perf(libs/json): Lower heap overhead of JSON encoding (backport #2846…

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 * [#27](https://github.com/osmosis-labs/cometbft/pull/27) Lower allocation overhead of txIndex matchRange
 * [#28](https://github.com/osmosis-labs/cometbft/pull/28) Significantly speedup bitArray.PickRandom
+* [#29](https://github.com/osmosis-labs/cometbft/pull/29) Lower heap overhead of JSON encoding
 
 ## v0.37.4-v24-osmo-3
 

libs/json/encoder.go

@@ -42,7 +42,7 @@ func MarshalIndent(v interface{}, prefix, indent string) ([]byte, error) {
 	return buf.Bytes(), nil
 }
 
-func encode(w io.Writer, v interface{}) error {
+func encode(w *bytes.Buffer, v any) error {
 	// Bare nil values can't be reflected, so we must handle them here.
 	if v == nil {
 		return writeStr(w, "null")
@@ -60,7 +60,7 @@ func encode(w io.Writer, v interface{}) error {
 	return encodeReflect(w, rv)
 }
 
-func encodeReflect(w io.Writer, rv reflect.Value) error {
+func encodeReflect(w *bytes.Buffer, rv reflect.Value) error {
 	if !rv.IsValid() {
 		return errors.New("invalid reflect value")
 	}
@@ -115,7 +115,7 @@ func encodeReflect(w io.Writer, rv reflect.Value) error {
 	}
 }
 
-func encodeReflectList(w io.Writer, rv reflect.Value) error {
+func encodeReflectList(w *bytes.Buffer, rv reflect.Value) error {
 	// Emit nil slices as null.
 	if rv.Kind() == reflect.Slice && rv.IsNil() {
 		return writeStr(w, "null")
@@ -150,7 +150,7 @@ func encodeReflectList(w io.Writer, rv reflect.Value) error {
 	return writeStr(w, "]")
 }
 
-func encodeReflectMap(w io.Writer, rv reflect.Value) error {
+func encodeReflectMap(w *bytes.Buffer, rv reflect.Value) error {
 	if rv.Type().Key().Kind() != reflect.String {
 		return errors.New("map key must be string")
 	}
@@ -181,7 +181,7 @@ func encodeReflectMap(w io.Writer, rv reflect.Value) error {
 	return writeStr(w, "}")
 }
 
-func encodeReflectStruct(w io.Writer, rv reflect.Value) error {
+func encodeReflectStruct(w *bytes.Buffer, rv reflect.Value) error {
 	sInfo := makeStructInfo(rv.Type())
 	if err := writeStr(w, "{"); err != nil {
 		return err
@@ -212,7 +212,7 @@ func encodeReflectStruct(w io.Writer, rv reflect.Value) error {
 	return writeStr(w, "}")
 }
 
-func encodeReflectInterface(w io.Writer, rv reflect.Value) error {
+func encodeReflectInterface(w *bytes.Buffer, rv reflect.Value) error {
 	// Get concrete value and dereference pointers.
 	for rv.Kind() == reflect.Ptr || rv.Kind() == reflect.Interface {
 		if rv.IsNil() {
@@ -237,14 +237,17 @@ func encodeReflectInterface(w io.Writer, rv reflect.Value) error {
 	return writeStr(w, "}")
 }
 
-func encodeStdlib(w io.Writer, v interface{}) error {
-	// Doesn't stream the output because that adds a newline, as per:
-	// https://golang.org/pkg/encoding/json/#Encoder.Encode
-	blob, err := json.Marshal(v)
+func encodeStdlib(w *bytes.Buffer, v any) error {
+	// Stream the output of the JSON marshaling directly into the buffer.
+	// The stdlib encoder will write a newline, so we must truncate it,
+	// which is why we pass in a bytes.Buffer throughout, not io.Writer.
+	enc := json.NewEncoder(w)
+	err := enc.Encode(v)
 	if err != nil {
 		return err
 	}
-	_, err = w.Write(blob)
+	// Remove the last byte from the buffer
+	w.Truncate(w.Len() - 1)
 	return err
 }
 

libs/json/encoder_test.go

@@ -102,3 +102,20 @@ func TestMarshal(t *testing.T) {
 		})
 	}
 }
+
+func BenchmarkJsonMarshalStruct(b *testing.B) {
+	s := "string"
+	sPtr := &s
+	i64 := int64(64)
+	ti := time.Date(2020, 6, 2, 18, 5, 13, 4346374, time.FixedZone("UTC+2", 2*60*60))
+	car := &Car{Wheels: 4}
+	boat := Boat{Sail: true}
+	for i := 0; i < b.N; i++ {
+		_, _ = json.Marshal(Struct{
+			Bool: true, Float64: 3.14, Int32: 32, Int64: 64, Int64Ptr: &i64,
+			String: "foo", StringPtrPtr: &sPtr, Bytes: []byte{1, 2, 3},
+			Time: ti, Car: car, Boat: boat, Vehicles: []Vehicle{car, boat},
+			Child: &Struct{Bool: false, String: "child"}, private: "private",
+		})
+	}
+}