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// Copyright 2009 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.
// Package scanner implements a scanner for gcfg configuration text.
// It takes a []byte as source which can then be tokenized
// through repeated calls to the Scan method.
//
// Note that the API for the scanner package may change to accommodate new
// features or implementation changes in gcfg.
//
package scanner
import (
"fmt"
"path/filepath"
"unicode"
"unicode/utf8"
)
import (
"code.google.com/p/gcfg/token"
)
// An ErrorHandler may be provided to Scanner.Init. If a syntax error is
// encountered and a handler was installed, the handler is called with a
// position and an error message. The position points to the beginning of
// the offending token.
//
type ErrorHandler func(pos token.Position, msg string)
// A Scanner holds the scanner's internal state while processing
// a given text. It can be allocated as part of another data
// structure but must be initialized via Init before use.
//
type Scanner struct {
// immutable state
file *token.File // source file handle
dir string // directory portion of file.Name()
src []byte // source
err ErrorHandler // error reporting; or nil
mode Mode // scanning mode
// scanning state
ch rune // current character
offset int // character offset
rdOffset int // reading offset (position after current character)
lineOffset int // current line offset
nextVal bool // next token is expected to be a value
// public state - ok to modify
ErrorCount int // number of errors encountered
}
// Read the next Unicode char into s.ch.
// s.ch < 0 means end-of-file.
//
func (s *Scanner) next() {
if s.rdOffset < len(s.src) {
s.offset = s.rdOffset
if s.ch == '\n' {
s.lineOffset = s.offset
s.file.AddLine(s.offset)
}
r, w := rune(s.src[s.rdOffset]), 1
switch {
case r == 0:
s.error(s.offset, "illegal character NUL")
case r >= 0x80:
// not ASCII
r, w = utf8.DecodeRune(s.src[s.rdOffset:])
if r == utf8.RuneError && w == 1 {
s.error(s.offset, "illegal UTF-8 encoding")
}
}
s.rdOffset += w
s.ch = r
} else {
s.offset = len(s.src)
if s.ch == '\n' {
s.lineOffset = s.offset
s.file.AddLine(s.offset)
}
s.ch = -1 // eof
}
}
// A mode value is a set of flags (or 0).
// They control scanner behavior.
//
type Mode uint
const (
ScanComments Mode = 1 << iota // return comments as COMMENT tokens
)
// Init prepares the scanner s to tokenize the text src by setting the
// scanner at the beginning of src. The scanner uses the file set file
// for position information and it adds line information for each line.
// It is ok to re-use the same file when re-scanning the same file as
// line information which is already present is ignored. Init causes a
// panic if the file size does not match the src size.
//
// Calls to Scan will invoke the error handler err if they encounter a
// syntax error and err is not nil. Also, for each error encountered,
// the Scanner field ErrorCount is incremented by one. The mode parameter
// determines how comments are handled.
//
// Note that Init may call err if there is an error in the first character
// of the file.
//
func (s *Scanner) Init(file *token.File, src []byte, err ErrorHandler, mode Mode) {
// Explicitly initialize all fields since a scanner may be reused.
if file.Size() != len(src) {
panic(fmt.Sprintf("file size (%d) does not match src len (%d)", file.Size(), len(src)))
}
s.file = file
s.dir, _ = filepath.Split(file.Name())
s.src = src
s.err = err
s.mode = mode
s.ch = ' '
s.offset = 0
s.rdOffset = 0
s.lineOffset = 0
s.ErrorCount = 0
s.nextVal = false
s.next()
}
func (s *Scanner) error(offs int, msg string) {
if s.err != nil {
s.err(s.file.Position(s.file.Pos(offs)), msg)
}
s.ErrorCount++
}
func (s *Scanner) scanComment() string {
// initial [;#] already consumed
offs := s.offset - 1 // position of initial [;#]
s.next()
for s.ch != '\n' && s.ch >= 0 {
s.next()
}
return string(s.src[offs:s.offset])
}
func isLetter(ch rune) bool {
return 'a' <= ch && ch <= 'z' || 'A' <= ch && ch <= 'Z' || ch >= 0x80 && unicode.IsLetter(ch)
}
func isDigit(ch rune) bool {
return '0' <= ch && ch <= '9' || ch >= 0x80 && unicode.IsDigit(ch)
}
func (s *Scanner) scanIdentifier() string {
offs := s.offset
for isLetter(s.ch) || isDigit(s.ch) || s.ch == '-' {
s.next()
}
return string(s.src[offs:s.offset])
}
func (s *Scanner) scanEscape() {
offs := s.offset
switch s.ch {
case 'n', '\\', '"':
s.next()
return
}
s.next() // always make progress
s.error(offs, "unknown escape sequence")
return
}
func (s *Scanner) scanString() string {
// '"' opening already consumed
offs := s.offset - 1
for s.ch != '"' {
ch := s.ch
s.next()
if ch == '\n' || ch < 0 {
s.error(offs, "string not terminated")
break
}
if ch == '\\' {
s.scanEscape()
}
}
s.next()
return string(s.src[offs:s.offset])
}
func stripCR(b []byte) []byte {
c := make([]byte, len(b))
i := 0
for _, ch := range b {
if ch != '\r' {
c[i] = ch
i++
}
}
return c[:i]
}
func (s *Scanner) scanValString() string {
offs := s.offset
hasCR := false
end := offs
inQuote := false
loop:
for inQuote || s.ch >= 0 && s.ch != '\n' && s.ch != ';' && s.ch != '#' {
ch := s.ch
s.next()
switch {
case inQuote && ch == '\\':
s.scanEscape()
case !inQuote && ch == '\\':
if s.ch == '\r' {
hasCR = true
s.next()
}
if s.ch != '\n' {
s.error(offs, "unquoted '\\' must be followed by new line")
break loop
}
s.next()
case ch == '"':
inQuote = !inQuote
case ch == '\r':
hasCR = true
case ch < 0 || inQuote && ch == '\n':
s.error(offs, "string not terminated")
break loop
}
if inQuote || !isWhiteSpace(ch) {
end = s.offset
}
}
lit := s.src[offs:end]
if hasCR {
lit = stripCR(lit)
}
return string(lit)
}
func isWhiteSpace(ch rune) bool {
return ch == ' ' || ch == '\t' || ch == '\r'
}
func (s *Scanner) skipWhitespace() {
for isWhiteSpace(s.ch) {
s.next()
}
}
// Scan scans the next token and returns the token position, the token,
// and its literal string if applicable. The source end is indicated by
// token.EOF.
//
// If the returned token is a literal (token.IDENT, token.STRING) or
// token.COMMENT, the literal string has the corresponding value.
//
// If the returned token is token.ILLEGAL, the literal string is the
// offending character.
//
// In all other cases, Scan returns an empty literal string.
//
// For more tolerant parsing, Scan will return a valid token if
// possible even if a syntax error was encountered. Thus, even
// if the resulting token sequence contains no illegal tokens,
// a client may not assume that no error occurred. Instead it
// must check the scanner's ErrorCount or the number of calls
// of the error handler, if there was one installed.
//
// Scan adds line information to the file added to the file
// set with Init. Token positions are relative to that file
// and thus relative to the file set.
//
func (s *Scanner) Scan() (pos token.Pos, tok token.Token, lit string) {
scanAgain:
s.skipWhitespace()
// current token start
pos = s.file.Pos(s.offset)
// determine token value
switch ch := s.ch; {
case s.nextVal:
lit = s.scanValString()
tok = token.STRING
s.nextVal = false
case isLetter(ch):
lit = s.scanIdentifier()
tok = token.IDENT
default:
s.next() // always make progress
switch ch {
case -1:
tok = token.EOF
case '\n':
tok = token.EOL
case '"':
tok = token.STRING
lit = s.scanString()
case '[':
tok = token.LBRACK
case ']':
tok = token.RBRACK
case ';', '#':
// comment
lit = s.scanComment()
if s.mode&ScanComments == 0 {
// skip comment
goto scanAgain
}
tok = token.COMMENT
case '=':
tok = token.ASSIGN
s.nextVal = true
default:
s.error(s.file.Offset(pos), fmt.Sprintf("illegal character %#U", ch))
tok = token.ILLEGAL
lit = string(ch)
}
}
return
}