Implement Process Block Receipt Root Records (#1105)

* process receipt root records

* complete process pow roots

* gazelle

* remote print

beacon-chain/core/blocks/block_operations.go

@@ -13,6 +13,37 @@ import (
 	"github.com/prysmaticlabs/prysm/shared/slices"
 )
 
+// ProcessPOWReceiptRoots processes the proof-of-work chain's receipts
+// contained in a beacon block and appends them as candidate receipt roots
+// in the beacon state.
+//
+// Official spec definition for processing pow receipt roots:
+//   If block.candidate_pow_receipt_root is x.candidate_pow_receipt_root
+//     for some x in state.candidate_pow_receipt_roots, set x.vote_count += 1.
+//   Otherwise, append to state.candidate_pow_receipt_roots a
+//   new CandidatePoWReceiptRootRecord(
+//     candidate_pow_receipt_root=block.candidate_pow_receipt_root,
+//     vote_count=1
+//   )
+func ProcessPOWReceiptRoots(
+	beaconState *types.BeaconState,
+	block *pb.BeaconBlock,
+) []*pb.CandidatePoWReceiptRootRecord {
+	var newCandidateReceiptRoots []*pb.CandidatePoWReceiptRootRecord
+	currentCandidateReceiptRoots := beaconState.CandidatePowReceiptRoots()
+	for idx, root := range currentCandidateReceiptRoots {
+		if bytes.Equal(block.GetCandidatePowReceiptRootHash32(), root.GetCandidatePowReceiptRootHash32()) {
+			currentCandidateReceiptRoots[idx].Votes++
+		} else {
+			newCandidateReceiptRoots = append(newCandidateReceiptRoots, &pb.CandidatePoWReceiptRootRecord{
+				CandidatePowReceiptRootHash32: block.GetCandidatePowReceiptRootHash32(),
+				Votes:                         1,
+			})
+		}
+	}
+	return append(currentCandidateReceiptRoots, newCandidateReceiptRoots...)
+}
+
 // ProcessProposerSlashings is one of the operations performed
 // on each processed beacon block to penalize proposers based on
 // slashing conditions if any slashable events occurred.

beacon-chain/core/blocks/block_operations_test.go

@@ -1,6 +1,7 @@
 package blocks
 
 import (
+	"bytes"
 	"fmt"
 	"reflect"
 	"strings"
@@ -11,6 +12,55 @@ import (
 	"github.com/prysmaticlabs/prysm/shared/params"
 )
 
+func TestProcessPOWReceiptRoots_SameRootHash(t *testing.T) {
+	beaconState := types.NewBeaconState(&pb.BeaconState{
+		CandidatePowReceiptRoots: []*pb.CandidatePoWReceiptRootRecord{
+			{
+				CandidatePowReceiptRootHash32: []byte{1},
+				Votes:                         5,
+			},
+		},
+	})
+	block := &pb.BeaconBlock{
+		CandidatePowReceiptRootHash32: []byte{1},
+	}
+	newReceiptRoots := ProcessPOWReceiptRoots(beaconState, block)
+	if newReceiptRoots[0].Votes != 6 {
+		t.Errorf("expected votes to increase from 5 to 6, received %v", newReceiptRoots[0].Votes)
+	}
+}
+
+func TestProcessPOWReceiptRoots_NewCandidateRecord(t *testing.T) {
+	beaconState := types.NewBeaconState(&pb.BeaconState{
+		CandidatePowReceiptRoots: []*pb.CandidatePoWReceiptRootRecord{
+			{
+				CandidatePowReceiptRootHash32: []byte{0},
+				Votes:                         5,
+			},
+		},
+	})
+	block := &pb.BeaconBlock{
+		CandidatePowReceiptRootHash32: []byte{1},
+	}
+	newReceiptRoots := ProcessPOWReceiptRoots(beaconState, block)
+	if len(newReceiptRoots) == 1 {
+		t.Error("expected new receipt roots to have length > 1")
+	}
+	if newReceiptRoots[1].Votes != 1 {
+		t.Errorf(
+			"expected new receipt roots to have a new element with votes = 1, received votes = %d",
+			newReceiptRoots[1].Votes,
+		)
+	}
+	if !bytes.Equal(newReceiptRoots[1].CandidatePowReceiptRootHash32, []byte{1}) {
+		t.Errorf(
+			"expected new receipt roots to have a new element with root = %#x, received root = %#x",
+			[]byte{1},
+			newReceiptRoots[1].CandidatePowReceiptRootHash32,
+		)
+	}
+}
+
 func TestProcessProposerSlashings_ThresholdReached(t *testing.T) {
 	slashings := make([]*pb.ProposerSlashing, params.BeaconConfig().MaxProposerSlashings+1)
 	registry := []*pb.ValidatorRecord{}