By default, the new `experimental-nodejs` feature is
disabled. However, when enabled, it uses our own fork of
`indexed_db_futures` that make it work on Node.js, and so this entire
`matrix-sdk-indexebdb` crate.
The crypto crate consumes to-device events, if needed decrypts them, and
in the end reserializes while zeroizing secrets.
It needs to do this reserialization cycle as loslessly as possible, this
is why we have a bunch of BTreeMaps lying in events and contents that
capture unknown fields.
The Deserialize implementation of ToDeviceEvent<C> put the event type
into this BTreeMap but the Serialize implementation figures it out from
the EventType trait of the content.
This patch simplifies things by putting the event type into
ToDeviceEvent<C>, this also means that we can just derive the Serialize
implementation for ToDeviceEvent<C>.
Inspired by the changes in #1013 I was thinking about the use case for `sync_*` and how we handle error cases. Most notably while we give the callback the option to stop the loop, we don't really give an indication to the outside, how to interpret that cancellation: was there a failure? should we restart?
Take e.g. a connectivity issue on the wire, we'd constantly loop and just `warn`, what you might or might not see. Even if you handle that in the `sync_with_result_callback` and thus break the loop, the outer caller now still doesn't know whether everything is honky dory or whether they should restart.
This Changes reworks that area by having all the `sync` return `Result<(), Error>`, where `()` means it was ended by the inner callback (which in `sync()` never occurs) or `Error` is the error either the inner `result_callback` found or the that was coming from the `send` in the first place. Thus allowing us to e.g. back down to sync as it was a dead wire or restart it if there was only a temporary problem. Making all that a just a bit more "rust-y".
… for matrix-sdk, matrix-sdk-base, matrix-sdk-common and matrix-sdk-crypto.
matrix-sdk-indexeddb as well as the JS bindings and wasm_command_bot are
left as-is because they will likely always require JS.
Benjamin Kampmann