(feat): Add PreCodec modifier (#961)

pkg/codec/config.go

@@ -24,6 +24,7 @@ import (
 // - epoch to time -> [EpochToTimeModifierConfig]
 // - address to string -> [AddressBytesToStringModifierConfig]
 // - field wrapper -> [WrapperModifierConfig]
+// - precodec -> [PrecodecModifierConfig]
 type ModifiersConfig []ModifierConfig
 
 func (m *ModifiersConfig) UnmarshalJSON(data []byte) error {
@@ -58,6 +59,8 @@ func (m *ModifiersConfig) UnmarshalJSON(data []byte) error {
 			(*m)[i] = &AddressBytesToStringModifierConfig{}
 		case ModifierWrapper:
 			(*m)[i] = &WrapperModifierConfig{}
+		case ModifierPreCodec:
+			(*m)[i] = &PreCodecModifierConfig{}
 		default:
 			return fmt.Errorf("%w: unknown modifier type: %s", types.ErrInvalidConfig, mType)
 		}
@@ -84,6 +87,7 @@ func (m *ModifiersConfig) ToModifier(onChainHooks ...mapstructure.DecodeHookFunc
 type ModifierType string
 
 const (
+	ModifierPreCodec        ModifierType = "precodec"
 	ModifierRename          ModifierType = "rename"
 	ModifierDrop            ModifierType = "drop"
 	ModifierHardCode        ModifierType = "hard code"
@@ -199,6 +203,69 @@ func (h *HardCodeModifierConfig) MarshalJSON() ([]byte, error) {
 	})
 }
 
+// PreCodec creates a modifier that will transform data using a preliminary encoding/decoding step.
+// 'Off-chain' values will be overwritten with the encoded data as a byte array.
+// 'On-chain' values will be typed using the optimistic types from the codec.
+// This is useful when wanting to move the data as generic bytes.
+//
+//				Example:
+//
+//				Based on this input struct:
+//					type example struct {
+//						A []B
+//					}
+//
+//					type B struct {
+//						C string
+//						D string
+//					}
+//
+//				And the fields config defined as:
+//			 		{"A": "string C, string D"}
+//
+//				The codec config gives a map of strings (the values from fields config map) to implementation for encoding/decoding
+//
+//		           RemoteCodec {
+//		              func (types.TypeProvider) CreateType(itemType string, forEncoding bool) (any, error)
+//		              func (types.Decoder) Decode(ctx context.Context, raw []byte, into any, itemType string) error
+//		              func (types.Encoder) Encode(ctx context.Context, item any, itemType string) ([]byte, error)
+//		              func (types.Decoder) GetMaxDecodingSize(ctx context.Context, n int, itemType string) (int, error)
+//		              func (types.Encoder) GetMaxEncodingSize(ctx context.Context, n int, itemType string) (int, error)
+//		           }
+//
+//		  		   {"string C, string D": RemoteCodec}
+//
+//				Result:
+//					type example struct {
+//						A [][]bytes
+//					}
+//
+//	             Where []bytes are the encoded input struct B
+type PreCodecModifierConfig struct {
+	// A map of a path of properties to encoding scheme.
+	// If the path leads to an array, encoding will occur on every entry.
+	//
+	// Example: "a.b" -> "uint256 Value"
+	Fields map[string]string
+	// Codecs is skipped in JSON serialization, it will be injected later.
+	// The map should be keyed using the value from "Fields" to a corresponding Codec that can encode/decode for it
+	// This allows encoding and decoding implementations to be handled outside of the modifier.
+	//
+	// Example: "uint256 Value" -> a chain specific encoder for "uint256 Value"
+	Codecs map[string]types.RemoteCodec `json:"-"`
+}
+
+func (c *PreCodecModifierConfig) ToModifier(_ ...mapstructure.DecodeHookFunc) (Modifier, error) {
+	return NewPreCodec(c.Fields, c.Codecs)
+}
+
+func (c *PreCodecModifierConfig) MarshalJSON() ([]byte, error) {
+	return json.Marshal(&modifierMarshaller[PreCodecModifierConfig]{
+		Type: ModifierPreCodec,
+		T:    c,
+	})
+}
+
 // EpochToTimeModifierConfig is used to convert epoch seconds as uint64 fields on-chain to time.Time
 type EpochToTimeModifierConfig struct {
 	Fields []string

pkg/codec/precodec.go

@@ -0,0 +1,113 @@
+package codec
+
+import (
+	"context"
+	"fmt"
+	"reflect"
+
+	"github.com/go-viper/mapstructure/v2"
+	"github.com/smartcontractkit/chainlink-common/pkg/types"
+)
+
+// PreCodec creates a modifier that will run a preliminary encoding/decoding step.
+// This is useful when wanting to move nested data as generic bytes.
+func NewPreCodec(fields map[string]string, codecs map[string]types.RemoteCodec) (Modifier, error) {
+	m := &preCodec{
+		modifierBase: modifierBase[string]{
+			fields:           fields,
+			onToOffChainType: map[reflect.Type]reflect.Type{},
+			offToOnChainType: map[reflect.Type]reflect.Type{},
+		},
+		codecs: codecs,
+	}
+
+	// validate that there is a codec for each unique type definition
+	for _, typeDef := range fields {
+		if _, ok := m.codecs[typeDef]; ok {
+			continue
+		}
+		return nil, fmt.Errorf("codec not supplied for: %s", typeDef)
+	}
+
+	m.modifyFieldForInput = func(_ string, field *reflect.StructField, _ string, typeDef string) error {
+		if field.Type != reflect.SliceOf(reflect.TypeFor[uint8]()) {
+			return fmt.Errorf("can only decode []byte from on-chain: %s", field.Type)
+		}
+
+		codec, ok := m.codecs[typeDef]
+		if !ok || codec == nil {
+			return fmt.Errorf("codec not found for type definition: '%s'", typeDef)
+		}
+
+		newType, err := codec.CreateType("", false)
+		if err != nil {
+			return err
+		}
+		field.Type = reflect.TypeOf(newType)
+
+		return nil
+	}
+
+	return m, nil
+}
+
+type preCodec struct {
+	modifierBase[string]
+	codecs map[string]types.RemoteCodec
+}
+
+func (pc *preCodec) TransformToOffChain(onChainValue any, _ string) (any, error) {
+	allHooks := make([]mapstructure.DecodeHookFunc, 1)
+	allHooks[0] = hardCodeManyHook
+
+	return transformWithMaps(onChainValue, pc.onToOffChainType, pc.fields, pc.decodeFieldMapAction, allHooks...)
+}
+
+func (pc *preCodec) decodeFieldMapAction(extractMap map[string]any, key string, typeDef string) error {
+	_, exists := extractMap[key]
+	if !exists {
+		return fmt.Errorf("field %s does not exist", key)
+	}
+
+	codec, ok := pc.codecs[typeDef]
+	if !ok || codec == nil {
+		return fmt.Errorf("codec not found for type definition: '%s'", typeDef)
+	}
+
+	to, err := codec.CreateType("", false)
+	if err != nil {
+		return err
+	}
+	err = codec.Decode(context.Background(), extractMap[key].([]byte), &to, "")
+	if err != nil {
+		return err
+	}
+	extractMap[key] = to
+	return nil
+}
+
+func (pc *preCodec) TransformToOnChain(offChainValue any, _ string) (any, error) {
+	allHooks := make([]mapstructure.DecodeHookFunc, 1)
+	allHooks[0] = hardCodeManyHook
+
+	return transformWithMaps(offChainValue, pc.offToOnChainType, pc.fields, pc.encodeFieldMapAction, allHooks...)
+}
+
+func (pc *preCodec) encodeFieldMapAction(extractMap map[string]any, key string, typeDef string) error {
+	_, exists := extractMap[key]
+	if !exists {
+		return fmt.Errorf("field %s does not exist", key)
+	}
+
+	codec, ok := pc.codecs[typeDef]
+	if !ok || codec == nil {
+		return fmt.Errorf("codec not found for type definition: '%s'", typeDef)
+	}
+
+	encoded, err := codec.Encode(context.Background(), extractMap[key], "")
+	if err != nil {
+		return err
+	}
+	extractMap[key] = encoded
+	return nil
+}