conduit/src/database/users.rs

use crate::{utils, Error, Result};
use js_int::UInt;
use ruma::{
    api::client::{
        error::ErrorKind,
        r0::{
            device::Device,
            keys::{AlgorithmAndDeviceId, CrossSigningKey, DeviceKeys, KeyAlgorithm, OneTimeKey},
        },
    },
    events::{AnyToDeviceEvent, EventType},
    DeviceId, Raw, UserId,
};
use std::{collections::BTreeMap, convert::TryFrom, mem, time::SystemTime};

pub struct Users {
    pub(super) userid_password: sled::Tree,
    pub(super) userid_displayname: sled::Tree,
    pub(super) userid_avatarurl: sled::Tree,
    pub(super) userdeviceid_token: sled::Tree,
    pub(super) userdeviceid_metadata: sled::Tree, // This is also used to check if a device exists
    pub(super) token_userdeviceid: sled::Tree,

    pub(super) onetimekeyid_onetimekeys: sled::Tree, // OneTimeKeyId = UserId + AlgorithmAndDeviceId
    pub(super) userid_lastonetimekeyupdate: sled::Tree, // LastOneTimeKeyUpdate = Count
    pub(super) keychangeid_userid: sled::Tree,       // KeyChangeId = UserId/RoomId + Count
    pub(super) keyid_key: sled::Tree,                // KeyId = UserId + KeyId (depends on key type)
    pub(super) userid_masterkeyid: sled::Tree,
    pub(super) userid_selfsigningkeyid: sled::Tree,
    pub(super) userid_usersigningkeyid: sled::Tree,

    pub(super) todeviceid_events: sled::Tree, // ToDeviceId = UserId + DeviceId + Count
}

impl Users {
    /// Check if a user has an account on this homeserver.
    pub fn exists(&self, user_id: &UserId) -> Result<bool> {
        Ok(self.userid_password.contains_key(user_id.to_string())?)
    }

    /// Check if account is deactivated
    pub fn is_deactivated(&self, user_id: &UserId) -> Result<bool> {
        Ok(self
            .userid_password
            .get(user_id.to_string())?
            .ok_or(Error::BadRequest(
                ErrorKind::InvalidParam,
                "User does not exist.",
            ))?
            .is_empty())
    }

    /// Create a new user account on this homeserver.
    pub fn create(&self, user_id: &UserId, password: &str) -> Result<()> {
        self.set_password(user_id, password)?;
        Ok(())
    }

    /// Find out which user an access token belongs to.
    pub fn find_from_token(&self, token: &str) -> Result<Option<(UserId, String)>> {
        self.token_userdeviceid
            .get(token)?
            .map_or(Ok(None), |bytes| {
                let mut parts = bytes.split(|&b| b == 0xff);
                let user_bytes = parts.next().ok_or_else(|| {
                    Error::bad_database("User ID in token_userdeviceid is invalid.")
                })?;
                let device_bytes = parts.next().ok_or_else(|| {
                    Error::bad_database("Device ID in token_userdeviceid is invalid.")
                })?;

                Ok(Some((
                    UserId::try_from(utils::string_from_bytes(&user_bytes).map_err(|_| {
                        Error::bad_database("User ID in token_userdeviceid is invalid unicode.")
                    })?)
                    .map_err(|_| {
                        Error::bad_database("User ID in token_userdeviceid is invalid.")
                    })?,
                    utils::string_from_bytes(&device_bytes).map_err(|_| {
                        Error::bad_database("Device ID in token_userdeviceid is invalid.")
                    })?,
                )))
            })
    }

    /// Returns an iterator over all users on this homeserver.
    pub fn iter(&self) -> impl Iterator<Item = Result<UserId>> {
        self.userid_password.iter().keys().map(|bytes| {
            Ok(
                UserId::try_from(utils::string_from_bytes(&bytes?).map_err(|_| {
                    Error::bad_database("User ID in userid_password is invalid unicode.")
                })?)
                .map_err(|_| Error::bad_database("User ID in userid_password is invalid."))?,
            )
        })
    }

    /// Returns the password hash for the given user.
    pub fn password_hash(&self, user_id: &UserId) -> Result<Option<String>> {
        self.userid_password
            .get(user_id.to_string())?
            .map_or(Ok(None), |bytes| {
                Ok(Some(utils::string_from_bytes(&bytes).map_err(|_| {
                    Error::bad_database("Password hash in db is not valid string.")
                })?))
            })
    }

    /// Hash and set the user's password to the Argon2 hash
    pub fn set_password(&self, user_id: &UserId, password: &str) -> Result<()> {
        if let Ok(hash) = utils::calculate_hash(&password) {
            self.userid_password.insert(user_id.to_string(), &*hash)?;
            Ok(())
        } else {
            Err(Error::BadRequest(
                ErrorKind::InvalidParam,
                "Password does not meet the requirements.",
            ))
        }
    }

    /// Returns the displayname of a user on this homeserver.
    pub fn displayname(&self, user_id: &UserId) -> Result<Option<String>> {
        self.userid_displayname
            .get(user_id.to_string())?
            .map_or(Ok(None), |bytes| {
                Ok(Some(utils::string_from_bytes(&bytes).map_err(|_| {
                    Error::bad_database("Displayname in db is invalid.")
                })?))
            })
    }

    /// Sets a new displayname or removes it if displayname is None. You still need to nofify all rooms of this change.
    pub fn set_displayname(&self, user_id: &UserId, displayname: Option<String>) -> Result<()> {
        if let Some(displayname) = displayname {
            self.userid_displayname
                .insert(user_id.to_string(), &*displayname)?;
        } else {
            self.userid_displayname.remove(user_id.to_string())?;
        }

        Ok(())
    }

    /// Get a the avatar_url of a user.
    pub fn avatar_url(&self, user_id: &UserId) -> Result<Option<String>> {
        self.userid_avatarurl
            .get(user_id.to_string())?
            .map_or(Ok(None), |bytes| {
                Ok(Some(utils::string_from_bytes(&bytes).map_err(|_| {
                    Error::bad_database("Avatar URL in db is invalid.")
                })?))
            })
    }

    /// Sets a new avatar_url or removes it if avatar_url is None.
    pub fn set_avatar_url(&self, user_id: &UserId, avatar_url: Option<String>) -> Result<()> {
        if let Some(avatar_url) = avatar_url {
            self.userid_avatarurl
                .insert(user_id.to_string(), &*avatar_url)?;
        } else {
            self.userid_avatarurl.remove(user_id.to_string())?;
        }

        Ok(())
    }

    /// Adds a new device to a user.
    pub fn create_device(
        &self,
        user_id: &UserId,
        device_id: &DeviceId,
        token: &str,
        initial_device_display_name: Option<String>,
    ) -> Result<()> {
        // This method should never be called for nonexistent users.
        assert!(self.exists(user_id)?);

        let mut userdeviceid = user_id.to_string().as_bytes().to_vec();
        userdeviceid.push(0xff);
        userdeviceid.extend_from_slice(device_id.as_bytes());

        self.userdeviceid_metadata.insert(
            userdeviceid,
            serde_json::to_string(&Device {
                device_id: device_id.into(),
                display_name: initial_device_display_name,
                last_seen_ip: None, // TODO
                last_seen_ts: Some(SystemTime::now()),
            })
            .expect("Device::to_string never fails.")
            .as_bytes(),
        )?;

        self.set_token(user_id, &device_id, token)?;

        Ok(())
    }

    /// Removes a device from a user.
    pub fn remove_device(&self, user_id: &UserId, device_id: &DeviceId) -> Result<()> {
        let mut userdeviceid = user_id.to_string().as_bytes().to_vec();
        userdeviceid.push(0xff);
        userdeviceid.extend_from_slice(device_id.as_bytes());

        // Remove tokens
        if let Some(old_token) = self.userdeviceid_token.remove(&userdeviceid)? {
            self.token_userdeviceid.remove(&old_token)?;
        }

        // Remove todevice events
        let mut prefix = userdeviceid.clone();
        prefix.push(0xff);

        for key in self.todeviceid_events.scan_prefix(&prefix).keys() {
            self.todeviceid_events.remove(key?)?;
        }

        // TODO: Remove onetimekeys

        self.userdeviceid_metadata.remove(&userdeviceid)?;

        Ok(())
    }

    /// Returns an iterator over all device ids of this user.
    pub fn all_device_ids(&self, user_id: &UserId) -> impl Iterator<Item = Result<Box<DeviceId>>> {
        let mut prefix = user_id.to_string().as_bytes().to_vec();
        prefix.push(0xff);
        // All devices have metadata
        self.userdeviceid_metadata
            .scan_prefix(prefix)
            .keys()
            .map(|bytes| {
                Ok(utils::string_from_bytes(
                    &*bytes?
                        .rsplit(|&b| b == 0xff)
                        .next()
                        .ok_or_else(|| Error::bad_database("UserDevice ID in db is invalid."))?,
                )
                .map_err(|_| Error::bad_database("Device ID in userdeviceid_metadata is invalid."))?
                .into())
            })
    }

    /// Replaces the access token of one device.
    fn set_token(&self, user_id: &UserId, device_id: &DeviceId, token: &str) -> Result<()> {
        let mut userdeviceid = user_id.to_string().as_bytes().to_vec();
        userdeviceid.push(0xff);
        userdeviceid.extend_from_slice(device_id.as_bytes());

        // All devices have metadata
        assert!(self.userdeviceid_metadata.get(&userdeviceid)?.is_some());

        // Remove old token
        if let Some(old_token) = self.userdeviceid_token.get(&userdeviceid)? {
            self.token_userdeviceid.remove(old_token)?;
            // It will be removed from userdeviceid_token by the insert later
        }

        // Assign token to user device combination
        self.userdeviceid_token.insert(&userdeviceid, &*token)?;
        self.token_userdeviceid.insert(token, userdeviceid)?;

        Ok(())
    }

    pub fn add_one_time_key(
        &self,
        user_id: &UserId,
        device_id: &DeviceId,
        one_time_key_key: &AlgorithmAndDeviceId,
        one_time_key_value: &OneTimeKey,
        globals: &super::globals::Globals,
    ) -> Result<()> {
        let mut key = user_id.to_string().as_bytes().to_vec();
        key.push(0xff);
        key.extend_from_slice(device_id.as_bytes());

        // All devices have metadata
        // Only existing devices should be able to call this.
        assert!(self.userdeviceid_metadata.get(&key)?.is_some());

        key.push(0xff);
        // TODO: Use AlgorithmAndDeviceId::to_string when it's available (and update everything,
        // because there are no wrapping quotation marks anymore)
        key.extend_from_slice(
            &serde_json::to_string(one_time_key_key)
                .expect("AlgorithmAndDeviceId::to_string always works")
                .as_bytes(),
        );

        self.onetimekeyid_onetimekeys.insert(
            &key,
            &*serde_json::to_string(&one_time_key_value)
                .expect("OneTimeKey::to_string always works"),
        )?;

        self.userid_lastonetimekeyupdate.insert(
            &user_id.to_string().as_bytes(),
            &globals.next_count()?.to_be_bytes(),
        )?;

        Ok(())
    }

    pub fn last_one_time_keys_update(&self, user_id: &UserId) -> Result<u64> {
        self.userid_lastonetimekeyupdate
            .get(&user_id.to_string().as_bytes())?
            .map(|bytes| {
                utils::u64_from_bytes(&bytes).map_err(|_| {
                    Error::bad_database("Count in roomid_lastroomactiveupdate is invalid.")
                })
            })
            .unwrap_or(Ok(0))
    }

    pub fn take_one_time_key(
        &self,
        user_id: &UserId,
        device_id: &DeviceId,
        key_algorithm: &KeyAlgorithm,
        globals: &super::globals::Globals,
    ) -> Result<Option<(AlgorithmAndDeviceId, OneTimeKey)>> {
        let mut prefix = user_id.to_string().as_bytes().to_vec();
        prefix.push(0xff);
        prefix.extend_from_slice(device_id.as_bytes());
        prefix.push(0xff);
        prefix.push(b'"'); // Annoying quotation mark
        prefix.extend_from_slice(key_algorithm.to_string().as_bytes());
        prefix.push(b':');

        self.userid_lastonetimekeyupdate.insert(
            &user_id.to_string().as_bytes(),
            &globals.next_count()?.to_be_bytes(),
        )?;

        self.onetimekeyid_onetimekeys
            .scan_prefix(&prefix)
            .next()
            .map(|r| {
                let (key, value) = r?;
                self.onetimekeyid_onetimekeys.remove(&key)?;

                Ok((
                    serde_json::from_slice(
                        &*key
                            .rsplit(|&b| b == 0xff)
                            .next()
                            .ok_or_else(|| Error::bad_database("OneTimeKeyId in db is invalid."))?,
                    )
                    .map_err(|_| Error::bad_database("OneTimeKeyId in db is invalid."))?,
                    serde_json::from_slice(&*value)
                        .map_err(|_| Error::bad_database("OneTimeKeys in db are invalid."))?,
                ))
            })
            .transpose()
    }

    pub fn count_one_time_keys(
        &self,
        user_id: &UserId,
        device_id: &DeviceId,
    ) -> Result<BTreeMap<KeyAlgorithm, UInt>> {
        let mut userdeviceid = user_id.to_string().as_bytes().to_vec();
        userdeviceid.push(0xff);
        userdeviceid.extend_from_slice(device_id.as_bytes());

        let mut counts = BTreeMap::new();

        for algorithm in self
            .onetimekeyid_onetimekeys
            .scan_prefix(&userdeviceid)
            .keys()
            .map(|bytes| {
                Ok::<_, Error>(
                    serde_json::from_slice::<AlgorithmAndDeviceId>(
                        &*bytes?.rsplit(|&b| b == 0xff).next().ok_or_else(|| {
                            Error::bad_database("OneTimeKey ID in db is invalid.")
                        })?,
                    )
                    .map_err(|_| Error::bad_database("AlgorithmAndDeviceID in db is invalid."))?
                    .0,
                )
            })
        {
            *counts.entry(algorithm?).or_default() += UInt::from(1_u32);
        }

        Ok(counts)
    }

    pub fn add_device_keys(
        &self,
        user_id: &UserId,
        device_id: &DeviceId,
        device_keys: &DeviceKeys,
        rooms: &super::rooms::Rooms,
        globals: &super::globals::Globals,
    ) -> Result<()> {
        let mut userdeviceid = user_id.to_string().as_bytes().to_vec();
        userdeviceid.push(0xff);
        userdeviceid.extend_from_slice(device_id.as_bytes());

        self.keyid_key.insert(
            &userdeviceid,
            &*serde_json::to_string(&device_keys).expect("DeviceKeys::to_string always works"),
        )?;

        let count = globals.next_count()?.to_be_bytes();
        for room_id in rooms.rooms_joined(&user_id) {
            let mut key = room_id?.to_string().as_bytes().to_vec();
            key.push(0xff);
            key.extend_from_slice(&count);

            self.keychangeid_userid.insert(key, &*user_id.to_string())?;
        }

        let mut key = user_id.to_string().as_bytes().to_vec();
        key.push(0xff);
        key.extend_from_slice(&count);
        self.keychangeid_userid.insert(key, &*user_id.to_string())?;

        Ok(())
    }

    pub fn add_cross_signing_keys(
        &self,
        user_id: &UserId,
        master_key: &CrossSigningKey,
        self_signing_key: &Option<CrossSigningKey>,
        user_signing_key: &Option<CrossSigningKey>,
        rooms: &super::rooms::Rooms,
        globals: &super::globals::Globals,
    ) -> Result<()> {
        // TODO: Check signatures

        let mut prefix = user_id.to_string().as_bytes().to_vec();
        prefix.push(0xff);

        // Master key
        let mut master_key_ids = master_key.keys.values();
        let master_key_id = master_key_ids.next().ok_or(Error::BadRequest(
            ErrorKind::InvalidParam,
            "Master key contained no key.",
        ))?;

        if master_key_ids.next().is_some() {
            return Err(Error::BadRequest(
                ErrorKind::InvalidParam,
                "Master key contained more than one key.",
            ));
        }

        let mut master_key_key = prefix.clone();
        master_key_key.extend_from_slice(master_key_id.as_bytes());

        self.keyid_key.insert(
            &master_key_key,
            &*serde_json::to_string(&master_key).expect("CrossSigningKey::to_string always works"),
        )?;

        self.userid_masterkeyid
            .insert(&*user_id.to_string(), master_key_key)?;

        // Self-signing key
        if let Some(self_signing_key) = self_signing_key {
            let mut self_signing_key_ids = self_signing_key.keys.values();
            let self_signing_key_id = self_signing_key_ids.next().ok_or(Error::BadRequest(
                ErrorKind::InvalidParam,
                "Self signing key contained no key.",
            ))?;

            if self_signing_key_ids.next().is_some() {
                return Err(Error::BadRequest(
                    ErrorKind::InvalidParam,
                    "Self signing key contained more than one key.",
                ));
            }

            let mut self_signing_key_key = prefix.clone();
            self_signing_key_key.extend_from_slice(self_signing_key_id.as_bytes());

            self.keyid_key.insert(
                &self_signing_key_key,
                &*serde_json::to_string(&self_signing_key)
                    .expect("CrossSigningKey::to_string always works"),
            )?;

            self.userid_selfsigningkeyid
                .insert(&*user_id.to_string(), self_signing_key_key)?;
        }

        // User-signing key
        if let Some(user_signing_key) = user_signing_key {
            let mut user_signing_key_ids = user_signing_key.keys.values();
            let user_signing_key_id = user_signing_key_ids.next().ok_or(Error::BadRequest(
                ErrorKind::InvalidParam,
                "User signing key contained no key.",
            ))?;

            if user_signing_key_ids.next().is_some() {
                return Err(Error::BadRequest(
                    ErrorKind::InvalidParam,
                    "User signing key contained more than one key.",
                ));
            }

            let mut user_signing_key_key = prefix;
            user_signing_key_key.extend_from_slice(user_signing_key_id.as_bytes());

            self.keyid_key.insert(
                &user_signing_key_key,
                &*serde_json::to_string(&user_signing_key)
                    .expect("CrossSigningKey::to_string always works"),
            )?;

            self.userid_usersigningkeyid
                .insert(&*user_id.to_string(), user_signing_key_key)?;
        }

        let count = globals.next_count()?.to_be_bytes();
        for room_id in rooms.rooms_joined(&user_id) {
            let mut key = room_id?.to_string().as_bytes().to_vec();
            key.push(0xff);
            key.extend_from_slice(&count);

            self.keychangeid_userid.insert(key, &*user_id.to_string())?;
        }

        let mut key = user_id.to_string().as_bytes().to_vec();
        key.push(0xff);
        key.extend_from_slice(&count);
        self.keychangeid_userid.insert(key, &*user_id.to_string())?;

        Ok(())
    }

    pub fn sign_key(
        &self,
        target_id: &UserId,
        key_id: &str,
        signature: (String, String),
        sender_id: &UserId,
        rooms: &super::rooms::Rooms,
        globals: &super::globals::Globals,
    ) -> Result<()> {
        let mut key = target_id.to_string().as_bytes().to_vec();
        key.push(0xff);
        key.extend_from_slice(key_id.to_string().as_bytes());

        let mut cross_signing_key =
            serde_json::from_slice::<serde_json::Value>(&self.keyid_key.get(&key)?.ok_or(
                Error::BadRequest(ErrorKind::InvalidParam, "Tried to sign nonexistent key."),
            )?)
            .map_err(|_| Error::bad_database("key in keyid_key is invalid."))?;

        let signatures = cross_signing_key
            .get_mut("signatures")
            .ok_or_else(|| Error::bad_database("key in keyid_key has no signatures field."))?
            .as_object_mut()
            .ok_or_else(|| Error::bad_database("key in keyid_key has invalid signatures field."))?
            .entry(sender_id.clone())
            .or_insert_with(|| serde_json::Map::new().into());

        signatures
            .as_object_mut()
            .ok_or_else(|| Error::bad_database("signatures in keyid_key for a user is invalid."))?
            .insert(signature.0, signature.1.into());

        self.keyid_key.insert(
            &key,
            &*serde_json::to_string(&cross_signing_key)
                .expect("CrossSigningKey::to_string always works"),
        )?;

        // TODO: Should we notify about this change?
        let count = globals.next_count()?.to_be_bytes();
        for room_id in rooms.rooms_joined(&target_id) {
            let mut key = room_id?.to_string().as_bytes().to_vec();
            key.push(0xff);
            key.extend_from_slice(&count);

            self.keychangeid_userid
                .insert(key, &*target_id.to_string())?;
        }

        let mut key = target_id.to_string().as_bytes().to_vec();
        key.push(0xff);
        key.extend_from_slice(&count);
        self.keychangeid_userid
            .insert(key, &*target_id.to_string())?;

        Ok(())
    }

    pub fn keys_changed(
        &self,
        user_or_room_id: &str,
        from: u64,
        to: Option<u64>,
    ) -> impl Iterator<Item = Result<UserId>> {
        let mut prefix = user_or_room_id.as_bytes().to_vec();
        prefix.push(0xff);

        let mut start = prefix.clone();
        start.extend_from_slice(&(from + 1).to_be_bytes());

        let mut end = prefix.clone();
        end.extend_from_slice(&to.unwrap_or(u64::MAX).to_be_bytes());

        self.keychangeid_userid
            .range(start..end)
            .filter_map(|r| r.ok())
            .take_while(move |(k, _)| k.starts_with(&prefix))
            .map(|(_, bytes)| {
                Ok(
                    UserId::try_from(utils::string_from_bytes(&bytes).map_err(|_| {
                        Error::bad_database(
                            "User ID in devicekeychangeid_userid is invalid unicode.",
                        )
                    })?)
                    .map_err(|_| {
                        Error::bad_database("User ID in devicekeychangeid_userid is invalid.")
                    })?,
                )
            })
    }

    pub fn get_device_keys(
        &self,
        user_id: &UserId,
        device_id: &DeviceId,
    ) -> Result<Option<DeviceKeys>> {
        let mut key = user_id.to_string().as_bytes().to_vec();
        key.push(0xff);
        key.extend_from_slice(device_id.as_bytes());

        self.keyid_key.get(key)?.map_or(Ok(None), |bytes| {
            Ok(Some(serde_json::from_slice(&bytes).map_err(|_| {
                Error::bad_database("DeviceKeys in db are invalid.")
            })?))
        })
    }

    pub fn get_master_key(
        &self,
        user_id: &UserId,
        sender_id: &UserId,
    ) -> Result<Option<CrossSigningKey>> {
        // TODO: hide some signatures
        self.userid_masterkeyid
            .get(user_id.to_string())?
            .map_or(Ok(None), |key| {
                self.keyid_key.get(key)?.map_or(Ok(None), |bytes| {
                    let mut cross_signing_key = serde_json::from_slice::<CrossSigningKey>(&bytes)
                        .map_err(|_| {
                        Error::bad_database("CrossSigningKey in db is invalid.")
                    })?;

                    // A user is not allowed to see signatures from users other than himself and
                    // the target user
                    cross_signing_key.signatures = cross_signing_key
                        .signatures
                        .into_iter()
                        .filter(|(user, _)| user == user_id || user == sender_id)
                        .collect();

                    Ok(Some(cross_signing_key))
                })
            })
    }

    pub fn get_self_signing_key(
        &self,
        user_id: &UserId,
        sender_id: &UserId,
    ) -> Result<Option<CrossSigningKey>> {
        self.userid_selfsigningkeyid
            .get(user_id.to_string())?
            .map_or(Ok(None), |key| {
                self.keyid_key.get(key)?.map_or(Ok(None), |bytes| {
                    let mut cross_signing_key = serde_json::from_slice::<CrossSigningKey>(&bytes)
                        .map_err(|_| {
                        Error::bad_database("CrossSigningKey in db is invalid.")
                    })?;

                    // A user is not allowed to see signatures from users other than himself and
                    // the target user
                    cross_signing_key.signatures = cross_signing_key
                        .signatures
                        .into_iter()
                        .filter(|(user, _)| user == user_id || user == sender_id)
                        .collect();

                    Ok(Some(cross_signing_key))
                })
            })
    }

    pub fn get_user_signing_key(&self, user_id: &UserId) -> Result<Option<CrossSigningKey>> {
        self.userid_usersigningkeyid
            .get(user_id.to_string())?
            .map_or(Ok(None), |key| {
                self.keyid_key.get(key)?.map_or(Ok(None), |bytes| {
                    Ok(Some(serde_json::from_slice(&bytes).map_err(|_| {
                        Error::bad_database("CrossSigningKey in db is invalid.")
                    })?))
                })
            })
    }

    pub fn add_to_device_event(
        &self,
        sender: &UserId,
        target_user_id: &UserId,
        target_device_id: &DeviceId,
        event_type: &EventType,
        content: serde_json::Value,
        globals: &super::globals::Globals,
    ) -> Result<()> {
        let mut key = target_user_id.to_string().as_bytes().to_vec();
        key.push(0xff);
        key.extend_from_slice(target_device_id.as_bytes());
        key.push(0xff);
        key.extend_from_slice(&globals.next_count()?.to_be_bytes());

        let mut json = serde_json::Map::new();
        json.insert("type".to_owned(), event_type.to_string().into());
        json.insert("sender".to_owned(), sender.to_string().into());
        json.insert("content".to_owned(), content);

        self.todeviceid_events.insert(
            &key,
            &*serde_json::to_string(&json).expect("Map::to_string always works"),
        )?;

        Ok(())
    }

    pub fn get_to_device_events(
        &self,
        user_id: &UserId,
        device_id: &DeviceId,
    ) -> Result<Vec<Raw<AnyToDeviceEvent>>> {
        let mut events = Vec::new();

        let mut prefix = user_id.to_string().as_bytes().to_vec();
        prefix.push(0xff);
        prefix.extend_from_slice(device_id.as_bytes());
        prefix.push(0xff);

        for value in self.todeviceid_events.scan_prefix(&prefix).values() {
            events.push(
                serde_json::from_slice(&*value?)
                    .map_err(|_| Error::bad_database("Event in todeviceid_events is invalid."))?,
            );
        }

        Ok(events)
    }

    pub fn remove_to_device_events(
        &self,
        user_id: &UserId,
        device_id: &DeviceId,
        until: u64,
    ) -> Result<()> {
        let mut prefix = user_id.to_string().as_bytes().to_vec();
        prefix.push(0xff);
        prefix.extend_from_slice(device_id.as_bytes());
        prefix.push(0xff);

        let mut last = prefix.clone();
        last.extend_from_slice(&until.to_be_bytes());

        for (key, _) in self
            .todeviceid_events
            .range(&*prefix..=&*last)
            .keys()
            .map(|key| {
                let key = key?;
                Ok::<_, Error>((
                    key.clone(),
                    utils::u64_from_bytes(&key[key.len() - mem::size_of::<u64>()..key.len()])
                        .map_err(|_| Error::bad_database("ToDeviceId has invalid count bytes."))?,
                ))
            })
            .filter_map(|r| r.ok())
            .take_while(|&(_, count)| count <= until)
        {
            self.todeviceid_events.remove(key)?;
        }

        Ok(())
    }

    pub fn update_device_metadata(
        &self,
        user_id: &UserId,
        device_id: &DeviceId,
        device: &Device,
    ) -> Result<()> {
        let mut userdeviceid = user_id.to_string().as_bytes().to_vec();
        userdeviceid.push(0xff);
        userdeviceid.extend_from_slice(device_id.as_bytes());

        // Only existing devices should be able to call this.
        assert!(self.userdeviceid_metadata.get(&userdeviceid)?.is_some());

        self.userdeviceid_metadata.insert(
            userdeviceid,
            serde_json::to_string(device)
                .expect("Device::to_string always works")
                .as_bytes(),
        )?;

        Ok(())
    }

    /// Get device metadata.
    pub fn get_device_metadata(
        &self,
        user_id: &UserId,
        device_id: &DeviceId,
    ) -> Result<Option<Device>> {
        let mut userdeviceid = user_id.to_string().as_bytes().to_vec();
        userdeviceid.push(0xff);
        userdeviceid.extend_from_slice(device_id.as_bytes());

        self.userdeviceid_metadata
            .get(&userdeviceid)?
            .map_or(Ok(None), |bytes| {
                Ok(Some(serde_json::from_slice(&bytes).map_err(|_| {
                    Error::bad_database("Metadata in userdeviceid_metadata is invalid.")
                })?))
            })
    }

    pub fn all_devices_metadata(&self, user_id: &UserId) -> impl Iterator<Item = Result<Device>> {
        let mut key = user_id.to_string().as_bytes().to_vec();
        key.push(0xff);

        self.userdeviceid_metadata
            .scan_prefix(key)
            .values()
            .map(|bytes| {
                Ok(serde_json::from_slice::<Device>(&bytes?).map_err(|_| {
                    Error::bad_database("Device in userdeviceid_metadata is invalid.")
                })?)
            })
    }

    /// Deactivate account
    pub fn deactivate_account(&self, user_id: &UserId) -> Result<()> {
        // Remove all associated devices
        for device_id in self.all_device_ids(user_id) {
            self.remove_device(&user_id, &device_id?)?;
        }

        // Set the password to "" to indicate a deactivated account
        self.userid_password.insert(user_id.to_string(), "")?;

        // TODO: Unhook 3PID
        Ok(())
    }
}