matrix_sdk_common/

serde_helpers.rs

// Copyright 2025 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.

//! A collection of serde helpers to avoid having to deserialize an entire event
//! to access some fields.

use ruma::{
    MilliSecondsSinceUnixEpoch, OwnedEventId,
    events::{
        AnyMessageLikeEventContent, AnySyncMessageLikeEvent, AnySyncTimelineEvent,
        MessageLikeEventType,
        relation::{BundledThread, RelationType},
    },
    room_version_rules::RedactionRules,
    serde::Raw,
};
use serde::Deserialize;

#[derive(Deserialize)]
struct RelatesTo {
    #[serde(rename = "rel_type")]
    rel_type: RelationType,
    #[serde(rename = "event_id")]
    event_id: Option<OwnedEventId>,
}

#[allow(missing_debug_implementations)]
#[derive(Deserialize)]
struct SimplifiedContent {
    #[serde(rename = "m.relates_to")]
    relates_to: Option<RelatesTo>,
}

/// Try to extract the thread root from an event's content, if provided.
///
/// The thread root is the field located at `m.relates_to`.`event_id`,
/// if the field at `m.relates_to`.`rel_type` is `m.thread`.
///
/// Returns `None` if we couldn't find a thread root, or if there was an issue
/// during deserialization.
pub fn extract_thread_root_from_content(
    content: Raw<AnyMessageLikeEventContent>,
) -> Option<OwnedEventId> {
    let relates_to = content.deserialize_as_unchecked::<SimplifiedContent>().ok()?.relates_to?;
    match relates_to.rel_type {
        RelationType::Thread => relates_to.event_id,
        _ => None,
    }
}

/// Try to extract the thread root from a timeline event, if provided.
///
/// The thread root is the field located at `content`.`m.relates_to`.`event_id`,
/// if the field at `content`.`m.relates_to`.`rel_type` is `m.thread`.
///
/// Returns `None` if we couldn't find a thread root, or if there was an issue
/// during deserialization.
pub fn extract_thread_root(event: &Raw<AnySyncTimelineEvent>) -> Option<OwnedEventId> {
    extract_thread_root_from_content(event.get_field("content").ok().flatten()?)
}

/// Try to extract the type and target of a relation, from a raw timeline event,
/// if provided.
pub fn extract_relation(event: &Raw<AnySyncTimelineEvent>) -> Option<(RelationType, OwnedEventId)> {
    let relates_to = event.get_field::<SimplifiedContent>("content").ok().flatten()?.relates_to?;
    Some((relates_to.rel_type, relates_to.event_id?))
}

/// Try to extract the event ID of the event targeted by `event` if it is of
/// type `m.room.redaction`.
pub fn extract_redaction_target(
    event: &Raw<AnySyncTimelineEvent>,
    redaction_rules: &RedactionRules,
) -> Option<OwnedEventId> {
    // Check if it's a `m.room.redaction`.
    let Ok(Some(MessageLikeEventType::RoomRedaction)) =
        event.get_field::<MessageLikeEventType>("type")
    else {
        // Not the expected event. Early return.
        return None;
    };

    // It is a `m.room.redaction`! We can deserialize it entirely.

    let Ok(AnySyncTimelineEvent::MessageLike(AnySyncMessageLikeEvent::RoomRedaction(redaction))) =
        event.deserialize()
    else {
        // Failed to deserialized. Early return.
        return None;
    };

    redaction.redacts(redaction_rules).map(ToOwned::to_owned)
}

/// Try to extract a bundled thread of a timeline event, if available.
pub fn extract_bundled_thread(event: &Raw<AnySyncTimelineEvent>) -> Option<BundledThread> {
    #[derive(Deserialize)]
    struct Unsigned {
        #[serde(rename = "m.relations")]
        relations: Option<Relations>,
    }

    #[derive(Deserialize)]
    struct Relations {
        #[serde(rename = "m.thread")]
        thread: Option<BundledThread>,
    }

    match event.get_field::<Unsigned>("unsigned") {
        Ok(Some(Unsigned { relations: Some(Relations { thread: Some(bundled_thread) }) })) => {
            Some(bundled_thread)
        }
        Ok(_) | Err(_) => None,
    }
}

/// Try to extract the `origin_server_ts`, if available.
///
/// If the value is larger than `max_value`, it becomes `max_value`. This is
/// necessary to prevent against user-forged value pretending an event is coming
/// from the future.
pub fn extract_timestamp(
    event: &Raw<AnySyncTimelineEvent>,
    max_value: MilliSecondsSinceUnixEpoch,
) -> Option<MilliSecondsSinceUnixEpoch> {
    let mut origin_server_ts = event.get_field("origin_server_ts").ok().flatten()?;

    if origin_server_ts > max_value {
        origin_server_ts = max_value;
    }

    Some(origin_server_ts)
}

#[cfg(test)]
mod tests {
    use assert_matches::assert_matches;
    use ruma::{UInt, event_id, owned_event_id};
    use serde_json::json;

    use super::{
        MilliSecondsSinceUnixEpoch, Raw, RelationType, extract_bundled_thread, extract_relation,
        extract_thread_root, extract_timestamp,
    };

    #[test]
    fn test_extract_thread_root() {
        // No event factory in this crate :( There would be a dependency cycle with the
        // `matrix-sdk-test` crate if we tried to use it here.

        // We can extract the thread root from a regular message that contains one.
        let thread_root = event_id!("$thread_root_event_id:example.com");
        let event = Raw::new(&json!({
            "event_id": "$eid:example.com",
            "type": "m.room.message",
            "sender": "@alice:example.com",
            "origin_server_ts": 42,
            "content": {
                "body": "Hello, world!",
                "m.relates_to": {
                    "rel_type": "m.thread",
                    "event_id": thread_root,
                }
            }
        }))
        .unwrap()
        .cast_unchecked();

        let observed_thread_root = extract_thread_root(&event);
        assert_eq!(observed_thread_root.as_deref(), Some(thread_root));
        let observed_relation = extract_relation(&event).unwrap();
        assert_eq!(observed_relation, (RelationType::Thread, thread_root.to_owned()));

        // If the event doesn't have a content for some reason (redacted), it returns
        // None.
        let event = Raw::new(&json!({
            "event_id": "$eid:example.com",
            "type": "m.room.message",
            "sender": "@alice:example.com",
            "origin_server_ts": 42,
        }))
        .unwrap()
        .cast_unchecked();

        let observed_thread_root = extract_thread_root(&event);
        assert_matches!(observed_thread_root, None);
        assert_matches!(extract_relation(&event), None);

        // If the event has a content but with no `m.relates_to` field, it returns None.
        let event = Raw::new(&json!({
            "event_id": "$eid:example.com",
            "type": "m.room.message",
            "sender": "@alice:example.com",
            "origin_server_ts": 42,
            "content": {
                "body": "Hello, world!",
            }
        }))
        .unwrap()
        .cast_unchecked();

        let observed_thread_root = extract_thread_root(&event);
        assert_matches!(observed_thread_root, None);
        assert_matches!(extract_relation(&event), None);

        // If the event has a relation, but it's not a thread reply, it returns None.
        let event = Raw::new(&json!({
            "event_id": "$eid:example.com",
            "type": "m.room.message",
            "sender": "@alice:example.com",
            "origin_server_ts": 42,
            "content": {
                "body": "Hello, world!",
                "m.relates_to": {
                    "rel_type": "m.reference",
                    "event_id": "$referenced_event_id:example.com",
                }
            }
        }))
        .unwrap()
        .cast_unchecked();

        let observed_thread_root = extract_thread_root(&event);
        assert_matches!(observed_thread_root, None);
        let observed_relation = extract_relation(&event).unwrap();
        assert_eq!(
            observed_relation,
            (RelationType::Reference, owned_event_id!("$referenced_event_id:example.com"))
        );
    }

    #[test]
    fn test_extract_bundled_thread() {
        // When there's a bundled thread summary, we can extract it.
        let event = Raw::new(&json!({
            "event_id": "$eid:example.com",
            "type": "m.room.message",
            "sender": "@alice:example.com",
            "origin_server_ts": 42,
            "content": {
                "body": "Hello, world!",
            },
            "unsigned": {
                "m.relations": {
                    "m.thread": {
                        "latest_event": {
                            "event_id": "$latest_event:example.com",
                            "type": "m.room.message",
                            "sender": "@bob:example.com",
                            "origin_server_ts": 42,
                            "content": {
                                "body": "Hello to you too!",
                            }
                        },
                        "count": 2,
                        "current_user_participated": true,
                    }
                }
            }
        }))
        .unwrap()
        .cast_unchecked();

        assert!(extract_bundled_thread(&event).is_some());

        // When there's not a bundled thread summary, we can assert it with certainty.
        let event = Raw::new(&json!({
            "event_id": "$eid:example.com",
            "type": "m.room.message",
            "sender": "@alice:example.com",
            "origin_server_ts": 42,
        }))
        .unwrap()
        .cast_unchecked();

        assert!(extract_bundled_thread(&event).is_none());

        // When there's a bundled replace, we can assert there's no thread summary.
        let event = Raw::new(&json!({
            "event_id": "$eid:example.com",
            "type": "m.room.message",
            "sender": "@alice:example.com",
            "origin_server_ts": 42,
            "content": {
                "body": "Bonjour, monde!",
            },
            "unsigned": {
                "m.relations": {
                    "m.replace":
                    {
                        "event_id": "$update:example.com",
                        "type": "m.room.message",
                        "sender": "@alice:example.com",
                        "origin_server_ts": 43,
                        "content": {
                            "body": "* Hello, world!",
                        }
                    },
                }
            }
        }))
        .unwrap()
        .cast_unchecked();

        assert!(extract_bundled_thread(&event).is_none());

        // When the bundled thread summary is malformed, we return `None`.
        let event = Raw::new(&json!({
            "event_id": "$eid:example.com",
            "type": "m.room.message",
            "sender": "@alice:example.com",
            "origin_server_ts": 42,
            "unsigned": {
                "m.relations": {
                    "m.thread": {
                        // Missing `latest_event` field.
                    }
                }
            }
        }))
        .unwrap()
        .cast_unchecked();

        assert!(extract_bundled_thread(&event).is_none());
    }

    #[test]
    fn test_extract_timestamp() {
        let event = Raw::new(&json!({
            "event_id": "$ev0",
            "type": "m.room.message",
            "sender": "@mnt_io:matrix.org",
            "origin_server_ts": 42,
            "content": {
                "body": "Le gras, c'est la vie",
            }
        }))
        .unwrap()
        .cast_unchecked();

        let timestamp = extract_timestamp(&event, MilliSecondsSinceUnixEpoch(UInt::from(100u32)));

        assert_eq!(timestamp, Some(MilliSecondsSinceUnixEpoch(UInt::from(42u32))));
    }

    #[test]
    fn test_extract_timestamp_no_origin_server_ts() {
        let event = Raw::new(&json!({
            "event_id": "$ev0",
            "type": "m.room.message",
            "sender": "@mnt_io:matrix.org",
            "content": {
                "body": "Le gras, c'est la vie",
            }
        }))
        .unwrap()
        .cast_unchecked();

        let timestamp = extract_timestamp(&event, MilliSecondsSinceUnixEpoch(UInt::from(100u32)));

        assert!(timestamp.is_none());
    }

    #[test]
    fn test_extract_timestamp_invalid_origin_server_ts() {
        let event = Raw::new(&json!({
            "event_id": "$ev0",
            "type": "m.room.message",
            "sender": "@mnt_io:matrix.org",
            "origin_server_ts": "saucisse",
            "content": {
                "body": "Le gras, c'est la vie",
            }
        }))
        .unwrap()
        .cast_unchecked();

        let timestamp = extract_timestamp(&event, MilliSecondsSinceUnixEpoch(UInt::from(100u32)));

        assert!(timestamp.is_none());
    }

    #[test]
    fn test_extract_timestamp_malicious_origin_server_ts() {
        let event = Raw::new(&json!({
            "event_id": "$ev0",
            "type": "m.room.message",
            "sender": "@mnt_io:matrix.org",
            "origin_server_ts": 101,
            "content": {
                "body": "Le gras, c'est la vie",
            }
        }))
        .unwrap()
        .cast_unchecked();

        let timestamp = extract_timestamp(&event, MilliSecondsSinceUnixEpoch(UInt::from(100u32)));

        assert_eq!(timestamp, Some(MilliSecondsSinceUnixEpoch(UInt::from(100u32))));
    }
}