package toml
import (
"fmt"
"strings"
"unicode"
"unicode/utf8"
)
type itemType int
const (
itemError itemType = iota
itemNIL // used in the parser to indicate no type
itemEOF
itemText
itemString
itemRawString
itemMultilineString
itemRawMultilineString
itemBool
itemInteger
itemFloat
itemDatetime
itemArray // the start of an array
itemArrayEnd
itemTableStart
itemTableEnd
itemArrayTableStart
itemArrayTableEnd
itemKeyStart
itemCommentStart
itemInlineTableStart
itemInlineTableEnd
)
const (
eof = 0
comma = ','
tableStart = '['
tableEnd = ']'
arrayTableStart = '['
arrayTableEnd = ']'
tableSep = '.'
keySep = '='
arrayStart = '['
arrayEnd = ']'
commentStart = '#'
stringStart = '"'
stringEnd = '"'
rawStringStart = '\''
rawStringEnd = '\''
inlineTableStart = '{'
inlineTableEnd = '}'
)
type stateFn func(lx *lexer) stateFn
type lexer struct {
input string
start int
pos int
line int
state stateFn
items chan item
// Allow for backing up up to three runes.
// This is necessary because TOML contains 3-rune tokens (""" and ''').
prevWidths [3]int
nprev int // how many of prevWidths are in use
// If we emit an eof, we can still back up, but it is not OK to call
// next again.
atEOF bool
// A stack of state functions used to maintain context.
// The idea is to reuse parts of the state machine in various places.
// For example, values can appear at the top level or within arbitrarily
// nested arrays. The last state on the stack is used after a value has
// been lexed. Similarly for comments.
stack []stateFn
}
type item struct {
typ itemType
val string
line int
}
func (lx *lexer) nextItem() item {
for {
select {
case item := <-lx.items:
return item
default:
lx.state = lx.state(lx)
}
}
}
func lex(input string) *lexer {
lx := &lexer{
input: input,
state: lexTop,
line: 1,
items: make(chan item, 10),
stack: make([]stateFn, 0, 10),
}
return lx
}
func (lx *lexer) push(state stateFn) {
lx.stack = append(lx.stack, state)
}
func (lx *lexer) pop() stateFn {
if len(lx.stack) == 0 {
return lx.errorf("BUG in lexer: no states to pop")
}
last := lx.stack[len(lx.stack)-1]
lx.stack = lx.stack[0 : len(lx.stack)-1]
return last
}
func (lx *lexer) current() string {
return lx.input[lx.start:lx.pos]
}
func (lx *lexer) emit(typ itemType) {
lx.items <- item{typ, lx.current(), lx.line}
lx.start = lx.pos
}
func (lx *lexer) emitTrim(typ itemType) {
lx.items <- item{typ, strings.TrimSpace(lx.current()), lx.line}
lx.start = lx.pos
}
func (lx *lexer) next() (r rune) {
if lx.atEOF {
panic("next called after EOF")
}
if lx.pos >= len(lx.input) {
lx.atEOF = true
return eof
}
if lx.input[lx.pos] == '\n' {
lx.line++
}
lx.prevWidths[2] = lx.prevWidths[1]
lx.prevWidths[1] = lx.prevWidths[0]
if lx.nprev < 3 {
lx.nprev++
}
r, w := utf8.DecodeRuneInString(lx.input[lx.pos:])
lx.prevWidths[0] = w
lx.pos += w
return r
}
// ignore skips over the pending input before this point.
func (lx *lexer) ignore() {
lx.start = lx.pos
}
// backup steps back one rune. Can be called only twice between calls to next.
func (lx *lexer) backup() {
if lx.atEOF {
lx.atEOF = false
return
}
if lx.nprev < 1 {
panic("backed up too far")
}
w := lx.prevWidths[0]
lx.prevWidths[0] = lx.prevWidths[1]
lx.prevWidths[1] = lx.prevWidths[2]
lx.nprev--
lx.pos -= w
if lx.pos < len(lx.input) && lx.input[lx.pos] == '\n' {
lx.line--
}
}
// accept consumes the next rune if it's equal to `valid`.
func (lx *lexer) accept(valid rune) bool {
if lx.next() == valid {
return true
}
lx.backup()
return false
}
// peek returns but does not consume the next rune in the input.
func (lx *lexer) peek() rune {
r := lx.next()
lx.backup()
return r
}
// skip ignores all input that matches the given predicate.
func (lx *lexer) skip(pred func(rune) bool) {
for {
r := lx.next()
if pred(r) {
continue
}
lx.backup()
lx.ignore()
return
}
}
// errorf stops all lexing by emitting an error and returning `nil`.
// Note that any value that is a character is escaped if it's a special
// character (newlines, tabs, etc.).
func (lx *lexer) errorf(format string, values ...interface{}) stateFn {
lx.items <- item{
itemError,
fmt.Sprintf(format, values...),
lx.line,
}
return nil
}
// lexTop consumes elements at the top level of TOML data.
func lexTop(lx *lexer) stateFn {
r := lx.next()
if isWhitespace(r) || isNL(r) {
return lexSkip(lx, lexTop)
}
switch r {
case commentStart:
lx.push(lexTop)
return lexCommentStart
case tableStart:
return lexTableStart
case eof:
if lx.pos > lx.start {
return lx.errorf("unexpected EOF")
}
lx.emit(itemEOF)
return nil
}
// At this point, the only valid item can be a key, so we back up
// and let the key lexer do the rest.
lx.backup()
lx.push(lexTopEnd)
return lexKeyStart
}
// lexTopEnd is entered whenever a top-level item has been consumed. (A value
// or a table.) It must see only whitespace, and will turn back to lexTop
// upon a newline. If it sees EOF, it will quit the lexer successfully.
func lexTopEnd(lx *lexer) stateFn {
r := lx.next()
switch {
case r == commentStart:
// a comment will read to a newline for us.
lx.push(lexTop)
return lexCommentStart
case isWhitespace(r):
return lexTopEnd
case isNL(r):
lx.ignore()
return lexTop
case r == eof:
lx.emit(itemEOF)
return nil
}
return lx.errorf("expected a top-level item to end with a newline, "+
"comment, or EOF, but got %q instead", r)
}
// lexTable lexes the beginning of a table. Namely, it makes sure that
// it starts with a character other than '.' and ']'.
// It assumes that '[' has already been consumed.
// It also handles the case that this is an item in an array of tables.
// e.g., '[[name]]'.
func lexTableStart(lx *lexer) stateFn {
if lx.peek() == arrayTableStart {
lx.next()
lx.emit(itemArrayTableStart)
lx.push(lexArrayTableEnd)
} else {
lx.emit(itemTableStart)
lx.push(lexTableEnd)
}
return lexTableNameStart
}
func lexTableEnd(lx *lexer) stateFn {
lx.emit(itemTableEnd)
return lexTopEnd
}
func lexArrayTableEnd(lx *lexer) stateFn {
if r := lx.next(); r != arrayTableEnd {
return lx.errorf("expected end of table array name delimiter %q, "+
"but got %q instead", arrayTableEnd, r)
}
lx.emit(itemArrayTableEnd)
return lexTopEnd
}
func lexTableNameStart(lx *lexer) stateFn {
lx.skip(isWhitespace)
switch r := lx.peek(); {
case r == tableEnd || r == eof:
return lx.errorf("unexpected end of table name " +
"(table names cannot be empty)")
case r == tableSep:
return lx.errorf("unexpected table separator " +
"(table names cannot be empty)")
case r == stringStart || r == rawStringStart:
lx.ignore()
lx.push(lexTableNameEnd)
return lexValue // reuse string lexing
default:
return lexBareTableName
}
}
// lexBareTableName lexes the name of a table. It assumes that at least one
// valid character for the table has already been read.
func lexBareTableName(lx *lexer) stateFn {
r := lx.next()
if isBareKeyChar(r) {
return lexBareTableName
}
lx.backup()
lx.emit(itemText)
return lexTableNameEnd
}
// lexTableNameEnd reads the end of a piece of a table name, optionally
// consuming whitespace.
func lexTableNameEnd(lx *lexer) stateFn {
lx.skip(isWhitespace)
switch r := lx.next(); {
case isWhitespace(r):
return lexTableNameEnd
case r == tableSep:
lx.ignore()
return lexTableNameStart
case r == tableEnd:
return lx.pop()
default:
return lx.errorf("expected '.' or ']' to end table name, "+
"but got %q instead", r)
}
}
// lexKeyStart consumes a key name up until the first non-whitespace character.
// lexKeyStart will ignore whitespace.
func lexKeyStart(lx *lexer) stateFn {
r := lx.peek()
switch {
case r == keySep:
return lx.errorf("unexpected key separator %q", keySep)
case isWhitespace(r) || isNL(r):
lx.next()
return lexSkip(lx, lexKeyStart)
case r == stringStart || r == rawStringStart:
lx.ignore()
lx.emit(itemKeyStart)
lx.push(lexKeyEnd)
return lexValue // reuse string lexing
default:
lx.ignore()
lx.emit(itemKeyStart)
return lexBareKey
}
}
// lexBareKey consumes the text of a bare key. Assumes that the first character
// (which is not whitespace) has not yet been consumed.
func lexBareKey(lx *lexer) stateFn {
switch r := lx.next(); {
case isBareKeyChar(r):
return lexBareKey
case isWhitespace(r):
lx.backup()
lx.emit(itemText)
return lexKeyEnd
case r == keySep:
lx.backup()
lx.emit(itemText)
return lexKeyEnd
default:
return lx.errorf("bare keys cannot contain %q", r)
}
}
// lexKeyEnd consumes the end of a key and trims whitespace (up to the key
// separator).
func lexKeyEnd(lx *lexer) stateFn {
switch r := lx.next(); {
case r == keySep:
return lexSkip(lx, lexValue)
case isWhitespace(r):
return lexSkip(lx, lexKeyEnd)
default:
return lx.errorf("expected key separator %q, but got %q instead",
keySep, r)
}
}
// lexValue starts the consumption of a value anywhere a value is expected.
// lexValue will ignore whitespace.
// After a value is lexed, the last state on the next is popped and returned.
func lexValue(lx *lexer) stateFn {
// We allow whitespace to precede a value, but NOT newlines.
// In array syntax, the array states are responsible for ignoring newlines.
r := lx.next()
switch {
case isWhitespace(r):
return lexSkip(lx, lexValue)
case isDigit(r):
lx.backup() // avoid an extra state and use the same as above
return lexNumberOrDateStart
}
switch r {
case arrayStart:
lx.ignore()
lx.emit(itemArray)
return lexArrayValue
case inlineTableStart:
lx.ignore()
lx.emit(itemInlineTableStart)
return lexInlineTableValue
case stringStart:
if lx.accept(stringStart) {
if lx.accept(stringStart) {
lx.ignore() // Ignore """
return lexMultilineString
}
lx.backup()
}
lx.ignore() // ignore the '"'
return lexString
case rawStringStart:
if lx.accept(rawStringStart) {
if lx.accept(rawStringStart) {
lx.ignore() // Ignore """
return lexMultilineRawString
}
lx.backup()
}
lx.ignore() // ignore the "'"
return lexRawString
case '+', '-':
return lexNumberStart
case '.': // special error case, be kind to users
return lx.errorf("floats must start with a digit, not '.'")
}
if unicode.IsLetter(r) {
// Be permissive here; lexBool will give a nice error if the
// user wrote something like
// x = foo
// (i.e. not 'true' or 'false' but is something else word-like.)
lx.backup()
return lexBool
}
return lx.errorf("expected value but found %q instead", r)
}
// lexArrayValue consumes one value in an array. It assumes that '[' or ','
// have already been consumed. All whitespace and newlines are ignored.
func lexArrayValue(lx *lexer) stateFn {
r := lx.next()
switch {
case isWhitespace(r) || isNL(r):
return lexSkip(lx, lexArrayValue)
case r == commentStart:
lx.push(lexArrayValue)
return lexCommentStart
case r == comma:
return lx.errorf("unexpected comma")
case r == arrayEnd:
// NOTE(caleb): The spec isn't clear about whether you can have
// a trailing comma or not, so we'll allow it.
return lexArrayEnd
}
lx.backup()
lx.push(lexArrayValueEnd)
return lexValue
}
// lexArrayValueEnd consumes everything between the end of an array value and
// the next value (or the end of the array): it ignores whitespace and newlines
// and expects either a ',' or a ']'.
func lexArrayValueEnd(lx *lexer) stateFn {
r := lx.next()
switch {
case isWhitespace(r) || isNL(r):
return lexSkip(lx, lexArrayValueEnd)
case r == commentStart:
lx.push(lexArrayValueEnd)
return lexCommentStart
case r == comma:
lx.ignore()
return lexArrayValue // move on to the next value
case r == arrayEnd:
return lexArrayEnd
}
return lx.errorf(
"expected a comma or array terminator %q, but got %q instead",
arrayEnd, r,
)
}
// lexArrayEnd finishes the lexing of an array.
// It assumes that a ']' has just been consumed.
func lexArrayEnd(lx *lexer) stateFn {
lx.ignore()
lx.emit(itemArrayEnd)
return lx.pop()
}
// lexInlineTableValue consumes one key/value pair in an inline table.
// It assumes that '{' or ',' have already been consumed. Whitespace is ignored.
func lexInlineTableValue(lx *lexer) stateFn {
r := lx.next()
switch {
case isWhitespace(r):
return lexSkip(lx, lexInlineTableValue)
case isNL(r):
return lx.errorf("newlines not allowed within inline tables")
case r == commentStart:
lx.push(lexInlineTableValue)
return lexCommentStart
case r == comma:
return lx.errorf("unexpected comma")
case r == inlineTableEnd:
return lexInlineTableEnd
}
lx.backup()
lx.push(lexInlineTableValueEnd)
return lexKeyStart
}
// lexInlineTableValueEnd consumes everything between the end of an inline table
// key/value pair and the next pair (or the end of the table):
// it ignores whitespace and expects either a ',' or a '}'.
func lexInlineTableValueEnd(lx *lexer) stateFn {
r := lx.next()
switch {
case isWhitespace(r):
return lexSkip(lx, lexInlineTableValueEnd)
case isNL(r):
return lx.errorf("newlines not allowed within inline tables")
case r == commentStart:
lx.push(lexInlineTableValueEnd)
return lexCommentStart
case r == comma:
lx.ignore()
return lexInlineTableValue
case r == inlineTableEnd:
return lexInlineTableEnd
}
return lx.errorf("expected a comma or an inline table terminator %q, "+
"but got %q instead", inlineTableEnd, r)
}
// lexInlineTableEnd finishes the lexing of an inline table.
// It assumes that a '}' has just been consumed.
func lexInlineTableEnd(lx *lexer) stateFn {
lx.ignore()
lx.emit(itemInlineTableEnd)
return lx.pop()
}
// lexString consumes the inner contents of a string. It assumes that the
// beginning '"' has already been consumed and ignored.
func lexString(lx *lexer) stateFn {
r := lx.next()
switch {
case r == eof:
return lx.errorf("unexpected EOF")
case isNL(r):
return lx.errorf("strings cannot contain newlines")
case r == '\\':
lx.push(lexString)
return lexStringEscape
case r == stringEnd:
lx.backup()
lx.emit(itemString)
lx.next()
lx.ignore()
return lx.pop()
}
return lexString
}
// lexMultilineString consumes the inner contents of a string. It assumes that
// the beginning '"""' has already been consumed and ignored.
func lexMultilineString(lx *lexer) stateFn {
switch lx.next() {
case eof:
return lx.errorf("unexpected EOF")
case '\\':
return lexMultilineStringEscape
case stringEnd:
if lx.accept(stringEnd) {
if lx.accept(stringEnd) {
lx.backup()
lx.backup()
lx.backup()
lx.emit(itemMultilineString)
lx.next()
lx.next()
lx.next()
lx.ignore()
return lx.pop()
}
lx.backup()
}
}
return lexMultilineString
}
// lexRawString consumes a raw string. Nothing can be escaped in such a string.
// It assumes that the beginning "'" has already been consumed and ignored.
func lexRawString(lx *lexer) stateFn {
r := lx.next()
switch {
case r == eof:
return lx.errorf("unexpected EOF")
case isNL(r):
return lx.errorf("strings cannot contain newlines")
case r == rawStringEnd:
lx.backup()
lx.emit(itemRawString)
lx.next()
lx.ignore()
return lx.pop()
}
return lexRawString
}
// lexMultilineRawString consumes a raw string. Nothing can be escaped in such
// a string. It assumes that the beginning "'''" has already been consumed and
// ignored.
func lexMultilineRawString(lx *lexer) stateFn {
switch lx.next() {
case eof:
return lx.errorf("unexpected EOF")
case rawStringEnd:
if lx.accept(rawStringEnd) {
if lx.accept(rawStringEnd) {
lx.backup()
lx.backup()
lx.backup()
lx.emit(itemRawMultilineString)
lx.next()
lx.next()
lx.next()
lx.ignore()
return lx.pop()
}
lx.backup()
}
}
return lexMultilineRawString
}
// lexMultilineStringEscape consumes an escaped character. It assumes that the
// preceding '\\' has already been consumed.
func lexMultilineStringEscape(lx *lexer) stateFn {
// Handle the special case first:
if isNL(lx.next()) {
return lexMultilineString
}
lx.backup()
lx.push(lexMultilineString)
return lexStringEscape(lx)
}
func lexStringEscape(lx *lexer) stateFn {
r := lx.next()
switch r {
case 'b':
fallthrough
case 't':
fallthrough
case 'n':
fallthrough
case 'f':
fallthrough
case 'r':
fallthrough
case '"':
fallthrough
case '\\':
return lx.pop()
case 'u':
return lexShortUnicodeEscape
case 'U':
return lexLongUnicodeEscape
}
return lx.errorf("invalid escape character %q; only the following "+
"escape characters are allowed: "+
`\b, \t, \n, \f, \r, \", \\, \uXXXX, and \UXXXXXXXX`, r)
}
func lexShortUnicodeEscape(lx *lexer) stateFn {
var r rune
for i := 0; i < 4; i++ {
r = lx.next()
if !isHexadecimal(r) {
return lx.errorf(`expected four hexadecimal digits after '\u', `+
"but got %q instead", lx.current())
}
}
return lx.pop()
}
func lexLongUnicodeEscape(lx *lexer) stateFn {
var r rune
for i := 0; i < 8; i++ {
r = lx.next()
if !isHexadecimal(r) {
return lx.errorf(`expected eight hexadecimal digits after '\U', `+
"but got %q instead", lx.current())
}
}
return lx.pop()
}
// lexNumberOrDateStart consumes either an integer, a float, or datetime.
func lexNumberOrDateStart(lx *lexer) stateFn {
r := lx.next()
if isDigit(r) {
return lexNumberOrDate
}
switch r {
case '_':
return lexNumber
case 'e', 'E':
return lexFloat
case '.':
return lx.errorf("floats must start with a digit, not '.'")
}
return lx.errorf("expected a digit but got %q", r)
}
// lexNumberOrDate consumes either an integer, float or datetime.
func lexNumberOrDate(lx *lexer) stateFn {
r := lx.next()
if isDigit(r) {
return lexNumberOrDate
}
switch r {
case '-':
return lexDatetime
case '_':
return lexNumber
case '.', 'e', 'E':
return lexFloat
}
lx.backup()
lx.emit(itemInteger)
return lx.pop()
}
// lexDatetime consumes a Datetime, to a first approximation.
// The parser validates that it matches one of the accepted formats.
func lexDatetime(lx *lexer) stateFn {
r := lx.next()
if isDigit(r) {
return lexDatetime
}
switch r {
case '-', 'T', ':', '.', 'Z', '+':
return lexDatetime
}
lx.backup()
lx.emit(itemDatetime)
return lx.pop()
}
// lexNumberStart consumes either an integer or a float. It assumes that a sign
// has already been read, but that *no* digits have been consumed.
// lexNumberStart will move to the appropriate integer or float states.
func lexNumberStart(lx *lexer) stateFn {
// We MUST see a digit. Even floats have to start with a digit.
r := lx.next()
if !isDigit(r) {
if r == '.' {
return lx.errorf("floats must start with a digit, not '.'")
}
return lx.errorf("expected a digit but got %q", r)
}
return lexNumber
}
// lexNumber consumes an integer or a float after seeing the first digit.
func lexNumber(lx *lexer) stateFn {
r := lx.next()
if isDigit(r) {
return lexNumber
}
switch r {
case '_':
return lexNumber
case '.', 'e', 'E':
return lexFloat
}
lx.backup()
lx.emit(itemInteger)
return lx.pop()
}
// lexFloat consumes the elements of a float. It allows any sequence of
// float-like characters, so floats emitted by the lexer are only a first
// approximation and must be validated by the parser.
func lexFloat(lx *lexer) stateFn {
r := lx.next()
if isDigit(r) {
return lexFloat
}
switch r {
case '_', '.', '-', '+', 'e', 'E':
return lexFloat
}
lx.backup()
lx.emit(itemFloat)
return lx.pop()
}
// lexBool consumes a bool string: 'true' or 'false.
func lexBool(lx *lexer) stateFn {
var rs []rune
for {
r := lx.next()
if !unicode.IsLetter(r) {
lx.backup()
break
}
rs = append(rs, r)
}
s := string(rs)
switch s {
case "true", "false":
lx.emit(itemBool)
return lx.pop()
}
return lx.errorf("expected value but found %q instead", s)
}
// lexCommentStart begins the lexing of a comment. It will emit
// itemCommentStart and consume no characters, passing control to lexComment.
func lexCommentStart(lx *lexer) stateFn {
lx.ignore()
lx.emit(itemCommentStart)
return lexComment
}
// lexComment lexes an entire comment. It assumes that '#' has been consumed.
// It will consume *up to* the first newline character, and pass control
// back to the last state on the stack.
func lexComment(lx *lexer) stateFn {
r := lx.peek()
if isNL(r) || r == eof {
lx.emit(itemText)
return lx.pop()
}
lx.next()
return lexComment
}
// lexSkip ignores all slurped input and moves on to the next state.
func lexSkip(lx *lexer, nextState stateFn) stateFn {
return func(lx *lexer) stateFn {
lx.ignore()
return nextState
}
}
// isWhitespace returns true if `r` is a whitespace character according
// to the spec.
func isWhitespace(r rune) bool {
return r == '\t' || r == ' '
}
func isNL(r rune) bool {
return r == '\n' || r == '\r'
}
func isDigit(r rune) bool {
return r >= '0' && r <= '9'
}
func isHexadecimal(r rune) bool {
return (r >= '0' && r <= '9') ||
(r >= 'a' && r <= 'f') ||
(r >= 'A' && r <= 'F')
}
func isBareKeyChar(r rune) bool {
return (r >= 'A' && r <= 'Z') ||
(r >= 'a' && r <= 'z') ||
(r >= '0' && r <= '9') ||
r == '_' ||
r == '-'
}
func (itype itemType) String() string {
switch itype {
case itemError:
return "Error"
case itemNIL:
return "NIL"
case itemEOF:
return "EOF"
case itemText:
return "Text"
case itemString, itemRawString, itemMultilineString, itemRawMultilineString:
return "String"
case itemBool:
return "Bool"
case itemInteger:
return "Integer"
case itemFloat:
return "Float"
case itemDatetime:
return "DateTime"
case itemTableStart:
return "TableStart"
case itemTableEnd:
return "TableEnd"
case itemKeyStart:
return "KeyStart"
case itemArray:
return "Array"
case itemArrayEnd:
return "ArrayEnd"
case itemCommentStart:
return "CommentStart"
}
panic(fmt.Sprintf("BUG: Unknown type '%d'.", int(itype)))
}
func (item item) String() string {
return fmt.Sprintf("(%s, %s)", item.typ.String(), item.val)
}