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// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// The line package implements a Reader that reads lines delimited by '\n' or ' \r\n'.
package line
import (
"io"
"os"
)
// Reader reads lines, delimited by '\n' or \r\n', from an io.Reader.
type Reader struct {
buf []byte
consumed int
in io.Reader
err os.Error
}
// NewReader returns a new Reader that will read successive
// lines from the input Reader.
func NewReader(input io.Reader, maxLineLength int) *Reader {
return &Reader{
buf: make([]byte, 0, maxLineLength),
consumed: 0,
in: input,
}
}
// Read reads from any buffered data past the last line read, or from the underlying
// io.Reader if the buffer is empty.
func (l *Reader) Read(p []byte) (n int, err os.Error) {
l.removeConsumedFromBuffer()
if len(l.buf) > 0 {
n = copy(p, l.buf)
l.consumed += n
return
}
return l.in.Read(p)
}
func (l *Reader) removeConsumedFromBuffer() {
if l.consumed > 0 {
n := copy(l.buf, l.buf[l.consumed:])
l.buf = l.buf[:n]
l.consumed = 0
}
}
// ReadLine tries to return a single line, not including the end-of-line bytes.
// If the line was found to be longer than the maximum length then isPrefix is
// set and the beginning of the line is returned. The rest of the line will be
// returned from future calls. isPrefix will be false when returning the last
// fragment of the line. The returned buffer points into the internal state of
// the Reader and is only valid until the next call to ReadLine. ReadLine
// either returns a non-nil line or it returns an error, never both.
func (l *Reader) ReadLine() (line []byte, isPrefix bool, err os.Error) {
l.removeConsumedFromBuffer()
if len(l.buf) == 0 && l.err != nil {
err = l.err
return
}
scannedTo := 0
for {
i := scannedTo
for ; i < len(l.buf); i++ {
if l.buf[i] == '\r' && len(l.buf) > i+1 && l.buf[i+1] == '\n' {
line = l.buf[:i]
l.consumed = i + 2
return
} else if l.buf[i] == '\n' {
line = l.buf[:i]
l.consumed = i + 1
return
}
}
if i == cap(l.buf) {
line = l.buf[:i]
l.consumed = i
isPrefix = true
return
}
if l.err != nil {
line = l.buf
l.consumed = i
return
}
// We don't want to rescan the input that we just scanned.
// However, we need to back up one byte because the last byte
// could have been a '\r' and we do need to rescan that.
scannedTo = i
if scannedTo > 0 {
scannedTo--
}
oldLen := len(l.buf)
l.buf = l.buf[:cap(l.buf)]
n, readErr := l.in.Read(l.buf[oldLen:])
l.buf = l.buf[:oldLen+n]
if readErr != nil {
l.err = readErr
if len(l.buf) == 0 {
return nil, false, readErr
}
}
}
panic("unreachable")
}
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