From 9f9401e61504f93dd300bbc80d47f8039a10915a Mon Sep 17 00:00:00 2001
From: Jun Song <87601811+syjn99@users.noreply.github.com>
Date: Fri, 19 Sep 2025 22:58:56 +0900
Subject: [PATCH] SSZ-QL: Handle `Bitlist` and `Bitvector` (#15704)

* Add bitvector field for FixedTestContainer

* Handle Bitvector type using isBitfield flag

* Add Bitvector case for Stringify

* Add bitlist field for VariableTestContainer

* Add bitlistInfo

* Changelog

* Add bitvectorInfo

* Remove analyzeBit* functions and just inline them

* Fix misleading comments

* Add comments for bitlistInfo's Size

* Apply reviews from Radek
---
 changelog/syjn99_ssz-ql-bitlist-bitvector.md |   3 +
 encoding/ssz/query/BUILD.bazel               |   4 +
 encoding/ssz/query/analyzer.go               |  62 ++++++-
 encoding/ssz/query/analyzer_test.go          |   2 +-
 encoding/ssz/query/bitlist.go                |  65 ++++++++
 encoding/ssz/query/bitvector.go              |  15 ++
 encoding/ssz/query/query_test.go             |  75 ++++++++-
 encoding/ssz/query/ssz_info.go               |  41 ++++-
 encoding/ssz/query/tag_parser.go             |  16 +-
 encoding/ssz/query/testutil/BUILD.bazel      |   1 +
 encoding/ssz/query/testutil/util.go          |  22 ++-
 proto/ssz_query/BUILD.bazel                  |   1 +
 proto/ssz_query/ssz_query.pb.go              | 164 ++++++++++++-------
 proto/ssz_query/ssz_query.proto              |  40 +++--
 proto/ssz_query/ssz_query.ssz.go             | 118 ++++++++++---
 15 files changed, 519 insertions(+), 110 deletions(-)
 create mode 100644 changelog/syjn99_ssz-ql-bitlist-bitvector.md
 create mode 100644 encoding/ssz/query/bitlist.go
 create mode 100644 encoding/ssz/query/bitvector.go

diff --git a/changelog/syjn99_ssz-ql-bitlist-bitvector.md b/changelog/syjn99_ssz-ql-bitlist-bitvector.md
new file mode 100644
index 0000000000..956e18b0cb
--- /dev/null
+++ b/changelog/syjn99_ssz-ql-bitlist-bitvector.md
@@ -0,0 +1,3 @@
+### Added
+
+- SSZ-QL: Handle `Bitlist` and `Bitvector` types.
diff --git a/encoding/ssz/query/BUILD.bazel b/encoding/ssz/query/BUILD.bazel
index 9bf99e6552..93caf3b170 100644
--- a/encoding/ssz/query/BUILD.bazel
+++ b/encoding/ssz/query/BUILD.bazel
@@ -4,6 +4,8 @@ go_library(
     name = "go_default_library",
     srcs = [
         "analyzer.go",
+        "bitlist.go",
+        "bitvector.go",
         "container.go",
         "list.go",
         "path.go",
@@ -15,6 +17,7 @@ go_library(
     ],
     importpath = "github.com/OffchainLabs/prysm/v6/encoding/ssz/query",
     visibility = ["//visibility:public"],
+    deps = ["@com_github_prysmaticlabs_go_bitfield//:go_default_library"],
 )
 
 go_test(
@@ -30,5 +33,6 @@ go_test(
         "//encoding/ssz/query/testutil:go_default_library",
         "//proto/ssz_query:go_default_library",
         "//testing/require:go_default_library",
+        "@com_github_prysmaticlabs_go_bitfield//:go_default_library",
     ],
 )
diff --git a/encoding/ssz/query/analyzer.go b/encoding/ssz/query/analyzer.go
index 2d983464d6..5bd882b802 100644
--- a/encoding/ssz/query/analyzer.go
+++ b/encoding/ssz/query/analyzer.go
@@ -67,6 +67,25 @@ func PopulateVariableLengthInfo(sszInfo *sszInfo, value any) error {
 		}
 
 		return nil
+
+	// In Bitlist case, we have to set the actual length of the bitlist.
+	case Bitlist:
+		bitlistInfo, err := sszInfo.BitlistInfo()
+		if err != nil {
+			return fmt.Errorf("could not get bitlist info: %w", err)
+		}
+
+		if bitlistInfo == nil {
+			return errors.New("bitlistInfo is nil")
+		}
+
+		val := reflect.ValueOf(value)
+		if err := bitlistInfo.SetLengthFromBytes(val.Bytes()); err != nil {
+			return fmt.Errorf("could not set bitlist length from bytes: %w", err)
+		}
+
+		return nil
+
 	// In Container case, we need to recursively populate variable-sized fields.
 	case Container:
 		containerInfo, err := sszInfo.ContainerInfo()
@@ -194,7 +213,7 @@ func analyzeHomogeneousColType(typ reflect.Type, tag *reflect.StructTag) (*sszIn
 			return nil, fmt.Errorf("could not get list limit: %w", err)
 		}
 
-		return analyzeListType(typ, elementInfo, limit)
+		return analyzeListType(typ, elementInfo, limit, sszDimension.isBitfield)
 	}
 
 	// 2. Handle Vector/Bitvector type
@@ -204,7 +223,7 @@ func analyzeHomogeneousColType(typ reflect.Type, tag *reflect.StructTag) (*sszIn
 			return nil, fmt.Errorf("could not get vector length: %w", err)
 		}
 
-		return analyzeVectorType(typ, elementInfo, length)
+		return analyzeVectorType(typ, elementInfo, length, sszDimension.isBitfield)
 	}
 
 	// Parsing ssz tag doesn't provide enough information to determine the collection type,
@@ -212,8 +231,22 @@ func analyzeHomogeneousColType(typ reflect.Type, tag *reflect.StructTag) (*sszIn
 	return nil, errors.New("could not determine collection type from tags")
 }
 
-// analyzeListType analyzes SSZ List type and returns its SSZ info.
-func analyzeListType(typ reflect.Type, elementInfo *sszInfo, limit uint64) (*sszInfo, error) {
+// analyzeListType analyzes SSZ List/Bitlist type and returns its SSZ info.
+func analyzeListType(typ reflect.Type, elementInfo *sszInfo, limit uint64, isBitfield bool) (*sszInfo, error) {
+	if isBitfield {
+		return &sszInfo{
+			sszType: Bitlist,
+			typ:     typ,
+
+			fixedSize:  offsetBytes,
+			isVariable: true,
+
+			bitlistInfo: &bitlistInfo{
+				limit: limit,
+			},
+		}, nil
+	}
+
 	if elementInfo == nil {
 		return nil, errors.New("element info is required for List")
 	}
@@ -232,10 +265,25 @@ func analyzeListType(typ reflect.Type, elementInfo *sszInfo, limit uint64) (*ssz
 	}, nil
 }
 
-// analyzeVectorType analyzes SSZ Vector type and returns its SSZ info.
-func analyzeVectorType(typ reflect.Type, elementInfo *sszInfo, length uint64) (*sszInfo, error) {
+// analyzeVectorType analyzes SSZ Vector/Bitvector type and returns its SSZ info.
+func analyzeVectorType(typ reflect.Type, elementInfo *sszInfo, length uint64, isBitfield bool) (*sszInfo, error) {
+	if isBitfield {
+		return &sszInfo{
+			sszType: Bitvector,
+			typ:     typ,
+
+			// Size in bytes
+			fixedSize:  length,
+			isVariable: false,
+
+			bitvectorInfo: &bitvectorInfo{
+				length: length * 8, // length in bits
+			},
+		}, nil
+	}
+
 	if elementInfo == nil {
-		return nil, errors.New("element info is required for Vector")
+		return nil, errors.New("element info is required for Vector/Bitvector")
 	}
 
 	// Validate the given length.
diff --git a/encoding/ssz/query/analyzer_test.go b/encoding/ssz/query/analyzer_test.go
index 089cf915ae..7c8d4666fa 100644
--- a/encoding/ssz/query/analyzer_test.go
+++ b/encoding/ssz/query/analyzer_test.go
@@ -13,5 +13,5 @@ func TestAnalyzeSSZInfo(t *testing.T) {
 	require.NoError(t, err)
 
 	require.NotNil(t, info, "Expected non-nil SSZ info")
-	require.Equal(t, uint64(493), info.FixedSize(), "Expected fixed size to be 333")
+	require.Equal(t, uint64(565), info.FixedSize())
 }
diff --git a/encoding/ssz/query/bitlist.go b/encoding/ssz/query/bitlist.go
new file mode 100644
index 0000000000..91e39690c9
--- /dev/null
+++ b/encoding/ssz/query/bitlist.go
@@ -0,0 +1,65 @@
+package query
+
+import (
+	"errors"
+	"fmt"
+
+	"github.com/prysmaticlabs/go-bitfield"
+)
+
+// bitlistInfo holds information about a SSZ Bitlist type.
+//
+// Same as listInfo, but limit/length are in bits, not elements.
+type bitlistInfo struct {
+	// limit is the maximum number of bits in the bitlist.
+	limit uint64
+	// length is the actual number of bits at runtime (0 if not set).
+	length uint64
+}
+
+func (l *bitlistInfo) Limit() uint64 {
+	if l == nil {
+		return 0
+	}
+	return l.limit
+}
+
+func (l *bitlistInfo) Length() uint64 {
+	if l == nil {
+		return 0
+	}
+	return l.length
+}
+
+func (l *bitlistInfo) SetLength(length uint64) error {
+	if l == nil {
+		return errors.New("bitlistInfo is nil")
+	}
+
+	if length > l.limit {
+		return fmt.Errorf("length %d exceeds limit %d", length, l.limit)
+	}
+
+	l.length = length
+	return nil
+}
+
+// SetLengthFromBytes determines the actual bitlist length from SSZ-encoded bytes.
+func (l *bitlistInfo) SetLengthFromBytes(rawBytes []byte) error {
+	// Wrap rawBytes in a Bitlist to use existing methods.
+	bl := bitfield.Bitlist(rawBytes)
+	return l.SetLength(bl.Len())
+}
+
+// Size returns the size in bytes for this bitlist.
+// Note that while serializing, 1 bit is added for the delimiter bit,
+// which results in ceil((length + 1) / 8) bytes.
+// Note that `(length / 8) + 1` is equivalent to `ceil((length + 1) / 8)`.
+// Example: length=0 -> size=1, length=7 -> size=1, length=8 -> size=2
+// Reference: https://github.com/ethereum/consensus-specs/blob/master/ssz/simple-serialize.md#bitlistn-progressivebitlist
+func (l *bitlistInfo) Size() uint64 {
+	if l == nil {
+		return 0
+	}
+	return (l.length / 8) + 1
+}
diff --git a/encoding/ssz/query/bitvector.go b/encoding/ssz/query/bitvector.go
new file mode 100644
index 0000000000..046189d232
--- /dev/null
+++ b/encoding/ssz/query/bitvector.go
@@ -0,0 +1,15 @@
+package query
+
+// bitvectorInfo holds information about a SSZ Bitvector type.
+type bitvectorInfo struct {
+	// length is the fixed length of bits of the Bitvector.
+	length uint64
+}
+
+func (v *bitvectorInfo) Length() uint64 {
+	if v == nil {
+		return 0
+	}
+
+	return v.length
+}
diff --git a/encoding/ssz/query/query_test.go b/encoding/ssz/query/query_test.go
index 90df5fd2da..3541274703 100644
--- a/encoding/ssz/query/query_test.go
+++ b/encoding/ssz/query/query_test.go
@@ -8,6 +8,7 @@ import (
 	"github.com/OffchainLabs/prysm/v6/encoding/ssz/query/testutil"
 	sszquerypb "github.com/OffchainLabs/prysm/v6/proto/ssz_query"
 	"github.com/OffchainLabs/prysm/v6/testing/require"
+	"github.com/prysmaticlabs/go-bitfield"
 )
 
 func TestCalculateOffsetAndLength(t *testing.T) {
@@ -80,11 +81,24 @@ func TestCalculateOffsetAndLength(t *testing.T) {
 				expectedOffset: 277,
 				expectedLength: 160, // 5 * 32 bytes
 			},
+			// Bitvector fields
+			{
+				name:           "bitvector64_field",
+				path:           ".bitvector64_field",
+				expectedOffset: 437,
+				expectedLength: 8,
+			},
+			{
+				name:           "bitvector512_field",
+				path:           ".bitvector512_field",
+				expectedOffset: 445,
+				expectedLength: 64,
+			},
 			// Trailing field
 			{
 				name:           "trailing_field",
 				path:           ".trailing_field",
-				expectedOffset: 437,
+				expectedOffset: 509,
 				expectedLength: 56,
 			},
 		}
@@ -119,26 +133,26 @@ func TestCalculateOffsetAndLength(t *testing.T) {
 			{
 				name:           "field_list_uint64",
 				path:           ".field_list_uint64",
-				expectedOffset: 104, // First part of variable-sized type.
+				expectedOffset: 108, // First part of variable-sized type.
 				expectedLength: 40,  // 5 elements * uint64 (8 bytes each)
 			},
 			{
 				name:           "field_list_container",
 				path:           ".field_list_container",
-				expectedOffset: 144, // Second part of variable-sized type.
+				expectedOffset: 148, // Second part of variable-sized type.
 				expectedLength: 120, // 3 elements * FixedNestedContainer (40 bytes each)
 			},
 			{
 				name:           "field_list_bytes32",
 				path:           ".field_list_bytes32",
-				expectedOffset: 264,
+				expectedOffset: 268,
 				expectedLength: 96, // 3 elements * 32 bytes each
 			},
 			// Nested paths
 			{
 				name:           "nested",
 				path:           ".nested",
-				expectedOffset: 360,
+				expectedOffset: 364,
 				// Calculated with:
 				// - Value1: 8 bytes
 				// - field_list_uint64 offset: 4 bytes
@@ -148,20 +162,27 @@ func TestCalculateOffsetAndLength(t *testing.T) {
 			{
 				name:           "nested.value1",
 				path:           ".nested.value1",
-				expectedOffset: 360,
+				expectedOffset: 364,
 				expectedLength: 8,
 			},
 			{
 				name:           "nested.field_list_uint64",
 				path:           ".nested.field_list_uint64",
-				expectedOffset: 372,
+				expectedOffset: 376,
 				expectedLength: 40,
 			},
+			// Bitlist field
+			{
+				name:           "bitlist_field",
+				path:           ".bitlist_field",
+				expectedOffset: 416,
+				expectedLength: 33, // 32 bytes + 1 byte for length delimiter
+			},
 			// Fixed trailing field
 			{
 				name:           "trailing_field",
 				path:           ".trailing_field",
-				expectedOffset: 48, // After leading_field + 4 offset pointers
+				expectedOffset: 52, // After leading_field + 5 offset pointers
 				expectedLength: 56,
 			},
 		}
@@ -208,6 +229,16 @@ func createFixedTestContainer() *sszquerypb.FixedTestContainer {
 		nestedValue2[i] = byte(i + 56)
 	}
 
+	bitvector64 := bitfield.NewBitvector64()
+	for i := range bitvector64 {
+		bitvector64[i] = 0x42
+	}
+
+	bitvector512 := bitfield.NewBitvector512()
+	for i := range bitvector512 {
+		bitvector512[i] = 0x24
+	}
+
 	trailingField := make([]byte, 56)
 	for i := range trailingField {
 		trailingField[i] = byte(i + 88)
@@ -240,6 +271,10 @@ func createFixedTestContainer() *sszquerypb.FixedTestContainer {
 			make([]byte, 32),
 		},
 
+		// Bitvector fields
+		Bitvector64Field:  bitvector64,
+		Bitvector512Field: bitvector512,
+
 		// Trailing field
 		TrailingField: trailingField,
 	}
@@ -294,6 +329,15 @@ func getFixedTestContainerSpec() testutil.TestSpec {
 				Path:     ".two_dimension_bytes_field",
 				Expected: testContainer.TwoDimensionBytesField,
 			},
+			// Bitvector fields
+			{
+				Path:     ".bitvector64_field",
+				Expected: testContainer.Bitvector64Field,
+			},
+			{
+				Path:     ".bitvector512_field",
+				Expected: testContainer.Bitvector512Field,
+			},
 			// Trailing field
 			{
 				Path:     ".trailing_field",
@@ -326,6 +370,13 @@ func createVariableTestContainer() *sszquerypb.VariableTestContainer {
 		}
 	}
 
+	bitlistField := bitfield.NewBitlist(256)
+	bitlistField.SetBitAt(0, true)
+	bitlistField.SetBitAt(10, true)
+	bitlistField.SetBitAt(50, true)
+	bitlistField.SetBitAt(100, true)
+	bitlistField.SetBitAt(255, true)
+
 	return &sszquerypb.VariableTestContainer{
 		// Fixed leading field
 		LeadingField: leadingField,
@@ -345,6 +396,9 @@ func createVariableTestContainer() *sszquerypb.VariableTestContainer {
 			FieldListUint64: []uint64{1, 2, 3, 4, 5},
 		},
 
+		// Bitlist field
+		BitlistField: bitlistField,
+
 		// Fixed trailing field
 		TrailingField: trailingField,
 	}
@@ -391,6 +445,11 @@ func getVariableTestContainerSpec() testutil.TestSpec {
 				Path:     ".nested.field_list_uint64",
 				Expected: testContainer.Nested.FieldListUint64,
 			},
+			// Bitlist field
+			{
+				Path:     ".bitlist_field",
+				Expected: testContainer.BitlistField,
+			},
 			// Fixed trailing field
 			{
 				Path:     ".trailing_field",
diff --git a/encoding/ssz/query/ssz_info.go b/encoding/ssz/query/ssz_info.go
index 71f57d8965..ca0c7e466c 100644
--- a/encoding/ssz/query/ssz_info.go
+++ b/encoding/ssz/query/ssz_info.go
@@ -27,6 +27,12 @@ type sszInfo struct {
 
 	// For Vector types.
 	vectorInfo *vectorInfo
+
+	// For Bitlist types.
+	bitlistInfo *bitlistInfo
+
+	// For Bitvector types.
+	bitvectorInfo *bitvectorInfo
 }
 
 func (info *sszInfo) FixedSize() uint64 {
@@ -53,6 +59,9 @@ func (info *sszInfo) Size() uint64 {
 
 		return length * elementSize
 
+	case Bitlist:
+		return info.bitlistInfo.Size()
+
 	case Container:
 		size := info.fixedSize
 		for _, fieldInfo := range info.containerInfo.fields {
@@ -65,7 +74,6 @@ func (info *sszInfo) Size() uint64 {
 		return size
 
 	default:
-		// NOTE: Handle other variable-sized types.
 		return 0
 	}
 }
@@ -110,6 +118,30 @@ func (info *sszInfo) VectorInfo() (*vectorInfo, error) {
 	return info.vectorInfo, nil
 }
 
+func (info *sszInfo) BitlistInfo() (*bitlistInfo, error) {
+	if info == nil {
+		return nil, errors.New("sszInfo is nil")
+	}
+
+	if info.sszType != Bitlist {
+		return nil, fmt.Errorf("sszInfo is not a Bitlist type, got %s", info.sszType)
+	}
+
+	return info.bitlistInfo, nil
+}
+
+func (info *sszInfo) BitvectorInfo() (*bitvectorInfo, error) {
+	if info == nil {
+		return nil, errors.New("sszInfo is nil")
+	}
+
+	if info.sszType != Bitvector {
+		return nil, fmt.Errorf("sszInfo is not a Bitvector type, got %s", info.sszType)
+	}
+
+	return info.bitvectorInfo, nil
+}
+
 // String implements the Stringer interface for sszInfo.
 // This follows the notation used in the consensus specs.
 func (info *sszInfo) String() string {
@@ -128,6 +160,10 @@ func (info *sszInfo) String() string {
 			return fmt.Sprintf("Bytes%d", info.vectorInfo.length)
 		}
 		return fmt.Sprintf("Vector[%s, %d]", info.vectorInfo.element, info.vectorInfo.length)
+	case Bitlist:
+		return fmt.Sprintf("Bitlist[%d]", info.bitlistInfo.limit)
+	case Bitvector:
+		return fmt.Sprintf("Bitvector[%d]", info.bitvectorInfo.length)
 	default:
 		return info.typ.Name()
 	}
@@ -175,6 +211,9 @@ func printRecursive(info *sszInfo, builder *strings.Builder, prefix string) {
 	case List:
 		builder.WriteString(fmt.Sprintf("%s (%s / length: %d, size: %d)\n", info, sizeDesc, info.listInfo.length, info.Size()))
 
+	case Bitlist:
+		builder.WriteString(fmt.Sprintf("%s (%s / length (bit): %d, size: %d)\n", info, sizeDesc, info.bitlistInfo.length, info.Size()))
+
 	default:
 		builder.WriteString(fmt.Sprintf("%s (%s / size: %d)\n", info, sizeDesc, info.Size()))
 	}
diff --git a/encoding/ssz/query/tag_parser.go b/encoding/ssz/query/tag_parser.go
index 3ec848d1b5..0dd9e26735 100644
--- a/encoding/ssz/query/tag_parser.go
+++ b/encoding/ssz/query/tag_parser.go
@@ -15,6 +15,10 @@ const (
 	// sszSizeTag specifies the length of a fixed-sized collection, like an SSZ Vector.
 	// A wildcard ('?') indicates that the dimension is variable-sized (a List).
 	sszSizeTag = "ssz-size"
+
+	// castTypeTag specifies special custom casting instructions.
+	// e.g., "github.com/prysmaticlabs/go-bitfield.Bitlist".
+	castTypeTag = "cast-type"
 )
 
 // SSZDimension holds parsed SSZ tag information for current dimension.
@@ -22,6 +26,9 @@ const (
 type SSZDimension struct {
 	vectorLength *uint64
 	listLimit    *uint64
+
+	// isBitfield indicates if the dimension represents a bitfield type (Bitlist, Bitvector).
+	isBitfield bool
 }
 
 // ParseSSZTag parses SSZ-specific tags (like `ssz-max` and `ssz-size`)
@@ -34,6 +41,11 @@ func ParseSSZTag(tag *reflect.StructTag) (*SSZDimension, *reflect.StructTag, err
 
 	var newTagParts []string
 	var sizeStr, maxStr string
+	var isBitfield bool
+
+	if castType := tag.Get(castTypeTag); strings.Contains(castType, "go-bitfield") {
+		isBitfield = true
+	}
 
 	// Parse ssz-size tag
 	if sszSize := tag.Get(sszSizeTag); sszSize != "" {
@@ -88,7 +100,7 @@ func ParseSSZTag(tag *reflect.StructTag) (*SSZDimension, *reflect.StructTag, err
 			return nil, nil, errors.New("ssz-max must be greater than 0")
 		}
 
-		return &SSZDimension{listLimit: &limit}, newTag, nil
+		return &SSZDimension{listLimit: &limit, isBitfield: isBitfield}, newTag, nil
 	}
 
 	// 2. If ssz-size is specified, it must be a vector.
@@ -100,7 +112,7 @@ func ParseSSZTag(tag *reflect.StructTag) (*SSZDimension, *reflect.StructTag, err
 		return nil, nil, errors.New("ssz-size must be greater than 0")
 	}
 
-	return &SSZDimension{vectorLength: &length}, newTag, nil
+	return &SSZDimension{vectorLength: &length, isBitfield: isBitfield}, newTag, nil
 }
 
 // IsVector returns true if this dimension represents a vector.
diff --git a/encoding/ssz/query/testutil/BUILD.bazel b/encoding/ssz/query/testutil/BUILD.bazel
index d97421eaa9..8e66a56bb3 100644
--- a/encoding/ssz/query/testutil/BUILD.bazel
+++ b/encoding/ssz/query/testutil/BUILD.bazel
@@ -14,5 +14,6 @@ go_library(
         "//encoding/ssz/query:go_default_library",
         "//testing/require:go_default_library",
         "@com_github_prysmaticlabs_fastssz//:go_default_library",
+        "@com_github_prysmaticlabs_go_bitfield//:go_default_library",
     ],
 )
diff --git a/encoding/ssz/query/testutil/util.go b/encoding/ssz/query/testutil/util.go
index 3f99357230..f9ec4bd34f 100644
--- a/encoding/ssz/query/testutil/util.go
+++ b/encoding/ssz/query/testutil/util.go
@@ -3,8 +3,10 @@ package testutil
 import (
 	"fmt"
 	"reflect"
+	"strings"
 
 	ssz "github.com/prysmaticlabs/fastssz"
+	"github.com/prysmaticlabs/go-bitfield"
 )
 
 // marshalAny marshals any value into SSZ format.
@@ -20,7 +22,25 @@ func marshalAny(value any) ([]byte, error) {
 	}
 
 	// Handle custom type aliases by checking if they're based on primitive types
-	if valueType.PkgPath() != "" {
+	if pkgPath := valueType.PkgPath(); pkgPath != "" {
+		// Special handling for bitfield types.
+		if strings.Contains(pkgPath, "go-bitfield") {
+			// Check if it's a Bitlist (variable-length) that needs SSZ encoding
+			if bl, ok := value.(bitfield.Bitlist); ok {
+				// The Bitlist type already contains the SSZ delimiter bit in its internal representation
+				// The raw []byte contains the delimiter as the most significant bit
+				// So we just return the raw bytes directly for SSZ encoding
+				return []byte(bl), nil
+			}
+
+			// For other bitfield types (Bitvector), just return the bytes
+			if bitfield, ok := value.(bitfield.Bitfield); ok {
+				return bitfield.Bytes(), nil
+			}
+
+			return nil, fmt.Errorf("expected bitfield type, got %T", value)
+		}
+
 		switch valueType.Kind() {
 		case reflect.Uint64:
 			return ssz.MarshalUint64(make([]byte, 0), reflect.ValueOf(value).Uint()), nil
diff --git a/proto/ssz_query/BUILD.bazel b/proto/ssz_query/BUILD.bazel
index 933689529d..16991bf95c 100644
--- a/proto/ssz_query/BUILD.bazel
+++ b/proto/ssz_query/BUILD.bazel
@@ -25,6 +25,7 @@ go_proto_library(
     visibility = ["//visibility:public"],
     deps = [
         "//proto/eth/ext:go_default_library",
+        "@com_github_prysmaticlabs_go_bitfield//:go_default_library",
         "@com_github_golang_protobuf//proto:go_default_library",
         "@org_golang_google_protobuf//reflect/protoreflect:go_default_library",
         "@org_golang_google_protobuf//runtime/protoimpl:go_default_library",
diff --git a/proto/ssz_query/ssz_query.pb.go b/proto/ssz_query/ssz_query.pb.go
index 169444d04b..0c25240fec 100755
--- a/proto/ssz_query/ssz_query.pb.go
+++ b/proto/ssz_query/ssz_query.pb.go
@@ -11,6 +11,7 @@ import (
 	sync "sync"
 
 	_ "github.com/OffchainLabs/prysm/v6/proto/eth/ext"
+	github_com_prysmaticlabs_go_bitfield "github.com/prysmaticlabs/go-bitfield"
 	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
 	protoimpl "google.golang.org/protobuf/runtime/protoimpl"
 )
@@ -82,14 +83,16 @@ type FixedTestContainer struct {
 	sizeCache     protoimpl.SizeCache
 	unknownFields protoimpl.UnknownFields
 
-	FieldUint32            uint32                `protobuf:"varint,3,opt,name=field_uint32,json=fieldUint32,proto3" json:"field_uint32,omitempty"`
-	FieldUint64            uint64                `protobuf:"varint,4,opt,name=field_uint64,json=fieldUint64,proto3" json:"field_uint64,omitempty"`
-	FieldBool              bool                  `protobuf:"varint,5,opt,name=field_bool,json=fieldBool,proto3" json:"field_bool,omitempty"`
-	FieldBytes32           []byte                `protobuf:"bytes,8,opt,name=field_bytes32,json=fieldBytes32,proto3" json:"field_bytes32,omitempty" ssz-size:"32"`
-	Nested                 *FixedNestedContainer `protobuf:"bytes,9,opt,name=nested,proto3" json:"nested,omitempty"`
-	VectorField            []uint64              `protobuf:"varint,10,rep,packed,name=vector_field,json=vectorField,proto3" json:"vector_field,omitempty" ssz-size:"24"`
-	TwoDimensionBytesField [][]byte              `protobuf:"bytes,11,rep,name=two_dimension_bytes_field,json=twoDimensionBytesField,proto3" json:"two_dimension_bytes_field,omitempty" ssz-size:"5,32"`
-	TrailingField          []byte                `protobuf:"bytes,12,opt,name=trailing_field,json=trailingField,proto3" json:"trailing_field,omitempty" ssz-size:"56"`
+	FieldUint32            uint32                                            `protobuf:"varint,1,opt,name=field_uint32,json=fieldUint32,proto3" json:"field_uint32,omitempty"`
+	FieldUint64            uint64                                            `protobuf:"varint,2,opt,name=field_uint64,json=fieldUint64,proto3" json:"field_uint64,omitempty"`
+	FieldBool              bool                                              `protobuf:"varint,3,opt,name=field_bool,json=fieldBool,proto3" json:"field_bool,omitempty"`
+	FieldBytes32           []byte                                            `protobuf:"bytes,4,opt,name=field_bytes32,json=fieldBytes32,proto3" json:"field_bytes32,omitempty" ssz-size:"32"`
+	Nested                 *FixedNestedContainer                             `protobuf:"bytes,5,opt,name=nested,proto3" json:"nested,omitempty"`
+	VectorField            []uint64                                          `protobuf:"varint,6,rep,packed,name=vector_field,json=vectorField,proto3" json:"vector_field,omitempty" ssz-size:"24"`
+	TwoDimensionBytesField [][]byte                                          `protobuf:"bytes,7,rep,name=two_dimension_bytes_field,json=twoDimensionBytesField,proto3" json:"two_dimension_bytes_field,omitempty" ssz-size:"5,32"`
+	Bitvector64Field       github_com_prysmaticlabs_go_bitfield.Bitvector64  `protobuf:"bytes,8,opt,name=bitvector64_field,json=bitvector64Field,proto3" json:"bitvector64_field,omitempty" cast-type:"github.com/prysmaticlabs/go-bitfield.Bitvector64" ssz-size:"8"`
+	Bitvector512Field      github_com_prysmaticlabs_go_bitfield.Bitvector512 `protobuf:"bytes,9,opt,name=bitvector512_field,json=bitvector512Field,proto3" json:"bitvector512_field,omitempty" cast-type:"github.com/prysmaticlabs/go-bitfield.Bitvector512" ssz-size:"64"`
+	TrailingField          []byte                                            `protobuf:"bytes,10,opt,name=trailing_field,json=trailingField,proto3" json:"trailing_field,omitempty" ssz-size:"56"`
 }
 
 func (x *FixedTestContainer) Reset() {
@@ -173,6 +176,20 @@ func (x *FixedTestContainer) GetTwoDimensionBytesField() [][]byte {
 	return nil
 }
 
+func (x *FixedTestContainer) GetBitvector64Field() github_com_prysmaticlabs_go_bitfield.Bitvector64 {
+	if x != nil {
+		return x.Bitvector64Field
+	}
+	return github_com_prysmaticlabs_go_bitfield.Bitvector64(nil)
+}
+
+func (x *FixedTestContainer) GetBitvector512Field() github_com_prysmaticlabs_go_bitfield.Bitvector512 {
+	if x != nil {
+		return x.Bitvector512Field
+	}
+	return github_com_prysmaticlabs_go_bitfield.Bitvector512(nil)
+}
+
 func (x *FixedTestContainer) GetTrailingField() []byte {
 	if x != nil {
 		return x.TrailingField
@@ -240,12 +257,13 @@ type VariableTestContainer struct {
 	sizeCache     protoimpl.SizeCache
 	unknownFields protoimpl.UnknownFields
 
-	LeadingField       []byte                   `protobuf:"bytes,1,opt,name=leading_field,json=leadingField,proto3" json:"leading_field,omitempty" ssz-size:"32"`
-	FieldListUint64    []uint64                 `protobuf:"varint,2,rep,packed,name=field_list_uint64,json=fieldListUint64,proto3" json:"field_list_uint64,omitempty" ssz-max:"2048"`
-	FieldListContainer []*FixedNestedContainer  `protobuf:"bytes,3,rep,name=field_list_container,json=fieldListContainer,proto3" json:"field_list_container,omitempty" ssz-max:"128"`
-	FieldListBytes32   [][]byte                 `protobuf:"bytes,4,rep,name=field_list_bytes32,json=fieldListBytes32,proto3" json:"field_list_bytes32,omitempty" ssz-max:"100" ssz-size:"?,32"`
-	Nested             *VariableNestedContainer `protobuf:"bytes,5,opt,name=nested,proto3" json:"nested,omitempty"`
-	TrailingField      []byte                   `protobuf:"bytes,6,opt,name=trailing_field,json=trailingField,proto3" json:"trailing_field,omitempty" ssz-size:"56"`
+	LeadingField       []byte                                       `protobuf:"bytes,1,opt,name=leading_field,json=leadingField,proto3" json:"leading_field,omitempty" ssz-size:"32"`
+	FieldListUint64    []uint64                                     `protobuf:"varint,2,rep,packed,name=field_list_uint64,json=fieldListUint64,proto3" json:"field_list_uint64,omitempty" ssz-max:"2048"`
+	FieldListContainer []*FixedNestedContainer                      `protobuf:"bytes,3,rep,name=field_list_container,json=fieldListContainer,proto3" json:"field_list_container,omitempty" ssz-max:"128"`
+	FieldListBytes32   [][]byte                                     `protobuf:"bytes,4,rep,name=field_list_bytes32,json=fieldListBytes32,proto3" json:"field_list_bytes32,omitempty" ssz-max:"100" ssz-size:"?,32"`
+	Nested             *VariableNestedContainer                     `protobuf:"bytes,5,opt,name=nested,proto3" json:"nested,omitempty"`
+	BitlistField       github_com_prysmaticlabs_go_bitfield.Bitlist `protobuf:"bytes,6,opt,name=bitlist_field,json=bitlistField,proto3" json:"bitlist_field,omitempty" cast-type:"github.com/prysmaticlabs/go-bitfield.Bitlist" ssz-max:"2048"`
+	TrailingField      []byte                                       `protobuf:"bytes,7,opt,name=trailing_field,json=trailingField,proto3" json:"trailing_field,omitempty" ssz-size:"56"`
 }
 
 func (x *VariableTestContainer) Reset() {
@@ -315,6 +333,13 @@ func (x *VariableTestContainer) GetNested() *VariableNestedContainer {
 	return nil
 }
 
+func (x *VariableTestContainer) GetBitlistField() github_com_prysmaticlabs_go_bitfield.Bitlist {
+	if x != nil {
+		return x.BitlistField
+	}
+	return github_com_prysmaticlabs_go_bitfield.Bitlist(nil)
+}
+
 func (x *VariableTestContainer) GetTrailingField() []byte {
 	if x != nil {
 		return x.TrailingField
@@ -334,66 +359,85 @@ var file_proto_ssz_query_ssz_query_proto_rawDesc = []byte{
 	0x72, 0x12, 0x16, 0x0a, 0x06, 0x76, 0x61, 0x6c, 0x75, 0x65, 0x31, 0x18, 0x01, 0x20, 0x01, 0x28,
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+	0x6f, 0x74, 0x6f, 0x33,
 }
 
 var (
diff --git a/proto/ssz_query/ssz_query.proto b/proto/ssz_query/ssz_query.proto
index fec55bc482..5902c2b120 100644
--- a/proto/ssz_query/ssz_query.proto
+++ b/proto/ssz_query/ssz_query.proto
@@ -20,29 +20,42 @@ message FixedNestedContainer {
 
 // FixedTestContainer - comprehensive fixed-size container for SSZ query testing
 // Tests: All basic fixed-size SSZ types, nested containers, vectors, offset/length calculations
-// Total size: 493 bytes (4+8+1+32+40+192+160+56)
+// Total size: 565 bytes (4+8+1+32+40+192+160+8+64+56)
 message FixedTestContainer {
   // Basic integer types - test different integer sizes and their SSZ serialization
-  uint32 field_uint32 = 3;  // Test: uint32 basic type, offset: 0
-  uint64 field_uint64 = 4;  // Test: uint64 basic type, offset: 4
+  uint32 field_uint32 = 1;  // Test: uint32 basic type, offset: 0
+  uint64 field_uint64 = 2;  // Test: uint64 basic type, offset: 4
   
   // Boolean type - test boolean serialization (1 byte in SSZ)
-  bool field_bool = 5;      // Test: boolean basic type, offset: 12
+  bool field_bool = 3;      // Test: boolean basic type, offset: 12
   
   // Fixed-size bytes - test byte array
-  bytes field_bytes32 = 8 [ (ethereum.eth.ext.ssz_size) = "32" ]; // Test: 32-byte array, offset: 13
+  bytes field_bytes32 = 4 [ (ethereum.eth.ext.ssz_size) = "32" ]; // Test: 32-byte array, offset: 13
   
   // Nested container - test container nesting and field access
-  FixedNestedContainer nested = 9;  // Test: nested container navigation (8+32=40 bytes), offset: 45
+  FixedNestedContainer nested = 5;  // Test: nested container navigation (8+32=40 bytes), offset: 45
   
   // Vector type - test fixed-size array of basic elements  
-  repeated uint64 vector_field = 10 [ (ethereum.eth.ext.ssz_size) = "24" ];  // Test: Vector[24] of uint64 (24*8=192 bytes), offset: 85
+  repeated uint64 vector_field = 6 [ (ethereum.eth.ext.ssz_size) = "24" ];  // Test: Vector[24] of uint64 (24*8=192 bytes), offset: 85
 
   // 2D bytes type - test 2-dimensional byte arrays, common in blockchain state roots (e.g., beacon_state.block_roots)
-  repeated bytes two_dimension_bytes_field = 11 [ (ethereum.eth.ext.ssz_size) = "5,32" ]; // Test: Vector[Bytes32, 5] (32*5=160 bytes), offset: 277
+  repeated bytes two_dimension_bytes_field = 7 [ (ethereum.eth.ext.ssz_size) = "5,32" ]; // Test: Vector[Bytes32, 5] (32*5=160 bytes), offset: 277
+
+  // Bitvector types - test bitfield serialization
+  bytes bitvector64_field = 8 [
+    (ethereum.eth.ext.ssz_size) = "8",
+    (ethereum.eth.ext.cast_type) =
+        "github.com/prysmaticlabs/go-bitfield.Bitvector64"
+  ]; // Test: Bitvector64 (8 bytes), offset: 437
+
+  bytes bitvector512_field = 9 [
+    (ethereum.eth.ext.ssz_size) = "64",
+    (ethereum.eth.ext.cast_type) =
+        "github.com/prysmaticlabs/go-bitfield.Bitvector512"
+  ]; // Test: Bitvector512 (64 bytes), offset: 445
   
   // Additional bytes field - test field ordering and offset calculation
-  bytes trailing_field = 12 [ (ethereum.eth.ext.ssz_size) = "56" ]; // Test: trailing field after vector, offset: 437
+  bytes trailing_field = 10 [ (ethereum.eth.ext.ssz_size) = "56" ]; // Test: trailing field after vector, offset: 509
 }
 
 // ===== VARIABLE-SIZE TEST CONTAINERS =====
@@ -76,7 +89,14 @@ message VariableTestContainer {
   // Variable nested container - test nested container access within variable container
   VariableNestedContainer nested = 5;
 
+  // Bitlist type - test bitlist serialization
+  bytes bitlist_field = 6 [
+    (ethereum.eth.ext.ssz_max) = "2048",
+    (ethereum.eth.ext.cast_type) =
+        "github.com/prysmaticlabs/go-bitfield.Bitlist"
+  ];
+
   // Fixed-size trailing field - test fixed field after variable fields
   // Verifies correct offset calculation after variable-size fields
-  bytes trailing_field = 6 [ (ethereum.eth.ext.ssz_size) = "56" ];  // Test: fixed 56-byte field at end, offset: 32 + 4 + 4 + 4 + 4 = 48
+  bytes trailing_field = 7 [ (ethereum.eth.ext.ssz_size) = "56" ];  // Test: fixed 56-byte field at end, offset: 32 + 4 + 4 + 4 + 4 + 4 = 52
 }
diff --git a/proto/ssz_query/ssz_query.ssz.go b/proto/ssz_query/ssz_query.ssz.go
index 2cd9dbd77c..2f20bb8c59 100644
--- a/proto/ssz_query/ssz_query.ssz.go
+++ b/proto/ssz_query/ssz_query.ssz.go
@@ -131,7 +131,21 @@ func (f *FixedTestContainer) MarshalSSZTo(buf []byte) (dst []byte, err error) {
 		dst = append(dst, f.TwoDimensionBytesField[ii]...)
 	}
 
-	// Field (7) 'TrailingField'
+	// Field (7) 'Bitvector64Field'
+	if size := len(f.Bitvector64Field); size != 8 {
+		err = ssz.ErrBytesLengthFn("--.Bitvector64Field", size, 8)
+		return
+	}
+	dst = append(dst, f.Bitvector64Field...)
+
+	// Field (8) 'Bitvector512Field'
+	if size := len(f.Bitvector512Field); size != 64 {
+		err = ssz.ErrBytesLengthFn("--.Bitvector512Field", size, 64)
+		return
+	}
+	dst = append(dst, f.Bitvector512Field...)
+
+	// Field (9) 'TrailingField'
 	if size := len(f.TrailingField); size != 56 {
 		err = ssz.ErrBytesLengthFn("--.TrailingField", size, 56)
 		return
@@ -145,7 +159,7 @@ func (f *FixedTestContainer) MarshalSSZTo(buf []byte) (dst []byte, err error) {
 func (f *FixedTestContainer) UnmarshalSSZ(buf []byte) error {
 	var err error
 	size := uint64(len(buf))
-	if size != 493 {
+	if size != 565 {
 		return ssz.ErrSize
 	}
 
@@ -190,18 +204,30 @@ func (f *FixedTestContainer) UnmarshalSSZ(buf []byte) error {
 		f.TwoDimensionBytesField[ii] = append(f.TwoDimensionBytesField[ii], buf[277:437][ii*32:(ii+1)*32]...)
 	}
 
-	// Field (7) 'TrailingField'
-	if cap(f.TrailingField) == 0 {
-		f.TrailingField = make([]byte, 0, len(buf[437:493]))
+	// Field (7) 'Bitvector64Field'
+	if cap(f.Bitvector64Field) == 0 {
+		f.Bitvector64Field = make([]byte, 0, len(buf[437:445]))
 	}
-	f.TrailingField = append(f.TrailingField, buf[437:493]...)
+	f.Bitvector64Field = append(f.Bitvector64Field, buf[437:445]...)
+
+	// Field (8) 'Bitvector512Field'
+	if cap(f.Bitvector512Field) == 0 {
+		f.Bitvector512Field = make([]byte, 0, len(buf[445:509]))
+	}
+	f.Bitvector512Field = append(f.Bitvector512Field, buf[445:509]...)
+
+	// Field (9) 'TrailingField'
+	if cap(f.TrailingField) == 0 {
+		f.TrailingField = make([]byte, 0, len(buf[509:565]))
+	}
+	f.TrailingField = append(f.TrailingField, buf[509:565]...)
 
 	return err
 }
 
 // SizeSSZ returns the ssz encoded size in bytes for the FixedTestContainer object
 func (f *FixedTestContainer) SizeSSZ() (size int) {
-	size = 493
+	size = 565
 	return
 }
 
@@ -265,7 +291,21 @@ func (f *FixedTestContainer) HashTreeRootWith(hh *ssz.Hasher) (err error) {
 		hh.Merkleize(subIndx)
 	}
 
-	// Field (7) 'TrailingField'
+	// Field (7) 'Bitvector64Field'
+	if size := len(f.Bitvector64Field); size != 8 {
+		err = ssz.ErrBytesLengthFn("--.Bitvector64Field", size, 8)
+		return
+	}
+	hh.PutBytes(f.Bitvector64Field)
+
+	// Field (8) 'Bitvector512Field'
+	if size := len(f.Bitvector512Field); size != 64 {
+		err = ssz.ErrBytesLengthFn("--.Bitvector512Field", size, 64)
+		return
+	}
+	hh.PutBytes(f.Bitvector512Field)
+
+	// Field (9) 'TrailingField'
 	if size := len(f.TrailingField); size != 56 {
 		err = ssz.ErrBytesLengthFn("--.TrailingField", size, 56)
 		return
@@ -393,7 +433,7 @@ func (v *VariableTestContainer) MarshalSSZ() ([]byte, error) {
 // MarshalSSZTo ssz marshals the VariableTestContainer object to a target array
 func (v *VariableTestContainer) MarshalSSZTo(buf []byte) (dst []byte, err error) {
 	dst = buf
-	offset := int(104)
+	offset := int(108)
 
 	// Field (0) 'LeadingField'
 	if size := len(v.LeadingField); size != 32 {
@@ -421,7 +461,11 @@ func (v *VariableTestContainer) MarshalSSZTo(buf []byte) (dst []byte, err error)
 	}
 	offset += v.Nested.SizeSSZ()
 
-	// Field (5) 'TrailingField'
+	// Offset (5) 'BitlistField'
+	dst = ssz.WriteOffset(dst, offset)
+	offset += len(v.BitlistField)
+
+	// Field (6) 'TrailingField'
 	if size := len(v.TrailingField); size != 56 {
 		err = ssz.ErrBytesLengthFn("--.TrailingField", size, 56)
 		return
@@ -466,6 +510,13 @@ func (v *VariableTestContainer) MarshalSSZTo(buf []byte) (dst []byte, err error)
 		return
 	}
 
+	// Field (5) 'BitlistField'
+	if size := len(v.BitlistField); size > 2048 {
+		err = ssz.ErrBytesLengthFn("--.BitlistField", size, 2048)
+		return
+	}
+	dst = append(dst, v.BitlistField...)
+
 	return
 }
 
@@ -473,12 +524,12 @@ func (v *VariableTestContainer) MarshalSSZTo(buf []byte) (dst []byte, err error)
 func (v *VariableTestContainer) UnmarshalSSZ(buf []byte) error {
 	var err error
 	size := uint64(len(buf))
-	if size < 104 {
+	if size < 108 {
 		return ssz.ErrSize
 	}
 
 	tail := buf
-	var o1, o2, o3, o4 uint64
+	var o1, o2, o3, o4, o5 uint64
 
 	// Field (0) 'LeadingField'
 	if cap(v.LeadingField) == 0 {
@@ -491,7 +542,7 @@ func (v *VariableTestContainer) UnmarshalSSZ(buf []byte) error {
 		return ssz.ErrOffset
 	}
 
-	if o1 != 104 {
+	if o1 != 108 {
 		return ssz.ErrInvalidVariableOffset
 	}
 
@@ -510,11 +561,16 @@ func (v *VariableTestContainer) UnmarshalSSZ(buf []byte) error {
 		return ssz.ErrOffset
 	}
 
-	// Field (5) 'TrailingField'
-	if cap(v.TrailingField) == 0 {
-		v.TrailingField = make([]byte, 0, len(buf[48:104]))
+	// Offset (5) 'BitlistField'
+	if o5 = ssz.ReadOffset(buf[48:52]); o5 > size || o4 > o5 {
+		return ssz.ErrOffset
 	}
-	v.TrailingField = append(v.TrailingField, buf[48:104]...)
+
+	// Field (6) 'TrailingField'
+	if cap(v.TrailingField) == 0 {
+		v.TrailingField = make([]byte, 0, len(buf[52:108]))
+	}
+	v.TrailingField = append(v.TrailingField, buf[52:108]...)
 
 	// Field (1) 'FieldListUint64'
 	{
@@ -565,7 +621,7 @@ func (v *VariableTestContainer) UnmarshalSSZ(buf []byte) error {
 
 	// Field (4) 'Nested'
 	{
-		buf = tail[o4:]
+		buf = tail[o4:o5]
 		if v.Nested == nil {
 			v.Nested = new(VariableNestedContainer)
 		}
@@ -573,12 +629,24 @@ func (v *VariableTestContainer) UnmarshalSSZ(buf []byte) error {
 			return err
 		}
 	}
+
+	// Field (5) 'BitlistField'
+	{
+		buf = tail[o5:]
+		if err = ssz.ValidateBitlist(buf, 2048); err != nil {
+			return err
+		}
+		if cap(v.BitlistField) == 0 {
+			v.BitlistField = make([]byte, 0, len(buf))
+		}
+		v.BitlistField = append(v.BitlistField, buf...)
+	}
 	return err
 }
 
 // SizeSSZ returns the ssz encoded size in bytes for the VariableTestContainer object
 func (v *VariableTestContainer) SizeSSZ() (size int) {
-	size = 104
+	size = 108
 
 	// Field (1) 'FieldListUint64'
 	size += len(v.FieldListUint64) * 8
@@ -595,6 +663,9 @@ func (v *VariableTestContainer) SizeSSZ() (size int) {
 	}
 	size += v.Nested.SizeSSZ()
 
+	// Field (5) 'BitlistField'
+	size += len(v.BitlistField)
+
 	return
 }
 
@@ -670,7 +741,14 @@ func (v *VariableTestContainer) HashTreeRootWith(hh *ssz.Hasher) (err error) {
 		return
 	}
 
-	// Field (5) 'TrailingField'
+	// Field (5) 'BitlistField'
+	if len(v.BitlistField) == 0 {
+		err = ssz.ErrEmptyBitlist
+		return
+	}
+	hh.PutBitlist(v.BitlistField, 2048)
+
+	// Field (6) 'TrailingField'
 	if size := len(v.TrailingField); size != 56 {
 		err = ssz.ErrBytesLengthFn("--.TrailingField", size, 56)
 		return