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// Copyright 2024 The Matrix.org Foundation C.I.C.
//
// Licensed 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.
use ruma::{events::AnySyncTimelineEvent, serde::Raw};
use serde::Deserialize;
/// Our best guess at the reason why an event can't be decrypted.
#[derive(Clone, Copy, Debug, Default, Hash, PartialEq, Eq)]
#[cfg_attr(feature = "uniffi", derive(uniffi::Enum))]
pub enum UtdCause {
/// We don't have an explanation for why this UTD happened - it is probably
/// a bug, or a network split between the two homeservers.
#[default]
Unknown = 0,
/// This event was sent when we were not a member of the room (or invited),
/// so it is impossible to decrypt (without MSC3061).
Membership = 1,
//
// TODO: Other causes for UTDs. For example, this message is device-historical, information
// extracted from the WithheldCode in the MissingRoomKey object, or various types of Olm
// session problems.
//
// Note: This needs to be a simple enum so we can export it via FFI, so if more information
// needs to be provided, it should be through a separate type.
}
/// MSC4115 membership info in the unsigned area.
#[derive(Deserialize)]
struct UnsignedWithMembership {
#[serde(alias = "io.element.msc4115.membership")]
membership: Membership,
}
/// MSC4115 contents of the membership property
#[derive(Deserialize)]
#[serde(rename_all = "lowercase")]
enum Membership {
Leave,
Invite,
Join,
}
impl UtdCause {
/// Decide the cause of this UTD, based on the evidence we have.
pub fn determine(raw_event: Option<&Raw<AnySyncTimelineEvent>>) -> Self {
// TODO: in future, use more information to give a richer answer. E.g.
// is this event device-historical? Was the Olm communication disrupted?
// Did the sender refuse to send the key because we're not verified?
// Look in the unsigned area for a `membership` field.
if let Some(raw_event) = raw_event {
if let Ok(Some(unsigned)) = raw_event.get_field::<UnsignedWithMembership>("unsigned") {
if let Membership::Leave = unsigned.membership {
// We were not a member - this is the cause of the UTD
return UtdCause::Membership;
}
}
}
// We can't find an explanation for this UTD
UtdCause::Unknown
}
}
#[cfg(test)]
mod tests {
use ruma::{events::AnySyncTimelineEvent, serde::Raw};
use serde_json::{json, value::to_raw_value};
use crate::types::events::UtdCause;
#[test]
fn a_missing_raw_event_means_we_guess_unknown() {
// When we don't provide any JSON to check for membership, then we guess the UTD
// is unknown.
assert_eq!(UtdCause::determine(None), UtdCause::Unknown);
}
#[test]
fn if_there_is_no_membership_info_we_guess_unknown() {
// If our JSON contains no membership info, then we guess the UTD is unknown.
assert_eq!(UtdCause::determine(Some(&raw_event(json!({})))), UtdCause::Unknown);
}
#[test]
fn if_membership_info_cant_be_parsed_we_guess_unknown() {
// If our JSON contains a membership property but not the JSON we expected, then
// we guess the UTD is unknown.
assert_eq!(
UtdCause::determine(Some(&raw_event(json!({ "unsigned": { "membership": 3 } })))),
UtdCause::Unknown
);
}
#[test]
fn if_membership_is_invite_we_guess_unknown() {
// If membership=invite then we expected to be sent the keys so the cause of the
// UTD is unknown.
assert_eq!(
UtdCause::determine(Some(&raw_event(
json!({ "unsigned": { "membership": "invite" } }),
))),
UtdCause::Unknown
);
}
#[test]
fn if_membership_is_join_we_guess_unknown() {
// If membership=join then we expected to be sent the keys so the cause of the
// UTD is unknown.
assert_eq!(
UtdCause::determine(Some(&raw_event(json!({ "unsigned": { "membership": "join" } })))),
UtdCause::Unknown
);
}
#[test]
fn if_membership_is_leave_we_guess_membership() {
// If membership=leave then we have an explanation for why we can't decrypt,
// until we have MSC3061.
assert_eq!(
UtdCause::determine(Some(&raw_event(json!({ "unsigned": { "membership": "leave" } })))),
UtdCause::Membership
);
}
#[test]
fn if_unstable_prefix_membership_is_leave_we_guess_membership() {
// Before MSC4115 is merged, we support the unstable prefix too.
assert_eq!(
UtdCause::determine(Some(&raw_event(
json!({ "unsigned": { "io.element.msc4115.membership": "leave" } })
))),
UtdCause::Membership
);
}
fn raw_event(value: serde_json::Value) -> Raw<AnySyncTimelineEvent> {
Raw::from_json(to_raw_value(&value).unwrap())
}
}