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// Copyright 2017 Frank Schroeder. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//
// Parts of the lexer are from the template/text/parser package
// For these parts the following applies:
//
// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file of the go 1.2
// distribution.
package properties
import (
"fmt"
"strconv"
"strings"
"unicode/utf8"
)
// item represents a token or text string returned from the scanner.
type item struct {
typ itemType // The type of this item.
pos int // The starting position, in bytes, of this item in the input string.
val string // The value of this item.
}
func (i item) String() string {
switch {
case i.typ == itemEOF:
return "EOF"
case i.typ == itemError:
return i.val
case len(i.val) > 10:
return fmt.Sprintf("%.10q...", i.val)
}
return fmt.Sprintf("%q", i.val)
}
// itemType identifies the type of lex items.
type itemType int
const (
itemError itemType = iota // error occurred; value is text of error
itemEOF
itemKey // a key
itemValue // a value
itemComment // a comment
)
// defines a constant for EOF
const eof = -1
// permitted whitespace characters space, FF and TAB
const whitespace = " \f\t"
// stateFn represents the state of the scanner as a function that returns the next state.
type stateFn func(*lexer) stateFn
// lexer holds the state of the scanner.
type lexer struct {
input string // the string being scanned
state stateFn // the next lexing function to enter
pos int // current position in the input
start int // start position of this item
width int // width of last rune read from input
lastPos int // position of most recent item returned by nextItem
runes []rune // scanned runes for this item
items chan item // channel of scanned items
}
// next returns the next rune in the input.
func (l *lexer) next() rune {
if l.pos >= len(l.input) {
l.width = 0
return eof
}
r, w := utf8.DecodeRuneInString(l.input[l.pos:])
l.width = w
l.pos += l.width
return r
}
// peek returns but does not consume the next rune in the input.
func (l *lexer) peek() rune {
r := l.next()
l.backup()
return r
}
// backup steps back one rune. Can only be called once per call of next.
func (l *lexer) backup() {
l.pos -= l.width
}
// emit passes an item back to the client.
func (l *lexer) emit(t itemType) {
i := item{t, l.start, string(l.runes)}
l.items <- i
l.start = l.pos
l.runes = l.runes[:0]
}
// ignore skips over the pending input before this point.
func (l *lexer) ignore() {
l.start = l.pos
}
// appends the rune to the current value
func (l *lexer) appendRune(r rune) {
l.runes = append(l.runes, r)
}
// accept consumes the next rune if it's from the valid set.
func (l *lexer) accept(valid string) bool {
if strings.ContainsRune(valid, l.next()) {
return true
}
l.backup()
return false
}
// acceptRun consumes a run of runes from the valid set.
func (l *lexer) acceptRun(valid string) {
for strings.ContainsRune(valid, l.next()) {
}
l.backup()
}
// acceptRunUntil consumes a run of runes up to a terminator.
func (l *lexer) acceptRunUntil(term rune) {
for term != l.next() {
}
l.backup()
}
// hasText returns true if the current parsed text is not empty.
func (l *lexer) isNotEmpty() bool {
return l.pos > l.start
}
// lineNumber reports which line we're on, based on the position of
// the previous item returned by nextItem. Doing it this way
// means we don't have to worry about peek double counting.
func (l *lexer) lineNumber() int {
return 1 + strings.Count(l.input[:l.lastPos], "\n")
}
// errorf returns an error token and terminates the scan by passing
// back a nil pointer that will be the next state, terminating l.nextItem.
func (l *lexer) errorf(format string, args ...interface{}) stateFn {
l.items <- item{itemError, l.start, fmt.Sprintf(format, args...)}
return nil
}
// nextItem returns the next item from the input.
func (l *lexer) nextItem() item {
i := <-l.items
l.lastPos = i.pos
return i
}
// lex creates a new scanner for the input string.
func lex(input string) *lexer {
l := &lexer{
input: input,
items: make(chan item),
runes: make([]rune, 0, 32),
}
go l.run()
return l
}
// run runs the state machine for the lexer.
func (l *lexer) run() {
for l.state = lexBeforeKey(l); l.state != nil; {
l.state = l.state(l)
}
}
// state functions
// lexBeforeKey scans until a key begins.
func lexBeforeKey(l *lexer) stateFn {
switch r := l.next(); {
case isEOF(r):
l.emit(itemEOF)
return nil
case isEOL(r):
l.ignore()
return lexBeforeKey
case isComment(r):
return lexComment
case isWhitespace(r):
l.acceptRun(whitespace)
l.ignore()
return lexKey
default:
l.backup()
return lexKey
}
}
// lexComment scans a comment line. The comment character has already been scanned.
func lexComment(l *lexer) stateFn {
l.acceptRun(whitespace)
l.ignore()
for {
switch r := l.next(); {
case isEOF(r):
l.ignore()
l.emit(itemEOF)
return nil
case isEOL(r):
l.emit(itemComment)
return lexBeforeKey
default:
l.appendRune(r)
}
}
}
// lexKey scans the key up to a delimiter
func lexKey(l *lexer) stateFn {
var r rune
Loop:
for {
switch r = l.next(); {
case isEscape(r):
err := l.scanEscapeSequence()
if err != nil {
return l.errorf(err.Error())
}
case isEndOfKey(r):
l.backup()
break Loop
case isEOF(r):
break Loop
default:
l.appendRune(r)
}
}
if len(l.runes) > 0 {
l.emit(itemKey)
}
if isEOF(r) {
l.emit(itemEOF)
return nil
}
return lexBeforeValue
}
// lexBeforeValue scans the delimiter between key and value.
// Leading and trailing whitespace is ignored.
// We expect to be just after the key.
func lexBeforeValue(l *lexer) stateFn {
l.acceptRun(whitespace)
l.accept(":=")
l.acceptRun(whitespace)
l.ignore()
return lexValue
}
// lexValue scans text until the end of the line. We expect to be just after the delimiter.
func lexValue(l *lexer) stateFn {
for {
switch r := l.next(); {
case isEscape(r):
if isEOL(l.peek()) {
l.next()
l.acceptRun(whitespace)
} else {
err := l.scanEscapeSequence()
if err != nil {
return l.errorf(err.Error())
}
}
case isEOL(r):
l.emit(itemValue)
l.ignore()
return lexBeforeKey
case isEOF(r):
l.emit(itemValue)
l.emit(itemEOF)
return nil
default:
l.appendRune(r)
}
}
}
// scanEscapeSequence scans either one of the escaped characters
// or a unicode literal. We expect to be after the escape character.
func (l *lexer) scanEscapeSequence() error {
switch r := l.next(); {
case isEscapedCharacter(r):
l.appendRune(decodeEscapedCharacter(r))
return nil
case atUnicodeLiteral(r):
return l.scanUnicodeLiteral()
case isEOF(r):
return fmt.Errorf("premature EOF")
// silently drop the escape character and append the rune as is
default:
l.appendRune(r)
return nil
}
}
// scans a unicode literal in the form \uXXXX. We expect to be after the \u.
func (l *lexer) scanUnicodeLiteral() error {
// scan the digits
d := make([]rune, 4)
for i := 0; i < 4; i++ {
d[i] = l.next()
if d[i] == eof || !strings.ContainsRune("0123456789abcdefABCDEF", d[i]) {
return fmt.Errorf("invalid unicode literal")
}
}
// decode the digits into a rune
r, err := strconv.ParseInt(string(d), 16, 0)
if err != nil {
return err
}
l.appendRune(rune(r))
return nil
}
// decodeEscapedCharacter returns the unescaped rune. We expect to be after the escape character.
func decodeEscapedCharacter(r rune) rune {
switch r {
case 'f':
return '\f'
case 'n':
return '\n'
case 'r':
return '\r'
case 't':
return '\t'
default:
return r
}
}
// atUnicodeLiteral reports whether we are at a unicode literal.
// The escape character has already been consumed.
func atUnicodeLiteral(r rune) bool {
return r == 'u'
}
// isComment reports whether we are at the start of a comment.
func isComment(r rune) bool {
return r == '#' || r == '!'
}
// isEndOfKey reports whether the rune terminates the current key.
func isEndOfKey(r rune) bool {
return strings.ContainsRune(" \f\t\r\n:=", r)
}
// isEOF reports whether we are at EOF.
func isEOF(r rune) bool {
return r == eof
}
// isEOL reports whether we are at a new line character.
func isEOL(r rune) bool {
return r == '\n' || r == '\r'
}
// isEscape reports whether the rune is the escape character which
// prefixes unicode literals and other escaped characters.
func isEscape(r rune) bool {
return r == '\\'
}
// isEscapedCharacter reports whether we are at one of the characters that need escaping.
// The escape character has already been consumed.
func isEscapedCharacter(r rune) bool {
return strings.ContainsRune(" :=fnrt", r)
}
// isWhitespace reports whether the rune is a whitespace character.
func isWhitespace(r rune) bool {
return strings.ContainsRune(whitespace, r)
}