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

4 files changed, 118 insertions, 92 deletions

diff --git a/doc/go1.html b/doc/go1.html
index 95953dc79b..4191c4ba25 100644
--- a/doc/go1.html
+++ b/doc/go1.html
@@ -929,6 +929,61 @@ to be implemented in the future.
 No changes will be needed.
 </p>
 
+<h3 id="encoding_binary">The encoding/binary package</h3>
+
+<p>
+In Go 1, the <code>binary.TotalSize</code></a> function is no longer exported.
+</p>
+
+<p>
+<em>Updating</em>:
+Code that depends on the function will need to be updated.
+</p>
+
+<h3 id="encoding_xml">The encoding/xml package</h3>
+
+<p>
+In Go 1, the <a href="/pkg/encoding/xml/"><code>xml</code></a> package
+has been brought closer in design to the other marshaling packages such
+as <a href="/pkg/encoding/gob/"><code>encoding/gob</code></a>.
+</p>
+
+<p>
+The old <code>Parser</code> type is renamed
+<a href="/pkg/encoding/xml/#Decoder"><code>Decoder</code></a> and has a new
+<a href="/pkg/encoding/xml/#Decoder.Decode"><code>Decode</code></a> method. An
+<a href="/pkg/encoding/xml/#Encoder"><code>Encoder</code></a> type was also
+introduced.
+</p>
+
+<p>
+The functions <a href="/pkg/encoding/xml/#Marshal"><code>Marshal</code></a>
+and <a href="/pkg/encoding/xml/#Unmarshal"><code>Unmarshal</code></a>
+work with <code>[]byte</code> values now. To work with streams,
+use the new <a href="/pkg/encoding/xml/#Encoder"><code>Encoder</code></a>
+and <a href="/pkg/encoding/xml/#Decoder"><code>Decoder</code></a> types.
+</p>
+
+<p>
+When marshaling or unmarshaling values, the format of supported flags in
+field tags has changed to be closer to the
+<a href="/pkg/encoding/json"><code>json</code></a> package
+(<code>`xml:"name,flag"`</code>). The matching done between field tags, field
+names, and the XML attribute and element names is now case-sensitive.
+The <code>XMLName</code> field tag, if present, must also match the name
+of the XML element being marshaled.
+</p>
+
+<p>
+<em>Updating</em>:
+Running <code>go fix</code> will update most uses of the package except for some calls to
+<code>Unmarshal</code>. Special care must be taken with field tags,
+since the fix tool will not update them and if not fixed by hand they will
+misbehave silently in some cases. For example, the old
+<code>"attr"</code> is now written <code>",attr"</code> while plain
+<code>"attr"</code> remains valid but with a different meaning.
+</p>
+
 <h3 id="expvar">The expvar package</h3>
 
 <p>
@@ -1575,50 +1630,6 @@ Code that uses the old fields will fail to compile and must be updated by hand.
 The semantic changes make it difficult for the fix tool to update automatically.
 </p>
 
-<h3 id="xml">The xml package</h3>
-
-<p>
-In Go 1, the <a href="/pkg/encoding/xml/"><code>xml</code></a> package
-has been brought closer in design to the other marshaling packages such
-as <a href="/pkg/encoding/gob/"><code>encoding/gob</code></a>.
-</p>
-
-<p>
-The old <code>Parser</code> type is renamed
-<a href="/pkg/encoding/xml/#Decoder"><code>Decoder</code></a> and has a new
-<a href="/pkg/encoding/xml/#Decoder.Decode"><code>Decode</code></a> method. An
-<a href="/pkg/encoding/xml/#Encoder"><code>Encoder</code></a> type was also
-introduced.
-</p>
-
-<p>
-The functions <a href="/pkg/encoding/xml/#Marshal"><code>Marshal</code></a>
-and <a href="/pkg/encoding/xml/#Unmarshal"><code>Unmarshal</code></a>
-work with <code>[]byte</code> values now. To work with streams,
-use the new <a href="/pkg/encoding/xml/#Encoder"><code>Encoder</code></a>
-and <a href="/pkg/encoding/xml/#Decoder"><code>Decoder</code></a> types.
-</p>
-
-<p>
-When marshaling or unmarshaling values, the format of supported flags in
-field tags has changed to be closer to the
-<a href="/pkg/encoding/json"><code>json</code></a> package
-(<code>`xml:"name,flag"`</code>). The matching done between field tags, field
-names, and the XML attribute and element names is now case-sensitive.
-The <code>XMLName</code> field tag, if present, must also match the name
-of the XML element being marshaled.
-</p>
-
-<p>
-<em>Updating</em>:
-Running <code>go fix</code> will update most uses of the package except for some calls to
-<code>Unmarshal</code>. Special care must be taken with field tags,
-since the fix tool will not update them and if not fixed by hand they will
-misbehave silently in some cases. For example, the old
-<code>"attr"</code> is now written <code>",attr"</code> while plain
-<code>"attr"</code> remains valid but with a different meaning.
-</p>
-
 <h2 id="go_command">The go command</h2>
 
 <h2 id="releases">Packaged releases</h2>
diff --git a/doc/go1.tmpl b/doc/go1.tmpl
index 5400198291..819c71ed38 100644
--- a/doc/go1.tmpl
+++ b/doc/go1.tmpl
@@ -833,6 +833,61 @@ to be implemented in the future.
 No changes will be needed.
 </p>
 
+<h3 id="encoding_binary">The encoding/binary package</h3>
+
+<p>
+In Go 1, the <code>binary.TotalSize</code></a> function is no longer exported.
+</p>
+
+<p>
+<em>Updating</em>:
+Code that depends on the function will need to be updated.
+</p>
+
+<h3 id="encoding_xml">The encoding/xml package</h3>
+
+<p>
+In Go 1, the <a href="/pkg/encoding/xml/"><code>xml</code></a> package
+has been brought closer in design to the other marshaling packages such
+as <a href="/pkg/encoding/gob/"><code>encoding/gob</code></a>.
+</p>
+
+<p>
+The old <code>Parser</code> type is renamed
+<a href="/pkg/encoding/xml/#Decoder"><code>Decoder</code></a> and has a new
+<a href="/pkg/encoding/xml/#Decoder.Decode"><code>Decode</code></a> method. An
+<a href="/pkg/encoding/xml/#Encoder"><code>Encoder</code></a> type was also
+introduced.
+</p>
+
+<p>
+The functions <a href="/pkg/encoding/xml/#Marshal"><code>Marshal</code></a>
+and <a href="/pkg/encoding/xml/#Unmarshal"><code>Unmarshal</code></a>
+work with <code>[]byte</code> values now. To work with streams,
+use the new <a href="/pkg/encoding/xml/#Encoder"><code>Encoder</code></a>
+and <a href="/pkg/encoding/xml/#Decoder"><code>Decoder</code></a> types.
+</p>
+
+<p>
+When marshaling or unmarshaling values, the format of supported flags in
+field tags has changed to be closer to the
+<a href="/pkg/encoding/json"><code>json</code></a> package
+(<code>`xml:"name,flag"`</code>). The matching done between field tags, field
+names, and the XML attribute and element names is now case-sensitive.
+The <code>XMLName</code> field tag, if present, must also match the name
+of the XML element being marshaled.
+</p>
+
+<p>
+<em>Updating</em>:
+Running <code>go fix</code> will update most uses of the package except for some calls to
+<code>Unmarshal</code>. Special care must be taken with field tags,
+since the fix tool will not update them and if not fixed by hand they will
+misbehave silently in some cases. For example, the old
+<code>"attr"</code> is now written <code>",attr"</code> while plain
+<code>"attr"</code> remains valid but with a different meaning.
+</p>
+
 <h3 id="expvar">The expvar package</h3>
 
 <p>
@@ -1465,50 +1520,6 @@ Code that uses the old fields will fail to compile and must be updated by hand.
 The semantic changes make it difficult for the fix tool to update automatically.
 </p>
 
-<h3 id="xml">The xml package</h3>
-
-<p>
-In Go 1, the <a href="/pkg/encoding/xml/"><code>xml</code></a> package
-has been brought closer in design to the other marshaling packages such
-as <a href="/pkg/encoding/gob/"><code>encoding/gob</code></a>.
-</p>
-
-<p>
-The old <code>Parser</code> type is renamed
-<a href="/pkg/encoding/xml/#Decoder"><code>Decoder</code></a> and has a new
-<a href="/pkg/encoding/xml/#Decoder.Decode"><code>Decode</code></a> method. An
-<a href="/pkg/encoding/xml/#Encoder"><code>Encoder</code></a> type was also
-introduced.
-</p>
-
-<p>
-The functions <a href="/pkg/encoding/xml/#Marshal"><code>Marshal</code></a>
-and <a href="/pkg/encoding/xml/#Unmarshal"><code>Unmarshal</code></a>
-work with <code>[]byte</code> values now. To work with streams,
-use the new <a href="/pkg/encoding/xml/#Encoder"><code>Encoder</code></a>
-and <a href="/pkg/encoding/xml/#Decoder"><code>Decoder</code></a> types.
-</p>
-
-<p>
-When marshaling or unmarshaling values, the format of supported flags in
-field tags has changed to be closer to the
-<a href="/pkg/encoding/json"><code>json</code></a> package
-(<code>`xml:"name,flag"`</code>). The matching done between field tags, field
-names, and the XML attribute and element names is now case-sensitive.
-The <code>XMLName</code> field tag, if present, must also match the name
-of the XML element being marshaled.
-</p>
-
-<p>
-<em>Updating</em>:
-Running <code>go fix</code> will update most uses of the package except for some calls to
-<code>Unmarshal</code>. Special care must be taken with field tags,
-since the fix tool will not update them and if not fixed by hand they will
-misbehave silently in some cases. For example, the old
-<code>"attr"</code> is now written <code>",attr"</code> while plain
-<code>"attr"</code> remains valid but with a different meaning.
-</p>
-
 <h2 id="go_command">The go command</h2>
 
 <h2 id="releases">Packaged releases</h2>
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()