encoding/binary: add Size, to replace the functionality of the old TotalSize

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/5644063

doc/go1.html

@@ -931,7 +931,8 @@ No changes will be needed.
 <h3 id="encoding_binary">The encoding/binary package</h3>
 
 <p>
-In Go 1, the <code>binary.TotalSize</code></a> function is no longer exported.
+In Go 1, the <code>binary.TotalSize</code> function is renamed
+<a href="/pkg/encoding/binary/#Size"><code>Size</code></a>.
 </p>
 
 <p>

doc/go1.tmpl

@@ -835,7 +835,10 @@ No changes will be needed.
 <h3 id="encoding_binary">The encoding/binary package</h3>
 
 <p>
-In Go 1, the <code>binary.TotalSize</code></a> function is no longer exported.
+In Go 1, the <code>binary.TotalSize</code> function has been replaced by
+<a href="/pkg/encoding/binary/#Size"><code>Size</code></a>,
+which takes an <code>interface{}</code> argument rather than
+a <code>reflect.Value</code>.
 </p>
 
 <p>

src/pkg/encoding/binary/binary.go

@@ -253,6 +253,12 @@ func Write(w io.Writer, order ByteOrder, data interface{}) error {
 	return err
 }
 
+// Size returns how many bytes Write would generate to encode the value v, assuming
+// the Write would succeed.
+func Size(v interface{}) int {
+	return dataSize(reflect.ValueOf(v))
+}
+
 // 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