_objectstore_path", fallback="")
+        compression = conf.get(SECTION, "xcom_objectstore_compression", fallback=None)
+
+        if compression:
+            suffix = "." + _get_compression_suffix(compression)
+        else:
+            suffix = ""
+
+        threshold = conf.getint(SECTION, "xcom_objectstore_threshold", fallback=-1)
+
+        if path and -1 < threshold < len(s_val):
+            # safeguard against collisions
+            while True:
+                p = ObjectStoragePath(path) / f"{dag_id}/{run_id}/{task_id}/{str(uuid.uuid4())}{suffix}"
+                if not p.exists():
+                    break
+
+            if not p.parent.exists():
+                p.parent.mkdir(parents=True, exist_ok=True)
+
+            with p.open("wb", compression=compression) as f:
+                f.write(s_val)
+
+            return BaseXCom.serialize_value(str(p))
+        else:
+            return s_val

Review Comment:
   I believe we are missing calling the BaseXCom serializer here.



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