add codec option to use encoding.Text/Binary(Un)Marshaler when present (

#2666)

.changelog/a7a833ea4c9c42bcbecc39d0597c7b88.json

@@ -0,0 +1,8 @@
+{
+    "id": "a7a833ea-4c9c-42bc-becc-39d0597c7b88",
+    "type": "feature",
+    "description": "Add codec options to use encoding.Text/Binary(Un)Marshaler when present on targets.",
+    "modules": [
+        "feature/dynamodb/attributevalue"
+    ]
+}

feature/dynamodb/attributevalue/decode.go

@@ -231,6 +231,18 @@ type DecoderOptions struct {
 	// Default string parsing format is time.RFC3339
 	// Default number parsing format is seconds since January 1, 1970 UTC
 	DecodeTime DecodeTimeAttributes
+
+	// When enabled, the decoder will use implementations of
+	// encoding.TextUnmarshaler and encoding.BinaryUnmarshaler when present on
+	// unmarshaling targets.
+	//
+	// If a target implements [Unmarshaler], encoding unmarshaler
+	// implementations are ignored.
+	//
+	// If the attributevalue is a string, its underlying value will be used to
+	// call UnmarshalText on the target. If the attributevalue is a binary, its
+	// value will be used to call UnmarshalBinary.
+	UseEncodingUnmarshalers bool
 }
 
 // A Decoder provides unmarshaling AttributeValues to Go value types.
@@ -288,17 +300,30 @@ func (d *Decoder) decode(av types.AttributeValue, v reflect.Value, fieldTag tag)
 	var u Unmarshaler
 	_, isNull := av.(*types.AttributeValueMemberNULL)
 	if av == nil || isNull {
-		u, v = indirect(v, indirectOptions{decodeNull: true})
+		u, v = indirect[Unmarshaler](v, indirectOptions{decodeNull: true})
 		if u != nil {
 			return u.UnmarshalDynamoDBAttributeValue(av)
 		}
 		return d.decodeNull(v)
 	}
 
-	u, v = indirect(v, indirectOptions{})
+	v0 := v
+	u, v = indirect[Unmarshaler](v, indirectOptions{})
 	if u != nil {
 		return u.UnmarshalDynamoDBAttributeValue(av)
 	}
+	if d.options.UseEncodingUnmarshalers {
+		if s, ok := av.(*types.AttributeValueMemberS); ok {
+			if u, _ := indirect[encoding.TextUnmarshaler](v0, indirectOptions{}); u != nil {
+				return u.UnmarshalText([]byte(s.Value))
+			}
+		}
+		if b, ok := av.(*types.AttributeValueMemberB); ok {
+			if u, _ := indirect[encoding.BinaryUnmarshaler](v0, indirectOptions{}); u != nil {
+				return u.UnmarshalBinary(b.Value)
+			}
+		}
+	}
 
 	switch tv := av.(type) {
 	case *types.AttributeValueMemberB:
@@ -420,7 +445,7 @@ func (d *Decoder) decodeBinarySet(bs [][]byte, v reflect.Value) error {
 		if !isArray {
 			v.SetLen(i + 1)
 		}
-		u, elem := indirect(v.Index(i), indirectOptions{})
+		u, elem := indirect[Unmarshaler](v.Index(i), indirectOptions{})
 		if u != nil {
 			return u.UnmarshalDynamoDBAttributeValue(&types.AttributeValueMemberBS{Value: bs})
 		}
@@ -555,7 +580,7 @@ func (d *Decoder) decodeNumberSet(ns []string, v reflect.Value) error {
 		if !isArray {
 			v.SetLen(i + 1)
 		}
-		u, elem := indirect(v.Index(i), indirectOptions{})
+		u, elem := indirect[Unmarshaler](v.Index(i), indirectOptions{})
 		if u != nil {
 			return u.UnmarshalDynamoDBAttributeValue(&types.AttributeValueMemberNS{Value: ns})
 		}
@@ -634,7 +659,7 @@ func (d *Decoder) decodeMap(avMap map[string]types.AttributeValue, v reflect.Val
 		for k, av := range avMap {
 			key := reflect.New(keyType).Elem()
 			// handle pointer keys
-			_, indirectKey := indirect(key, indirectOptions{skipUnmarshaler: true})
+			_, indirectKey := indirect[Unmarshaler](key, indirectOptions{skipUnmarshaler: true})
 			if err := decodeMapKey(k, indirectKey, tag{}); err != nil {
 				return &UnmarshalTypeError{
 					Value: fmt.Sprintf("map key %q", k),
@@ -777,7 +802,7 @@ func (d *Decoder) decodeStringSet(ss []string, v reflect.Value) error {
 		if !isArray {
 			v.SetLen(i + 1)
 		}
-		u, elem := indirect(v.Index(i), indirectOptions{})
+		u, elem := indirect[Unmarshaler](v.Index(i), indirectOptions{})
 		if u != nil {
 			return u.UnmarshalDynamoDBAttributeValue(&types.AttributeValueMemberSS{Value: ss})
 		}
@@ -825,7 +850,7 @@ type indirectOptions struct {
 //
 // Based on the enoding/json type reflect value type indirection in Go Stdlib
 // https://golang.org/src/encoding/json/decode.go indirect func.
-func indirect(v reflect.Value, opts indirectOptions) (Unmarshaler, reflect.Value) {
+func indirect[U any](v reflect.Value, opts indirectOptions) (U, reflect.Value) {
 	// Issue #24153 indicates that it is generally not a guaranteed property
 	// that you may round-trip a reflect.Value by calling Value.Addr().Elem()
 	// and expect the value to still be settable for values derived from
@@ -859,7 +884,8 @@ func indirect(v reflect.Value, opts indirectOptions) (Unmarshaler, reflect.Value
 				continue
 			}
 			if e.Kind() != reflect.Ptr && e.IsValid() {
-				return nil, e
+				var u U
+				return u, e
 			}
 		}
 		if v.Kind() != reflect.Ptr {
@@ -880,7 +906,7 @@ func indirect(v reflect.Value, opts indirectOptions) (Unmarshaler, reflect.Value
 			v.Set(reflect.New(v.Type().Elem()))
 		}
 		if !opts.skipUnmarshaler && v.Type().NumMethod() > 0 && v.CanInterface() {
-			if u, ok := v.Interface().(Unmarshaler); ok {
+			if u, ok := v.Interface().(U); ok {
 				return u, reflect.Value{}
 			}
 		}
@@ -893,7 +919,8 @@ func indirect(v reflect.Value, opts indirectOptions) (Unmarshaler, reflect.Value
 		}
 	}
 
-	return nil, v
+	var u U
+	return u, v
 }
 
 // A Number represents a Attributevalue number literal.

feature/dynamodb/attributevalue/decode_test.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"reflect"
 	"strconv"
+	"strings"
 	"testing"
 	"time"
 
@@ -1173,3 +1174,97 @@ func TestUnmarshalMap_keyPtrTypes(t *testing.T) {
 	}
 
 }
+
+type textUnmarshalerString string
+
+func (v *textUnmarshalerString) UnmarshalText(text []byte) error {
+	*v = textUnmarshalerString("[[" + string(text) + "]]")
+	return nil
+}
+
+func TestUnmarshalTextString(t *testing.T) {
+	in := &types.AttributeValueMemberS{Value: "foo"}
+
+	var actual textUnmarshalerString
+	err := UnmarshalWithOptions(in, &actual, func(o *DecoderOptions) {
+		o.UseEncodingUnmarshalers = true
+	})
+	if err != nil {
+		t.Fatalf("expect no error, got %v", err)
+	}
+
+	if string(actual) != "[[foo]]" {
+		t.Errorf("expected [[foo]], got %s", actual)
+	}
+}
+
+func TestUnmarshalTextStringDisabled(t *testing.T) {
+	in := &types.AttributeValueMemberS{Value: "foo"}
+
+	var actual textUnmarshalerString
+	err := UnmarshalWithOptions(in, &actual, func(o *DecoderOptions) {
+		o.UseEncodingUnmarshalers = false
+	})
+	if err != nil {
+		t.Fatalf("expect no error, got %v", err)
+	}
+
+	if string(actual) != "foo" {
+		t.Errorf("expected foo, got %s", actual)
+	}
+}
+
+type textUnmarshalerStruct struct {
+	I, J string
+}
+
+func (v *textUnmarshalerStruct) UnmarshalText(text []byte) error {
+	parts := strings.Split(string(text), ";")
+	v.I = parts[0]
+	v.J = parts[1]
+	return nil
+}
+
+func TestUnmarshalTextStruct(t *testing.T) {
+	in := &types.AttributeValueMemberS{Value: "foo;bar"}
+
+	var actual textUnmarshalerStruct
+	err := UnmarshalWithOptions(in, &actual, func(o *DecoderOptions) {
+		o.UseEncodingUnmarshalers = true
+	})
+	if err != nil {
+		t.Fatalf("expect no error, got %v", err)
+	}
+
+	expected := textUnmarshalerStruct{"foo", "bar"}
+	if actual != expected {
+		t.Errorf("expected %v, got %v", expected, actual)
+	}
+}
+
+type binaryUnmarshaler struct {
+	I, J byte
+}
+
+func (v *binaryUnmarshaler) UnmarshalBinary(b []byte) error {
+	v.I = b[0]
+	v.J = b[1]
+	return nil
+}
+
+func TestUnmarshalBinary(t *testing.T) {
+	in := &types.AttributeValueMemberB{Value: []byte{1, 2}}
+
+	var actual binaryUnmarshaler
+	err := UnmarshalWithOptions(in, &actual, func(o *DecoderOptions) {
+		o.UseEncodingUnmarshalers = true
+	})
+	if err != nil {
+		t.Fatalf("expect no error, got %v", err)
+	}
+
+	expected := binaryUnmarshaler{1, 2}
+	if actual != expected {
+		t.Errorf("expected %v, got %v", expected, actual)
+	}
+}

feature/dynamodb/attributevalue/encode.go

@@ -354,8 +354,7 @@ func MarshalListWithOptions(in interface{}, optFns ...func(*EncoderOptions)) ([]
 	return asList.Value, nil
 }
 
-// EncoderOptions is a collection of options shared between marshaling
-// and unmarshaling
+// EncoderOptions is a collection of options used by the marshaler.
 type EncoderOptions struct {
 	// Support other custom struct tag keys, such as `yaml`, `json`, or `toml`.
 	// Note that values provided with a custom TagKey must also be supported
@@ -380,6 +379,19 @@ type EncoderOptions struct {
 	//
 	// Default encoding is time.RFC3339Nano in a DynamoDB String (S) data type.
 	EncodeTime func(time.Time) (types.AttributeValue, error)
+
+	// When enabled, the encoder will use implementations of
+	// encoding.TextMarshaler and encoding.BinaryMarshaler when present on
+	// marshaled values.
+	//
+	// Implementations are checked in the following order:
+	//   - [Marshaler]
+	//   - encoding.TextMarshaler
+	//   - encoding.BinaryMarshaler
+	//
+	// The results of a MarshalText call will convert to string (S), results
+	// from a MarshalBinary call will convert to binary (B).
+	UseEncodingMarshalers bool
 }
 
 // An Encoder provides marshaling Go value types to AttributeValues.
@@ -438,7 +450,7 @@ func (e *Encoder) encode(v reflect.Value, fieldTag tag) (types.AttributeValue, e
 	v = valueElem(v)
 
 	if v.Kind() != reflect.Invalid {
-		if av, err := tryMarshaler(v); err != nil {
+		if av, err := e.tryMarshaler(v); err != nil {
 			return nil, err
 		} else if av != nil {
 			return av, nil
@@ -822,7 +834,7 @@ func isNullableZeroValue(v reflect.Value) bool {
 	return false
 }
 
-func tryMarshaler(v reflect.Value) (types.AttributeValue, error) {
+func (e *Encoder) tryMarshaler(v reflect.Value) (types.AttributeValue, error) {
 	if v.Kind() != reflect.Ptr && v.Type().Name() != "" && v.CanAddr() {
 		v = v.Addr()
 	}
@@ -831,9 +843,35 @@ func tryMarshaler(v reflect.Value) (types.AttributeValue, error) {
 		return nil, nil
 	}
 
-	if m, ok := v.Interface().(Marshaler); ok {
+	i := v.Interface()
+	if m, ok := i.(Marshaler); ok {
 		return m.MarshalDynamoDBAttributeValue()
 	}
+	if e.options.UseEncodingMarshalers {
+		return e.tryEncodingMarshaler(i)
+	}
+
+	return nil, nil
+}
+
+func (e *Encoder) tryEncodingMarshaler(v any) (types.AttributeValue, error) {
+	if m, ok := v.(encoding.TextMarshaler); ok {
+		s, err := m.MarshalText()
+		if err != nil {
+			return nil, err
+		}
+
+		return &types.AttributeValueMemberS{Value: string(s)}, nil
+	}
+
+	if m, ok := v.(encoding.BinaryMarshaler); ok {
+		b, err := m.MarshalBinary()
+		if err != nil {
+			return nil, err
+		}
+
+		return &types.AttributeValueMemberB{Value: b}, nil
+	}
 
 	return nil, nil
 }