6 files changed, 67 insertions, 29 deletions

diff --git a/src/pkg/io/io.go b/src/pkg/io/io.go
index f7073ffc0..022fdb676 100644
--- a/src/pkg/io/io.go
+++ b/src/pkg/io/io.go
@@ -74,6 +74,7 @@ type Reader interface {
 // It returns the number of bytes written from p (0 <= n <= len(p))
 // and any error encountered that caused the write to stop early.
 // Write must return a non-nil error if it returns n < len(p).
+// Write must not modify the slice data, even temporarily.
 type Writer interface {
 	Write(p []byte) (n int, err error)
 }
diff --git a/src/pkg/io/io_test.go b/src/pkg/io/io_test.go
index bd7a82f17..57db1fbf0 100644
--- a/src/pkg/io/io_test.go
+++ b/src/pkg/io/io_test.go
@@ -281,6 +281,8 @@ func TestSectionReader_ReadAt(t *testing.T) {
 		{data: dat, off: 3, n: len(dat), bufLen: len(dat) / 2, at: 2, exp: dat[5 : 5+len(dat)/2], err: nil},
 		{data: dat, off: 3, n: len(dat) / 2, bufLen: len(dat)/2 - 2, at: 2, exp: dat[5 : 5+len(dat)/2-2], err: nil},
 		{data: dat, off: 3, n: len(dat) / 2, bufLen: len(dat)/2 + 2, at: 2, exp: dat[5 : 5+len(dat)/2-2], err: EOF},
+		{data: dat, off: 0, n: 0, bufLen: 0, at: -1, exp: "", err: EOF},
+		{data: dat, off: 0, n: 0, bufLen: 0, at: 1, exp: "", err: EOF},
 	}
 	for i, tt := range tests {
 		r := strings.NewReader(tt.data)
@@ -319,3 +321,21 @@ func TestSectionReader_Seek(t *testing.T) {
 		t.Errorf("Read = %v, %v; want 0, EOF", n, err)
 	}
 }
+
+func TestSectionReader_Size(t *testing.T) {
+	tests := []struct {
+		data string
+		want int64
+	}{
+		{"a long sample data, 1234567890", 30},
+		{"", 0},
+	}
+
+	for _, tt := range tests {
+		r := strings.NewReader(tt.data)
+		sr := NewSectionReader(r, 0, int64(len(tt.data)))
+		if got := sr.Size(); got != tt.want {
+			t.Errorf("Size = %v; want %v", got, tt.want)
+		}
+	}
+}
diff --git a/src/pkg/io/ioutil/blackhole.go b/src/pkg/io/ioutil/blackhole.go
deleted file mode 100644
index 101d2c121..000000000
--- a/src/pkg/io/ioutil/blackhole.go
+++ /dev/null
@@ -1,23 +0,0 @@
-// Copyright 2012 The Go Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-package ioutil
-
-var blackHoleBuf = make(chan []byte, 1)
-
-func blackHole() []byte {
-	select {
-	case b := <-blackHoleBuf:
-		return b
-	default:
-	}
-	return make([]byte, 8192)
-}
-
-func blackHolePut(p []byte) {
-	select {
-	case blackHoleBuf <- p:
-	default:
-	}
-}
diff --git a/src/pkg/io/ioutil/ioutil.go b/src/pkg/io/ioutil/ioutil.go
index b2508b789..909a81563 100644
--- a/src/pkg/io/ioutil/ioutil.go
+++ b/src/pkg/io/ioutil/ioutil.go
@@ -10,6 +10,7 @@ import (
 	"io"
 	"os"
 	"sort"
+	"sync"
 )
 
 // readAll reads from r until an error or EOF and returns the data it read
@@ -136,14 +137,21 @@ func (devNull) WriteString(s string) (int, error) {
 	return len(s), nil
 }
 
+var blackHolePool = sync.Pool{
+	New: func() interface{} {
+		b := make([]byte, 8192)
+		return &b
+	},
+}
+
 func (devNull) ReadFrom(r io.Reader) (n int64, err error) {
-	buf := blackHole()
-	defer blackHolePut(buf)
+	bufp := blackHolePool.Get().(*[]byte)
 	readSize := 0
 	for {
-		readSize, err = r.Read(buf)
+		readSize, err = r.Read(*bufp)
 		n += int64(readSize)
 		if err != nil {
+			blackHolePool.Put(bufp)
 			if err == io.EOF {
 				return n, nil
 			}
diff --git a/src/pkg/io/multi.go b/src/pkg/io/multi.go
index 2c7e816cf..e26cc53e9 100644
--- a/src/pkg/io/multi.go
+++ b/src/pkg/io/multi.go
@@ -26,9 +26,12 @@ func (mr *multiReader) Read(p []byte) (n int, err error) {
 
 // MultiReader returns a Reader that's the logical concatenation of
 // the provided input readers.  They're read sequentially.  Once all
-// inputs are drained, Read will return EOF.
+// inputs have returned EOF, Read will return EOF.  If any of the readers
+// return a non-nil, non-EOF error, Read will return that error.
 func MultiReader(readers ...Reader) Reader {
-	return &multiReader{readers}
+	r := make([]Reader, len(readers))
+	copy(r, readers)
+	return &multiReader{r}
 }
 
 type multiWriter struct {
@@ -52,5 +55,7 @@ func (t *multiWriter) Write(p []byte) (n int, err error) {
 // MultiWriter creates a writer that duplicates its writes to all the
 // provided writers, similar to the Unix tee(1) command.
 func MultiWriter(writers ...Writer) Writer {
-	return &multiWriter{writers}
+	w := make([]Writer, len(writers))
+	copy(w, writers)
+	return &multiWriter{w}
 }
diff --git a/src/pkg/io/multi_test.go b/src/pkg/io/multi_test.go
index eb717f7bc..56c6769a9 100644
--- a/src/pkg/io/multi_test.go
+++ b/src/pkg/io/multi_test.go
@@ -9,6 +9,7 @@ import (
 	"crypto/sha1"
 	"fmt"
 	. "io"
+	"io/ioutil"
 	"strings"
 	"testing"
 )
@@ -86,3 +87,29 @@ func TestMultiWriter(t *testing.T) {
 		t.Errorf("expected %q; got %q", sourceString, sink.String())
 	}
 }
+
+// Test that MultiReader copies the input slice and is insulated from future modification.
+func TestMultiReaderCopy(t *testing.T) {
+	slice := []Reader{strings.NewReader("hello world")}
+	r := MultiReader(slice...)
+	slice[0] = nil
+	data, err := ioutil.ReadAll(r)
+	if err != nil || string(data) != "hello world" {
+		t.Errorf("ReadAll() = %q, %v, want %q, nil", data, err, "hello world")
+	}
+}
+
+// Test that MultiWriter copies the input slice and is insulated from future modification.
+func TestMultiWriterCopy(t *testing.T) {
+	var buf bytes.Buffer
+	slice := []Writer{&buf}
+	w := MultiWriter(slice...)
+	slice[0] = nil
+	n, err := w.Write([]byte("hello world"))
+	if err != nil || n != 11 {
+		t.Errorf("Write(`hello world`) = %d, %v, want 11, nil", n, err)
+	}
+	if buf.String() != "hello world" {
+		t.Errorf("buf.String() = %q, want %q", buf.String(), "hello world")
+	}
+}