1 files changed, 46 insertions, 13 deletions

diff --git a/libgo/go/strings/reader.go b/libgo/go/strings/reader.go
index 8ff851f36a8..8569805552d 100644
--- a/libgo/go/strings/reader.go
+++ b/libgo/go/strings/reader.go
@@ -10,8 +10,9 @@ import (
 	"unicode/utf8"
 )
 
-// A Reader implements the io.Reader, 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
@@ -21,10 +22,16 @@ type Reader struct {
 // Len returns the number of bytes of the unread portion of the
 // string.
 func (r *Reader) Len() int {
+	if r.i >= len(r.s) {
+		return 0
+	}
 	return len(r.s) - r.i
 }
 
 func (r *Reader) Read(b []byte) (n int, err error) {
+	if len(b) == 0 {
+		return 0, nil
+	}
 	if r.i >= len(r.s) {
 		return 0, io.EOF
 	}
@@ -34,6 +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
@@ -44,9 +65,6 @@ func (r *Reader) ReadByte() (b byte, err error) {
 	return
 }
 
-// UnreadByte moves the reading position back by one byte.
-// It is an error to call UnreadByte if nothing has been
-// read yet.
 func (r *Reader) UnreadByte() error {
 	if r.i <= 0 {
 		return errors.New("strings.Reader: at beginning of string")
@@ -56,11 +74,6 @@ func (r *Reader) UnreadByte() error {
 	return nil
 }
 
-// ReadRune reads and returns the next UTF-8-encoded
-// Unicode code point from the buffer.
-// If no bytes are available, the error returned is io.EOF.
-// If the bytes are an erroneous UTF-8 encoding, it
-// consumes one byte and returns U+FFFD, 1.
 func (r *Reader) ReadRune() (ch rune, size int, err error) {
 	if r.i >= len(r.s) {
 		return 0, 0, io.EOF
@@ -75,9 +88,6 @@ func (r *Reader) ReadRune() (ch rune, size int, err error) {
 	return
 }
 
-// UnreadRune causes the next call to ReadRune to return the same rune
-// as the previous call to ReadRune.
-// The last method called on r must have been ReadRune.
 func (r *Reader) UnreadRune() error {
 	if r.prevRune < 0 {
 		return errors.New("strings.Reader: previous operation was not ReadRune")
@@ -87,6 +97,29 @@ func (r *Reader) UnreadRune() error {
 	return nil
 }
 
+// Seek implements the io.Seeker interface.
+func (r *Reader) Seek(offset int64, whence int) (int64, error) {
+	var abs int64
+	switch whence {
+	case 0:
+		abs = offset
+	case 1:
+		abs = int64(r.i) + offset
+	case 2:
+		abs = int64(len(r.s)) + offset
+	default:
+		return 0, errors.New("strings: invalid whence")
+	}
+	if abs < 0 {
+		return 0, errors.New("strings: negative position")
+	}
+	if abs >= 1<<31 {
+		return 0, errors.New("strings: position out of range")
+	}
+	r.i = int(abs)
+	return abs, nil
+}
+
 // NewReader returns a new Reader reading from s.
 // It is similar to bytes.NewBufferString but more efficient and read-only.
 func NewReader(s string) *Reader { return &Reader{s, 0, -1} }