159 lines
3.7 KiB
Go
159 lines
3.7 KiB
Go
package buffer
|
|
|
|
import (
|
|
"io"
|
|
"io/ioutil"
|
|
)
|
|
|
|
var nullBuffer = []byte{0}
|
|
|
|
// Lexer is a buffered reader that allows peeking forward and shifting, taking an io.Reader.
|
|
// It keeps data in-memory until Free, taking a byte length, is called to move beyond the data.
|
|
type Lexer struct {
|
|
buf []byte
|
|
pos int // index in buf
|
|
start int // index in buf
|
|
err error
|
|
|
|
restore func()
|
|
}
|
|
|
|
// NewLexerBytes returns a new Lexer for a given io.Reader, and uses ioutil.ReadAll to read it into a byte slice.
|
|
// If the io.Reader implements Bytes, that is used instead.
|
|
// It will append a NULL at the end of the buffer.
|
|
func NewLexer(r io.Reader) *Lexer {
|
|
var b []byte
|
|
if r != nil {
|
|
if buffer, ok := r.(interface {
|
|
Bytes() []byte
|
|
}); ok {
|
|
b = buffer.Bytes()
|
|
} else {
|
|
var err error
|
|
b, err = ioutil.ReadAll(r)
|
|
if err != nil {
|
|
return &Lexer{
|
|
buf: []byte{0},
|
|
err: err,
|
|
}
|
|
}
|
|
}
|
|
}
|
|
return NewLexerBytes(b)
|
|
}
|
|
|
|
// NewLexerBytes returns a new Lexer for a given byte slice, and appends NULL at the end.
|
|
// To avoid reallocation, make sure the capacity has room for one more byte.
|
|
func NewLexerBytes(b []byte) *Lexer {
|
|
z := &Lexer{
|
|
buf: b,
|
|
}
|
|
|
|
n := len(b)
|
|
if n == 0 {
|
|
z.buf = nullBuffer
|
|
} else {
|
|
// Append NULL to buffer, but try to avoid reallocation
|
|
if cap(b) > n {
|
|
// Overwrite next byte but restore when done
|
|
b = b[:n+1]
|
|
c := b[n]
|
|
b[n] = 0
|
|
|
|
z.buf = b
|
|
z.restore = func() {
|
|
b[n] = c
|
|
}
|
|
} else {
|
|
z.buf = append(b, 0)
|
|
}
|
|
}
|
|
return z
|
|
}
|
|
|
|
// Restore restores the replaced byte past the end of the buffer by NULL.
|
|
func (z *Lexer) Restore() {
|
|
if z.restore != nil {
|
|
z.restore()
|
|
z.restore = nil
|
|
}
|
|
}
|
|
|
|
// Err returns the error returned from io.Reader or io.EOF when the end has been reached.
|
|
func (z *Lexer) Err() error {
|
|
return z.PeekErr(0)
|
|
}
|
|
|
|
// PeekErr returns the error at position pos. When pos is zero, this is the same as calling Err().
|
|
func (z *Lexer) PeekErr(pos int) error {
|
|
if z.err != nil {
|
|
return z.err
|
|
} else if z.pos+pos >= len(z.buf)-1 {
|
|
return io.EOF
|
|
}
|
|
return nil
|
|
}
|
|
|
|
// Peek returns the ith byte relative to the end position.
|
|
// Peek returns 0 when an error has occurred, Err returns the error.
|
|
func (z *Lexer) Peek(pos int) byte {
|
|
pos += z.pos
|
|
return z.buf[pos]
|
|
}
|
|
|
|
// PeekRune returns the rune and rune length of the ith byte relative to the end position.
|
|
func (z *Lexer) PeekRune(pos int) (rune, int) {
|
|
// from unicode/utf8
|
|
c := z.Peek(pos)
|
|
if c < 0xC0 || z.Peek(pos+1) == 0 {
|
|
return rune(c), 1
|
|
} else if c < 0xE0 || z.Peek(pos+2) == 0 {
|
|
return rune(c&0x1F)<<6 | rune(z.Peek(pos+1)&0x3F), 2
|
|
} else if c < 0xF0 || z.Peek(pos+3) == 0 {
|
|
return rune(c&0x0F)<<12 | rune(z.Peek(pos+1)&0x3F)<<6 | rune(z.Peek(pos+2)&0x3F), 3
|
|
}
|
|
return rune(c&0x07)<<18 | rune(z.Peek(pos+1)&0x3F)<<12 | rune(z.Peek(pos+2)&0x3F)<<6 | rune(z.Peek(pos+3)&0x3F), 4
|
|
}
|
|
|
|
// Move advances the position.
|
|
func (z *Lexer) Move(n int) {
|
|
z.pos += n
|
|
}
|
|
|
|
// Pos returns a mark to which can be rewinded.
|
|
func (z *Lexer) Pos() int {
|
|
return z.pos - z.start
|
|
}
|
|
|
|
// Rewind rewinds the position to the given position.
|
|
func (z *Lexer) Rewind(pos int) {
|
|
z.pos = z.start + pos
|
|
}
|
|
|
|
// Lexeme returns the bytes of the current selection.
|
|
func (z *Lexer) Lexeme() []byte {
|
|
return z.buf[z.start:z.pos]
|
|
}
|
|
|
|
// Skip collapses the position to the end of the selection.
|
|
func (z *Lexer) Skip() {
|
|
z.start = z.pos
|
|
}
|
|
|
|
// Shift returns the bytes of the current selection and collapses the position to the end of the selection.
|
|
func (z *Lexer) Shift() []byte {
|
|
b := z.buf[z.start:z.pos]
|
|
z.start = z.pos
|
|
return b
|
|
}
|
|
|
|
// Offset returns the character position in the buffer.
|
|
func (z *Lexer) Offset() int {
|
|
return z.pos
|
|
}
|
|
|
|
// Bytes returns the underlying buffer.
|
|
func (z *Lexer) Bytes() []byte {
|
|
return z.buf[:len(z.buf)-1]
|
|
}
|