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reader.go
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reader.go
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package encoding
import (
"io"
"golang.org/x/text/encoding"
"golang.org/x/text/transform"
"github.com/elastic/beats/libbeat/common/streambuf"
)
// lineReader reads lines from underlying reader, decoding the input stream
// using the configured codec. The reader keeps track of bytes consumed
// from raw input stream for every decoded line.
type LineReader struct {
rawInput io.Reader
codec encoding.Encoding
bufferSize int
nl []byte
inBuffer *streambuf.Buffer
outBuffer *streambuf.Buffer
inOffset int // input buffer read offset
byteCount int // number of bytes decoded from input buffer into output buffer
decoder transform.Transformer
}
func NewLineReader(
input io.Reader,
codec encoding.Encoding,
bufferSize int,
) (*LineReader, error) {
l := &LineReader{}
if err := l.init(input, codec, bufferSize); err != nil {
return nil, err
}
return l, nil
}
func (l *LineReader) init(
input io.Reader,
codec encoding.Encoding,
bufferSize int,
) error {
l.rawInput = input
l.codec = codec
l.bufferSize = bufferSize
l.codec.NewEncoder()
nl, _, err := transform.Bytes(l.codec.NewEncoder(), []byte{'\n'})
if err != nil {
return err
}
l.nl = nl
l.decoder = l.codec.NewDecoder()
l.inBuffer = streambuf.New(nil)
l.outBuffer = streambuf.New(nil)
return nil
}
func (l *LineReader) Next() ([]byte, int, error) {
for {
// read next 'potential' line from input buffer/reader
err := l.advance()
if err != nil {
return nil, 0, err
}
// check last decoded byte really being '\n'
buf := l.outBuffer.Bytes()
if buf[len(buf)-1] == '\n' {
break
}
}
// output buffer contains complete line ending with '\n'. Extract
// byte slice from buffer and reset output buffer.
bytes, err := l.outBuffer.Collect(l.outBuffer.Len())
l.outBuffer.Reset()
if err != nil {
// This should never happen as otherwise we have a broken state
panic(err)
}
// return and reset consumed bytes count
sz := l.byteCount
l.byteCount = 0
return bytes, sz, nil
}
func (l *LineReader) advance() error {
var idx int
var err error
// fill inBuffer until '\n' sequence has been found in input buffer
for {
idx = l.inBuffer.IndexFrom(l.inOffset, l.nl)
if idx >= 0 {
break
}
if err != nil {
// if no newline and last read returned error, return error now
return err
}
// increase search offset to reduce iterations on buffer when looping
newOffset := l.inBuffer.Len() - len(l.nl)
if newOffset > l.inOffset {
l.inOffset = newOffset
}
// try to read more bytes into buffer
n := 0
buf := make([]byte, l.bufferSize)
n, err := l.rawInput.Read(buf)
l.inBuffer.Append(buf[:n])
if n == 0 && err != nil {
// return error only if no bytes have been received. Otherwise try to
// parse '\n' before returning the error.
return err
}
// empty read => return buffer error (more bytes required error)
if n == 0 {
return streambuf.ErrNoMoreBytes
}
}
// found encoded byte sequence for '\n' in buffer
// -> decode input sequence into outBuffer
sz, err := l.decode(idx + len(l.nl))
// consume transformed bytes from input buffer
err = l.inBuffer.Advance(sz)
l.inBuffer.Reset()
l.inOffset = idx + 1 - sz // continue scanning input buffer from last position + 1
if l.inOffset < 0 {
// fix inOffset if '\n' has encoding > 8bits + fill line has been decoded
l.inOffset = 0
}
return err
}
func (l *LineReader) decode(end int) (int, error) {
var err error
buffer := make([]byte, 1024)
inBytes := l.inBuffer.Bytes()
start := 0
for start < end {
var nDst, nSrc int
nDst, nSrc, err = l.decoder.Transform(buffer, inBytes[start:end], false)
start += nSrc
l.outBuffer.Write(buffer[:nDst])
if err != nil {
if err == transform.ErrShortDst { // continue transforming
continue
}
break
}
}
l.byteCount += start
return start, err
}