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