Revert "postgresql: drop fallback for extra_headers in Revision.metadata"

This reverts commit 8435607b

swh/storage/postgresql/converters.py

@@ -252,10 +252,13 @@ def db_to_revision(db_revision: Dict[str, Any]) -> Revision:
                 parents.append(parent)
 
     metadata = db_revision["metadata"]
-    if metadata and "extra_headers" in metadata:
-        del metadata["extra_headers"]
-
-    extra_headers = db_revision["extra_headers"] or ()
+    extra_headers = db_revision["extra_headers"]
+    if not extra_headers:
+        if metadata and "extra_headers" in metadata:
+            extra_headers = db_to_git_headers(metadata.pop("extra_headers"))
+        else:
+            # For older versions of the database that were not migrated to schema v161
+            extra_headers = ()
 
     return Revision(
         id=db_revision["id"],

swh/storage/tests/test_revision_bw_compat.py

+# Copyright (C) 2020  The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+import attr
+
+from swh.core.utils import decode_with_escape
+from swh.storage import get_storage
+from swh.storage.tests.test_postgresql import db_transaction
+
+
+def headers_to_db(git_headers):
+    return [[key, decode_with_escape(value)] for key, value in git_headers]
+
+
+def test_revision_extra_header_in_metadata(swh_storage_backend_config, sample_data):
+    storage = get_storage(**swh_storage_backend_config)
+    rev = sample_data.revision
+
+    md_w_extra = dict(
+        rev.metadata.items(),
+        extra_headers=headers_to_db(
+            [
+                ["gpgsig", b"test123"],
+                ["mergetag", b"foo\\bar"],
+                ["mergetag", b"\x22\xaf\x89\x80\x01\x00"],
+            ]
+        ),
+    )
+
+    bw_rev = attr.evolve(rev, extra_headers=())
+    object.__setattr__(bw_rev, "metadata", md_w_extra)
+    assert bw_rev.extra_headers == ()
+
+    assert storage.revision_add([bw_rev]) == {"revision:add": 1}
+
+    # check data in the db are old format
+    with db_transaction(storage) as (_, cur):
+        cur.execute("SELECT metadata, extra_headers FROM revision")
+        metadata, extra_headers = cur.fetchone()
+    assert extra_headers == []
+    assert metadata == bw_rev.metadata
+
+    # check the Revision build from revision_get is the original, "new style", Revision
+    assert storage.revision_get([rev.id]) == [rev]