src/db.rs

@@ -25,12 +25,18 @@ impl Database {
     fn new_db(db: sled::Db) -> Result<Database, DataError> {
         let migrations = db.open_tree("migrations")?;
 
-        Ok(Database {
+        let database = Database {
             db: db.clone(),
             variables: Variables::new(&db)?,
             migrations: Migrations(migrations),
             rooms: Rooms::new(&db)?,
-        })
+        };
+
+        //Start any event handlers.
+        database.rooms.start_handler();
+
+        info!("Opened database.");
+        Ok(database)
     }
 
     pub fn new<P: AsRef<Path>>(path: P) -> Result<Database, DataError> {

src/db/errors.rs

@@ -26,6 +26,9 @@ pub enum DataError {
     #[error("expected i32, but i32 schema was violated")]
     I32SchemaViolation,
 
+    #[error("unexpected or corruptd data bytes")]
+    InvalidValue,
+
     #[error("expected string, but utf8 schema was violated: {0}")]
     Utf8chemaViolation(#[from] std::str::Utf8Error),
 

src/db/rooms.rs

@@ -1,9 +1,16 @@
 use crate::db::errors::DataError;
+use crate::db::schema::convert_u64;
+use byteorder::BigEndian;
+use log::{error, log_enabled, trace};
 use sled::transaction::TransactionalTree;
 use sled::Transactional;
-use sled::Tree;
+use sled::{CompareAndSwapError, Tree};
 use std::collections::HashSet;
 use std::str;
+use std::time::{SystemTime, UNIX_EPOCH};
+use tokio::task::JoinHandle;
+use zerocopy::byteorder::U64;
+use zerocopy::AsBytes;
 
 #[derive(Clone)]
 pub struct Rooms {
@@ -15,8 +22,23 @@ pub struct Rooms {
 
     /// Username -> list of room IDs user is in.
     pub(in crate::db) username_roomids: Tree,
+
+    /// Room ID(str) 0xff event ID(str) -> timestamp. Records event
+    /// IDs that we have received, so we do not process twice.
+    pub(in crate::db) roomeventid_timestamp: Tree,
+
+    /// Room ID(str) 0xff timestamp(u64) -> event ID. Records event
+    /// IDs with timestamp as the primary key instead. Exists to allow
+    /// easy scanning of old roomeventid_timestamp records for
+    /// removal. Be careful with u64, it can have 0xff and 0xfe bytes.
+    /// A simple split on 0xff will not work with this key. Instead,
+    /// it is meant to be split on the first 0xff byte only, and
+    /// separated into room ID and timestamp.
+    pub(in crate::db) roomtimestamp_eventid: Tree,
 }
 
+/// An enum that can hold either a regular sled Tree, or a
+/// Transactional tree.
 #[derive(Clone, Copy)]
 enum TxableTree<'a> {
     Tree(&'a Tree),
@@ -35,7 +57,30 @@ impl<'a> Into<TxableTree<'a>> for &'a TransactionalTree {
     }
 }
 
-fn get_set<'a, T: Into<TxableTree<'a>>>(tree: T, key: &[u8]) -> Result<HashSet<String>, DataError> {
+/// A set of functions that can be used with a sled::Tree that stores
+/// HashSets as its values. Atomicity is partially handled. If the
+/// Tree is a transactional tree, operations will be atomic.
+/// Otherwise, there is a potential non-atomic step.
+mod hashset_tree {
+    use super::*;
+
+    fn insert_set<'a, T: Into<TxableTree<'a>>>(
+        tree: T,
+        key: &[u8],
+        set: HashSet<String>,
+    ) -> Result<(), DataError> {
+        let serialized = bincode::serialize(&set)?;
+        match tree.into() {
+            TxableTree::Tree(tree) => tree.insert(key, serialized)?,
+            TxableTree::Tx(tx) => tx.insert(key, serialized)?,
+        };
+        Ok(())
+    }
+
+    pub(super) fn get_set<'a, T: Into<TxableTree<'a>>>(
+        tree: T,
+        key: &[u8],
+    ) -> Result<HashSet<String>, DataError> {
         let set: HashSet<String> = match tree.into() {
             TxableTree::Tree(tree) => tree.get(key)?,
             TxableTree::Tx(tx) => tx.get(key)?,
@@ -44,30 +89,75 @@ fn get_set<'a, T: Into<TxableTree<'a>>>(tree: T, key: &[u8]) -> Result<HashSet<S
         .unwrap_or(Ok(HashSet::new()))?;
 
         Ok(set)
-}
+    }
 
-fn remove_from_set<'a, T: Into<TxableTree<'a>> + Copy>(
+    pub(super) fn remove_from_set<'a, T: Into<TxableTree<'a>> + Copy>(
         tree: T,
         key: &[u8],
         value_to_remove: &str,
-) -> Result<(), DataError> {
+    ) -> Result<(), DataError> {
         let mut set = get_set(tree, key)?;
         set.remove(value_to_remove);
         insert_set(tree, key, set)?;
         Ok(())
-}
+    }
 
-fn insert_set<'a, T: Into<TxableTree<'a>>>(
+    pub(super) fn add_to_set<'a, T: Into<TxableTree<'a>> + Copy>(
         tree: T,
         key: &[u8],
-    set: HashSet<String>,
+        value_to_add: String,
-) -> Result<(), DataError> {
+    ) -> Result<(), DataError> {
-    let serialized = bincode::serialize(&set)?;
+        let mut set = get_set(tree, key)?;
-    match tree.into() {
+        set.insert(value_to_add);
-        TxableTree::Tree(tree) => tree.insert(key, serialized)?,
+        insert_set(tree, key, set)?;
-        TxableTree::Tx(tx) => tx.insert(key, serialized)?,
-    };
         Ok(())
+    }
+}
+
+/// Functions that specifically relate to the "timestamp index" tree,
+/// which is stored on the Room sinstance as a tree called
+/// roomtimestamp_eventid. Tightly coupled to the event watcher in the
+/// Rooms impl, and only factored out for unit testing.
+mod timestamp_index {
+    use super::*;
+
+    /// Insert an entry from the main roomeventid_timestamp Tree into
+    /// the timestamp index. Keys in this Tree are stored as room ID
+    /// 0xff timestamp, with the value being a hashset of event IDs
+    /// received at the time. The parameters come from an insert to
+    /// that Tree, where the key is room ID 0xff event ID, and the
+    /// value is the timestamp.
+    pub(super) fn insert(
+        roomtimestamp_eventid: &Tree,
+        key: &[u8],
+        timestamp_bytes: &[u8],
+    ) -> Result<(), DataError> {
+        let parts: Vec<&[u8]> = key.split(|&b| b == 0xff).collect();
+        if let [room_id, event_id] = parts[..] {
+            let mut ts_key = room_id.to_vec();
+            ts_key.push(0xff);
+            ts_key.extend_from_slice(&timestamp_bytes);
+            trace_index_record(room_id, event_id, &timestamp_bytes);
+
+            let event_id = str::from_utf8(event_id)?;
+            hashset_tree::add_to_set(roomtimestamp_eventid, &ts_key, event_id.to_owned())?;
+            Ok(())
+        } else {
+            Err(DataError::InvalidValue)
+        }
+    }
+
+    /// Log a trace message.
+    fn trace_index_record(room_id: &[u8], event_id: &[u8], timestamp: &[u8]) {
+        if log_enabled!(log::Level::Trace) {
+            trace!(
+                "Recording event {} | {} received at {} in timestamp index.",
+                str::from_utf8(room_id).unwrap_or("[invalid room id]"),
+                str::from_utf8(event_id).unwrap_or("[invalid event id]"),
+                convert_u64(timestamp).unwrap_or(0)
+            );
+        }
+    }
 }
 
 impl Rooms {
@@ -76,29 +166,81 @@ impl Rooms {
             roomid_roominfo: db.open_tree("roomid_roominfo")?,
             roomid_usernames: db.open_tree("roomid_usernames")?,
             username_roomids: db.open_tree("username_roomids")?,
+            roomeventid_timestamp: db.open_tree("roomeventid_timestamp")?,
+            roomtimestamp_eventid: db.open_tree("roomtimestamp_eventid")?,
         })
     }
 
+    /// Start an event subscriber that listens for inserts made by the
+    /// `should_process` function. This event handler duplicates the
+    /// entry by timestamp instead of event ID.
+    pub(in crate::db) fn start_handler(&self) -> JoinHandle<()> {
+        //Clone due to lifetime requirements.
+        let roomeventid_timestamp = self.roomeventid_timestamp.clone();
+        let roomtimestamp_eventid = self.roomtimestamp_eventid.clone();
+
+        tokio::spawn(async move {
+            let mut subscriber = roomeventid_timestamp.watch_prefix(b"");
+
+            // TODO make this handler receive kill messages somehow so
+            // we can unit test it and gracefully shut it down.
+            while let Some(event) = (&mut subscriber).await {
+                if let sled::Event::Insert { key, value } = event {
+                    match timestamp_index::insert(&roomtimestamp_eventid, &key, &value) {
+                        Err(e) => {
+                            error!("Unable to update the timestamp index: {}", e);
+                        }
+                        _ => (),
+                    }
+                }
+            }
+        })
+    }
+
+    /// Determine if an event in a room should be processed. The event
+    /// is atomically recorded and true returned if the database has
+    /// not seen tis event yet. If the event already exists in the
+    /// database, the function returns false. Events are recorded by
+    /// this function by inserting the (system-local) timestamp in
+    /// epoch seconds.
+    pub fn should_process(&self, room_id: &str, event_id: &str) -> Result<bool, DataError> {
+        let mut key = room_id.as_bytes().to_vec();
+        key.push(0xff);
+        key.extend_from_slice(event_id.as_bytes());
+
+        let timestamp: U64<BigEndian> = U64::new(
+            SystemTime::now()
+                .duration_since(UNIX_EPOCH)
+                .expect("Clock has gone backwards")
+                .as_secs(),
+        );
+
+        match self.roomeventid_timestamp.compare_and_swap(
+            key,
+            None as Option<&[u8]>,
+            Some(timestamp.as_bytes()),
+        )? {
+            Ok(()) => Ok(true),
+            Err(CompareAndSwapError { .. }) => Ok(false),
+        }
+    }
+
     pub fn get_rooms_for_user(&self, username: &str) -> Result<HashSet<String>, DataError> {
-        get_set(&self.username_roomids, username.as_bytes())
+        hashset_tree::get_set(&self.username_roomids, username.as_bytes())
     }
 
     pub fn get_users_in_room(&self, room_id: &str) -> Result<HashSet<String>, DataError> {
-        get_set(&self.roomid_usernames, room_id.as_bytes())
+        hashset_tree::get_set(&self.roomid_usernames, room_id.as_bytes())
     }
 
     pub fn add_user_to_room(&self, username: &str, room_id: &str) -> Result<(), DataError> {
         (&self.username_roomids, &self.roomid_usernames).transaction(
             |(tx_username_rooms, tx_room_usernames)| {
                 let username_key = &username.as_bytes();
-                let mut user_to_rooms = get_set(tx_username_rooms, username_key)?;
+                hashset_tree::add_to_set(tx_username_rooms, username_key, room_id.to_owned())?;
-                user_to_rooms.insert(room_id.to_string());
-                insert_set(tx_username_rooms, username_key, user_to_rooms)?;
 
                 let roomid_key = &room_id.as_bytes();
-                let mut room_to_users = get_set(tx_room_usernames, roomid_key)?;
+                hashset_tree::add_to_set(tx_room_usernames, roomid_key, username.to_owned())?;
-                room_to_users.insert(username.to_string());
-                insert_set(tx_room_usernames, roomid_key, room_to_users)?;
 
                 Ok(())
             },
@@ -111,14 +253,10 @@ impl Rooms {
         (&self.username_roomids, &self.roomid_usernames).transaction(
             |(tx_username_rooms, tx_room_usernames)| {
                 let username_key = &username.as_bytes();
-                let mut user_to_rooms = get_set(tx_username_rooms, username_key)?;
+                hashset_tree::remove_from_set(tx_username_rooms, username_key, room_id)?;
-                user_to_rooms.remove(room_id);
-                insert_set(tx_username_rooms, username_key, user_to_rooms)?;
 
                 let roomid_key = &room_id.as_bytes();
-                let mut room_to_users = get_set(tx_room_usernames, roomid_key)?;
+                hashset_tree::remove_from_set(tx_room_usernames, roomid_key, username)?;
-                room_to_users.remove(username);
-                insert_set(tx_room_usernames, roomid_key, room_to_users)?;
 
                 Ok(())
             },
@@ -131,11 +269,15 @@ impl Rooms {
         (&self.username_roomids, &self.roomid_usernames).transaction(
             |(tx_username_roomids, tx_roomid_usernames)| {
                 let roomid_key = room_id.as_bytes();
-                let users_in_room = get_set(tx_roomid_usernames, roomid_key)?;
+                let users_in_room = hashset_tree::get_set(tx_roomid_usernames, roomid_key)?;
 
                 //Remove the room ID from every user's room ID list.
                 for username in users_in_room {
-                    remove_from_set(tx_username_roomids, username.as_bytes(), room_id)?;
+                    hashset_tree::remove_from_set(
+                        tx_username_roomids,
+                        username.as_bytes(),
+                        room_id,
+                    )?;
                 }
 
                 //Remove this room entry for the room ID -> username tree.
@@ -164,6 +306,7 @@ mod tests {
     #[test]
     fn add_user_to_room() {
         let rooms = create_test_instance();
+
         rooms
             .add_user_to_room("testuser", "myroom")
             .expect("Could not add user to room");
@@ -189,6 +332,7 @@ mod tests {
     #[test]
     fn remove_user_from_room() {
         let rooms = create_test_instance();
+
         rooms
             .add_user_to_room("testuser", "myroom")
             .expect("Could not add user to room");
@@ -212,6 +356,7 @@ mod tests {
     #[test]
     fn clear_info() {
         let rooms = create_test_instance();
+
         rooms
             .add_user_to_room("testuser", "myroom1")
             .expect("Could not add user to room1");
@@ -246,4 +391,37 @@ mod tests {
         assert_eq!(expected_users_in_room2, users_in_room2);
         assert_eq!(expected_rooms_for_user, rooms_for_user);
     }
+
+    #[test]
+    fn insert_to_timestamp_index() {
+        let rooms = create_test_instance();
+
+        // Insertion into timestamp index based on data that would go
+        // into main room x eventID -> timestamp tree.
+        let mut key = b"myroom".to_vec();
+        key.push(0xff);
+        key.extend_from_slice(b"myeventid");
+
+        let timestamp: U64<BigEndian> = U64::new(1000);
+
+        let result = timestamp_index::insert(
+            &rooms.roomtimestamp_eventid,
+            key.as_bytes(),
+            timestamp.as_bytes(),
+        );
+
+        assert!(result.is_ok());
+
+        // Retrieval of data from the timestamp index tree.
+        let mut ts_key = b"myroom".to_vec();
+        ts_key.push(0xff);
+        ts_key.extend_from_slice(timestamp.as_bytes());
+
+        let expected_events: HashSet<String> =
+            vec![String::from("myeventid")].into_iter().collect();
+
+        let event_ids = hashset_tree::get_set(&rooms.roomtimestamp_eventid, &ts_key)
+            .expect("Could not get set out of Tree");
+        assert_eq!(expected_events, event_ids);
+    }
 }

src/db/schema.rs

@@ -1,6 +1,6 @@
 use crate::db::errors::DataError;
-use byteorder::LittleEndian;
+use byteorder::{BigEndian, LittleEndian};
-use zerocopy::byteorder::{I32, U32};
+use zerocopy::byteorder::{I32, U32, U64};
 use zerocopy::LayoutVerified;
 
 /// User variables are stored as little-endian 32-bit integers in the
@@ -10,6 +10,11 @@ type LittleEndianI32Layout<'a> = LayoutVerified<&'a [u8], I32<LittleEndian>>;
 
 type LittleEndianU32Layout<'a> = LayoutVerified<&'a [u8], U32<LittleEndian>>;
 
+#[allow(dead_code)]
+type LittleEndianU64Layout<'a> = LayoutVerified<&'a [u8], U64<LittleEndian>>;
+
+type BigEndianU64Layout<'a> = LayoutVerified<&'a [u8], U64<BigEndian>>;
+
 /// Convert bytes to an i32 with zero-copy deserialization. An error
 /// is returned if the bytes do not represent an i32.
 pub(super) fn convert_i32(raw_value: &[u8]) -> Result<i32, DataError> {
@@ -33,3 +38,15 @@ pub(super) fn convert_u32(raw_value: &[u8]) -> Result<u32, DataError> {
         Err(DataError::I32SchemaViolation)
     }
 }
+
+#[allow(dead_code)]
+pub(super) fn convert_u64(raw_value: &[u8]) -> Result<u64, DataError> {
+    let layout = BigEndianU64Layout::new_unaligned(raw_value.as_ref());
+
+    if let Some(layout) = layout {
+        let value: U64<BigEndian> = *layout;
+        Ok(value.get())
+    } else {
+        Err(DataError::I32SchemaViolation)
+    }
+}