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bolt_transport.go
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bolt_transport.go
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package mercure
import (
"bytes"
"encoding/binary"
"encoding/json"
"fmt"
"math/rand"
"net/url"
"strconv"
"sync"
"time"
bolt "go.etcd.io/bbolt"
"go.uber.org/zap"
)
const BoltDefaultCleanupFrequency = 0.3
func init() { //nolint:gochecknoinits
RegisterTransportFactory("bolt", NewBoltTransport)
}
const defaultBoltBucketName = "updates"
// BoltTransport implements the TransportInterface using the Bolt database.
type BoltTransport struct {
sync.RWMutex
subscribers *SubscriberList
logger Logger
db *bolt.DB
bucketName string
size uint64
cleanupFrequency float64
closed chan struct{}
closedOnce sync.Once
lastSeq uint64
lastEventID string
}
// NewBoltTransport create a new boltTransport.
func NewBoltTransport(u *url.URL, l Logger) (Transport, error) { //nolint:ireturn
var err error
q := u.Query()
bucketName := defaultBoltBucketName
if q.Get("bucket_name") != "" {
bucketName = q.Get("bucket_name")
}
size := uint64(0)
if sizeParameter := q.Get("size"); sizeParameter != "" {
size, err = strconv.ParseUint(sizeParameter, 10, 64)
if err != nil {
return nil, &TransportError{u.Redacted(), fmt.Sprintf(`invalid "size" parameter %q`, sizeParameter), err}
}
}
cleanupFrequency := BoltDefaultCleanupFrequency
cleanupFrequencyParameter := q.Get("cleanup_frequency")
if cleanupFrequencyParameter != "" {
cleanupFrequency, err = strconv.ParseFloat(cleanupFrequencyParameter, 64)
if err != nil {
return nil, &TransportError{u.Redacted(), fmt.Sprintf(`invalid "cleanup_frequency" parameter %q`, cleanupFrequencyParameter), err}
}
}
path := u.Path // absolute path (bolt:///path.db)
if path == "" {
path = u.Host // relative path (bolt://path.db)
}
if path == "" {
return nil, &TransportError{u.Redacted(), "missing path", err}
}
db, err := bolt.Open(path, 0o600, &bolt.Options{Timeout: 1 * time.Second})
if err != nil {
return nil, &TransportError{dsn: u.Redacted(), err: err}
}
return &BoltTransport{
logger: l,
db: db,
bucketName: bucketName,
size: size,
cleanupFrequency: cleanupFrequency,
subscribers: NewSubscriberList(1e5),
closed: make(chan struct{}),
lastEventID: getDBLastEventID(db, bucketName),
}, nil
}
func getDBLastEventID(db *bolt.DB, bucketName string) string {
lastEventID := EarliestLastEventID
db.View(func(tx *bolt.Tx) error {
b := tx.Bucket([]byte(bucketName))
if b == nil {
return nil // No data
}
if k, _ := b.Cursor().Last(); k != nil {
lastEventID = string(k[8:])
}
return nil
})
return lastEventID
}
// Dispatch dispatches an update to all subscribers and persists it in Bolt DB.
func (t *BoltTransport) Dispatch(update *Update) error {
select {
case <-t.closed:
return ErrClosedTransport
default:
}
AssignUUID(update)
updateJSON, err := json.Marshal(*update)
if err != nil {
return fmt.Errorf("error when marshaling update: %w", err)
}
// We cannot use RLock() because Bolt allows only one read-write transaction at a time
t.Lock()
defer t.Unlock()
if err := t.persist(update.ID, updateJSON); err != nil {
return err
}
for _, s := range t.subscribers.MatchAny(update) {
s.Dispatch(update, false)
}
return nil
}
// persist stores update in the database.
func (t *BoltTransport) persist(updateID string, updateJSON []byte) error {
if err := t.db.Update(func(tx *bolt.Tx) error {
bucket, err := tx.CreateBucketIfNotExists([]byte(t.bucketName))
if err != nil {
return fmt.Errorf("error when creating Bolt DB bucket: %w", err)
}
seq, err := bucket.NextSequence()
if err != nil {
return fmt.Errorf("error when generating Bolt DB sequence: %w", err)
}
prefix := make([]byte, 8)
binary.BigEndian.PutUint64(prefix, seq)
// The sequence value is prepended to the update id to create an ordered list
key := bytes.Join([][]byte{prefix, []byte(updateID)}, []byte{})
// The DB is append only
bucket.FillPercent = 1
t.lastSeq = seq
t.lastEventID = updateID
if err := bucket.Put(key, updateJSON); err != nil {
return fmt.Errorf("unable to put value in Bolt DB: %w", err)
}
return t.cleanup(bucket, seq)
}); err != nil {
return fmt.Errorf("bolt error: %w", err)
}
return nil
}
// AddSubscriber adds a new subscriber to the transport.
func (t *BoltTransport) AddSubscriber(s *Subscriber) error {
select {
case <-t.closed:
return ErrClosedTransport
default:
}
t.Lock()
t.subscribers.Add(s)
toSeq := t.lastSeq //nolint:ifshort
t.Unlock()
if s.RequestLastEventID != "" {
t.dispatchHistory(s, toSeq)
}
s.Ready()
return nil
}
// RemoveSubscriber removes a new subscriber from the transport.
func (t *BoltTransport) RemoveSubscriber(s *Subscriber) error {
select {
case <-t.closed:
return ErrClosedTransport
default:
}
t.Lock()
defer t.Unlock()
t.subscribers.Remove(s)
return nil
}
// GetSubscribers get the list of active subscribers.
func (t *BoltTransport) GetSubscribers() (string, []*Subscriber, error) {
t.RLock()
defer t.RUnlock()
return t.lastEventID, getSubscribers(t.subscribers), nil
}
//nolint:gocognit
func (t *BoltTransport) dispatchHistory(s *Subscriber, toSeq uint64) {
t.db.View(func(tx *bolt.Tx) error {
b := tx.Bucket([]byte(t.bucketName))
if b == nil {
s.HistoryDispatched(EarliestLastEventID)
return nil // No data
}
c := b.Cursor()
responseLastEventID := EarliestLastEventID
afterFromID := s.RequestLastEventID == EarliestLastEventID
for k, v := c.First(); k != nil; k, v = c.Next() {
if !afterFromID {
responseLastEventID = string(k[8:])
if responseLastEventID == s.RequestLastEventID {
afterFromID = true
}
continue
}
var update *Update
if err := json.Unmarshal(v, &update); err != nil {
s.HistoryDispatched(responseLastEventID)
if c := t.logger.Check(zap.ErrorLevel, "Unable to unmarshal update coming from the Bolt DB"); c != nil {
c.Write(zap.Error(err))
}
return fmt.Errorf("unable to unmarshal update: %w", err)
}
if (s.Match(update) && !s.Dispatch(update, true)) || (toSeq > 0 && binary.BigEndian.Uint64(k[:8]) >= toSeq) {
s.HistoryDispatched(responseLastEventID)
return nil
}
}
s.HistoryDispatched(responseLastEventID)
if !afterFromID {
if c := t.logger.Check(zap.InfoLevel, "Can't find requested LastEventID"); c != nil {
c.Write(zap.String("LastEventID", s.RequestLastEventID))
}
}
return nil
})
}
// Close closes the Transport.
func (t *BoltTransport) Close() (err error) {
t.closedOnce.Do(func() {
close(t.closed)
t.Lock()
defer t.Unlock()
t.subscribers.Walk(0, func(s *Subscriber) bool {
s.Disconnect()
return true
})
err = t.db.Close()
})
if err == nil {
return nil
}
return fmt.Errorf("unable to close Bolt DB: %w", err)
}
// cleanup removes entries in the history above the size limit, triggered probabilistically.
func (t *BoltTransport) cleanup(bucket *bolt.Bucket, lastID uint64) error {
if t.size == 0 ||
t.cleanupFrequency == 0 ||
t.size >= lastID ||
(t.cleanupFrequency != 1 && rand.Float64() < t.cleanupFrequency) { //nolint:gosec
return nil
}
removeUntil := lastID - t.size
c := bucket.Cursor()
for k, _ := c.First(); k != nil; k, _ = c.Next() {
if binary.BigEndian.Uint64(k[:8]) > removeUntil {
break
}
if err := bucket.Delete(k); err != nil {
return fmt.Errorf("unable to delete value in Bolt DB: %w", err)
}
}
return nil
}
// Interface guards.
var (
_ Transport = (*BoltTransport)(nil)
_ TransportSubscribers = (*BoltTransport)(nil)
)