encoding/binary: hide TotalSize

The function has a bizarre signature: it was the only public function there
that exposed the reflect package. Also, its definition is peculiar and hard to
explain. It doesn't merit being exported.

This is an API change but really, it should never have been exported and
it's certain very few programs will depend on it: it's too weird.

Fixes #2846.

R=golang-dev, gri, bradfitz
CC=golang-dev
https://golang.org/cl/5639054

2 files changed, 8 insertions, 4 deletions

diff --git a/src/pkg/encoding/binary/binary.go b/src/pkg/encoding/binary/binary.go
index d2f8b1e624..4be83f53bd 100644
--- a/src/pkg/encoding/binary/binary.go
+++ b/src/pkg/encoding/binary/binary.go
@@ -163,7 +163,7 @@ func Read(r io.Reader, order ByteOrder, data interface{}) error {
 	default:
 		return errors.New("binary.Read: invalid type " + d.Type().String())
 	}
-	size := TotalSize(v)
+	size := dataSize(v)
 	if size < 0 {
 		return errors.New("binary.Read: invalid type " + v.Type().String())
 	}
@@ -242,7 +242,7 @@ func Write(w io.Writer, order ByteOrder, data interface{}) error {
 		return err
 	}
 	v := reflect.Indirect(reflect.ValueOf(data))
-	size := TotalSize(v)
+	size := dataSize(v)
 	if size < 0 {
 		return errors.New("binary.Write: invalid type " + v.Type().String())
 	}
@@ -253,7 +253,11 @@ func Write(w io.Writer, order ByteOrder, data interface{}) error {
 	return err
 }
 
-func TotalSize(v reflect.Value) int {
+// dataSize returns the number of bytes the actual data represented by v occupies in memory.
+// For compound structures, it sums the sizes of the elements. Thus, for instance, for a slice
+// it returns the length of the slice times the element size and does not count the memory
+// occupied by the header.
+func dataSize(v reflect.Value) int {
 	if v.Kind() == reflect.Slice {
 		elem := sizeof(v.Type().Elem())
 		if elem < 0 {
diff --git a/src/pkg/encoding/binary/binary_test.go b/src/pkg/encoding/binary/binary_test.go
index 3e7057ea22..ff361b7e37 100644
--- a/src/pkg/encoding/binary/binary_test.go
+++ b/src/pkg/encoding/binary/binary_test.go
@@ -187,7 +187,7 @@ func BenchmarkReadStruct(b *testing.B) {
 	bsr := &byteSliceReader{}
 	var buf bytes.Buffer
 	Write(&buf, BigEndian, &s)
-	n := TotalSize(reflect.ValueOf(s))
+	n := dataSize(reflect.ValueOf(s))
 	b.SetBytes(int64(n))
 	t := s
 	b.ResetTimer()