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store.go
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store.go
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//go:generate mockgen -source=$GOFILE -destination=store_mock.go -package=main
package main
import (
"bytes"
"encoding/binary"
"encoding/json"
"errors"
"fmt"
"os"
"strconv"
"strings"
"sync"
"time"
"github.com/rs/zerolog/log"
"github.com/syndtr/goleveldb/leveldb"
"github.com/syndtr/goleveldb/leveldb/iterator"
"github.com/syndtr/goleveldb/leveldb/opt"
"github.com/syndtr/goleveldb/leveldb/util"
)
type metadata struct {
topics []string
}
// storer should be safe for concurrent use.
type storer interface {
// Insert inserts a new record for a given topic.
Insert(topic string, val *value) error
// GetNext will retrieve the next value in the topic, as well as the AckKey
// allowing future acking/nacking of the value.
GetNext(topic string) (val *value, ackOffset int, err error)
// Ack will acknowledge the processing of a message, removing it from the
// topic entirely.
Ack(topic string, ackOffset int) error
// Nack will negatively acknowledge the message on a given topic, returning it
// to the *front* of the consumption queue.
Nack(topic string, ackOffset int) error
// Back will negatively acknowledge the message on a given topic, returning it
// to the *back* of the consumption queue.
Back(topic string, ackOffset int) error
// Dack will negatively acknowledge the message on a given topic, placing on
// the delay queue with a given timestamp as part of the key for later
// retrieval.
Dack(topic string, ackOffset int, delaySeconds int) error
// GetDelayed returns an iterator and a closer function allowing the caller to
// iterate over the currently waiting messages for a given topic in
// chronological delay order (those with soonest "done" time first).
GetDelayed(topic string) (delayedIterator, func() error)
// ReturnDelayed returns delayed messages with done times before the given
// time back to the main queue returning the number of messages returned or an
// error.
ReturnDelayed(topic string, before time.Time) (count int, err error)
// Meta returns the metadata of the database.
Meta() (*metadata, error)
// Close closes the store.
Close() error
// Purge deletes all data associated with a topic.
Purge(topic string) error
// Destroy removes the store from persistence. This is a destructive
// operation.
Destroy()
}
const (
errTopicEmpty = storeError("topic is empty")
errTopicNotExist = storeError("topic does not exist")
errNackMsgNotExist = storeError("msg to nack does not exist")
errBackMsgNotExist = storeError("msg to back does not exist")
errDackMsgNotExist = storeError("msg to dack does not exist")
)
type storeError string
func (s storeError) Error() string {
return string(s)
}
const (
// metaTopics is a key which contains a JSON encoded slice
metaTopics = "m-topics"
// The topic queue is the primary queue containing the records to be
// processed. We need to keep track of the head and the tail offsets of the
// queue in their respective keys in order to quickly append/pop messages from
// the queue.
topicFmt = "t-%s-%d" // topic: [topic]-[offset]
headPosKeyFmt = "t-%s-head" // key: [topic]-head
tailPosKeyFmt = "t-%s-tail" // key: [topic]-tail
// The ack topic queue is an auxiliary queue which allows keeping track of
// outstanding messages which are waiting on a consumer acknowledgement
// command. We only ever append to the end of this queue, delete records once
// they have been ACK'ed or moved back to the primary queue for reprocessing.
ackTopicFmt = "t-%s-ack-%d" // topic: [topic]-ack-[offset]
ackTailPosKeyFmt = "t-%s-ack-tail" // key: [topic]-ack-tail
// The delay topic contains messages in buckets with their designated return
// time as a unix timestamp. This provides strict ordering, allowing iteration
// over the items in prefixed byte-order.
delayTopicPrefix = "t-%s-delay-" // topic: [topic]-delay-
delayTopicFmt = delayTopicPrefix + "%d-%d" // topic: [topic]-delay-[until_unix_timestamp]-[local_index]
)
// store handles the the underlying leveldb implementation.
type store struct {
path string
db *leveldb.DB
sync.Mutex
}
func newStore(dbPath string) storer {
db, err := leveldb.OpenFile(dbPath, nil)
if err != nil {
log.Fatal().Err(err).Msg("failed to open levelDB")
}
return &store{
path: dbPath,
db: db,
}
}
// Ack will acknowledge the processing of a value, removing it from the topic
// entirely.
func (s *store) Ack(topic string, ackOffset int) error {
s.Lock()
defer s.Unlock()
// Delete the used value
key := fmt.Sprintf(ackTopicFmt, topic, ackOffset)
if err := s.db.Delete([]byte(key), nil); err != nil {
return fmt.Errorf("deleting from ack topic: %v", err)
}
return nil
}
// Nack will negatively acknowledge the value, on a given topic, returning it
// to the front of the consumption queue.
func (s *store) Nack(topic string, ackOffset int) error {
s.Lock()
defer s.Unlock()
nackKey := []byte(fmt.Sprintf(ackTopicFmt, topic, ackOffset))
tx, err := s.db.OpenTransaction()
if err != nil {
return fmt.Errorf("opening transaction: %v", err)
}
exists, err := tx.Has(nackKey, nil)
if err != nil {
tx.Discard()
return fmt.Errorf("checking has %s: %v", nackKey, err)
}
if !exists {
tx.Discard()
return errNackMsgNotExist
}
val, err := getOffset(tx, ackTopicFmt, topic, ackOffset)
if err != nil {
tx.Discard()
return fmt.Errorf("getting ack msg from topic %s at offset %d: %v", topic, ackOffset, err)
}
if _, err := prependValue(tx, topicFmt, headPosKeyFmt, topic, val); err != nil {
tx.Discard()
return fmt.Errorf("prepending value to topic %s: %v", topic, err)
}
if err := tx.Delete(nackKey, nil); err != nil {
tx.Discard()
return fmt.Errorf("deleting ackKey %s: %v", nackKey, err)
}
if err := tx.Commit(); err != nil {
tx.Discard()
return fmt.Errorf("committing nack transaction: %v", err)
}
return nil
}
// Back will negatively acknowledge the value, on a given topic, returning it
// to the back of the consumption queue.
func (s *store) Back(topic string, ackOffset int) error {
s.Lock()
defer s.Unlock()
backKey := []byte(fmt.Sprintf(ackTopicFmt, topic, ackOffset))
tx, err := s.db.OpenTransaction()
if err != nil {
return fmt.Errorf("opening transaction: %v", err)
}
exists, err := tx.Has(backKey, nil)
if err != nil {
tx.Discard()
return fmt.Errorf("checking has %s: %v", backKey, err)
}
if !exists {
tx.Discard()
return errBackMsgNotExist
}
val, err := getOffset(tx, ackTopicFmt, topic, ackOffset)
if err != nil {
tx.Discard()
return fmt.Errorf("getting ack msg from topic %s at offset %d: %v", topic, ackOffset, err)
}
if _, err := appendValue(tx, topicFmt, tailPosKeyFmt, topic, val); err != nil {
tx.Discard()
return fmt.Errorf("appending value to topic %s: %v", topic, err)
}
if err := tx.Delete(backKey, nil); err != nil {
tx.Discard()
return fmt.Errorf("deleting ackKey %s: %v", backKey, err)
}
if err := tx.Commit(); err != nil {
tx.Discard()
return fmt.Errorf("committing back transaction: %v", err)
}
return nil
}
// Insert creates a new record for a given topic, creating the topic in the
// store if it doesn't already exist. If it does, the record is placed at the
// end of the queue.
func (s *store) Insert(topic string, val *value) error {
s.Lock()
defer s.Unlock()
headPosKey := []byte(fmt.Sprintf(headPosKeyFmt, topic))
tailPosKey := []byte(fmt.Sprintf(tailPosKeyFmt, topic))
ackTailPosKey := []byte(fmt.Sprintf(ackTailPosKeyFmt, topic))
exists, err := s.db.Has(tailPosKey, nil)
if err != nil {
return fmt.Errorf("checking has %s: %v", tailPosKey, err)
}
// The key already exists
if exists {
if _, err := appendValue(s.db, topicFmt, tailPosKeyFmt, topic, val); err != nil {
return err
}
return nil
}
// Add the topic to the list of topics
if err := addTopicMeta(s.db, topic); err != nil {
return fmt.Errorf("adding topic to meta: %v", err)
}
// Write initial head position
headPos := make([]byte, 8)
binary.PutVarint(headPos, 0)
if err := s.db.Put(headPosKey, headPos, nil); err != nil {
return fmt.Errorf("putting head position value: %v", err)
}
// Write initial ack topic head position
ackTailPos := make([]byte, 8)
binary.PutVarint(ackTailPos, 0)
if err := s.db.Put(ackTailPosKey, ackTailPos, nil); err != nil {
return fmt.Errorf("putting ack head position value: %v", err)
}
// Write initial tail position
tailPos := make([]byte, 8)
binary.PutVarint(tailPos, 1)
if err := s.db.Put(tailPosKey, tailPos, nil); err != nil {
return fmt.Errorf("putting tail position value: %v", err)
}
// Write new message to head
newKey := []byte(fmt.Sprintf(topicFmt, topic, 0))
b, err := val.Encode()
if err != nil {
return fmt.Errorf("encoding value: %v", err)
}
if err := s.db.Put(newKey, b, nil); err != nil {
return fmt.Errorf("putting first value for topic: %v", err)
}
return nil
}
// GetNext retrieves the first record for a topic, incrementing the head
// position of the main array and pushing the value onto the ack array.
func (s *store) GetNext(topic string) (*value, int, error) {
s.Lock()
defer s.Unlock()
headOffset, err := getPos(s.db, headPosKeyFmt, topic)
if err != nil {
return nil, 0, err
}
val, err := getValue(s.db, topicFmt, topic, headOffset)
if err != nil {
return nil, 0, err
}
insertedOffset, err := appendValue(s.db, ackTopicFmt, ackTailPosKeyFmt, topic, val)
if err != nil {
return nil, 0, err
}
if _, _, err := addPos(s.db, headPosKeyFmt, topic, 1); err != nil {
return nil, 0, err
}
return val, insertedOffset, nil
}
// Dack will negatively acknowledge the message on a given topic, placing on
// the delay queue with a given timestamp as part of the key for later
// retrieval.
func (s *store) Dack(topic string, ackOffset int, delaySeconds int) error {
s.Lock()
defer s.Unlock()
dackKey := []byte(fmt.Sprintf(ackTopicFmt, topic, ackOffset))
tx, err := s.db.OpenTransaction()
if err != nil {
return fmt.Errorf("opening transaction: %v", err)
}
exists, err := tx.Has(dackKey, nil)
if err != nil {
tx.Discard()
return fmt.Errorf("checking has %s: %v", dackKey, err)
}
if !exists {
tx.Discard()
return errDackMsgNotExist
}
val, err := getOffset(tx, ackTopicFmt, topic, ackOffset)
if err != nil {
tx.Discard()
return fmt.Errorf("getting ack msg from topic %s at offset %d: %v", topic, ackOffset, err)
}
val.DackCount++
if err := insertDelay(tx, topic, val, delaySeconds); err != nil {
tx.Discard()
return fmt.Errorf("inserting ack msg into delay topic from topic %s at offset %d: %v", topic, ackOffset, err)
}
if err := tx.Delete(dackKey, nil); err != nil {
tx.Discard()
return fmt.Errorf("deleting ackKey %s: %v", dackKey, err)
}
if err := tx.Commit(); err != nil {
tx.Discard()
return fmt.Errorf("committing dack transaction: %v", err)
}
return nil
}
// Requires version of mockgen with https://github.com/golang/mock/pull/405 due
// to exposing a bug in previous versions. Unfortunately for now-
// $ go get github.com/golang/mock/mockgen@HEAD
// until a new release made.
type delayedIterator interface {
iterator.Iterator
}
// GetDelayed returns an iterator and a closer function allowing the caller to
// iterate over the currently waiting messages for a given topic in
// chronological delay order (those with soonest "done" time first).
func (s *store) GetDelayed(topic string) (iterator delayedIterator, closer func() error) {
s.Lock()
defer s.Unlock()
key := fmt.Sprintf(delayTopicPrefix, topic)
prefix := util.BytesPrefix([]byte(key))
iter := s.db.NewIterator(prefix, nil)
closer = func() error {
iter.Release()
return iter.Error()
}
return iter, closer
}
// ReturnDelayed returns delayed messages with done times before the given time
// back to the main queue.
func (s *store) ReturnDelayed(topic string, before time.Time) (int, error) {
s.Lock()
defer s.Unlock()
key := fmt.Sprintf(delayTopicPrefix, topic)
prefix := util.BytesPrefix([]byte(key))
iter := s.db.NewIterator(prefix, nil)
defer iter.Release() // In case we return early, it is safe to call multiple times.
tx, err := s.db.OpenTransaction()
if err != nil {
return 0, fmt.Errorf("opening transaction: %v", err)
}
count := 0
// For each record, check if the timestamp is earlier than the given cutoff,
// returning the record to the front of the main queue if it is.
//
// TODO fix returned messages being in reverse chronological order if there
// are multiple being done at once
for iter.Next() {
key := iter.Key()
delayTime, err := timeFromDelayKey(string(key))
if err != nil {
tx.Discard()
return 0, err
}
// The message has passed the delay point so should be returned to the front
// of the main queue to be processed again.
if delayTime.Before(before) {
count++
val := iter.Value()
v, err := decodeValue(val)
if err != nil {
return 0, err
}
if _, err := prependValue(tx, topicFmt, headPosKeyFmt, topic, v); err != nil {
tx.Discard()
return 0, err
}
if err := tx.Delete(key, nil); err != nil {
tx.Discard()
return 0, err
}
} else {
// We've already reached a timestamp that is in the future, no need to
// continue.
break
}
}
iter.Release()
if err := iter.Error(); err != nil {
tx.Discard()
return 0, fmt.Errorf("iterating over delayed messages for topic %s: %v", topic, err)
}
if err := tx.Commit(); err != nil {
tx.Discard()
return 0, fmt.Errorf("committing nack transaction: %v", err)
}
return count, nil
}
func (s *store) Meta() (*metadata, error) {
s.Lock()
defer s.Unlock()
topics, err := getTopicMeta(s.db)
if err != nil {
return nil, err
}
return &metadata{
topics: topics,
}, nil
}
// Purge deletes all data associated with a topic.
func (s *store) Purge(topic string) error {
s.Lock()
defer s.Unlock()
batch := new(leveldb.Batch)
prefix := util.BytesPrefix([]byte(fmt.Sprintf("t-%s", topic)))
iter := s.db.NewIterator(prefix, nil)
for iter.Next() {
key := iter.Key()
batch.Delete(key)
}
iter.Release()
if err := iter.Error(); err != nil {
return fmt.Errorf("iterating over purge prefix: %v", err)
}
if err := s.db.Write(batch, nil); err != nil {
return fmt.Errorf("writing purge batch: %v", err)
}
// TODO measure performance impact of immediate compaction
// if err := s.db.CompactRange(*prefix); err != nil {
// return fmt.Errorf("compacting purged range: %v", err)
// }
return nil
}
// Close the store.
func (s *store) Close() error {
return s.db.Close()
}
// Destroy the underlying store.
func (s *store) Destroy() {
_ = s.Close()
_ = os.RemoveAll(s.path)
}
// leveldber describes methods available on both a leveldb.DB and a
// leveldb.Transaction.
type leveldber interface {
Has(key []byte, ro *opt.ReadOptions) (ret bool, err error)
Put(key, value []byte, wo *opt.WriteOptions) error
Get(key []byte, ro *opt.ReadOptions) ([]byte, error)
}
func insertDelay(db leveldber, topic string, val *value, delaySeconds int) error {
delayTo := time.Now().Unix() + int64(delaySeconds)
var (
key string
// localOffset to enable inserting multiple records at a given timestamp
localOffset = 0
)
for {
key = fmt.Sprintf(delayTopicFmt, topic, delayTo, localOffset)
exists, err := db.Has([]byte(key), nil)
if err != nil {
return fmt.Errorf("checking has %s: %v", key, err)
}
// A value in this position already exists, we need to combine them.
if !exists {
break
}
localOffset++
}
b, err := val.Encode()
if err != nil {
return fmt.Errorf("encoding value: %v", err)
}
if err := db.Put([]byte(key), b, nil); err != nil {
return fmt.Errorf("putting value: %v", err)
}
return nil
}
// getOffset retrieves a record for a topic with a specific offset.
func getOffset(db leveldber, topicFmt string, topic string, offset int) (*value, error) {
key := fmt.Sprintf(topicFmt, topic, offset)
val, err := db.Get([]byte(key), nil)
if err != nil {
return nil, err
}
v, err := decodeValue(val)
if err != nil {
return nil, err
}
return v, nil
}
// getPos gets the integer position value (aka offset) for topic and key format.
func getPos(db leveldber, topicFmt string, topic string) (int, error) {
key := []byte(fmt.Sprintf(topicFmt, topic))
pos, err := db.Get(key, nil)
if errors.Is(err, leveldb.ErrNotFound) {
return 0, errTopicNotExist
}
if err != nil {
return 0, fmt.Errorf("getting offset position position: %v", err)
}
i, err := binary.ReadVarint(bytes.NewReader(pos))
if err != nil {
return 0, fmt.Errorf("reading offset position varint: %v", err)
}
return int(i), nil
}
// getValue returns the raw value stored given a key format, topic and offset.
func getValue(db leveldber, topicFmt string, topic string, offset int) (*value, error) {
key := fmt.Sprintf(topicFmt, topic, offset)
val, err := db.Get([]byte(key), nil)
if errors.Is(err, leveldb.ErrNotFound) {
return nil, errTopicEmpty
}
if err != nil {
return nil, fmt.Errorf("getting value with fmt [%s] from topic %s at offset %d: %v", topicFmt, topic, offset, err)
}
v, err := decodeValue(val)
if err != nil {
return nil, err
}
return v, nil
}
// appendValue returns inserts a new value to the end of a topic given,
// returning the inserted offset.
func appendValue(db leveldber, topicFmt, tailPosKeyFmt, topic string, val *value) (offset int, err error) {
tailPosKey := []byte(fmt.Sprintf(tailPosKeyFmt, topic))
// Fetch the current tail position
tailPosVal, err := db.Get(tailPosKey, nil)
if err != nil {
return 0, fmt.Errorf("getting tail position from db: %v", err)
}
origOffset, err := binary.ReadVarint(bytes.NewReader(tailPosVal))
if err != nil {
return 0, fmt.Errorf("reading tail pos varint: %v", err)
}
// Write new record to next tail position
newKey := []byte(fmt.Sprintf(topicFmt, topic, origOffset))
b, err := val.Encode()
if err != nil {
return 0, fmt.Errorf("encoding value: %v", err)
}
if err := db.Put(newKey, b, nil); err != nil {
return 0, fmt.Errorf("putting value: %v", err)
}
// Update tail position
tail := make([]byte, 8)
binary.PutVarint(tail, origOffset+1)
if err := db.Put(tailPosKey, tail, nil); err != nil {
return 0, fmt.Errorf("putting new tail position: %v", err)
}
return int(origOffset), nil
}
// prependValue inserts a value to the head of a topic, decrementing the head
// position and returning the offset of the prepended value.
func prependValue(tx leveldber, topicFmt, headPosKeyFmt, topic string, val *value) (offset int, err error) {
headPosKey := []byte(fmt.Sprintf(headPosKeyFmt, topic))
// Fetch the current head position
headPosVal, err := tx.Get(headPosKey, nil)
if err != nil {
return 0, fmt.Errorf("getting head position from db: %v", err)
}
headOffset, err := binary.ReadVarint(bytes.NewReader(headPosVal))
if err != nil {
return 0, fmt.Errorf("reading head pos varint: %v", err)
}
// Write new record to lower neighbouring position
newHeadOffset := headOffset - 1
newKey := []byte(fmt.Sprintf(topicFmt, topic, newHeadOffset))
b, err := val.Encode()
if err != nil {
return 0, fmt.Errorf("encoding value: %v", err)
}
if err := tx.Put(newKey, b, nil); err != nil {
return 0, fmt.Errorf("putting value: %v", err)
}
// Update head position
_, newPosition, err := addPos(tx, headPosKeyFmt, topic, -1)
if err != nil {
return 0, fmt.Errorf("decrementing head pos by 1: %v", err)
}
return int(newPosition), nil
}
// addPos adds the an integer to a given position pointer.
func addPos(db leveldber, posKeyFmt string, topic string, sum int) (oldPosition, newPosition int, err error) {
oldPos, err := getPos(db, posKeyFmt, topic)
if err != nil {
return 0, 0, err
}
newPos := oldPos + sum
newPosBytes := make([]byte, 8)
binary.PutVarint(newPosBytes, int64(newPos))
key := []byte(fmt.Sprintf(posKeyFmt, topic))
if err := db.Put(key, newPosBytes, nil); err != nil {
return 0, 0, fmt.Errorf("putting new increment position: %v", err)
}
return oldPos, newPos, nil
}
// timeFromDelayKey returns the "done" timestamp from the key of a message in a
// delay queue.
func timeFromDelayKey(key string) (time.Time, error) {
splitKey := strings.Split(key, "-")
if len(splitKey) < 3 {
return time.Time{}, fmt.Errorf("invalid delay key format: %s", key)
}
timestampInt, err := strconv.Atoi(splitKey[3])
if err != nil {
return time.Time{}, fmt.Errorf("converting timestamp to int: %v", err)
}
timestampTime := time.Unix(int64(timestampInt), 0)
return timestampTime, nil
}
func getTopicMeta(db leveldber) ([]string, error) {
var topics []string
key := []byte(metaTopics)
exists, err := db.Has(key, nil)
if err != nil {
return nil, fmt.Errorf("checking has %s: %v", key, err)
}
if !exists {
return []string{}, nil
}
val, err := db.Get(key, nil)
if err != nil {
return nil, fmt.Errorf("getting topics meta: %v", err)
}
if err := json.Unmarshal(val, &topics); err != nil {
return nil, fmt.Errorf("unmarshalling topics meta: %v", err)
}
return topics, nil
}
func addTopicMeta(db leveldber, topic string) error {
key := []byte(metaTopics)
topics := []string{topic}
exists, err := db.Has(key, nil)
if err != nil {
return fmt.Errorf("checking has %s: %v", key, err)
}
if exists {
val, err := db.Get(key, nil)
if err != nil {
return fmt.Errorf("getting key %s: %v", key, err)
}
var existingTopics []string
if err := json.Unmarshal(val, &existingTopics); err != nil {
return fmt.Errorf("unmarshalling topics meta: %v", err)
}
topics = append(existingTopics, topic)
}
val, err := json.Marshal(topics)
if err != nil {
return fmt.Errorf("marshalling topics meta: %v", err)
}
if err := db.Put(key, val, nil); err != nil {
return fmt.Errorf("putting topics meta %s: %v", key, err)
}
return nil
}