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lexer.go
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lexer.go
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package schemalex
import (
"bytes"
"strings"
"unicode/utf8"
"github.com/schemalex/schemalex/internal/errors"
"golang.org/x/net/context"
)
const eof = rune(0)
type lrune struct {
r rune
w int
}
type position struct {
pos int // byte count
col int
line int
}
type lexer struct {
out chan *Token
input []byte
peekCount int
peekRunes [3]lrune
start position // position where we last emitted
cur position // current position including read-ahead
width int
}
func lex(ctx context.Context, input []byte) chan *Token {
ch := make(chan *Token, 3)
l := newLexer(ch, input)
go l.Run(ctx)
return ch
}
func newLexer(out chan *Token, input []byte) *lexer {
var l lexer
l.out = out
l.input = input
l.start.line = 1
l.start.col = 1
l.cur.line = 1
l.cur.col = 1
l.peekCount = -1
return &l
}
func (l *lexer) emit(ctx context.Context, typ TokenType) {
var t Token
t.Line = l.start.line
t.Col = l.start.col
t.Type = typ
t.Pos = l.start.pos
if typ == EOF {
t.EOF = true
t.Pos = len(l.input)
} else {
t.Value = l.str()
switch typ {
case SINGLE_QUOTE_IDENT:
t.Value = unescapeQuotes(t.Value, '\'')
case DOUBLE_QUOTE_IDENT:
t.Value = unescapeQuotes(t.Value, '"')
case BACKTICK_IDENT:
t.Value = unescapeQuotes(t.Value, '`')
}
}
select {
case <-ctx.Done():
case l.out <- &t:
}
// when we emit, we must copy the value of cur to start
// but we also must adjust the position by the read-ahead offset
l.start = l.cur
l.start.pos = l.start.pos - (l.peekCount + 1)
}
func (l *lexer) str() string {
return string(l.input[l.start.pos : l.cur.pos-(l.peekCount+1)])
}
func (l *lexer) Run(ctx context.Context) {
defer close(l.out)
OUTER:
for {
select {
case <-ctx.Done():
return
default:
}
r := l.peek()
// These require peek, and then consume
switch {
case isSpace(r):
// read until space end
l.runSpace()
l.emit(ctx, SPACE)
continue OUTER
case isLetter(r):
t := l.runIdent()
s := l.str()
if typ, ok := keywordIdentMap[strings.ToUpper(s)]; ok {
t = typ
}
l.emit(ctx, t)
continue OUTER
case isDigit(r):
l.runNumber()
l.emit(ctx, NUMBER)
continue OUTER
}
// once we got here, we can consume
l.advance()
switch r {
case eof:
l.emit(ctx, EOF)
return
case '`':
if err := l.runQuote('`'); err != nil {
l.emit(ctx, ILLEGAL)
return
}
l.emit(ctx, BACKTICK_IDENT)
case '"':
if err := l.runQuote('"'); err != nil {
l.emit(ctx, ILLEGAL)
return
}
l.emit(ctx, DOUBLE_QUOTE_IDENT)
case '\'':
if err := l.runQuote('\''); err != nil {
l.emit(ctx, ILLEGAL)
return
}
l.emit(ctx, SINGLE_QUOTE_IDENT)
case '/':
switch c := l.peek(); c {
case '*':
l.runCComment()
l.emit(ctx, COMMENT_IDENT)
default:
l.emit(ctx, SLASH)
}
case '-':
switch r1 := l.peek(); {
case r1 == '-':
l.advance()
// TODO: https://dev.mysql.com/doc/refman/5.6/en/comments.html
// TODO: not only space. control character
if !isSpace(l.peek()) {
l.emit(ctx, DASH)
continue OUTER
}
l.runToEOL()
l.emit(ctx, COMMENT_IDENT)
case isDigit(r1):
l.runNumber()
l.emit(ctx, NUMBER)
default:
l.emit(ctx, DASH)
}
case '#':
// https://dev.mysql.com/doc/refman/5.6/en/comments.html
l.runToEOL()
l.emit(ctx, COMMENT_IDENT)
case '(':
l.emit(ctx, LPAREN)
case ')':
l.emit(ctx, RPAREN)
case ';':
l.emit(ctx, SEMICOLON)
case ',':
l.emit(ctx, COMMA)
case '.':
if isDigit(l.peek()) {
l.runNumber()
l.emit(ctx, NUMBER)
} else {
l.emit(ctx, DOT)
}
case '+':
if isDigit(l.peek()) {
l.runNumber()
l.emit(ctx, NUMBER)
} else {
l.emit(ctx, PLUS)
}
case '=':
l.emit(ctx, EQUAL)
default:
l.emit(ctx, ILLEGAL)
}
}
}
func (l *lexer) next() rune {
r := l.peek()
l.advance()
return r
}
func (l *lexer) peek() rune {
if l.peekCount >= 0 {
return l.peekRunes[l.peekCount].r
}
if l.cur.pos >= len(l.input) {
l.width = 0
return eof
}
r, w := utf8.DecodeRune(l.input[l.cur.pos:])
l.peekCount++
l.peekRunes[l.peekCount].r = r
l.peekRunes[l.peekCount].w = w
l.cur.pos += w
return r
}
func (l *lexer) advance() {
// if the current rune is a new line, we line++
r := l.peek()
switch r {
case '\n':
l.cur.line++
l.cur.col = 0
case eof:
default:
l.cur.col++
}
l.peekCount--
}
func (l *lexer) runSpace() {
for isSpace(l.peek()) {
l.advance()
}
}
func (l *lexer) runIdent() TokenType {
OUTER:
for {
r := l.peek()
switch {
case r == eof:
l.advance()
break OUTER
case isCharacter(r):
l.advance()
default:
break OUTER
}
}
return IDENT
}
func unescapeQuotes(s string, quot rune) string {
var buf bytes.Buffer
max := utf8.RuneCountInString(s)
rdr := strings.NewReader(s)
for i := 0; i < max; i++ {
r, _, _ := rdr.ReadRune()
// assume first rune and last rune are quot
if i == 0 || i == max-1 {
continue
}
switch r {
case '\\', quot: // possible escape sequence
if r2, _, _ := rdr.ReadRune(); r2 == quot {
i++
r = quot
} else {
rdr.UnreadRune()
}
}
buf.WriteRune(r)
}
return buf.String()
}
func (l *lexer) runQuote(pair rune) error {
for {
r := l.next()
if r == eof {
return errors.New(`unexpected eof`)
} else if r == '\\' {
if l.peek() == pair {
r = l.next()
}
} else if r == pair {
if l.peek() == pair {
// it is escape
r = l.next()
} else {
return nil
}
}
}
}
// https://dev.mysql.com/doc/refman/5.6/en/comments.html
func (l *lexer) runCComment() {
for {
r := l.next()
switch r {
case eof:
return
case '*':
if l.peek() == '/' {
l.advance()
return
}
}
}
}
func (l *lexer) runToEOL() TokenType {
for {
r := l.next()
switch r {
case eof, '\n':
return COMMENT_IDENT
}
}
}
// https://dev.mysql.com/doc/refman/5.6/en/number-literals.html
func (l *lexer) runDigit() {
for {
if !isDigit(l.peek()) {
break
}
l.advance()
}
}
func (l *lexer) runNumber() {
l.runDigit()
if l.peek() == '.' {
l.advance()
l.runDigit()
}
switch l.peek() {
case 'E', 'e':
l.advance()
if l.peek() == '-' {
l.advance()
}
l.runDigit()
}
}
func isSpace(r rune) bool {
return r == ' ' || r == '\n' || r == '\t'
}
func isLetter(r rune) bool {
return (r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z')
}
func isCharacter(r rune) bool {
return isDigit(r) || isLetter(r) || r == '_'
}
func isDigit(r rune) bool {
return r >= '0' && r <= '9'
}