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https://github.com/golang/go
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bufio: introduce Peek.
I'll leave whether or not this obsoletes UnreadByte for a future CL. R=r, rsc CC=golang-dev https://golang.org/cl/1912042
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@ -28,6 +28,7 @@ type Error struct {
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var (
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ErrInvalidUnreadByte os.Error = &Error{"bufio: invalid use of UnreadByte"}
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ErrBufferFull os.Error = &Error{"bufio: buffer full"}
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ErrNegativeCount os.Error = &Error{"bufio: negative count"}
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errInternal os.Error = &Error{"bufio: internal error"}
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)
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@ -83,13 +84,11 @@ func NewReader(rd io.Reader) *Reader {
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// fill reads a new chunk into the buffer.
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func (b *Reader) fill() {
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// Slide existing data to beginning.
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if b.w > b.r {
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copy(b.buf[0:b.w-b.r], b.buf[b.r:b.w])
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if b.r > 0 {
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copy(b.buf, b.buf[b.r:b.w])
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b.w -= b.r
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} else {
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b.w = 0
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b.r = 0
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}
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b.r = 0
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// Read new data.
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n, e := b.rd.Read(b.buf[b.w:])
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@ -99,6 +98,31 @@ func (b *Reader) fill() {
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}
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}
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// Peek returns the next n bytes without advancing the reader. The bytes stop
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// being valid at the next read call. If Peek returns fewer than n bytes, it
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// also returns an error explaining why the read is short. The error is
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// ErrBufferFull if n is larger than b's buffer size.
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func (b *Reader) Peek(n int) ([]byte, os.Error) {
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if n < 0 {
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return nil, ErrNegativeCount
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}
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if n > len(b.buf) {
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return nil, ErrBufferFull
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}
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for b.w-b.r < n && b.err == nil {
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b.fill()
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}
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m := b.w - b.r
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if m > n {
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m = n
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}
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err := b.err
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if m < n && err == nil {
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err = ErrBufferFull
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}
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return b.buf[b.r : b.r+m], err
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}
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// Read reads data into p.
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// It returns the number of bytes read into p.
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// If nn < len(p), also returns an error explaining
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@ -129,7 +153,7 @@ func (b *Reader) Read(p []byte) (nn int, err os.Error) {
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if n > b.w-b.r {
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n = b.w - b.r
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}
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copy(p[0:n], b.buf[b.r:b.r+n])
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copy(p[0:n], b.buf[b.r:])
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p = p[n:]
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b.r += n
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b.lastbyte = int(b.buf[b.r-1])
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@ -291,10 +315,10 @@ func (b *Reader) ReadBytes(delim byte) (line []byte, err os.Error) {
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buf := make([]byte, n)
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n = 0
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for i := 0; i < nfull; i++ {
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copy(buf[n:n+len(full[i])], full[i])
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copy(buf[n:], full[i])
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n += len(full[i])
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}
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copy(buf[n:n+len(frag)], frag)
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copy(buf[n:], frag)
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return buf, err
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}
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@ -419,3 +419,41 @@ func TestBufferFull(t *testing.T) {
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t.Errorf("second ReadSlice(,) = %q, %v", line, err)
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}
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}
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func TestPeek(t *testing.T) {
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p := make([]byte, 10)
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buf, _ := NewReaderSize(strings.NewReader("abcdefghij"), 4)
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if s, err := buf.Peek(1); string(s) != "a" || err != nil {
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t.Fatalf("want %q got %q, err=%v", "a", string(s), err)
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}
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if s, err := buf.Peek(4); string(s) != "abcd" || err != nil {
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t.Fatalf("want %q got %q, err=%v", "abcd", string(s), err)
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}
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if _, err := buf.Peek(5); err != ErrBufferFull {
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t.Fatalf("want ErrBufFull got %v", err)
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}
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if _, err := buf.Read(p[0:3]); string(p[0:3]) != "abc" || err != nil {
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t.Fatalf("want %q got %q, err=%v", "abc", string(p[0:3]), err)
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}
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if s, err := buf.Peek(1); string(s) != "d" || err != nil {
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t.Fatalf("want %q got %q, err=%v", "d", string(s), err)
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}
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if s, err := buf.Peek(2); string(s) != "de" || err != nil {
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t.Fatalf("want %q got %q, err=%v", "de", string(s), err)
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}
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if _, err := buf.Read(p[0:3]); string(p[0:3]) != "def" || err != nil {
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t.Fatalf("want %q got %q, err=%v", "def", string(p[0:3]), err)
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}
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if s, err := buf.Peek(4); string(s) != "ghij" || err != nil {
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t.Fatalf("want %q got %q, err=%v", "ghij", string(s), err)
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}
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if _, err := buf.Read(p[0:4]); string(p[0:4]) != "ghij" || err != nil {
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t.Fatalf("want %q got %q, err=%v", "ghij", string(p[0:3]), err)
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}
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if s, err := buf.Peek(0); string(s) != "" || err != nil {
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t.Fatalf("want %q got %q, err=%v", "", string(s), err)
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}
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if _, err := buf.Peek(1); err != os.EOF {
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t.Fatalf("want EOF got %v", err)
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}
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}
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