Nested Value Codec Access

This commit introduces the ability to use a codec to encode/decode individual
fields of a struct, including traversal to nested structs.

pkg/codec/by_item_type_modifier.go

@@ -1,10 +1,7 @@
 package codec
 
 import (
-	"fmt"
 	"reflect"
-
-	"github.com/smartcontractkit/chainlink-common/pkg/types"
 )
 
 // NewByItemTypeModifier returns a Modifier that uses modByItemType to determine which Modifier to use for a given itemType.
@@ -22,13 +19,14 @@ type byItemTypeModifier struct {
 	modByitemType map[string]Modifier
 }
 
+// RetypeToOffChain attempts to apply a modifier using the provided itemType. To allow access to nested fields, this
+// function applies no modifications if a modifier by the specified name is not found.
 func (b *byItemTypeModifier) RetypeToOffChain(onChainType reflect.Type, itemType string) (reflect.Type, error) {
-	mod, ok := b.modByitemType[itemType]
-	if !ok {
-		return nil, fmt.Errorf("%w: cannot find modifier for %s", types.ErrInvalidType, itemType)
+	if mod, ok := b.modByitemType[itemType]; ok {
+		return mod.RetypeToOffChain(onChainType, itemType)
 	}
 
-	return mod.RetypeToOffChain(onChainType, itemType)
+	return onChainType, nil
 }
 
 func (b *byItemTypeModifier) TransformToOnChain(offChainValue any, itemType string) (any, error) {
@@ -40,13 +38,15 @@ func (b *byItemTypeModifier) TransformToOffChain(onChainValue any, itemType stri
 }
 
 func (b *byItemTypeModifier) transform(
-	val any, itemType string, transform func(Modifier, any, string) (any, error)) (any, error) {
-	mod, ok := b.modByitemType[itemType]
-	if !ok {
-		return nil, fmt.Errorf("%w: cannot find modifier for %s", types.ErrInvalidType, itemType)
+	val any,
+	itemType string,
+	transform func(Modifier, any, string) (any, error),
+) (any, error) {
+	if mod, ok := b.modByitemType[itemType]; ok {
+		return transform(mod, val, itemType)
 	}
 
-	return transform(mod, val, itemType)
+	return val, nil
 }
 
 var _ Modifier = &byItemTypeModifier{}

pkg/codec/encodings/struct.go

@@ -3,6 +3,7 @@ package encodings
 import (
 	"fmt"
 	"reflect"
+	"strings"
 
 	"github.com/smartcontractkit/chainlink-common/pkg/types"
 )
@@ -24,6 +25,8 @@ func NewStructCodec(fields []NamedTypeCodec) (c TopLevelCodec, err error) {
 
 	sfs := make([]reflect.StructField, len(fields))
 	codecFields := make([]TypeCodec, len(fields))
+	lookup := make(map[string]int)
+
 	for i, field := range fields {
 		ft := field.Codec.GetType()
 		if ft.Kind() != reflect.Pointer {
@@ -35,18 +38,22 @@ func NewStructCodec(fields []NamedTypeCodec) (c TopLevelCodec, err error) {
 			Name: field.Name,
 			Type: ft,
 		}
+
 		codecFields[i] = field.Codec
+		lookup[field.Name] = i
 	}
 
 	return &structCodec{
-		fields: codecFields,
-		tpe:    reflect.PointerTo(reflect.StructOf(sfs)),
+		fields:      codecFields,
+		fieldLookup: lookup,
+		tpe:         reflect.PointerTo(reflect.StructOf(sfs)),
 	}, nil
 }
 
 type structCodec struct {
-	fields []TypeCodec
-	tpe    reflect.Type
+	fields      []TypeCodec
+	fieldLookup map[string]int
+	tpe         reflect.Type
 }
 
 func (s *structCodec) Encode(value any, into []byte) ([]byte, error) {
@@ -113,3 +120,46 @@ func (s *structCodec) SizeAtTopLevel(numItems int) (int, error) {
 	}
 	return size, nil
 }
+
+func (s *structCodec) FieldCodec(itemType string) (TypeCodec, error) {
+	path := extendedItemType(itemType)
+
+	// itemType could recurse into nested structs
+	fieldName, tail := path.next()
+	if fieldName == "" {
+		return nil, fmt.Errorf("%w: field name required", types.ErrInvalidType)
+	}
+
+	idx, ok := s.fieldLookup[fieldName]
+	if !ok {
+		return nil, fmt.Errorf("%w: cannot find type %s", types.ErrInvalidType, itemType)
+	}
+
+	codec := s.fields[idx]
+
+	if tail == "" {
+		return codec, nil
+	}
+
+	structType, ok := codec.(StructTypeCodec)
+	if !ok {
+		return nil, fmt.Errorf("%w: extended path not traversable for type %s", types.ErrInvalidType, itemType)
+	}
+
+	return structType.FieldCodec(tail)
+}
+
+type extendedItemType string
+
+func (t extendedItemType) next() (string, string) {
+	if string(t) == "" {
+		return "", ""
+	}
+
+	path := strings.Split(string(t), ".")
+	if len(path) == 1 {
+		return path[0], ""
+	}
+
+	return path[0], strings.Join(path[1:], ".")
+}

pkg/codec/encodings/type_codec.go

@@ -33,6 +33,11 @@ type TopLevelCodec interface {
 	SizeAtTopLevel(numItems int) (int, error)
 }
 
+type StructTypeCodec interface {
+	TypeCodec
+	FieldCodec(string) (TypeCodec, error)
+}
+
 // CodecFromTypeCodec maps TypeCodec to types.RemoteCodec, using the key as the itemType
 // If the TypeCodec is a TopLevelCodec, GetMaxEncodingSize and GetMaxDecodingSize will call SizeAtTopLevel instead of Size.
 type CodecFromTypeCodec map[string]TypeCodec
@@ -45,9 +50,9 @@ type LenientCodecFromTypeCodec map[string]TypeCodec
 var _ types.RemoteCodec = &LenientCodecFromTypeCodec{}
 
 func (c CodecFromTypeCodec) CreateType(itemType string, _ bool) (any, error) {
-	ntcwt, ok := c[itemType]
-	if !ok {
-		return nil, fmt.Errorf("%w: cannot find type %s", types.ErrInvalidType, itemType)
+	ntcwt, err := getCodec(c, itemType)
+	if err != nil {
+		return nil, err
 	}
 
 	tpe := ntcwt.GetType()
@@ -59,9 +64,9 @@ func (c CodecFromTypeCodec) CreateType(itemType string, _ bool) (any, error) {
 }
 
 func (c CodecFromTypeCodec) Encode(_ context.Context, item any, itemType string) ([]byte, error) {
-	ntcwt, ok := c[itemType]
-	if !ok {
-		return nil, fmt.Errorf("%w: cannot find type %s", types.ErrInvalidType, itemType)
+	ntcwt, err := getCodec(c, itemType)
+	if err != nil {
+		return nil, err
 	}
 
 	if item != nil {
@@ -86,14 +91,15 @@ func (c CodecFromTypeCodec) Encode(_ context.Context, item any, itemType string)
 }
 
 func (c CodecFromTypeCodec) GetMaxEncodingSize(_ context.Context, n int, itemType string) (int, error) {
-	ntcwt, ok := c[itemType]
-	if !ok {
-		return 0, fmt.Errorf("%w: cannot find type %s", types.ErrInvalidType, itemType)
+	ntcwt, err := getCodec(c, itemType)
+	if err != nil {
+		return 0, err
 	}
 
 	if lp, ok := ntcwt.(TopLevelCodec); ok {
 		return lp.SizeAtTopLevel(n)
 	}
+
 	return ntcwt.Size(n)
 }
 
@@ -121,11 +127,16 @@ func (c LenientCodecFromTypeCodec) Decode(ctx context.Context, raw []byte, into
 	return decode(c, raw, into, itemType, false)
 }
 
+func (c CodecFromTypeCodec) GetMaxDecodingSize(ctx context.Context, n int, itemType string) (int, error) {
+	return c.GetMaxEncodingSize(ctx, n, itemType)
+}
+
 func decode(c map[string]TypeCodec, raw []byte, into any, itemType string, exactSize bool) error {
-	ntcwt, ok := c[itemType]
-	if !ok {
-		return fmt.Errorf("%w: cannot find type %s", types.ErrInvalidType, itemType)
+	ntcwt, err := getCodec(c, itemType)
+	if err != nil {
+		return err
 	}
+
 	val, remaining, err := ntcwt.Decode(raw)
 	if err != nil {
 		return err
@@ -138,6 +149,29 @@ func decode(c map[string]TypeCodec, raw []byte, into any, itemType string, exact
 	return codec.Convert(reflect.ValueOf(val), reflect.ValueOf(into), nil)
 }
 
-func (c CodecFromTypeCodec) GetMaxDecodingSize(ctx context.Context, n int, itemType string) (int, error) {
-	return c.GetMaxEncodingSize(ctx, n, itemType)
+func getCodec(c map[string]TypeCodec, itemType string) (TypeCodec, error) {
+	// itemType could recurse into nested structs
+	path := extendedItemType(itemType)
+
+	// itemType could recurse into nested structs
+	head, tail := path.next()
+	if head == "" {
+		return nil, fmt.Errorf("%w: cannot find type %s", types.ErrInvalidType, itemType)
+	}
+
+	ntcwt, ok := c[head]
+	if !ok {
+		return nil, fmt.Errorf("%w: cannot find type %s", types.ErrInvalidType, itemType)
+	}
+
+	if tail == "" {
+		return ntcwt, nil
+	}
+
+	structType, ok := ntcwt.(StructTypeCodec)
+	if !ok {
+		return nil, fmt.Errorf("%w: extended path not traversable for type %s", types.ErrInvalidType, itemType)
+	}
+
+	return structType.FieldCodec(tail)
 }

pkg/codec/encodings/type_codec_test.go

@@ -4,6 +4,7 @@ import (
 	rawbin "encoding/binary"
 	"math"
 	"reflect"
+	"strings"
 	"testing"
 
 	"github.com/smartcontractkit/libocr/bigbigendian"
@@ -122,6 +123,20 @@ func TestCodecFromTypeCodecs(t *testing.T) {
 
 		assert.Equal(t, singleItemSize*2, actual)
 	})
+
+	t.Run("CreateType works for nested struct values", func(t *testing.T) {
+		itemType := strings.Join([]string{TestItemType, "NestedDynamicStruct", "Inner", "S"}, ".")
+		ts := CreateTestStruct(0, biit)
+		c := biit.GetCodec(t)
+
+		encoded, err := c.Encode(tests.Context(t), ts, itemType)
+		require.NoError(t, err)
+
+		var actual string
+		require.NoError(t, c.Decode(tests.Context(t), encoded, &actual, itemType))
+
+		assert.Equal(t, ts.NestedDynamicStruct.Inner.S, actual)
+	})
 }
 
 type interfaceTesterBase struct{}