rlp: minor optimizations for slice/array encoding

rlp/decode.go

@@ -379,7 +379,7 @@ func decodeByteArray(s *Stream, val reflect.Value) error {
 	if err != nil {
 		return err
 	}
-	slice := byteArrayBytes(val)
+	slice := byteArrayBytes(val, val.Len())
 	switch kind {
 	case Byte:
 		if len(slice) == 0 {

rlp/encode.go

@@ -432,7 +432,20 @@ func makeByteArrayWriter(typ reflect.Type) writer {
 	case 1:
 		return writeLengthOneByteArray
 	default:
-		return writeByteArray
+		length := typ.Len()
+		return func(val reflect.Value, w *encbuf) error {
+			if !val.CanAddr() {
+				// Getting the byte slice of val requires it to be addressable. Make it
+				// addressable by copying.
+				copy := reflect.New(val.Type()).Elem()
+				copy.Set(val)
+				val = copy
+			}
+			slice := byteArrayBytes(val, length)
+			w.encodeStringHeader(len(slice))
+			w.str = append(w.str, slice...)
+			return nil
+		}
 	}
 }
 
@@ -451,21 +464,6 @@ func writeLengthOneByteArray(val reflect.Value, w *encbuf) error {
 	return nil
 }
 
-func writeByteArray(val reflect.Value, w *encbuf) error {
-	if !val.CanAddr() {
-		// Getting the byte slice of val requires it to be addressable. Make it
-		// addressable by copying.
-		copy := reflect.New(val.Type()).Elem()
-		copy.Set(val)
-		val = copy
-	}
-
-	slice := byteArrayBytes(val)
-	w.encodeStringHeader(len(slice))
-	w.str = append(w.str, slice...)
-	return nil
-}
-
 func writeString(val reflect.Value, w *encbuf) error {
 	s := val.String()
 	if len(s) == 1 && s[0] <= 0x7f {
@@ -499,19 +497,39 @@ func makeSliceWriter(typ reflect.Type, ts tags) (writer, error) {
 	if etypeinfo.writerErr != nil {
 		return nil, etypeinfo.writerErr
 	}
-	writer := func(val reflect.Value, w *encbuf) error {
-		if !ts.tail {
-			defer w.listEnd(w.list())
+
+	var wfn writer
+	if ts.tail {
+		// This is for struct tail slices.
+		// w.list is not called for them.
+		wfn = func(val reflect.Value, w *encbuf) error {
+			vlen := val.Len()
+			for i := 0; i < vlen; i++ {
+				if err := etypeinfo.writer(val.Index(i), w); err != nil {
+					return err
+				}
+			}
+			return nil
 		}
-		vlen := val.Len()
-		for i := 0; i < vlen; i++ {
-			if err := etypeinfo.writer(val.Index(i), w); err != nil {
-				return err
+	} else {
+		// This is for regular slices and arrays.
+		wfn = func(val reflect.Value, w *encbuf) error {
+			vlen := val.Len()
+			if vlen == 0 {
+				w.str = append(w.str, 0xC0)
+				return nil
 			}
+			listOffset := w.list()
+			for i := 0; i < vlen; i++ {
+				if err := etypeinfo.writer(val.Index(i), w); err != nil {
+					return err
+				}
+			}
+			w.listEnd(listOffset)
+			return nil
 		}
-		return nil
 	}
-	return writer, nil
+	return wfn, nil
 }
 
 func makeStructWriter(typ reflect.Type) (writer, error) {
@@ -562,29 +580,38 @@ func makeStructWriter(typ reflect.Type) (writer, error) {
 	return writer, nil
 }
 
-func makePtrWriter(typ reflect.Type, ts tags) (writer, error) {
-	etypeinfo := theTC.infoWhileGenerating(typ.Elem(), tags{})
-	if etypeinfo.writerErr != nil {
-		return nil, etypeinfo.writerErr
-	}
-	// Determine how to encode nil pointers.
+// nilEncoding returns the encoded value of a nil pointer.
+func nilEncoding(typ reflect.Type, ts tags) uint8 {
 	var nilKind Kind
 	if ts.nilOK {
 		nilKind = ts.nilKind // use struct tag if provided
 	} else {
 		nilKind = defaultNilKind(typ.Elem())
 	}
 
+	switch nilKind {
+	case String:
+		return 0x80
+	case List:
+		return 0xC0
+	default:
+		panic(fmt.Errorf("rlp: invalid nil kind %d", nilKind))
+	}
+}
+
+func makePtrWriter(typ reflect.Type, ts tags) (writer, error) {
+	etypeinfo := theTC.infoWhileGenerating(typ.Elem(), tags{})
+	if etypeinfo.writerErr != nil {
+		return nil, etypeinfo.writerErr
+	}
+	nilEncoding := nilEncoding(typ, ts)
+
 	writer := func(val reflect.Value, w *encbuf) error {
-		if val.IsNil() {
-			if nilKind == String {
-				w.str = append(w.str, 0x80)
-			} else {
-				w.listEnd(w.list())
-			}
-			return nil
+		if ev := val.Elem(); ev.IsValid() {
+			return etypeinfo.writer(ev, w)
 		}
-		return etypeinfo.writer(val.Elem(), w)
+		w.str = append(w.str, nilEncoding)
+		return nil
 	}
 	return writer, nil
 }

rlp/encode_test.go

@@ -540,3 +540,31 @@ func BenchmarkEncodeByteArrayStruct(b *testing.B) {
 		}
 	}
 }
+
+type structSliceElem struct {
+	X uint64
+	Y uint64
+	Z uint64
+}
+
+type structPtrSlice []*structSliceElem
+
+func BenchmarkEncodeStructPtrSlice(b *testing.B) {
+	var out bytes.Buffer
+	var value = structPtrSlice{
+		&structSliceElem{1, 1, 1},
+		&structSliceElem{2, 2, 2},
+		&structSliceElem{3, 3, 3},
+		&structSliceElem{5, 5, 5},
+		&structSliceElem{6, 6, 6},
+		&structSliceElem{7, 7, 7},
+	}
+
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		out.Reset()
+		if err := Encode(&out, &value); err != nil {
+			b.Fatal(err)
+		}
+	}
+}

rlp/safe.go

@@ -21,6 +21,6 @@ package rlp
 import "reflect"
 
 // byteArrayBytes returns a slice of the byte array v.
-func byteArrayBytes(v reflect.Value) []byte {
-	return v.Slice(0, v.Len()).Bytes()
+func byteArrayBytes(v reflect.Value, length int) []byte {
+	return v.Slice(0, length).Bytes()
 }

rlp/unsafe.go

@@ -24,12 +24,11 @@ import (
 )
 
 // byteArrayBytes returns a slice of the byte array v.
-func byteArrayBytes(v reflect.Value) []byte {
-	len := v.Len()
+func byteArrayBytes(v reflect.Value, length int) []byte {
 	var s []byte
 	hdr := (*reflect.SliceHeader)(unsafe.Pointer(&s))
 	hdr.Data = v.UnsafeAddr()
-	hdr.Cap = len
-	hdr.Len = len
+	hdr.Cap = length
+	hdr.Len = length
 	return s
 }