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package rfc5322
import (
"bytes"
"io"
)
type BacktrackingByteScanner struct {
data []byte
offset int
}
func NewBacktrackingByteScanner(data []byte) *BacktrackingByteScanner {
return &BacktrackingByteScanner{
data: data,
}
}
type BacktrackingByteScannerScope struct {
offset int
}
func (bs *BacktrackingByteScanner) Read(dst []byte) (int, error) {
thisLen := len(bs.data)
if bs.offset >= thisLen {
return 0, io.EOF
}
dstLen := len(dst)
if bs.offset+dstLen >= thisLen {
bytesRead := thisLen - bs.offset
copy(dst, bs.data[bs.offset:])
return bytesRead, nil
}
nextOffset := bs.offset + dstLen
copy(dst, bs.data[bs.offset:nextOffset])
bs.offset = nextOffset
return dstLen, nil
}
func (bs *BacktrackingByteScanner) ReadByte() (byte, error) {
if bs.offset >= len(bs.data) {
return 0, io.EOF
}
b := bs.data[bs.offset]
bs.offset++
return b, nil
}
func (bs *BacktrackingByteScanner) ReadBytes(delim byte) ([]byte, error) {
if bs.offset >= len(bs.data) {
return nil, io.EOF
}
var result []byte
index := bytes.IndexByte(bs.data[bs.offset:], delim)
if index < 0 {
copy(result, bs.data[bs.offset:])
bs.offset = len(bs.data)
return result, nil
}
nextOffset := bs.offset + index + 1
if nextOffset >= len(bs.data) {
copy(result, bs.data[bs.offset:])
bs.offset = len(bs.data)
} else {
copy(result, bs.data[bs.offset:nextOffset])
bs.offset = nextOffset
}
return result, nil
}
func (bs *BacktrackingByteScanner) SaveState() BacktrackingByteScannerScope {
return BacktrackingByteScannerScope{offset: bs.offset}
}
func (bs *BacktrackingByteScanner) RestoreState(scope BacktrackingByteScannerScope) {
bs.offset = scope.offset
}
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