move FindGuarantors to protocol

engine/access/ingestion/engine.go

@@ -19,7 +19,6 @@ import (
 	"github.com/onflow/flow-go/module/mempool/stdmap"
 	"github.com/onflow/flow-go/network"
 	"github.com/onflow/flow-go/state/protocol"
-	"github.com/onflow/flow-go/state/protocol/guarantor"
 	"github.com/onflow/flow-go/storage"
 	"github.com/onflow/flow-go/utils/logging"
 )
@@ -628,7 +627,7 @@ func (e *Engine) lookupCollection(collId flow.Identifier) (bool, error) {
 func (e *Engine) requestCollections(missingColls []*flow.CollectionGuarantee) {
 	for _, cg := range missingColls {
 		// TODO: move this query out of for loop?
-		guarantors, err := guarantor.FindGuarantors(e.state, cg)
+		guarantors, err := protocol.FindGuarantors(e.state, cg)
 		if err != nil {
 			e.log.Fatal().Err(err).Msgf("could not find guarantors for guarantee %v", cg.ID())
 		}

engine/execution/ingestion/engine.go

@@ -31,7 +31,6 @@ import (
 	"github.com/onflow/flow-go/network"
 	"github.com/onflow/flow-go/state/protocol"
 	psEvents "github.com/onflow/flow-go/state/protocol/events"
-	"github.com/onflow/flow-go/state/protocol/guarantor"
 	"github.com/onflow/flow-go/storage"
 	"github.com/onflow/flow-go/utils/logging"
 )
@@ -996,7 +995,7 @@ func (e *Engine) matchOrRequestCollections(
 			Hex("collection_id", logging.ID(guarantee.ID())).
 			Msg("requesting collection")
 
-		guarantors, err := guarantor.FindGuarantors(e.state, guarantee)
+		guarantors, err := protocol.FindGuarantors(e.state, guarantee)
 		if err != nil {
 			return fmt.Errorf("could not find guarantors: %w", err)
 		}

state/protocol/util.go

@@ -5,6 +5,7 @@ import (
 
 	"github.com/onflow/flow-go/model/flow"
 	"github.com/onflow/flow-go/model/flow/filter"
+	"github.com/onflow/flow-go/module/signature"
 )
 
 // IsNodeStakedAt returns whether the node with the given ID is a valid
@@ -69,3 +70,26 @@ func IsSporkRootSnapshot(snapshot Snapshot) (bool, error) {
 	}
 	return true, nil
 }
+
+// FindGuarantors decodes the signer indices from the guarantee, and finds the guarantor identifiers from protocol state
+func FindGuarantors(state State, guarantee *flow.CollectionGuarantee) ([]flow.Identifier, error) {
+	snapshot := state.AtBlockID(guarantee.ReferenceBlockID)
+	epochs := snapshot.Epochs()
+	epoch := epochs.Current()
+	cluster, err := epoch.ClusterByChainID(guarantee.ChainID)
+
+	if err != nil {
+		// protocol state must have validated the block that contains the guarantee, so the cluster
+		// must be found, otherwise, it's an internal error
+		return nil, fmt.Errorf(
+			"internal error retrieving collector clusters for guarantee (ReferenceBlockID: %v, ChainID: %v): %w",
+			guarantee.ReferenceBlockID, guarantee.ChainID, err)
+	}
+
+	guarantorIDs, err := signature.DecodeSignerIndicesToIdentifiers(cluster.Members().NodeIDs(), guarantee.SignerIndices)
+	if err != nil {
+		return nil, fmt.Errorf("could not decode guarantor indices: %v", err)
+	}
+
+	return guarantorIDs, nil
+}