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Code Releases Activity

bufio: introduce Peek.

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I'll leave whether or not this obsoletes UnreadByte for a future CL.

R=r, rsc
CC=golang-dev
https://golang.org/cl/1912042
This commit is contained in:
Nigel Tao 2010-08-04 09:44:02 +10:00
parent e45b58fe96
commit 27e249049e
2 changed files with 70 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

40
src/pkg/bufio/bufio.go
View File

@ -28,6 +28,7 @@ type Error struct {
var (
ErrInvalidUnreadByte os.Error = &Error{"bufio: invalid use of UnreadByte"}
ErrBufferFull os.Error = &Error{"bufio: buffer full"}
ErrNegativeCount os.Error = &Error{"bufio: negative count"}
errInternal os.Error = &Error{"bufio: internal error"}
)
@ -83,13 +84,11 @@ func NewReader(rd io.Reader) *Reader {
// fill reads a new chunk into the buffer.
func (b *Reader) fill() {
// Slide existing data to beginning.
if b.w > b.r {
copy(b.buf[0:b.w-b.r], b.buf[b.r:b.w])
if b.r > 0 {
copy(b.buf, b.buf[b.r:b.w])
b.w -= b.r
} else {
b.w = 0
b.r = 0
}
b.r = 0
// Read new data.
n, e := b.rd.Read(b.buf[b.w:])
@ -99,6 +98,31 @@ func (b *Reader) fill() {
}
}
// Peek returns the next n bytes without advancing the reader. The bytes stop
// being valid at the next read call. If Peek returns fewer than n bytes, it
// also returns an error explaining why the read is short. The error is
// ErrBufferFull if n is larger than b's buffer size.
func (b *Reader) Peek(n int) ([]byte, os.Error) {
if n < 0 {
return nil, ErrNegativeCount
}
if n > len(b.buf) {
return nil, ErrBufferFull
}
for b.w-b.r < n && b.err == nil {
b.fill()
}
m := b.w - b.r
if m > n {
m = n
}
err := b.err
if m < n && err == nil {
err = ErrBufferFull
}
return b.buf[b.r : b.r+m], err
}
// Read reads data into p.
// It returns the number of bytes read into p.
// If nn < len(p), also returns an error explaining
@ -129,7 +153,7 @@ func (b *Reader) Read(p []byte) (nn int, err os.Error) {
if n > b.w-b.r {
n = b.w - b.r
}
copy(p[0:n], b.buf[b.r:b.r+n])
copy(p[0:n], b.buf[b.r:])
p = p[n:]
b.r += n
b.lastbyte = int(b.buf[b.r-1])
@ -291,10 +315,10 @@ func (b *Reader) ReadBytes(delim byte) (line []byte, err os.Error) {
buf := make([]byte, n)
n = 0
for i := 0; i < nfull; i++ {
copy(buf[n:n+len(full[i])], full[i])
copy(buf[n:], full[i])
n += len(full[i])
}
copy(buf[n:n+len(frag)], frag)
copy(buf[n:], frag)
return buf, err
}

38
src/pkg/bufio/bufio_test.go
View File

@ -419,3 +419,41 @@ func TestBufferFull(t *testing.T) {
t.Errorf("second ReadSlice(,) = %q, %v", line, err)
}
}
func TestPeek(t *testing.T) {
p := make([]byte, 10)
buf, _ := NewReaderSize(strings.NewReader("abcdefghij"), 4)
if s, err := buf.Peek(1); string(s) != "a" || err != nil {
t.Fatalf("want %q got %q, err=%v", "a", string(s), err)
}
if s, err := buf.Peek(4); string(s) != "abcd" || err != nil {
t.Fatalf("want %q got %q, err=%v", "abcd", string(s), err)
}
if _, err := buf.Peek(5); err != ErrBufferFull {
t.Fatalf("want ErrBufFull got %v", err)
}
if _, err := buf.Read(p[0:3]); string(p[0:3]) != "abc" || err != nil {
t.Fatalf("want %q got %q, err=%v", "abc", string(p[0:3]), err)
}
if s, err := buf.Peek(1); string(s) != "d" || err != nil {
t.Fatalf("want %q got %q, err=%v", "d", string(s), err)
}
if s, err := buf.Peek(2); string(s) != "de" || err != nil {
t.Fatalf("want %q got %q, err=%v", "de", string(s), err)
}
if _, err := buf.Read(p[0:3]); string(p[0:3]) != "def" || err != nil {
t.Fatalf("want %q got %q, err=%v", "def", string(p[0:3]), err)
}
if s, err := buf.Peek(4); string(s) != "ghij" || err != nil {
t.Fatalf("want %q got %q, err=%v", "ghij", string(s), err)
}
if _, err := buf.Read(p[0:4]); string(p[0:4]) != "ghij" || err != nil {
t.Fatalf("want %q got %q, err=%v", "ghij", string(p[0:3]), err)
}
if s, err := buf.Peek(0); string(s) != "" || err != nil {
t.Fatalf("want %q got %q, err=%v", "", string(s), err)
}
if _, err := buf.Peek(1); err != os.EOF {
t.Fatalf("want EOF got %v", err)
}
}