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Go
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import ( "context" "encoding/json" "log/slog" "math/rand" "net/url" "sync" "time"
"tangled.org/core/eventconsumer/cursor" "tangled.org/core/log"
"github.com/avast/retry-go/v4" "github.com/gorilla/websocket")
type ProcessFunc func(ctx context.Context, source Source, message Message) error
type Message struct { Rkey string Nsid string // do not full deserialize this portion of the message, processFunc can do that EventJson json.RawMessage `json:"event"`}
type ConsumerConfig struct { Sources map[Source]struct{} ProcessFunc ProcessFunc RetryInterval time.Duration MaxRetryInterval time.Duration ConnectionTimeout time.Duration WorkerCount int QueueSize int Logger *slog.Logger Dev bool CursorStore cursor.Store}
func NewConsumerConfig() *ConsumerConfig { return &ConsumerConfig{ Sources: make(map[Source]struct{}), }}
type Source interface { // url to start streaming events from Url(cursor int64, dev bool) (*url.URL, error) // cache key for cursor storage Key() string}
type Consumer struct { wg sync.WaitGroup dialer *websocket.Dialer connMap sync.Map jobQueue chan job logger *slog.Logger randSource *rand.Rand
// rw lock over edits to ConsumerConfig cfgMu sync.RWMutex cfg ConsumerConfig}
type job struct { source Source message []byte}
func NewConsumer(cfg ConsumerConfig) *Consumer { if cfg.RetryInterval == 0 { cfg.RetryInterval = 15 * time.Minute } if cfg.ConnectionTimeout == 0 { cfg.ConnectionTimeout = 10 * time.Second } if cfg.WorkerCount <= 0 { cfg.WorkerCount = 5 } if cfg.MaxRetryInterval == 0 { cfg.MaxRetryInterval = 1 * time.Hour } if cfg.Logger == nil { cfg.Logger = log.New("consumer") } if cfg.QueueSize == 0 { cfg.QueueSize = 100 } if cfg.CursorStore == nil { cfg.CursorStore = &cursor.MemoryStore{} } return &Consumer{ cfg: cfg, dialer: websocket.DefaultDialer, jobQueue: make(chan job, cfg.QueueSize), // buffered job queue logger: cfg.Logger, randSource: rand.New(rand.NewSource(time.Now().UnixNano())), }}
func (c *Consumer) Start(ctx context.Context) { c.cfg.Logger.Info("starting consumer", "config", c.cfg)
// start workers for range c.cfg.WorkerCount { c.wg.Add(1) go c.worker(ctx) }
// start streaming for source := range c.cfg.Sources { c.wg.Add(1) go c.startConnectionLoop(ctx, source) }}
func (c *Consumer) Stop() { c.connMap.Range(func(_, val any) bool { if conn, ok := val.(*websocket.Conn); ok { conn.Close() } return true }) c.wg.Wait() close(c.jobQueue)}
func (c *Consumer) AddSource(ctx context.Context, s Source) { // we are already listening to this source if _, ok := c.cfg.Sources[s]; ok { c.logger.Info("source already present", "source", s) return }
c.cfgMu.Lock() c.cfg.Sources[s] = struct{}{} c.wg.Add(1) go c.startConnectionLoop(ctx, s) c.cfgMu.Unlock()}
func (c *Consumer) worker(ctx context.Context) { defer c.wg.Done() for { select { case <-ctx.Done(): return case j, ok := <-c.jobQueue: if !ok { return }
var msg Message err := json.Unmarshal(j.message, &msg) if err != nil { c.logger.Error("error deserializing message", "source", j.source.Key(), "err", err) return }
// update cursor c.cfg.CursorStore.Set(j.source.Key(), time.Now().UnixNano())
if err := c.cfg.ProcessFunc(ctx, j.source, msg); err != nil { c.logger.Error("error processing message", "source", j.source, "err", err) } } }}
func (c *Consumer) startConnectionLoop(ctx context.Context, source Source) { defer c.wg.Done()
// attempt connection initially err := c.runConnection(ctx, source) if err != nil { c.logger.Error("failed to run connection", "err", err) }
timer := time.NewTimer(1 * time.Minute) defer timer.Stop()
// every subsequent attempt is delayed by 1 minute for { select { case <-ctx.Done(): return case <-timer.C: err := c.runConnection(ctx, source) if err != nil { c.logger.Error("failed to run connection", "err", err) } timer.Reset(1 * time.Minute) } }}
func (c *Consumer) runConnection(ctx context.Context, source Source) error { cursor := c.cfg.CursorStore.Get(source.Key())
u, err := source.Url(cursor, c.cfg.Dev) if err != nil { return err }
c.logger.Info("connecting", "url", u.String())
retryOpts := []retry.Option{ retry.Attempts(0), // infinite attempts retry.DelayType(retry.BackOffDelay), retry.Delay(c.cfg.RetryInterval), retry.MaxDelay(c.cfg.MaxRetryInterval), retry.MaxJitter(c.cfg.RetryInterval / 5), retry.OnRetry(func(n uint, err error) { c.logger.Info("retrying connection", "source", source, "url", u.String(), "attempt", n+1, "err", err, ) }), retry.Context(ctx), }
var conn *websocket.Conn
err = retry.Do(func() error { connCtx, cancel := context.WithTimeout(ctx, c.cfg.ConnectionTimeout) defer cancel() conn, _, err = c.dialer.DialContext(connCtx, u.String(), nil) return err }, retryOpts...) if err != nil { return err }
c.connMap.Store(source, conn) defer conn.Close() defer c.connMap.Delete(source)
c.logger.Info("connected", "source", source)
for { select { case <-ctx.Done(): return nil default: msgType, msg, err := conn.ReadMessage() if err != nil { return err } if msgType != websocket.TextMessage { continue } select { case c.jobQueue <- job{source: source, message: msg}: case <-ctx.Done(): return nil } } }}