/
lexer.go
362 lines (301 loc) · 7.17 KB
/
lexer.go
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// Copyright 2015 Zalando SE
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package eskip
import (
"errors"
"fmt"
"strings"
"unicode"
)
type token struct {
id int
val string
}
type charPredicate func(byte) bool
type scanner interface {
scan(string) (token, string, error)
}
type scannerFunc func(string) (token, string, error)
func (sf scannerFunc) scan(code string) (token, string, error) { return sf(code) }
type eskipLex struct {
code string
lastToken *token
err error
initialLength int
routes []*parsedRoute
filters []*Filter
}
type fixedScanner string
const (
escapeChar = '\\'
decimalChar = '.'
newlineChar = '\n'
underscore = '_'
)
var (
invalidCharacter = errors.New("invalid character")
incompleteToken = errors.New("incomplete token")
unexpectedToken = errors.New("unexpected token")
void = errors.New("void")
eof = errors.New("eof")
)
var fixedTokens = map[fixedScanner]int{
"&&": and,
"*": any,
"->": arrow,
")": closeparen,
":": colon,
",": comma,
"(": openparen,
";": semicolon,
"<shunt>": shunt,
"<loopback>": loopback}
func (t token) String() string { return t.val }
func (fs fixedScanner) scan(code string) (t token, rest string, err error) {
if len(code) < len(fs) {
err = unexpectedToken
return
}
t.id = fixedTokens[fs]
t.val = string(fs)
rest = code[len(fs):]
return
}
func newLexer(code string) *eskipLex {
return &eskipLex{
code: code,
initialLength: len(code)}
}
func isWhitespace(c byte) bool { return unicode.IsSpace(rune(c)) }
func isNewline(c byte) bool { return c == newlineChar }
func isUnderscore(c byte) bool { return c == underscore }
func isAlpha(c byte) bool { return unicode.IsLetter(rune(c)) }
func isDigit(c byte) bool { return unicode.IsDigit(rune(c)) }
func isSymbolChar(c byte) bool { return isUnderscore(c) || isAlpha(c) || isDigit(c) }
func isDecimalChar(c byte) bool { return c == decimalChar }
func isNumberChar(c byte) bool { return isDecimalChar(c) || isDigit(c) }
func scanWhile(code string, p charPredicate) ([]byte, string) {
var b []byte
for len(code) > 0 && p(code[0]) {
b = append(b, code[0])
code = code[1:]
}
return b, code
}
func scanVoid(code string, p charPredicate) string {
_, rest := scanWhile(code, p)
return rest
}
func scanEscaped(delimiter byte, code string) ([]byte, string) {
var b []byte
escaped := false
for len(code) > 0 {
c := code[0]
isDelimiter := c == delimiter
isEscapeChar := c == escapeChar
if escaped {
if !isDelimiter && !isEscapeChar {
b = append(b, escapeChar)
}
b = append(b, c)
escaped = false
} else {
if isDelimiter {
return b, code
}
if isEscapeChar {
escaped = true
} else {
b = append(b, c)
}
}
code = code[1:]
}
return b, code
}
func scanRegexp(code string) ([]byte, string) {
var b []byte
escaped := false
var insideGroup = false
for len(code) > 0 {
c := code[0]
isDelimiter := c == '/'
isEscapeChar := c == escapeChar
//Check if starting [... or ending ...]. Ignore if group character is escaped i.e. \[ or \]
if !escaped && !insideGroup && c == '[' {
insideGroup = true
} else if !escaped && insideGroup && c == ']' {
insideGroup = false
}
if escaped {
//delimeter / is escaped in PathRegexp so that it means no end PathRegexp(/\//)
if !isDelimiter && !isEscapeChar {
b = append(b, escapeChar)
}
b = append(b, c)
escaped = false
} else {
if isDelimiter && !insideGroup {
return b, code
}
if isEscapeChar {
escaped = true
} else {
b = append(b, c)
}
}
code = code[1:]
}
return b, code
}
func scanRegexpLiteral(code string) (t token, rest string, err error) {
b, rest := scanRegexp(code[1:])
if len(rest) == 0 {
err = incompleteToken
return
}
rest = rest[1:]
t.id = regexpliteral
t.val = string(b)
return
}
func scanRegexpOrComment(code string) (t token, rest string, err error) {
if len(code) < 2 {
rest = code
err = invalidCharacter
return
}
if code[1] == '/' {
rest = scanComment(code)
err = void
return
}
t, rest, err = scanRegexpLiteral(code)
return
}
func scanStringLiteral(delimiter byte, code string) (t token, rest string, err error) {
b, rest := scanEscaped(delimiter, code[1:])
if len(rest) == 0 {
err = incompleteToken
return
}
rest = rest[1:]
t.id = stringliteral
t.val = string(b)
return
}
func scanWhitespace(code string) string { return scanVoid(code, isWhitespace) }
func scanComment(code string) string {
return scanVoid(code, func(c byte) bool { return !isNewline(c) })
}
func scanDoubleQuote(code string) (token, string, error) { return scanStringLiteral('"', code) }
func scanBacktick(code string) (token, string, error) { return scanStringLiteral('`', code) }
func scanNumber(code string) (t token, rest string, err error) {
decimal := false
b, rest := scanWhile(code, func(c byte) bool {
if isDecimalChar(c) {
if decimal {
return false
}
decimal = true
return true
}
return isDigit(c)
})
if isDecimalChar(b[len(b)-1]) {
err = incompleteToken
return
}
t.id = number
t.val = string(b)
return
}
func scanSymbol(code string) (t token, rest string, err error) {
b, rest := scanWhile(code, isSymbolChar)
t.id = symbol
t.val = string(b)
return
}
func selectFixed(code string) scanner {
for fixed := range fixedTokens {
if len(code) >= len(fixed) && strings.HasPrefix(code, string(fixed)) {
return fixed
}
}
return nil
}
func selectVaryingScanner(code string) scanner {
var sf scannerFunc
switch code[0] {
case '/':
sf = scanRegexpOrComment
case '"':
sf = scanDoubleQuote
case '`':
sf = scanBacktick
}
if isNumberChar(code[0]) {
sf = scanNumber
}
if isAlpha(code[0]) || isUnderscore(code[0]) {
sf = scanSymbol
}
if sf != nil {
return scanner(sf)
}
return nil
}
func selectScanner(code string) scanner {
if s := selectFixed(code); s != nil {
return s
}
return selectVaryingScanner(code)
}
func (l *eskipLex) next() (t token, err error) {
l.code = scanWhitespace(l.code)
if len(l.code) == 0 {
err = eof
return
}
s := selectScanner(l.code)
if s == nil {
err = unexpectedToken
return
}
t, l.code, err = s.scan(l.code)
if err == void {
return l.next()
}
if err == nil {
l.lastToken = &t
}
return
}
func (l *eskipLex) Lex(lval *eskipSymType) int {
token, err := l.next()
if err == eof {
return -1
}
if err != nil {
l.Error(err.Error())
return -1
}
lval.token = token.val
return token.id
}
func (l *eskipLex) Error(err string) {
l.err = fmt.Errorf(
"parse failed after token %v, position %d: %s",
l.lastToken, l.initialLength-len(l.code), err)
}