strings, bytes: fix Reader 0 byte read at EOF

0 byte reads at EOF weren't returning EOF.

Change-Id: I19b5fd5a72e83d49566a230ce4067be03f00d14b
Reviewed-on: https://go-review.googlesource.com/22740Reviewed-by: Bryan Mills <bcmills@google.com>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/bytes/reader.go

@@ -36,9 +36,6 @@ func (r *Reader) Len() int {
 func (r *Reader) Size() int64 { return int64(len(r.s)) }
 
 func (r *Reader) Read(b []byte) (n int, err error) {
-	if len(b) == 0 {
-		return 0, nil
-	}
 	if r.i >= int64(len(r.s)) {
 		return 0, io.EOF
 	}

src/bytes/reader_test.go

@@ -21,14 +21,15 @@ func TestReader(t *testing.T) {
 		n       int
 		want    string
 		wantpos int64
+		readerr error
 		seekerr string
 	}{
 		{seek: io.SeekStart, off: 0, n: 20, want: "0123456789"},
 		{seek: io.SeekStart, off: 1, n: 1, want: "1"},
 		{seek: io.SeekCurrent, off: 1, wantpos: 3, n: 2, want: "34"},
 		{seek: io.SeekStart, off: -1, seekerr: "bytes.Reader.Seek: negative position"},
-		{seek: io.SeekStart, off: 1 << 33, wantpos: 1 << 33},
-		{seek: io.SeekCurrent, off: 1, wantpos: 1<<33 + 1},
+		{seek: io.SeekStart, off: 1 << 33, wantpos: 1 << 33, readerr: io.EOF},
+		{seek: io.SeekCurrent, off: 1, wantpos: 1<<33 + 1, readerr: io.EOF},
 		{seek: io.SeekStart, n: 5, want: "01234"},
 		{seek: io.SeekCurrent, n: 5, want: "56789"},
 		{seek: io.SeekEnd, off: -1, n: 1, wantpos: 9, want: "9"},
@@ -49,8 +50,8 @@ func TestReader(t *testing.T) {
 		}
 		buf := make([]byte, tt.n)
 		n, err := r.Read(buf)
-		if err != nil {
-			t.Errorf("%d. read = %v", i, err)
+		if err != tt.readerr {
+			t.Errorf("%d. read = %v; want %v", i, err, tt.readerr)
 			continue
 		}
 		got := string(buf[:n])
@@ -173,7 +174,7 @@ func TestReaderLen(t *testing.T) {
 		t.Errorf("r.Len(): got %d, want %d", got, want)
 	}
 	if n, err := r.Read(make([]byte, 1)); err != nil || n != 1 {
-		t.Errorf("Read failed: read %d %v", n, err)
+		t.Errorf("Read failed: read %d %v; want 1, nil", n, err)
 	}
 	if got, want := r.Len(), 0; got != want {
 		t.Errorf("r.Len(): got %d, want %d", got, want)

src/strings/reader.go

@@ -35,9 +35,6 @@ func (r *Reader) Len() int {
 func (r *Reader) Size() int64 { return int64(len(r.s)) }
 
 func (r *Reader) Read(b []byte) (n int, err error) {
-	if len(b) == 0 {
-		return 0, nil
-	}
 	if r.i >= int64(len(r.s)) {
 		return 0, io.EOF
 	}

src/strings/reader_test.go

@@ -22,14 +22,15 @@ func TestReader(t *testing.T) {
 		n       int
 		want    string
 		wantpos int64
+		readerr error
 		seekerr string
 	}{
 		{seek: io.SeekStart, off: 0, n: 20, want: "0123456789"},
 		{seek: io.SeekStart, off: 1, n: 1, want: "1"},
 		{seek: io.SeekCurrent, off: 1, wantpos: 3, n: 2, want: "34"},
 		{seek: io.SeekStart, off: -1, seekerr: "strings.Reader.Seek: negative position"},
-		{seek: io.SeekStart, off: 1 << 33, wantpos: 1 << 33},
-		{seek: io.SeekCurrent, off: 1, wantpos: 1<<33 + 1},
+		{seek: io.SeekStart, off: 1 << 33, wantpos: 1 << 33, readerr: io.EOF},
+		{seek: io.SeekCurrent, off: 1, wantpos: 1<<33 + 1, readerr: io.EOF},
 		{seek: io.SeekStart, n: 5, want: "01234"},
 		{seek: io.SeekCurrent, n: 5, want: "56789"},
 		{seek: io.SeekEnd, off: -1, n: 1, wantpos: 9, want: "9"},
@@ -50,8 +51,8 @@ func TestReader(t *testing.T) {
 		}
 		buf := make([]byte, tt.n)
 		n, err := r.Read(buf)
-		if err != nil {
-			t.Errorf("%d. read = %v", i, err)
+		if err != tt.readerr {
+			t.Errorf("%d. read = %v; want %v", i, err, tt.readerr)
 			continue
 		}
 		got := string(buf[:n])