ioutil: add Discard, update tree.

This also removes an unnecessary allocation in
http/transfer.go

R=r, rsc1, r2, adg
CC=golang-dev
https://golang.org/cl/4426066

src/pkg/compress/lzw/reader_test.go

@@ -112,12 +112,6 @@ func TestReader(t *testing.T) {
 	}
 }
 
-type devNull struct{}
-
-func (devNull) Write(p []byte) (int, os.Error) {
-	return len(p), nil
-}
-
 func benchmarkDecoder(b *testing.B, n int) {
 	b.StopTimer()
 	b.SetBytes(int64(n))
@@ -134,7 +128,7 @@ func benchmarkDecoder(b *testing.B, n int) {
 	runtime.GC()
 	b.StartTimer()
 	for i := 0; i < b.N; i++ {
-		io.Copy(devNull{}, NewReader(bytes.NewBuffer(buf1), LSB, 8))
+		io.Copy(ioutil.Discard, NewReader(bytes.NewBuffer(buf1), LSB, 8))
 	}
 }
 

src/pkg/compress/lzw/writer_test.go

@@ -113,7 +113,7 @@ func benchmarkEncoder(b *testing.B, n int) {
 	runtime.GC()
 	b.StartTimer()
 	for i := 0; i < b.N; i++ {
-		w := NewWriter(devNull{}, LSB, 8)
+		w := NewWriter(ioutil.Discard, LSB, 8)
 		w.Write(buf1)
 		w.Close()
 	}

src/pkg/html/parse_test.go

@@ -15,12 +15,6 @@ import (
 	"testing"
 )
 
-type devNull struct{}
-
-func (devNull) Write(p []byte) (int, os.Error) {
-	return len(p), nil
-}
-
 func pipeErr(err os.Error) io.Reader {
 	pr, pw := io.Pipe()
 	pw.CloseWithError(err)
@@ -141,7 +135,7 @@ func TestParser(t *testing.T) {
 				t.Fatal(err)
 			}
 			// Skip the #error section.
-			if _, err := io.Copy(devNull{}, <-rc); err != nil {
+			if _, err := io.Copy(ioutil.Discard, <-rc); err != nil {
 				t.Fatal(err)
 			}
 			// Compare the parsed tree to the #document section.

src/pkg/http/transfer.go

@@ -7,6 +7,7 @@ package http
 import (
 	"bufio"
 	"io"
+	"io/ioutil"
 	"os"
 	"strconv"
 	"strings"
@@ -447,17 +448,10 @@ func (b *body) Close() os.Error {
 		return nil
 	}
 
-	trashBuf := make([]byte, 1024) // local for thread safety
-	for {
-		_, err := b.Read(trashBuf)
-		if err == nil {
-			continue
-		}
-		if err == os.EOF {
-			break
-		}
+	if _, err := io.Copy(ioutil.Discard, b); err != nil {
 		return err
 	}
+
 	if b.hdr == nil { // not reading trailer
 		return nil
 	}

src/pkg/io/ioutil/ioutil.go

@@ -101,3 +101,13 @@ func (nopCloser) Close() os.Error { return nil }
 func NopCloser(r io.Reader) io.ReadCloser {
 	return nopCloser{r}
 }
+
+type devNull int
+
+func (devNull) Write(p []byte) (int, os.Error) {
+	return len(p), nil
+}
+
+// Discard is an io.Writer on which all Write calls succeed
+// without doing anything.
+var Discard io.Writer = devNull(0)

src/pkg/mime/multipart/multipart.go

@@ -16,6 +16,7 @@ import (
 	"bufio"
 	"bytes"
 	"io"
+	"io/ioutil"
 	"mime"
 	"net/textproto"
 	"os"
@@ -76,14 +77,6 @@ func NewReader(reader io.Reader, boundary string) Reader {
 
 // Implementation ....
 
-type devNullWriter bool
-
-func (*devNullWriter) Write(p []byte) (n int, err os.Error) {
-	return len(p), nil
-}
-
-var devNull = devNullWriter(false)
-
 func newPart(mr *multiReader) (bp *Part, err os.Error) {
 	bp = new(Part)
 	bp.Header = make(map[string][]string)
@@ -158,7 +151,7 @@ func (bp *Part) Read(p []byte) (n int, err os.Error) {
 }
 
 func (bp *Part) Close() os.Error {
-	io.Copy(&devNull, bp)
+	io.Copy(ioutil.Discard, bp)
 	return nil
 }