rlp: allow manually registering types implementing Encoder/Decoder

in tinygo

rlp/decode.go

@@ -168,7 +168,7 @@ func makeDecoder(typ reflect.Type, tags rlpstruct.Tags) (dec decoder, err error)
 		return decodeU256NoPtr, nil
 	case kind == reflect.Ptr:
 		return makePtrDecoder(typ, tags)
-	case reflect.PointerTo(typ).Implements(decoderInterface):
+	case implementsInterface(reflect.PointerTo(typ), decoderInterface):
 		return decodeDecoder, nil
 	case isUint(kind):
 		return decodeUint, nil
@@ -262,7 +262,7 @@ func decodeU256(s *Stream, val reflect.Value) error {
 
 func makeListDecoder(typ reflect.Type, tag rlpstruct.Tags) (decoder, error) {
 	etype := typ.Elem()
-	if etype.Kind() == reflect.Uint8 && !reflect.PointerTo(etype).Implements(decoderInterface) {
+	if etype.Kind() == reflect.Uint8 && !implementsInterface(reflect.PointerTo(etype), decoderInterface) {
 		if typ.Kind() == reflect.Array {
 			return decodeByteArray, nil
 		}

rlp/encode.go

@@ -151,7 +151,7 @@ func makeWriter(typ reflect.Type, ts rlpstruct.Tags) (writer, error) {
 		return writeU256IntNoPtr, nil
 	case kind == reflect.Ptr:
 		return makePtrWriter(typ, ts)
-	case reflect.PointerTo(typ).Implements(encoderInterface):
+	case implementsInterface(reflect.PointerTo(typ), encoderInterface):
 		return makeEncoderWriter(typ), nil
 	case isUint(kind):
 		return writeUint, nil
@@ -409,7 +409,7 @@ func makePtrWriter(typ reflect.Type, ts rlpstruct.Tags) (writer, error) {
 }
 
 func makeEncoderWriter(typ reflect.Type) writer {
-	if typ.Implements(encoderInterface) {
+	if implementsInterface(typ, encoderInterface) {
 		return func(val reflect.Value, w *encBuffer) error {
 			return val.Interface().(Encoder).EncodeRLP(w)
 		}

rlp/reflection.go

@@ -0,0 +1,25 @@
+// Copyright 2025 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+//go:build !tinygo
+
+package rlp
+
+import "reflect"
+
+func implementsInterface(t reflect.Type, i reflect.Type) bool {
+	return t.Implements(i)
+}

rlp/reflection_tinygo.go

@@ -0,0 +1,38 @@
+// Copyright 2025 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+//go:build tinygo
+
+package rlp
+
+import "reflect"
+
+var customEncodedTypes = make(map[reflect.Type]bool)
+
+func implementsInterface(t reflect.Type, i reflect.Type) bool {
+	// reflect implementation of tinygo cannot handle this automatically
+	// at runtime. So we need custom encoded types to be registered manually.
+	if i == decoderInterface || i == encoderInterface {
+		return customEncodedTypes[t]
+	}
+	return false
+}
+
+// RegisterCustomEncodedType manually registers a type as an implementation of
+// Decoder and Encoder interfaces
+func RegisterCustomEncodedType(t reflect.Type) {
+	customEncodedTypes[t] = true
+}

rlp/typecache.go

@@ -199,8 +199,8 @@ func rtypeToStructType(typ reflect.Type, rec map[reflect.Type]*rlpstruct.Type) *
 	t := &rlpstruct.Type{
 		Name:      typ.String(),
 		Kind:      k,
-		IsEncoder: typ.Implements(encoderInterface),
+		IsEncoder: implementsInterface(typ, encoderInterface),
-		IsDecoder: typ.Implements(decoderInterface),
+		IsDecoder: implementsInterface(typ, decoderInterface),
 	}
 	rec[typ] = t
 	if k == reflect.Array || k == reflect.Slice || k == reflect.Ptr {
@@ -234,5 +234,5 @@ func isUint(k reflect.Kind) bool {
 }
 
 func isByte(typ reflect.Type) bool {
-	return typ.Kind() == reflect.Uint8 && !typ.Implements(encoderInterface)
+	return typ.Kind() == reflect.Uint8 && !implementsInterface(typ, encoderInterface)
 }