feat(x/tx): add custom type encoder (#19786)

docs/build/building-modules/05-protobuf-annotations.md

@@ -125,3 +125,9 @@ Encoding instructs the amino json marshaler how to encode certain fields that ma
 ```proto reference
 https://github.com/cosmos/cosmos-sdk/blob/e8f28bf5db18b8d6b7e0d94b542ce4cf48fed9d6/proto/cosmos/bank/v1beta1/genesis.proto#L23
 ```
+
+Another example is how `bytes` is encoded when using the amino json encoding format. The `bytes_as_string` option tells the json marshaler [how to encode bytes as string](https://github.com/pinosu/cosmos-sdk/blob/9879ece09c58068402782fa2096199dc89a23d13/x/tx/signing/aminojson/json_marshal.go#L75).
+
+```proto
+(amino.encoding)         = "bytes_as_string",
+```

x/tx/CHANGELOG.md

@@ -31,6 +31,10 @@ Ref: https://keepachangelog.com/en/1.0.0/
 
 ## [Unreleased]
 
+### Features
+
+* [#19786](https://github.com/cosmos/cosmos-sdk/pull/19786) Add bytes as string option to encoder.
+
 ### Improvements
 
 * [#19845](https://github.com/cosmos/cosmos-sdk/pull/19845) Use hybrid resolver instead of only protov2 registry

x/tx/signing/aminojson/encoder.go

@@ -81,6 +81,22 @@ func nullSliceAsEmptyEncoder(enc *Encoder, v protoreflect.Value, w io.Writer) er
 	}
 }
 
+// cosmosBytesAsString replicates the behavior at:
+// https://github.com/CosmWasm/wasmd/blob/08567ff20e372e4f4204a91ca64a371538742bed/x/wasm/types/tx.go#L20-L22
+func cosmosBytesAsString(_ *Encoder, v protoreflect.Value, w io.Writer) error {
+	switch bz := v.Interface().(type) {
+	case []byte:
+		blob, err := json.RawMessage(bz).MarshalJSON()
+		if err != nil {
+			return err
+		}
+		_, err = w.Write(blob)
+		return err
+	default:
+		return fmt.Errorf("unsupported type %T", bz)
+	}
+}
+
 // keyFieldEncoder replicates the behavior at described at:
 // https://github.com/cosmos/cosmos-sdk/blob/b49f948b36bc991db5be431607b475633aed697e/proto/cosmos/crypto/secp256k1/keys.proto#L16
 // The message is treated if it were bytes directly without the key field specified.

x/tx/signing/aminojson/encoder_test.go

@@ -0,0 +1,51 @@
+package aminojson
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"google.golang.org/protobuf/reflect/protoreflect"
+	"gotest.tools/v3/assert"
+)
+
+func TestCosmosBytesAsString(t *testing.T) {
+	cases := map[string]struct {
+		value      protoreflect.Value
+		wantErr    bool
+		wantOutput string
+	}{
+		"valid bytes - json": {
+			value:      protoreflect.ValueOfBytes([]byte(`{"test":"value"}`)),
+			wantErr:    false,
+			wantOutput: `{"test":"value"}`,
+		},
+		"valid bytes - string": {
+			value:      protoreflect.ValueOfBytes([]byte(`foo`)),
+			wantErr:    false,
+			wantOutput: `foo`,
+		},
+		"unsupported type - bool": {
+			value:   protoreflect.ValueOfBool(true),
+			wantErr: true,
+		},
+		"unsupported type - int64": {
+			value:   protoreflect.ValueOfInt64(1),
+			wantErr: true,
+		},
+	}
+
+	for name, tc := range cases {
+		t.Run(name, func(t *testing.T) {
+			var buf bytes.Buffer
+			err := cosmosBytesAsString(nil, tc.value, &buf)
+
+			if tc.wantErr {
+				require.Error(t, err)
+				return
+			}
+			require.NoError(t, err)
+			assert.Equal(t, tc.wantOutput, buf.String())
+		})
+	}
+}

x/tx/signing/aminojson/json_marshal.go

@@ -72,7 +72,8 @@ func NewEncoder(options EncoderOptions) Encoder {
 			"threshold_string": thresholdStringEncoder,
 		},
 		aminoFieldEncoders: map[string]FieldEncoder{
-			"legacy_coins": nullSliceAsEmptyEncoder,
+			"legacy_coins":    nullSliceAsEmptyEncoder,
+			"bytes_as_string": cosmosBytesAsString,
 		},
 		protoTypeEncoders: map[string]MessageEncoder{
 			"google.protobuf.Timestamp": marshalTimestamp,