Log debug instead of trace for timestamp index inserts.

Also rename the existing `should_process` function to be more clear,
given presence of another similarly named function:
should_process_message.

src/bot.rs

@@ -4,27 +4,25 @@ use crate::context::Context;
 use crate::db::Database;
 use crate::error::BotError;
 use crate::state::DiceBotState;
-use async_trait::async_trait;
 use dirs;
-use log::{debug, error, info, warn};
+use log::{error, info};
 use matrix_sdk::Error as MatrixError;
 use matrix_sdk::{
     self,
     events::{
-        room::member::MemberEventContent,
-        room::message::{MessageEventContent, NoticeMessageEventContent, TextMessageEventContent},
-        AnyMessageEventContent, StrippedStateEvent, SyncMessageEvent,
+        room::message::{MessageEventContent, NoticeMessageEventContent},
+        AnyMessageEventContent,
     },
-    Client, ClientConfig, EventEmitter, JsonStore, Room, SyncRoom, SyncSettings,
+    Client, ClientConfig, JsonStore, Room, SyncSettings,
 };
 //use matrix_sdk_common_macros::async_trait;
 use std::clone::Clone;
-use std::ops::Sub;
 use std::path::PathBuf;
 use std::sync::{Arc, RwLock};
-use std::time::{Duration, SystemTime};
 use url::Url;
 
+pub mod event_handlers;
+
 /// The DiceBot struct represents an active dice bot. The bot is not
 /// connected to Matrix until its run() function is called.
 pub struct DiceBot {
@@ -167,104 +165,3 @@ impl DiceBot {
         }
     }
 }
-
-/// Check if a message is recent enough to actually process. If the
-/// message is within "oldest_message_age" seconds, this function
-/// returns true. If it's older than that, it returns false and logs a
-/// debug message.
-fn check_message_age(
-    event: &SyncMessageEvent<MessageEventContent>,
-    oldest_message_age: u64,
-) -> bool {
-    let sending_time = event.origin_server_ts;
-    let oldest_timestamp = SystemTime::now().sub(Duration::new(oldest_message_age, 0));
-
-    if sending_time > oldest_timestamp {
-        true
-    } else {
-        let age = match oldest_timestamp.duration_since(sending_time) {
-            Ok(n) => format!("{} seconds too old", n.as_secs()),
-            Err(_) => "before the UNIX epoch".to_owned(),
-        };
-
-        debug!("Ignoring message because it is {}: {:?}", age, event);
-        false
-    }
-}
-
-async fn should_process<'a>(
-    bot: &DiceBot,
-    event: &SyncMessageEvent<MessageEventContent>,
-) -> Result<(String, String), BotError> {
-    //Ignore messages that are older than configured duration.
-    if !check_message_age(event, bot.config.oldest_message_age()) {
-        let state_check = bot.state.read().unwrap();
-        if !((*state_check).logged_skipped_old_messages()) {
-            drop(state_check);
-            let mut state = bot.state.write().unwrap();
-            (*state).skipped_old_messages();
-        }
-
-        return Err(BotError::ShouldNotProcessError);
-    }
-
-    let (msg_body, sender_username) = if let SyncMessageEvent {
-        content: MessageEventContent::Text(TextMessageEventContent { body, .. }),
-        sender,
-        ..
-    } = event
-    {
-        (
-            body.clone(),
-            format!("@{}:{}", sender.localpart(), sender.server_name()),
-        )
-    } else {
-        (String::new(), String::new())
-    };
-
-    Ok((msg_body, sender_username))
-}
-
-/// This event emitter listens for messages with dice rolling commands.
-/// Originally adapted from the matrix-rust-sdk examples.
-#[async_trait]
-impl EventEmitter for DiceBot {
-    async fn on_stripped_state_member(
-        &self,
-        room: SyncRoom,
-        room_member: &StrippedStateEvent<MemberEventContent>,
-        _: Option<MemberEventContent>,
-    ) {
-        if let SyncRoom::Invited(room) = room {
-            if let Some(user_id) = self.client.user_id().await {
-                if room_member.state_key != user_id {
-                    return;
-                }
-            }
-
-            let room = room.read().await;
-            info!("Autojoining room {}", room.display_name());
-
-            if let Err(e) = self.client.join_room_by_id(&room.room_id).await {
-                warn!("Could not join room: {}", e.to_string())
-            }
-        }
-    }
-
-    async fn on_room_message(&self, room: SyncRoom, event: &SyncMessageEvent<MessageEventContent>) {
-        if let SyncRoom::Joined(room) = room {
-            let (msg_body, sender_username) =
-                if let Ok((msg_body, sender_username)) = should_process(self, &event).await {
-                    (msg_body, sender_username)
-                } else {
-                    return;
-                };
-
-            //we clone here to hold the lock for as little time as possible.
-            let real_room = room.read().await.clone();
-
-            self.execute_commands(&real_room, &sender_username, &msg_body)
-                .await;
-        }
-    }
-}

src/bot/event_handlers.rs

@@ -0,0 +1,210 @@
+use crate::db::Database;
+use crate::error::BotError;
+use async_trait::async_trait;
+use log::{debug, error, info, warn};
+use matrix_sdk::{
+    self,
+    events::{
+        room::member::{MemberEventContent, MembershipChange},
+        room::message::{MessageEventContent, TextMessageEventContent},
+        StrippedStateEvent, SyncMessageEvent, SyncStateEvent,
+    },
+    identifiers::RoomId,
+    Client, EventEmitter, SyncRoom,
+};
+//use matrix_sdk_common_macros::async_trait;
+use super::DiceBot;
+use std::clone::Clone;
+use std::ops::Sub;
+use std::time::{Duration, SystemTime};
+
+/// Check if a message is recent enough to actually process. If the
+/// message is within "oldest_message_age" seconds, this function
+/// returns true. If it's older than that, it returns false and logs a
+/// debug message.
+fn check_message_age(
+    event: &SyncMessageEvent<MessageEventContent>,
+    oldest_message_age: u64,
+) -> bool {
+    let sending_time = event.origin_server_ts;
+    let oldest_timestamp = SystemTime::now().sub(Duration::new(oldest_message_age, 0));
+
+    if sending_time > oldest_timestamp {
+        true
+    } else {
+        let age = match oldest_timestamp.duration_since(sending_time) {
+            Ok(n) => format!("{} seconds too old", n.as_secs()),
+            Err(_) => "before the UNIX epoch".to_owned(),
+        };
+
+        debug!("Ignoring message because it is {}: {:?}", age, event);
+        false
+    }
+}
+
+/// Determine whether or not to process a received message. This check
+/// is necessary in addition to the event processing check because we
+/// may receive message events when entering a room for the first
+/// time, and we don't want to respond to things before the bot was in
+/// the channel, but we do want to respond to things that were sent if
+/// the bot left and rejoined quickly.
+async fn should_process_message<'a>(
+    bot: &DiceBot,
+    event: &SyncMessageEvent<MessageEventContent>,
+) -> Result<(String, String), BotError> {
+    //Ignore messages that are older than configured duration.
+    if !check_message_age(event, bot.config.oldest_message_age()) {
+        let state_check = bot.state.read().unwrap();
+        if !((*state_check).logged_skipped_old_messages()) {
+            drop(state_check);
+            let mut state = bot.state.write().unwrap();
+            (*state).skipped_old_messages();
+        }
+
+        return Err(BotError::ShouldNotProcessError);
+    }
+
+    let (msg_body, sender_username) = if let SyncMessageEvent {
+        content: MessageEventContent::Text(TextMessageEventContent { body, .. }),
+        sender,
+        ..
+    } = event
+    {
+        (
+            body.clone(),
+            format!("@{}:{}", sender.localpart(), sender.server_name()),
+        )
+    } else {
+        (String::new(), String::new())
+    };
+
+    Ok((msg_body, sender_username))
+}
+
+fn should_process_event(db: &Database, room_id: &str, event_id: &str) -> bool {
+    db.rooms
+        .should_process(room_id, event_id)
+        .unwrap_or_else(|e| {
+            error!(
+                "Database error when checking if we should process an event: {}",
+                e.to_string()
+            );
+            false
+        })
+}
+
+async fn get_users_in_room(client: &Client, room_id: &RoomId) -> Vec<String> {
+    if let Some(joined_room) = client.get_joined_room(room_id).await {
+        let joined_room: matrix_sdk::Room = joined_room.read().await.clone();
+        joined_room
+            .joined_members
+            .keys()
+            .map(|user_id| format!("@{}:{}", user_id.localpart(), user_id.server_name()))
+            .collect()
+    } else {
+        vec![]
+    }
+}
+
+/// This event emitter listens for messages with dice rolling commands.
+/// Originally adapted from the matrix-rust-sdk examples.
+#[async_trait]
+impl EventEmitter for DiceBot {
+    async fn on_room_member(&self, room: SyncRoom, event: &SyncStateEvent<MemberEventContent>) {
+        if let SyncRoom::Joined(room) | SyncRoom::Left(room) = room {
+            //Clone to avoid holding lock.
+            let room = room.read().await.clone();
+            let (room_id, username) = (room.room_id.as_str(), &event.state_key);
+
+            if !should_process_event(&self.db, room_id, event.event_id.as_str()) {
+                return;
+            }
+
+            let event_affects_us = if let Some(our_user_id) = self.client.user_id().await {
+                event.state_key == our_user_id
+            } else {
+                false
+            };
+
+            use MembershipChange::*;
+            let adding_user = match event.membership_change() {
+                Joined => true,
+                Banned | Left | Kicked | KickedAndBanned => false,
+                _ => return,
+            };
+
+            let result = if event_affects_us && !adding_user {
+                info!("Clearing all information for room ID {}", room_id);
+                self.db.rooms.clear_info(room_id)
+            } else if event_affects_us && adding_user {
+                info!("Joined room {}; recording user information", room_id);
+                let usernames = get_users_in_room(&self.client, &room.room_id).await;
+                usernames
+                    .into_iter()
+                    .filter(|username| username != &event.state_key)
+                    .map(|username| self.db.rooms.add_user_to_room(&username, room_id))
+                    .collect() //Make use of collect impl on Result.
+            } else if !event_affects_us && adding_user {
+                info!("Adding user {} to room ID {}", username, room_id);
+                self.db.rooms.add_user_to_room(username, room_id)
+            } else if !event_affects_us && !adding_user {
+                info!("Removing user {} from room ID {}", username, room_id);
+                self.db.rooms.remove_user_from_room(username, room_id)
+            } else {
+                debug!("Ignoring a room member event: {:#?}", event);
+                Ok(())
+            };
+
+            if let Err(e) = result {
+                error!("Could not update room information: {}", e.to_string());
+            } else {
+                debug!("Successfully processed room member update.");
+            }
+        }
+    }
+
+    async fn on_stripped_state_member(
+        &self,
+        room: SyncRoom,
+        event: &StrippedStateEvent<MemberEventContent>,
+        _: Option<MemberEventContent>,
+    ) {
+        if let SyncRoom::Invited(room) = room {
+            if let Some(user_id) = self.client.user_id().await {
+                if event.state_key != user_id {
+                    return;
+                }
+            }
+
+            //Clone to avoid holding lock.
+            let room = room.read().await.clone();
+            info!("Autojoining room {}", room.display_name());
+
+            if let Err(e) = self.client.join_room_by_id(&room.room_id).await {
+                warn!("Could not join room: {}", e.to_string())
+            }
+        }
+    }
+
+    async fn on_room_message(&self, room: SyncRoom, event: &SyncMessageEvent<MessageEventContent>) {
+        if let SyncRoom::Joined(room) = room {
+            //Clone to avoid holding lock.
+            let room = room.read().await.clone();
+            let room_id = room.room_id.as_str();
+            if !should_process_event(&self.db, room_id, event.event_id.as_str()) {
+                return;
+            }
+
+            let (msg_body, sender_username) = if let Ok((msg_body, sender_username)) =
+                should_process_message(self, &event).await
+            {
+                (msg_body, sender_username)
+            } else {
+                return;
+            };
+
+            self.execute_commands(&room, &sender_username, &msg_body)
+                .await;
+        }
+    }
+}

src/db.rs

@@ -1,5 +1,6 @@
 use crate::db::errors::{DataError, MigrationError};
 use crate::db::migrations::{get_migration_version, Migrations};
+use crate::db::rooms::Rooms;
 use crate::db::variables::Variables;
 use log::info;
 use sled::{Config, Db};
@@ -8,6 +9,7 @@ use std::path::Path;
 pub mod data_migrations;
 pub mod errors;
 pub mod migrations;
+pub mod rooms;
 pub mod schema;
 pub mod variables;
 
@@ -16,17 +18,25 @@ pub struct Database {
     db: Db,
     pub(crate) variables: Variables,
     pub(crate) migrations: Migrations,
+    pub(crate) rooms: Rooms,
 }
 
 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),
 
@@ -62,13 +65,11 @@ impl From<TransactionError<DataError>> for DataError {
     }
 }
 
-// impl From<ConflictableTransactionError<DataError>> for DataError {
-//     fn from(error: ConflictableTransactionError<DataError>) -> Self {
-//         match error {
-//             ConflictableTransactionError::Abort(data_err) => data_err,
-//             ConflictableTransactionError::Storage(storage_err) => {
-//                 DataError::TransactionError(TransactionError::Storage(storage_err))
-//             }
-//         }
-//     }
-// }
+/// Automatically aborts transactions that hit a DataError by using
+/// the try (question mark) operator when this trait implementation is
+/// in scope.
+impl From<DataError> for sled::transaction::ConflictableTransactionError<DataError> {
+    fn from(error: DataError) -> Self {
+        sled::transaction::ConflictableTransactionError::Abort(error)
+    }
+}

src/db/rooms.rs

@@ -0,0 +1,430 @@
+use crate::db::errors::DataError;
+use crate::db::schema::convert_u64;
+use byteorder::BigEndian;
+use log::{debug, error, log_enabled};
+use sled::transaction::TransactionalTree;
+use sled::Transactional;
+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 {
+    /// Room ID -> RoomInfo struct (single entries)
+    pub(in crate::db) roomid_roominfo: Tree,
+
+    /// Room ID -> list of usernames in room.
+    pub(in crate::db) roomid_usernames: Tree,
+
+    /// 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),
+    Tx(&'a TransactionalTree),
+}
+
+impl<'a> Into<TxableTree<'a>> for &'a Tree {
+    fn into(self) -> TxableTree<'a> {
+        TxableTree::Tree(self)
+    }
+}
+
+impl<'a> Into<TxableTree<'a>> for &'a TransactionalTree {
+    fn into(self) -> TxableTree<'a> {
+        TxableTree::Tx(self)
+    }
+}
+
+/// 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)?,
+        }
+        .map(|bytes| bincode::deserialize::<HashSet<String>>(&bytes))
+        .unwrap_or(Ok(HashSet::new()))?;
+
+        Ok(set)
+    }
+
+    pub(super) fn remove_from_set<'a, T: Into<TxableTree<'a>> + Copy>(
+        tree: T,
+        key: &[u8],
+        value_to_remove: &str,
+    ) -> Result<(), DataError> {
+        let mut set = get_set(tree, key)?;
+        set.remove(value_to_remove);
+        insert_set(tree, key, set)?;
+        Ok(())
+    }
+
+    pub(super) fn add_to_set<'a, T: Into<TxableTree<'a>> + Copy>(
+        tree: T,
+        key: &[u8],
+        value_to_add: String,
+    ) -> Result<(), DataError> {
+        let mut set = get_set(tree, key)?;
+        set.insert(value_to_add);
+        insert_set(tree, key, set)?;
+        Ok(())
+    }
+}
+
+/// Functions that specifically relate to the "timestamp index" tree,
+/// which is stored on the Rooms instance 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);
+            log_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 debug message.
+    fn log_index_record(room_id: &[u8], event_id: &[u8], timestamp: &[u8]) {
+        if log_enabled!(log::Level::Debug) {
+            debug!(
+                "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 {
+    pub(in crate::db) fn new(db: &sled::Db) -> Result<Rooms, sled::Error> {
+        Ok(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> {
+        hashset_tree::get_set(&self.username_roomids, username.as_bytes())
+    }
+
+    pub fn get_users_in_room(&self, room_id: &str) -> Result<HashSet<String>, DataError> {
+        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> {
+        debug!("Adding user {} to room {}", username, room_id);
+        (&self.username_roomids, &self.roomid_usernames).transaction(
+            |(tx_username_rooms, tx_room_usernames)| {
+                let username_key = &username.as_bytes();
+                hashset_tree::add_to_set(tx_username_rooms, username_key, room_id.to_owned())?;
+
+                let roomid_key = &room_id.as_bytes();
+                hashset_tree::add_to_set(tx_room_usernames, roomid_key, username.to_owned())?;
+
+                Ok(())
+            },
+        )?;
+
+        Ok(())
+    }
+
+    pub fn remove_user_from_room(&self, username: &str, room_id: &str) -> Result<(), DataError> {
+        debug!("Removing user {} from room {}", username, room_id);
+        (&self.username_roomids, &self.roomid_usernames).transaction(
+            |(tx_username_rooms, tx_room_usernames)| {
+                let username_key = &username.as_bytes();
+                hashset_tree::remove_from_set(tx_username_rooms, username_key, room_id)?;
+
+                let roomid_key = &room_id.as_bytes();
+                hashset_tree::remove_from_set(tx_room_usernames, roomid_key, username)?;
+
+                Ok(())
+            },
+        )?;
+
+        Ok(())
+    }
+
+    pub fn clear_info(&self, room_id: &str) -> Result<(), DataError> {
+        debug!("Clearing all information for room {}", room_id);
+        (&self.username_roomids, &self.roomid_usernames).transaction(
+            |(tx_username_roomids, tx_roomid_usernames)| {
+                let roomid_key = room_id.as_bytes();
+                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 {
+                    hashset_tree::remove_from_set(
+                        tx_username_roomids,
+                        username.as_bytes(),
+                        room_id,
+                    )?;
+                }
+
+                //Remove this room entry for the room ID -> username tree.
+                tx_roomid_usernames.remove(roomid_key)?;
+
+                //TODO: delete roominfo struct from room info tree.
+                Ok(())
+            },
+        )?;
+
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use sled::Config;
+
+    fn create_test_instance() -> Rooms {
+        let config = Config::new().temporary(true);
+        let db = config.open().unwrap();
+        Rooms::new(&db).unwrap()
+    }
+
+    #[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");
+
+        let users_in_room = rooms
+            .get_users_in_room("myroom")
+            .expect("Could not retrieve users in room");
+
+        let rooms_for_user = rooms
+            .get_rooms_for_user("testuser")
+            .expect("Could not get rooms for user");
+
+        let expected_users_in_room: HashSet<String> =
+            vec![String::from("testuser")].into_iter().collect();
+
+        let expected_rooms_for_user: HashSet<String> =
+            vec![String::from("myroom")].into_iter().collect();
+
+        assert_eq!(expected_users_in_room, users_in_room);
+        assert_eq!(expected_rooms_for_user, rooms_for_user);
+    }
+
+    #[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");
+
+        rooms
+            .remove_user_from_room("testuser", "myroom")
+            .expect("Could not remove user from room");
+
+        let users_in_room = rooms
+            .get_users_in_room("myroom")
+            .expect("Could not retrieve users in room");
+
+        let rooms_for_user = rooms
+            .get_rooms_for_user("testuser")
+            .expect("Could not get rooms for user");
+
+        assert_eq!(HashSet::new(), users_in_room);
+        assert_eq!(HashSet::new(), rooms_for_user);
+    }
+
+    #[test]
+    fn clear_info() {
+        let rooms = create_test_instance();
+
+        rooms
+            .add_user_to_room("testuser", "myroom1")
+            .expect("Could not add user to room1");
+
+        rooms
+            .add_user_to_room("testuser", "myroom2")
+            .expect("Could not add user to room2");
+
+        rooms
+            .clear_info("myroom1")
+            .expect("Could not clear room info");
+
+        let users_in_room1 = rooms
+            .get_users_in_room("myroom1")
+            .expect("Could not retrieve users in room1");
+
+        let users_in_room2 = rooms
+            .get_users_in_room("myroom2")
+            .expect("Could not retrieve users in room2");
+
+        let rooms_for_user = rooms
+            .get_rooms_for_user("testuser")
+            .expect("Could not get rooms for user");
+
+        let expected_users_in_room2: HashSet<String> =
+            vec![String::from("testuser")].into_iter().collect();
+
+        let expected_rooms_for_user: HashSet<String> =
+            vec![String::from("myroom2")].into_iter().collect();
+
+        assert_eq!(HashSet::new(), users_in_room1);
+        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 zerocopy::byteorder::{I32, U32};
+use byteorder::{BigEndian, LittleEndian};
+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)
+    }
+}

src/lib.rs

@@ -9,6 +9,7 @@ pub mod db;
 pub mod dice;
 pub mod error;
 mod help;
+pub mod models;
 mod parser;
 pub mod state;
 pub mod variables;

src/models.rs

@@ -0,0 +1,5 @@
+/// RoomInfo has basic metadata about a room: its name, ID, etc.
+pub struct RoomInfo {
+    pub room_id: String,
+    pub room_name: String,
+}