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bytes: clarify documentation for UnreadByte/Rune

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Fixes #19522.

Change-Id: Ib3cf0336e0bf91580d533704ec1a9d45eb0bf62d
Reviewed-on: https://go-review.googlesource.com/42020
Reviewed-by: Rob Pike <r@golang.org>
This commit is contained in:
Robert Griesemer 2017-04-27 16:55:47 -07:00
parent 85d6a29ae6
commit 86cfe93515
2 changed files with 45 additions and 12 deletions
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13
src/bytes/buffer.go
View File

@ -346,12 +346,12 @@ func (b *Buffer) ReadRune() (r rune, size int, err error) {
// UnreadRune unreads the last rune returned by ReadRune.
// If the most recent read or write operation on the buffer was
// not a ReadRune, UnreadRune returns an error. (In this regard
// not a successful ReadRune, UnreadRune returns an error. (In this regard
// it is stricter than UnreadByte, which will unread the last byte
// from any read operation.)
func (b *Buffer) UnreadRune() error {
if b.lastRead <= opInvalid {
return errors.New("bytes.Buffer: UnreadRune: previous operation was not ReadRune")
return errors.New("bytes.Buffer: UnreadRune: previous operation was not a successful ReadRune")
}
if b.off >= int(b.lastRead) {
b.off -= int(b.lastRead)
@ -360,12 +360,13 @@ func (b *Buffer) UnreadRune() error {
return nil
}
// UnreadByte unreads the last byte returned by the most recent
// read operation. If write has happened since the last read, UnreadByte
// returns an error.
// UnreadByte unreads the last byte returned by the most recent successful
// read operation that read at least one byte. If a write has happened since
// the last read, if the last read returned an error, or if the read read zero
// bytes, UnreadByte returns an error.
func (b *Buffer) UnreadByte() error {
if b.lastRead == opInvalid {
return errors.New("bytes.Buffer: UnreadByte: previous operation was not a read")
return errors.New("bytes.Buffer: UnreadByte: previous operation was not a successful read")
}
b.lastRead = opInvalid
if b.off > 0 {

44
src/bytes/buffer_test.go
View File

@ -311,6 +311,19 @@ func TestRuneIO(t *testing.T) {
// Check that UnreadRune works
buf.Reset()
// check at EOF
if err := buf.UnreadRune(); err == nil {
t.Fatal("UnreadRune at EOF: got no error")
}
if _, _, err := buf.ReadRune(); err == nil {
t.Fatal("ReadRune at EOF: got no error")
}
if err := buf.UnreadRune(); err == nil {
t.Fatal("UnreadRune after ReadRune at EOF: got no error")
}
// check not at EOF
buf.Write(b)
for r := rune(0); r < NRune; r++ {
r1, size, _ := buf.ReadRune()
@ -473,15 +486,34 @@ func TestReadEmptyAtEOF(t *testing.T) {
func TestUnreadByte(t *testing.T) {
b := new(Buffer)
b.WriteString("abcdefghijklmnopqrstuvwxyz")
_, err := b.ReadBytes('m')
if err != nil {
t.Fatalf("ReadBytes: %v", err)
// check at EOF
if err := b.UnreadByte(); err == nil {
t.Fatal("UnreadByte at EOF: got no error")
}
if _, err := b.ReadByte(); err == nil {
t.Fatal("ReadByte at EOF: got no error")
}
if err := b.UnreadByte(); err == nil {
t.Fatal("UnreadByte after ReadByte at EOF: got no error")
}
err = b.UnreadByte()
if err != nil {
// check not at EOF
b.WriteString("abcdefghijklmnopqrstuvwxyz")
// after unsuccessful read
if n, err := b.Read(nil); n != 0 || err != nil {
t.Fatalf("Read(nil) = %d,%v; want 0,nil", n, err)
}
if err := b.UnreadByte(); err == nil {
t.Fatal("UnreadByte after Read(nil): got no error")
}
// after successful read
if _, err := b.ReadBytes('m'); err != nil {
t.Fatalf("ReadBytes: %v", err)
}
if err := b.UnreadByte(); err != nil {
t.Fatalf("UnreadByte: %v", err)
}
c, err := b.ReadByte()