Port `EventInternalMetadata` class to Rust (#16782)

There are a couple of things we need to be careful of here:

1. The current python code does no validation when loading from the DB,
so we need to be careful to ignore such errors (at least on jki.re there
are some old events with internal metadata fields of the wrong type).
2. We want to be memory efficient, as we often have many hundreds of
thousands of events in the cache at a time.

---------

Co-authored-by: Quentin Gliech <quenting@element.io>

1 files changed, 41 insertions, 0 deletions

diff --git a/rust/src/events/mod.rs b/rust/src/events/mod.rs
new file mode 100644

index 0000000000..ee857b3d72
--- /dev/null
+++ b/rust/src/events/mod.rs
@@ -0,0 +1,41 @@
+/*
+ * This file is licensed under the Affero General Public License (AGPL) version 3.
+ *
+ * Copyright (C) 2024 New Vector, Ltd
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * See the GNU Affero General Public License for more details:
+ * <https://www.gnu.org/licenses/agpl-3.0.html>.
+ *
+ * Originally licensed under the Apache License, Version 2.0:
+ * <http://www.apache.org/licenses/LICENSE-2.0>.
+ *
+ * [This file includes modifications made by New Vector Limited]
+ *
+ */
+
+//! Classes for representing Events.
+
+use pyo3::{types::PyModule, PyResult, Python};
+
+mod internal_metadata;
+
+/// Called when registering modules with python.
+pub fn register_module(py: Python<'_>, m: &PyModule) -> PyResult<()> {
+    let child_module = PyModule::new(py, "events")?;
+    child_module.add_class::<internal_metadata::EventInternalMetadata>()?;
+
+    m.add_submodule(child_module)?;
+
+    // We need to manually add the module to sys.modules to make `from
+    // synapse.synapse_rust import events` work.
+    py.import("sys")?
+        .getattr("modules")?
+        .set_item("synapse.synapse_rust.events", child_module)?;
+
+    Ok(())
+}