eth-blob-indexer/pkg/beacon/service.go

package beacon

import (
	"context"
	"encoding/hex"
	"encoding/json"
	"fmt"
	log "log/slog"
	"net/http"
	"time"

	"github.com/cerc-io/eth-blob-indexer/pkg/storage"
	"github.com/protolambda/zrnt/eth2/beacon/common"
)

var (
	// BeaconNodeHealthPath   = "/eth/v1/node/health"
	BeaconEventsPath       = "/eth/v1/events?topics=%s"
	BeaconBlobSidecarsPath = "/eth/v1/beacon/blob_sidecars/%s"
)

// BeaconClient subscribes to events from a beacon node and fetches newly available blobs.
type BeaconClient struct {
	URL string
}

func (bc *BeaconClient) Endpoint(path string, args ...any) string {
	return fmt.Sprintf(bc.URL+path, args...)
}

func (beacon *BeaconClient) CollectBlobs(ctx context.Context, db storage.KvStorage) error {
	events := make(chan *Event)

	subBlobs := CreateSubscription(ctx, beacon.Endpoint(BeaconEventsPath, "blob_sidecar"), events)
	defer subBlobs.Close()
	subHead := CreateSubscription(ctx, beacon.Endpoint(BeaconEventsPath, "head"), events)
	defer subHead.Close()

	// Last seen head slot
	// TODO: initialize with current head
	var lastHead common.Slot
	// Blobs we know about but haven't fetched yet
	// TOOD: persist and load?
	unfetched := map[common.Slot]int{}

	// blob_sidecar events are received after validation over gossip, and the blobs they reference
	// will not be available until head is updated with the corresponding block.
	// Reorgs should not cause an issue here as we aren't concerned with canonicity.
	timeout := 5 * time.Minute
	for {
		select {
		case event := <-events:
			switch string(event.Event) {
			case "head":
				var headEvent HeadEvent
				if err := json.Unmarshal(event.Data, &headEvent); err != nil {
					log.Error("Error unmarshalling event data", "error", err)
					return err
				}
				log.Debug("Received head event", "slot", headEvent.Slot, "block", headEvent.Block)
				if headEvent.Slot <= lastHead {
					log.Error("Unexpected head slot", "slot", headEvent.Slot)
				}
				lastHead = headEvent.Slot
			case "blob_sidecar":
				var blobEvent BlobSidecarEvent
				if err := json.Unmarshal(event.Data, &blobEvent); err != nil {
					log.Error("Error unmarshalling event data", "error", err)
					return err
				}
				log.Debug("Received blob_sidecar event",
					"slot", blobEvent.Slot,
					"block", blobEvent.BlockRoot,
					"vhash", blobEvent.VersionedHash,
				)
				unfetched[blobEvent.Slot]++
			}

			var fetched []common.Slot
			for slot := range unfetched {
				if slot <= lastHead {
					resp, err := fetchBlobs(beacon, slot.String())
					if err != nil {
						log.Error("Error fetching blobs", "error", err)
						return err
					}
					if len(resp.Data) == 0 {
						log.Error("No blobs in block", "slot", slot)
					}
					for _, blob := range resp.Data {
						if err := pushBlob(ctx, &blob, db); err != nil {
							return err
						}
						unfetched[slot]--
					}
				}
				if unfetched[slot] == 0 {
					fetched = append(fetched, slot)
				}
			}
			for _, slot := range fetched {
				delete(unfetched, slot)
			}
		case <-time.After(timeout):
			log.Debug("No events received", "for", timeout)

		case err := <-subBlobs.Err():
			if err != nil {
				return err
			}
		case err := <-subHead.Err():
			if err != nil {
				return err
			}
		case <-ctx.Done():
			log.Info("Context cancelled, exiting")
			return ctx.Err()
		}
	}
}

func pushBlob(ctx context.Context, blob *BlobSidecar, db storage.KvStorage) error {
	vhash := blob.KzgCommitment.ToVersionedHash()
	data, err := hex.DecodeString(blob.Blob[2:])
	if err != nil {
		log.Error("Error decoding blob", "error", err)
		return err
	}

	log.Info("Storing blob", "vhash", vhash)
	err = db.Set(ctx, storage.BlobKeyFromHash(vhash), data, 0)
	if err != nil {
		log.Error("Error storing blob", "error", err)
		return err
	}
	return nil
}

func fetchBlobs(beacon *BeaconClient, blockId string) (*BlobSidecarsResponse, error) {
	endpoint := beacon.Endpoint(BeaconBlobSidecarsPath, blockId)
	log.Debug("Fetching blobs", "endpoint", endpoint)
	resp, err := http.Get(endpoint)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()

	var obj BlobSidecarsResponse
	decoder := json.NewDecoder(resp.Body)
	return &obj, decoder.Decode(&obj)
}