bytes,strings: make *Reader implement io.ReaderAt

R=golang-dev, adg, bradfitz, r
CC=golang-dev
https://golang.org/cl/5675053

src/pkg/archive/zip/reader_test.go

@@ -278,7 +278,7 @@ func TestInvalidFiles(t *testing.T) {
 	b := make([]byte, size)
 
 	// zeroes
-	_, err := NewReader(sliceReaderAt(b), size)
+	_, err := NewReader(bytes.NewReader(b), size)
 	if err != ErrFormat {
 		t.Errorf("zeroes: error=%v, want %v", err, ErrFormat)
 	}
@@ -289,15 +289,8 @@ func TestInvalidFiles(t *testing.T) {
 	for i := 0; i < size-4; i += 4 {
 		copy(b[i:i+4], sig)
 	}
-	_, err = NewReader(sliceReaderAt(b), size)
+	_, err = NewReader(bytes.NewReader(b), size)
 	if err != ErrFormat {
 		t.Errorf("sigs: error=%v, want %v", err, ErrFormat)
 	}
 }
-
-type sliceReaderAt []byte
-
-func (r sliceReaderAt) ReadAt(b []byte, off int64) (int, error) {
-	copy(b, r[int(off):int(off)+len(b)])
-	return len(b), nil
-}

src/pkg/archive/zip/writer_test.go

@@ -77,7 +77,7 @@ func TestWriter(t *testing.T) {
 	}
 
 	// read it back
-	r, err := NewReader(sliceReaderAt(buf.Bytes()), int64(buf.Len()))
+	r, err := NewReader(bytes.NewReader(buf.Bytes()), int64(buf.Len()))
 	if err != nil {
 		t.Fatal(err)
 	}

src/pkg/archive/zip/zip_test.go

@@ -9,22 +9,12 @@ package zip
 import (
 	"bytes"
 	"fmt"
-	"io"
 	"reflect"
+	"strings"
 	"testing"
 	"time"
 )
 
-type stringReaderAt string
-
-func (s stringReaderAt) ReadAt(p []byte, off int64) (n int, err error) {
-	if off >= int64(len(s)) {
-		return 0, io.EOF
-	}
-	n = copy(p, s[off:])
-	return
-}
-
 func TestOver65kFiles(t *testing.T) {
 	if testing.Short() {
 		t.Logf("slow test; skipping")
@@ -42,8 +32,8 @@ func TestOver65kFiles(t *testing.T) {
 	if err := w.Close(); err != nil {
 		t.Fatalf("Writer.Close: %v", err)
 	}
-	rat := stringReaderAt(buf.String())
-	zr, err := NewReader(rat, int64(len(rat)))
+	s := buf.String()
+	zr, err := NewReader(strings.NewReader(s), int64(len(s)))
 	if err != nil {
 		t.Fatalf("NewReader: %v", err)
 	}

src/pkg/bytes/reader.go

@@ -10,8 +10,9 @@ import (
 	"unicode/utf8"
 )
 
-// A Reader implements the io.Reader, io.Seeker, io.ByteScanner, and
-// io.RuneScanner interfaces by reading from a byte slice.
+// A Reader implements the io.Reader, io.ReaderAt, io.Seeker,
+// io.ByteScanner, and io.RuneScanner interfaces by reading from
+// a byte slice.
 // Unlike a Buffer, a Reader is read-only and supports seeking.
 type Reader struct {
 	s        []byte
@@ -41,6 +42,20 @@ func (r *Reader) Read(b []byte) (n int, err error) {
 	return
 }
 
+func (r *Reader) ReadAt(b []byte, off int64) (n int, err error) {
+	if off < 0 {
+		return 0, errors.New("bytes: invalid offset")
+	}
+	if off >= int64(len(r.s)) {
+		return 0, io.EOF
+	}
+	n = copy(b, r.s[int(off):])
+	if n < len(b) {
+		err = io.EOF
+	}
+	return
+}
+
 func (r *Reader) ReadByte() (b byte, err error) {
 	if r.i >= len(r.s) {
 		return 0, io.EOF

src/pkg/bytes/reader_test.go

@@ -6,6 +6,8 @@ package bytes_test
 
 import (
 	. "bytes"
+	"fmt"
+	"io"
 	"os"
 	"testing"
 )
@@ -56,3 +58,31 @@ func TestReader(t *testing.T) {
 		}
 	}
 }
+
+func TestReaderAt(t *testing.T) {
+	r := NewReader([]byte("0123456789"))
+	tests := []struct {
+		off     int64
+		n       int
+		want    string
+		wanterr interface{}
+	}{
+		{0, 10, "0123456789", nil},
+		{1, 10, "123456789", io.EOF},
+		{1, 9, "123456789", nil},
+		{11, 10, "", io.EOF},
+		{0, 0, "", nil},
+		{-1, 0, "", "bytes: invalid offset"},
+	}
+	for i, tt := range tests {
+		b := make([]byte, tt.n)
+		rn, err := r.ReadAt(b, tt.off)
+		got := string(b[:rn])
+		if got != tt.want {
+			t.Errorf("%d. got %q; want %q", i, got, tt.want)
+		}
+		if fmt.Sprintf("%v", err) != fmt.Sprintf("%v", tt.wanterr) {
+			t.Errorf("%d. got error = %v; want %v", i, err, tt.wanterr)
+		}
+	}
+}

src/pkg/mime/multipart/formdata.go

@@ -130,7 +130,7 @@ type FileHeader struct {
 // Open opens and returns the FileHeader's associated File.
 func (fh *FileHeader) Open() (File, error) {
 	if b := fh.content; b != nil {
-		r := io.NewSectionReader(sliceReaderAt(b), 0, int64(len(b)))
+		r := io.NewSectionReader(bytes.NewReader(b), 0, int64(len(b)))
 		return sectionReadCloser{r}, nil
 	}
 	return os.Open(fh.tmpfile)
@@ -155,13 +155,3 @@ type sectionReadCloser struct {
 func (rc sectionReadCloser) Close() error {
 	return nil
 }
-
-type sliceReaderAt []byte
-
-func (r sliceReaderAt) ReadAt(b []byte, off int64) (int, error) {
-	if int(off) >= len(r) || off < 0 {
-		return 0, io.ErrUnexpectedEOF
-	}
-	n := copy(b, r[int(off):])
-	return n, nil
-}

src/pkg/strings/reader.go

@@ -10,8 +10,9 @@ import (
 	"unicode/utf8"
 )
 
-// A Reader implements the io.Reader, io.Seeker, io.ByteScanner, and
-// io.RuneScanner interfaces by reading from a string.
+// A Reader implements the io.Reader, io.ReaderAt, io.Seeker,
+// io.ByteScanner, and io.RuneScanner interfaces by reading
+// from a string.
 type Reader struct {
 	s        string
 	i        int // current reading index
@@ -40,6 +41,20 @@ func (r *Reader) Read(b []byte) (n int, err error) {
 	return
 }
 
+func (r *Reader) ReadAt(b []byte, off int64) (n int, err error) {
+	if off < 0 {
+		return 0, errors.New("strings: invalid offset")
+	}
+	if off >= int64(len(r.s)) {
+		return 0, io.EOF
+	}
+	n = copy(b, r.s[int(off):])
+	if n < len(b) {
+		err = io.EOF
+	}
+	return
+}
+
 func (r *Reader) ReadByte() (b byte, err error) {
 	if r.i >= len(r.s) {
 		return 0, io.EOF

src/pkg/strings/reader_test.go

@@ -5,6 +5,8 @@
 package strings_test
 
 import (
+	"fmt"
+	"io"
 	"os"
 	"strings"
 	"testing"
@@ -56,3 +58,31 @@ func TestReader(t *testing.T) {
 		}
 	}
 }
+
+func TestReaderAt(t *testing.T) {
+	r := strings.NewReader("0123456789")
+	tests := []struct {
+		off     int64
+		n       int
+		want    string
+		wanterr interface{}
+	}{
+		{0, 10, "0123456789", nil},
+		{1, 10, "123456789", io.EOF},
+		{1, 9, "123456789", nil},
+		{11, 10, "", io.EOF},
+		{0, 0, "", nil},
+		{-1, 0, "", "strings: invalid offset"},
+	}
+	for i, tt := range tests {
+		b := make([]byte, tt.n)
+		rn, err := r.ReadAt(b, tt.off)
+		got := string(b[:rn])
+		if got != tt.want {
+			t.Errorf("%d. got %q; want %q", i, got, tt.want)
+		}
+		if fmt.Sprintf("%v", err) != fmt.Sprintf("%v", tt.wanterr) {
+			t.Errorf("%d. got error = %v; want %v", i, err, tt.wanterr)
+		}
+	}
+}