(VDB-68) Verify log block hash matches header block hash

- Delete header on conflict to prompt data refresh (cascade deletes all
  data associated with that block)
- Derive header hash from rpc payload rather than computing it from data
  (prevents hash mismatch between blockchain and cache)

pkg/transformers/shared/constants/checked_headers.go

@@ -20,7 +20,7 @@ var (
 	PitFileStabilityFeeChecked = "pit_file_stability_fee_checked"
 	PriceFeedsChecked          = "price_feeds_checked"
 	TendChecked                = "tend_checked"
-  VatFluxChecked             = "vat_flux_checked"
+	VatFluxChecked             = "vat_flux_checked"
 	VatFoldChecked             = "vat_fold_checked"
 	VatGrabChecked             = "vat_grab_checked"
 	VatHealChecked             = "vat_heal_checked"

pkg/transformers/shared/constants/label.go

@@ -64,4 +64,4 @@ func AllTransformerLabels() []string {
 		VatTuneLabel,
 		VowFlogLabel,
 	}
-}
+}

pkg/transformers/shared/repository.go

@@ -2,10 +2,41 @@ package shared
 
 import (
 	"database/sql"
+	"encoding/json"
+	"errors"
+	"github.com/ethereum/go-ethereum/core/types"
 	"github.com/vulcanize/vulcanizedb/pkg/core"
 	"github.com/vulcanize/vulcanizedb/pkg/datastore/postgres"
 )
 
+var ErrHeaderMismatch = errors.New("log's block hash does not match associated header's block hash")
+
+func ValidateHeaderConsistency(headerID int64, rawLog []byte, db *postgres.DB) error {
+	var log types.Log
+	err := json.Unmarshal(rawLog, &log)
+	if err != nil {
+		return err
+	}
+	var hash string
+	err = db.Get(&hash, `SELECT hash FROM public.headers WHERE id = $1`, headerID)
+	if err != nil {
+		return err
+	}
+	if hash != log.BlockHash.String() {
+		err = deleteHeader(headerID, db)
+		if err != nil {
+			return err
+		}
+		return ErrHeaderMismatch
+	}
+	return nil
+}
+
+func deleteHeader(headerID int64, db *postgres.DB) error {
+	_, err := db.Exec(`DELETE FROM public.headers WHERE id = $1`, headerID)
+	return err
+}
+
 func MarkHeaderChecked(headerID int64, db *postgres.DB, checkedHeadersColumn string) error {
 	_, err := db.Exec(`INSERT INTO public.checked_headers (header_id, `+checkedHeadersColumn+`)
 		VALUES ($1, $2)