eth/protocols/snap: fix block accessList encoding rule (#34644)

This PR refactors the encoding rules for `AccessListsPacket` in the wire
protocol. Specifically:

- The response is now encoded as a list of `rlp.RawValue`
- `rlp.EmptyString` is used as a placeholder for unavailable BAL objects

eth/protocols/snap/handler_test.go

@@ -18,33 +18,48 @@ package snap
 
 import (
 	"bytes"
+	"encoding/binary"
+	"reflect"
 	"testing"
 	"time"
 
 	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/consensus/beacon"
 	"github.com/ethereum/go-ethereum/consensus/ethash"
 	"github.com/ethereum/go-ethereum/core"
 	"github.com/ethereum/go-ethereum/core/rawdb"
+	"github.com/ethereum/go-ethereum/core/types/bal"
 	"github.com/ethereum/go-ethereum/params"
 	"github.com/ethereum/go-ethereum/rlp"
 )
 
+func makeTestBAL(minSize int) *bal.BlockAccessList {
+	n := minSize/33 + 1 // 33 bytes per storage read slot in RLP
+	access := bal.AccountAccess{
+		Address:      common.HexToAddress("0x01"),
+		StorageReads: make([][32]byte, n),
+	}
+	for i := range access.StorageReads {
+		binary.BigEndian.PutUint64(access.StorageReads[i][24:], uint64(i))
+	}
+	return &bal.BlockAccessList{Accesses: []bal.AccountAccess{access}}
+}
+
 // getChainWithBALs creates a minimal test chain with BALs stored for each block.
 // It returns the chain, block hashes, and the stored BAL data.
 func getChainWithBALs(nBlocks int, balSize int) (*core.BlockChain, []common.Hash, []rlp.RawValue) {
 	gspec := &core.Genesis{
-		Config: params.TestChainConfig,
+		Config: params.MergedTestChainConfig,
 	}
 	db := rawdb.NewMemoryDatabase()
-	_, blocks, _ := core.GenerateChainWithGenesis(gspec, ethash.NewFaker(), nBlocks, func(i int, gen *core.BlockGen) {})
+	engine := beacon.New(ethash.NewFaker())
+	_, blocks, _ := core.GenerateChainWithGenesis(gspec, engine, nBlocks, func(i int, gen *core.BlockGen) {})
 	options := &core.BlockChainConfig{
-		TrieCleanLimit: 0,
-		TrieDirtyLimit: 0,
-		TrieTimeLimit:  5 * time.Minute,
-		NoPrefetch:     true,
-		SnapshotLimit:  0,
+		StateScheme:   rawdb.PathScheme,
+		TrieTimeLimit: 5 * time.Minute,
+		NoPrefetch:    true,
 	}
-	bc, err := core.NewBlockChain(db, gspec, ethash.NewFaker(), options)
+	bc, err := core.NewBlockChain(db, gspec, engine, options)
 	if err != nil {
 		panic(err)
 	}
@@ -53,20 +68,22 @@ func getChainWithBALs(nBlocks int, balSize int) (*core.BlockChain, []common.Hash
 	}
 
 	// Store BALs for each block
-	var hashes []common.Hash
-	var bals []rlp.RawValue
+	var (
+		hashes []common.Hash
+		bals   []rlp.RawValue
+	)
 	for _, block := range blocks {
 		hash := block.Hash()
 		number := block.NumberU64()
-		bal := make(rlp.RawValue, balSize)
 
 		// Fill with data based on block number
-		for j := range bal {
-			bal[j] = byte(number + uint64(j))
+		bytes, err := rlp.EncodeToBytes(makeTestBAL(balSize))
+		if err != nil {
+			panic(err)
 		}
-		rawdb.WriteAccessListRLP(db, hash, number, bal)
+		rawdb.WriteAccessListRLP(db, hash, number, bytes)
 		hashes = append(hashes, hash)
-		bals = append(bals, bal)
+		bals = append(bals, bytes)
 	}
 	return bc, hashes, bals
 }
@@ -85,13 +102,18 @@ func TestServiceGetAccessListsQuery(t *testing.T) {
 	result := ServiceGetAccessListsQuery(bc, req)
 
 	// Verify the results
-	if len(result) != len(hashes) {
-		t.Fatalf("expected %d results, got %d", len(hashes), len(result))
+	if result.Len() != len(hashes) {
+		t.Fatalf("expected %d results, got %d", len(hashes), result.Len())
 	}
-	for i, bal := range result {
-		if !bytes.Equal(bal, bals[i]) {
-			t.Errorf("BAL %d mismatch: got %x, want %x", i, bal, bals[i])
+	var (
+		index int
+		it    = result.ContentIterator()
+	)
+	for it.Next() {
+		if !bytes.Equal(it.Value(), bals[index]) {
+			t.Errorf("BAL %d mismatch: got %x, want %x", index, it.Value(), bals[index])
 		}
+		index++
 	}
 }
 
@@ -111,25 +133,23 @@ func TestServiceGetAccessListsQueryEmpty(t *testing.T) {
 	result := ServiceGetAccessListsQuery(bc, req)
 
 	// Verify length
-	if len(result) != len(mixed) {
-		t.Fatalf("expected %d results, got %d", len(mixed), len(result))
+	if result.Len() != len(mixed) {
+		t.Fatalf("expected %d results, got %d", len(mixed), result.Len())
 	}
 
 	// Check positional correspondence
-	if !bytes.Equal(result[0], bals[0]) {
-		t.Errorf("index 0: expected known BAL, got %x", result[0])
+	var expectVal = []rlp.RawValue{
+		bals[0], rlp.EmptyString, bals[1], rlp.EmptyString, bals[2],
 	}
-	if result[1] != nil {
-		t.Errorf("index 1: expected nil for unknown hash, got %x", result[1])
-	}
-	if !bytes.Equal(result[2], bals[1]) {
-		t.Errorf("index 2: expected known BAL, got %x", result[2])
-	}
-	if result[3] != nil {
-		t.Errorf("index 3: expected nil for unknown hash, got %x", result[3])
-	}
-	if !bytes.Equal(result[4], bals[2]) {
-		t.Errorf("index 4: expected known BAL, got %x", result[4])
+	var (
+		index int
+		it    = result.ContentIterator()
+	)
+	for it.Next() {
+		if !bytes.Equal(it.Value(), expectVal[index]) {
+			t.Errorf("BAL %d mismatch: got %x, want %x", index, it.Value(), expectVal[index])
+		}
+		index++
 	}
 }
 
@@ -154,8 +174,8 @@ func TestServiceGetAccessListsQueryCap(t *testing.T) {
 	result := ServiceGetAccessListsQuery(bc, req)
 
 	// Can't get more than maxAccessListLookups results
-	if len(result) > maxAccessListLookups {
-		t.Fatalf("expected at most %d results, got %d", maxAccessListLookups, len(result))
+	if result.Len() > maxAccessListLookups {
+		t.Fatalf("expected at most %d results, got %d", maxAccessListLookups, result.Len())
 	}
 }
 
@@ -179,21 +199,116 @@ func TestServiceGetAccessListsQueryByteLimit(t *testing.T) {
 	result := ServiceGetAccessListsQuery(bc, req)
 
 	// Should have stopped before returning all blocks
-	if len(result) >= nBlocks {
-		t.Fatalf("expected fewer than %d results due to byte limit, got %d", nBlocks, len(result))
+	if result.Len() >= nBlocks {
+		t.Fatalf("expected fewer than %d results due to byte limit, got %d", nBlocks, result.Len())
 	}
 
 	// Should have returned at least one
-	if len(result) == 0 {
+	if result.Len() == 0 {
 		t.Fatal("expected at least one result")
 	}
 
 	// The total size should exceed the limit (the entry that crosses it is included)
-	var total uint64
-	for _, bal := range result {
-		total += uint64(len(bal))
-	}
-	if total <= softResponseLimit {
-		t.Errorf("total response size %d should exceed soft limit %d (includes one entry past limit)", total, softResponseLimit)
+	if result.Size() <= softResponseLimit {
+		t.Errorf("total response size %d should exceed soft limit %d (includes one entry past limit)", result.Size(), softResponseLimit)
+	}
+}
+
+// TestGetAccessListResponseDecoding verifies that an AccessListsPacket
+// round-trips through RLP encode/decode, preserving positional
+// correspondence and correctly representing absent BALs as empty strings.
+func TestGetAccessListResponseDecoding(t *testing.T) {
+	t.Parallel()
+
+	// Build two real BALs of different sizes.
+	bal1 := makeTestBAL(100)
+	bal2 := makeTestBAL(200)
+	bytes1, _ := rlp.EncodeToBytes(bal1)
+	bytes2, _ := rlp.EncodeToBytes(bal2)
+
+	tests := []struct {
+		name   string
+		items  []rlp.RawValue // nil entry = unavailable BAL
+		counts int            // expected decoded length
+	}{
+		{
+			name:   "all present",
+			items:  []rlp.RawValue{bytes1, bytes2},
+			counts: 2,
+		},
+		{
+			name:   "all absent",
+			items:  []rlp.RawValue{rlp.EmptyString, rlp.EmptyString, rlp.EmptyString},
+			counts: 3,
+		},
+		{
+			name:   "mixed present and absent",
+			items:  []rlp.RawValue{bytes1, rlp.EmptyString, bytes2, rlp.EmptyString},
+			counts: 4,
+		},
+		{
+			name:   "empty response",
+			items:  []rlp.RawValue{},
+			counts: 0,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Build the packet using Append.
+			var orig AccessListsPacket
+			orig.ID = 42
+			for _, item := range tt.items {
+				if err := orig.AccessLists.AppendRaw(item); err != nil {
+					t.Fatalf("AppendRaw failed: %v", err)
+				}
+			}
+
+			// Encode -> Decode round-trip.
+			enc, err := rlp.EncodeToBytes(&orig)
+			if err != nil {
+				t.Fatalf("encode failed: %v", err)
+			}
+			var dec AccessListsPacket
+			if err := rlp.DecodeBytes(enc, &dec); err != nil {
+				t.Fatalf("decode failed: %v", err)
+			}
+
+			// Verify ID preserved.
+			if dec.ID != orig.ID {
+				t.Fatalf("ID mismatch: got %d, want %d", dec.ID, orig.ID)
+			}
+
+			// Verify element count.
+			if dec.AccessLists.Len() != tt.counts {
+				t.Fatalf("length mismatch: got %d, want %d", dec.AccessLists.Len(), tt.counts)
+			}
+
+			// Verify each element positionally.
+			it := dec.AccessLists.ContentIterator()
+			for i, want := range tt.items {
+				if !it.Next() {
+					t.Fatalf("iterator exhausted at index %d", i)
+				}
+				got := it.Value()
+				if !bytes.Equal(got, want) {
+					t.Errorf("element %d: got %x, want %x", i, got, want)
+				}
+				if !bytes.Equal(got, rlp.EmptyString) {
+					obj := new(bal.BlockAccessList)
+					if err := rlp.DecodeBytes(got, obj); err != nil {
+						t.Fatalf("decode failed: %v", err)
+					}
+					if bytes.Equal(got, bytes1) && !reflect.DeepEqual(obj, bal1) {
+						t.Fatalf("decode failed: got %x, want %x", obj, bal1)
+					}
+					if bytes.Equal(got, bytes2) && !reflect.DeepEqual(obj, bal2) {
+						t.Fatalf("decode failed: got %x, want %x", obj, bal2)
+					}
+				}
+			}
+			if it.Next() {
+				t.Error("iterator has extra elements after expected end")
+			}
+		})
 	}
 }

eth/protocols/snap/handlers.go

@@ -559,16 +559,15 @@ func handleGetAccessLists(backend Backend, msg Decoder, peer *Peer) error {
 	if err := msg.Decode(&req); err != nil {
 		return fmt.Errorf("%w: message %v: %v", errDecode, msg, err)
 	}
-	bals := ServiceGetAccessListsQuery(backend.Chain(), &req)
 	return p2p.Send(peer.rw, AccessListsMsg, &AccessListsPacket{
 		ID:          req.ID,
-		AccessLists: bals,
+		AccessLists: ServiceGetAccessListsQuery(backend.Chain(), &req),
 	})
 }
 
 // ServiceGetAccessListsQuery assembles the response to an access list query.
 // It is exposed to allow external packages to test protocol behavior.
-func ServiceGetAccessListsQuery(chain *core.BlockChain, req *GetAccessListsPacket) []rlp.RawValue {
+func ServiceGetAccessListsQuery(chain *core.BlockChain, req *GetAccessListsPacket) rlp.RawList[rlp.RawValue] {
 	if req.Bytes > softResponseLimit {
 		req.Bytes = softResponseLimit
 	}
@@ -577,20 +576,25 @@ func ServiceGetAccessListsQuery(chain *core.BlockChain, req *GetAccessListsPacke
 		req.Hashes = req.Hashes[:maxAccessListLookups]
 	}
 	var (
-		bals  []rlp.RawValue
-		bytes uint64
+		err      error
+		bytes    uint64
+		response = rlp.RawList[rlp.RawValue]{}
 	)
 	for _, hash := range req.Hashes {
 		if bal := chain.GetAccessListRLP(hash); len(bal) > 0 {
-			bals = append(bals, bal)
+			err = response.AppendRaw(bal)
 			bytes += uint64(len(bal))
 		} else {
 			// Either the block is unknown or the BAL doesn't exist
-			bals = append(bals, nil)
+			err = response.AppendRaw(rlp.EmptyString)
+			bytes += 1
+		}
+		if err != nil {
+			break
 		}
 		if bytes > req.Bytes {
 			break
 		}
 	}
-	return bals
+	return response
 }

eth/protocols/snap/protocol.go

@@ -229,8 +229,8 @@ type GetAccessListsPacket struct {
 // Each entry corresponds to the requested hash at the same index.
 // Empty entries indicate the BAL is unavailable.
 type AccessListsPacket struct {
-	ID          uint64         // ID of the request this is a response for
-	AccessLists []rlp.RawValue // Requested BALs
+	ID          uint64                    // ID of the request this is a response for
+	AccessLists rlp.RawList[rlp.RawValue] // Requested BALs
 }
 
 func (*GetAccountRangePacket) Name() string { return "GetAccountRange" }