Jason RPC

Filter Manager

The Filter Manager is a service that runs alongside the JSON RPC server.

It provides support for filtering blocks on the blockchain. Specifically, it includes both a log and a block level filter.

The Filter Manager relies heavily on Subscription Events, mentioned in the Blockchain section

type Filter struct {
	id string

	// block filter
	block *headElem

	// log cache
	logs []*Log

	// log filter
	logFilter *LogFilter

	// index of the filter in the timer array
	index int

	// next time to timeout
	timestamp time.Time

	// websocket connection
	ws wsConn
}


type FilterManager struct {
	logger hclog.Logger

	store   blockchainInterface
	closeCh chan struct{}

	subscription blockchain.Subscription

	filters map[string]*Filter
	lock    sync.Mutex

	updateCh chan struct{}
	timer    timeHeapImpl
	timeout  time.Duration

	blockStream *blockStream
}

Filter Manager events get dispatched in the Run method:

func (f *FilterManager) Run() {

	// watch for new events in the blockchain
	watchCh := make(chan *blockchain.Event)
	go func() {
		for {
			evnt := f.subscription.GetEvent()
			if evnt == nil {
				return
			}
			watchCh <- evnt
		}
	}()

	var timeoutCh <-chan time.Time
	for {
		// check for the next filter to be removed
		filter := f.nextTimeoutFilter()
		if filter == nil {
			timeoutCh = nil
		} else {
			timeoutCh = time.After(filter.timestamp.Sub(time.Now()))
		}

		select {
		case evnt := <-watchCh:
			// new blockchain event
			if err := f.dispatchEvent(evnt); err != nil {
				f.logger.Error("failed to dispatch event", "err", err)
			}

		case <-timeoutCh:
			// timeout for filter
			if !f.Uninstall(filter.id) {
				f.logger.Error("failed to uninstall filter", "id", filter.id)
			}

		case <-f.updateCh:
			// there is a new filter, reset the loop to start the timeout timer

		case <-f.closeCh:
			// stop the filter manager
			return
		}
	}
}

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