dendrite/keyserver/internal/device_list_update.go

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// Copyright 2020 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.
package internal
import (
"context"
"encoding/json"
"fmt"
"hash/fnv"
"sync"
"time"
"github.com/matrix-org/dendrite/keyserver/api"
"github.com/matrix-org/gomatrixserverlib"
"github.com/matrix-org/util"
"github.com/sirupsen/logrus"
)
// DeviceListUpdater handles device list updates from remote servers.
//
// In the case where we have the prev_id for an update, the updater just stores the update (after acquiring a per-user lock).
// In the case where we do not have the prev_id for an update, the updater marks the user_id as stale and notifies
// a worker to get the latest device list for this user. Note: stream IDs are scoped per user so missing a prev_id
// for a (user, device) does not mean that DEVICE is outdated as the previous ID could be for a different device:
// we have to invalidate all devices for that user. Once the list has been fetched, the per-user lock is acquired and the
// updater stores the latest list along with the latest stream ID.
//
// On startup, the updater spins up N workers which are responsible for querying device keys from remote servers.
// Workers are scoped by homeserver domain, with one worker responsible for many domains, determined by hashing
// mod N the server name. Work is sent via a channel which just serves to "poke" the worker as the data is retrieved
// from the database (which allows us to batch requests to the same server). This has a number of desirable properties:
// - We guarantee only 1 in-flight /keys/query request per server at any time as there is exactly 1 worker responsible
// for that domain.
// - We don't have unbounded growth in proportion to the number of servers (this is more important in a P2P world where
// we have many many servers)
// - We can adjust concurrency (at the cost of memory usage) by tuning N, to accommodate mobile devices vs servers.
// The downsides are that:
// - Query requests can get queued behind other servers if they hash to the same worker, even if there are other free
// workers elsewhere. Whilst suboptimal, provided we cap how long a single request can last (e.g using context timeouts)
// we guarantee we will get around to it. Also, more users on a given server does not increase the number of requests
// (as /keys/query allows multiple users to be specified) so being stuck behind matrix.org won't materially be any worse
// than being stuck behind foo.bar
// In the event that the query fails, the worker spins up a short-lived goroutine whose sole purpose is to inject the server
// name back into the channel after a certain amount of time. If in the interim the device lists have been updated, then
// the database query will return no stale lists. Reinjection into the channel continues until success or the server terminates,
// when it will be reloaded on startup.
type DeviceListUpdater struct {
// A map from user_id to a mutex. Used when we are missing prev IDs so we don't make more than 1
// request to the remote server and race.
// TODO: Put in an LRU cache to bound growth
userIDToMutex map[string]*sync.Mutex
mu *sync.Mutex // protects UserIDToMutex
db DeviceListUpdaterDatabase
producer KeyChangeProducer
fedClient *gomatrixserverlib.FederationClient
workerChans []chan gomatrixserverlib.ServerName
}
// DeviceListUpdaterDatabase is the subset of functionality from storage.Database required for the updater.
// Useful for testing.
type DeviceListUpdaterDatabase interface {
// StaleDeviceLists returns a list of user IDs ending with the domains provided who have stale device lists.
// If no domains are given, all user IDs with stale device lists are returned.
StaleDeviceLists(ctx context.Context, domains []gomatrixserverlib.ServerName) ([]string, error)
// MarkDeviceListStale sets the stale bit for this user to isStale.
MarkDeviceListStale(ctx context.Context, userID string, isStale bool) error
// StoreRemoteDeviceKeys persists the given keys. Keys with the same user ID and device ID will be replaced. An empty KeyJSON removes the key
// for this (user, device). Does not modify the stream ID for keys.
StoreRemoteDeviceKeys(ctx context.Context, keys []api.DeviceMessage) error
// PrevIDsExists returns true if all prev IDs exist for this user.
PrevIDsExists(ctx context.Context, userID string, prevIDs []int) (bool, error)
}
// KeyChangeProducer is the interface for producers.KeyChange useful for testing.
type KeyChangeProducer interface {
ProduceKeyChanges(keys []api.DeviceMessage) error
}
// NewDeviceListUpdater creates a new updater which fetches fresh device lists when they go stale.
func NewDeviceListUpdater(
db DeviceListUpdaterDatabase, producer KeyChangeProducer, fedClient *gomatrixserverlib.FederationClient,
numWorkers int,
) *DeviceListUpdater {
return &DeviceListUpdater{
userIDToMutex: make(map[string]*sync.Mutex),
mu: &sync.Mutex{},
db: db,
producer: producer,
fedClient: fedClient,
workerChans: make([]chan gomatrixserverlib.ServerName, numWorkers),
}
}
// Start the device list updater, which will try to refresh any stale device lists.
func (u *DeviceListUpdater) Start() error {
for i := 0; i < len(u.workerChans); i++ {
// Allocate a small buffer per channel.
// If the buffer limit is reached, backpressure will cause the processing of EDUs
// to stop (in this transaction) until key requests can be made.
ch := make(chan gomatrixserverlib.ServerName, 10)
u.workerChans[i] = ch
go u.worker(ch)
}
staleLists, err := u.db.StaleDeviceLists(context.Background(), []gomatrixserverlib.ServerName{})
if err != nil {
return err
}
for _, userID := range staleLists {
u.notifyWorkers(userID)
}
return nil
}
func (u *DeviceListUpdater) mutex(userID string) *sync.Mutex {
u.mu.Lock()
defer u.mu.Unlock()
if u.userIDToMutex[userID] == nil {
u.userIDToMutex[userID] = &sync.Mutex{}
}
return u.userIDToMutex[userID]
}
func (u *DeviceListUpdater) Update(ctx context.Context, event gomatrixserverlib.DeviceListUpdateEvent) error {
isDeviceListStale, err := u.update(ctx, event)
if err != nil {
return err
}
if isDeviceListStale {
// poke workers to handle stale device lists
u.notifyWorkers(event.UserID)
}
return nil
}
func (u *DeviceListUpdater) update(ctx context.Context, event gomatrixserverlib.DeviceListUpdateEvent) (bool, error) {
mu := u.mutex(event.UserID)
mu.Lock()
defer mu.Unlock()
// check if we have the prev IDs
exists, err := u.db.PrevIDsExists(ctx, event.UserID, event.PrevID)
if err != nil {
return false, fmt.Errorf("failed to check prev IDs exist for %s (%s): %w", event.UserID, event.DeviceID, err)
}
// if this is the first time we're hearing about this user, sync the device list manually.
if len(event.PrevID) == 0 {
exists = false
}
util.GetLogger(ctx).WithFields(logrus.Fields{
"prev_ids_exist": exists,
"user_id": event.UserID,
"device_id": event.DeviceID,
"stream_id": event.StreamID,
"prev_ids": event.PrevID,
"display_name": event.DeviceDisplayName,
}).Info("DeviceListUpdater.Update")
// if we haven't missed anything update the database and notify users
if exists {
keys := []api.DeviceMessage{
{
DeviceKeys: api.DeviceKeys{
DeviceID: event.DeviceID,
DisplayName: event.DeviceDisplayName,
KeyJSON: event.Keys,
UserID: event.UserID,
},
StreamID: event.StreamID,
},
}
err = u.db.StoreRemoteDeviceKeys(ctx, keys)
if err != nil {
return false, fmt.Errorf("failed to store remote device keys for %s (%s): %w", event.UserID, event.DeviceID, err)
}
// ALWAYS emit key changes when we've been poked over federation even if there's no change
// just in case this poke is important for something.
err = u.producer.ProduceKeyChanges(keys)
if err != nil {
return false, fmt.Errorf("failed to produce device key changes for %s (%s): %w", event.UserID, event.DeviceID, err)
}
return false, nil
}
err = u.db.MarkDeviceListStale(ctx, event.UserID, true)
if err != nil {
return false, fmt.Errorf("failed to mark device list for %s as stale: %w", event.UserID, err)
}
return true, nil
}
func (u *DeviceListUpdater) notifyWorkers(userID string) {
_, remoteServer, err := gomatrixserverlib.SplitID('@', userID)
if err != nil {
return
}
hash := fnv.New32a()
_, _ = hash.Write([]byte(remoteServer))
index := int(hash.Sum32()) % len(u.workerChans)
u.workerChans[index] <- remoteServer
}
func (u *DeviceListUpdater) worker(ch chan gomatrixserverlib.ServerName) {
// It's possible to get many of the same server name in the channel, so in order
// to prevent processing the same server over and over we keep track of when we
// last made a request to the server. If we get the server name during the cooloff
// period, we'll ignore the poke.
lastProcessed := make(map[gomatrixserverlib.ServerName]time.Time)
// this can't be too long else sytest will give up trying to do a test
cooloffPeriod := 500 * time.Millisecond
shouldProcess := func(srv gomatrixserverlib.ServerName) bool {
// we should process requests when now is after the last process time + cooloff
return time.Now().After(lastProcessed[srv].Add(cooloffPeriod))
}
// on failure, spin up a short-lived goroutine to inject the server name again.
inject := func(srv gomatrixserverlib.ServerName, duration time.Duration) {
time.Sleep(duration)
ch <- srv
}
for serverName := range ch {
if !shouldProcess(serverName) {
// do not inject into the channel as we know there will be a sleeping goroutine
// which will do it after the cooloff period expires
continue
}
lastProcessed[serverName] = time.Now()
shouldRetry := u.processServer(serverName)
if shouldRetry {
go inject(serverName, cooloffPeriod) // TODO: Backoff?
}
}
}
func (u *DeviceListUpdater) processServer(serverName gomatrixserverlib.ServerName) bool {
requestTimeout := time.Minute // max amount of time we want to spend on each request
ctx, cancel := context.WithTimeout(context.Background(), requestTimeout)
defer cancel()
logger := util.GetLogger(ctx).WithField("server_name", serverName)
// fetch stale device lists
userIDs, err := u.db.StaleDeviceLists(ctx, []gomatrixserverlib.ServerName{serverName})
if err != nil {
logger.WithError(err).Error("failed to load stale device lists")
return true
}
hasFailures := false
for _, userID := range userIDs {
if ctx.Err() != nil {
// we've timed out, give up and go to the back of the queue to let another server be processed.
hasFailures = true
break
}
res, err := u.fedClient.GetUserDevices(ctx, serverName, userID)
if err != nil {
logger.WithError(err).WithField("user_id", userID).Error("failed to query device keys for user")
hasFailures = true
continue
}
err = u.updateDeviceList(&res)
if err != nil {
logger.WithError(err).WithField("user_id", userID).Error("fetched device list but failed to store/emit it")
hasFailures = true
}
}
return hasFailures
}
func (u *DeviceListUpdater) updateDeviceList(res *gomatrixserverlib.RespUserDevices) error {
ctx := context.Background() // we've got the keys, don't time out when persisting them to the database.
keys := make([]api.DeviceMessage, len(res.Devices))
for i, device := range res.Devices {
keyJSON, err := json.Marshal(device.Keys)
if err != nil {
util.GetLogger(ctx).WithField("keys", device.Keys).Error("failed to marshal keys, skipping device")
continue
}
keys[i] = api.DeviceMessage{
StreamID: res.StreamID,
DeviceKeys: api.DeviceKeys{
DeviceID: device.DeviceID,
DisplayName: device.DisplayName,
UserID: res.UserID,
KeyJSON: keyJSON,
},
}
}
err := u.db.StoreRemoteDeviceKeys(ctx, keys)
if err != nil {
return fmt.Errorf("failed to store remote device keys: %w", err)
}
err = u.db.MarkDeviceListStale(ctx, res.UserID, false)
if err != nil {
return fmt.Errorf("failed to mark device list as fresh: %w", err)
}
err = u.producer.ProduceKeyChanges(keys)
if err != nil {
return fmt.Errorf("failed to emit key changes for fresh device list: %w", err)
}
return nil
}