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parser.go
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parser.go
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// Copyright (c) 2013, 2014 Martin Hilton <[email protected]>
//
// Permission to use, copy, modify, and distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
package config
import (
"fmt"
"unicode"
"unicode/utf8"
)
const (
eof rune = -(iota + 1)
invalid
)
// An Event is a type of event that can be detected by the parser.
type Event int
const (
Section Event = iota // A new section in the config file.
Key // A new key in the config file.
EOF // The end of the config file.
)
// ParseError is returned from Next when the file cannot be parsed
// correctly.
type ParseError struct {
Line int // The line where the error occurred.
Col int // The column in the line where the error occured.
Msg string // A description of the error.
}
// Error provides a string representation of the error generated by the parser.
func (p ParseError) Error() string {
return fmt.Sprintf("[%d, %d] %s", p.Line, p.Col, p.Msg)
}
// Parser reads the configuration file finding sections and keys
type Parser struct {
Section string // Current section name, "" if there is no section
Parameter string // Current section parameter\, "" if there is no section, or the current seciton has no parameter
Key string // Current name, "" if this is a Section event
Value string // Current value, "" if there is no value or we have a Section event
b []byte
r rune // current rune
pos int // position of current rune
npos int // position of next rune
line int // line of current rune
col int // column of current rune
err error // current active error
}
// NewParser creates a parser to parse the given input bytes
func NewParser(b []byte) *Parser {
return &Parser{b: b}
}
// Next finds the next Section or Key in the file.
func (p *Parser) Next() (e Event, err error) {
for p.err == nil {
p.read()
switch {
case p.r == eof:
e = EOF
return
case p.r == '\n':
continue
case p.r == ';' || p.r == '#':
p.scanComment()
continue
case p.r == '[':
p.read()
e = Section
p.Section, p.Parameter = p.parseSection()
err = p.err
return
case isSpace(p.r):
continue
case isName(p.r):
e = Key
p.Key, p.Value = p.parseKey()
err = p.err
return
default:
p.unexpected("'[', NAME, ';' or '#'")
}
}
err = p.err
return
}
// read the next rune from the input
func (p *Parser) read() {
var l int
if p.r == eof || p.r == invalid {
return
}
if p.r == '\n' || p.npos == 0 {
p.line++
p.col = 1
} else {
p.col++
}
if p.npos >= len(p.b) {
p.r = eof
l = 0
} else {
p.r, l = utf8.DecodeRune(p.b[p.npos:])
if p.r == utf8.RuneError && l < 2 {
p.error("UTF-8 encoding error")
p.r = invalid
}
}
p.pos, p.npos = p.npos, p.npos+l
}
// unexpected generates an error indicating that an invalid rune has been seen.
// msg should be used to indicate characters that are valid in the current position
func (p *Parser) unexpected(msg string) {
if p.r == eof {
p.error("Unexpected EOF, expecting " + msg + ".")
} else {
p.error(fmt.Sprintf("Unexpected %q, expecting %s.", p.r, msg))
}
}
// error generates a new error with the provided message
func (p *Parser) error(msg string) {
if p.err == nil {
p.err = ParseError{p.line, p.col, msg}
}
}
// parseKey parses a key/value line. if there is no value "" will be returned
func (p *Parser) parseKey() (key, value string) {
key = p.parseName()
p.scanSpace()
if p.r == ';' || p.r == '#' || p.r == '\n' || p.r == eof {
goto afterValue
}
if p.r != '=' {
p.unexpected("'=', ';' or '#'")
}
p.read()
p.scanSpace()
switch p.r {
case ';', '#', '\n':
// continue
case '"':
p.read()
value = p.parseString()
case '`':
p.read()
value = p.parseRawString()
default:
value = p.parseValue()
}
afterValue:
p.scanSpace()
if p.r == ';' || p.r == '#' {
p.scanComment()
}
if p.r != '\n' && p.r != eof {
p.unexpected("'\\n' or EOF")
}
return
}
// parseSection parses a section header, including optional parameter.
// If no parameter is used then "" will be returned
func (p *Parser) parseSection() (name, parameter string) {
p.scanSpace()
name = p.parseName()
if p.r == ']' {
goto closed
} else if !isSpace(p.r) {
p.unexpected("']' or space")
}
p.scanSpace()
if p.r == '"' {
p.read()
parameter = p.parseString()
p.scanSpace()
}
if p.r != ']' {
p.unexpected("']'")
}
closed:
p.read()
p.scanSpace()
if p.r == ';' || p.r == '#' {
p.scanComment()
}
if p.r != '\n' && p.r != eof {
p.unexpected("'\\n' or EOF")
}
return
}
// parseValue parses the value portion of a key/value line
func (p *Parser) parseValue() string {
var buf []rune
end := 0
for {
switch {
case isSpace(p.r):
buf = append(buf, p.r)
case p.r == ';' || p.r == '#' || p.r == '\n' || p.r == invalid || p.r == eof:
return string(buf[:end])
default:
buf = append(buf, p.r)
end = len(buf)
}
p.read()
}
panic("unreachable!")
}
// parseString parses a " wrapped string.
func (p *Parser) parseString() string {
var buf []rune
for {
switch p.r {
case '"':
p.read()
return string(buf)
case '\n', eof:
p.error("unterminated string")
return ""
case invalid:
return ""
case '\\':
p.read()
buf = p.parseStringEscape(buf)
default:
buf = append(buf, p.r)
p.read()
}
}
panic("unreachable!")
}
// parseStringEscape parses an escape sequence in a string.
func (p *Parser) parseStringEscape(buf []rune) []rune {
switch p.r {
case '\\', '"':
buf = append(buf, p.r)
case 'n':
buf = append(buf, '\n')
case 'r':
buf = append(buf, '\r')
case 't':
buf = append(buf, '\t')
default:
p.unexpected("'\\', '\"', 'n', 'r', 't'")
return buf
}
p.read()
return buf
}
// parseRawString parses a go style raw string.
func (p *Parser) parseRawString() string {
start := p.pos
end := start
for {
switch p.r {
case '`':
end = p.pos
p.read()
return string(p.b[start:end])
case eof:
p.error("Unterminated raw string")
return ""
case invalid:
return ""
default:
p.read()
}
}
panic("unreachable!")
}
// parseName parses a sequence of runes that form a section or key name.
func (p *Parser) parseName() string {
if !isName(p.r) {
p.unexpected("NAME")
}
start := p.pos
p.read()
for isName(p.r) {
p.read()
}
return string(p.b[start:p.pos])
}
// scanComment scans over any comments in the input.
func (p *Parser) scanComment() {
for p.r != '\n' && p.r != eof {
p.read()
}
}
// scanSpace scans over any whitespace in the input.
func (p *Parser) scanSpace() {
for isSpace(p.r) {
p.read()
}
}
// isSpace checks if a rune is skipable whitespace.
func isSpace(r rune) bool {
return r != '\n' && unicode.IsSpace(r)
}
// isName checks if a rune is a valid character in a name.
func isName(r rune) bool {
return r == '.' || r == '_' || r == '-' || unicode.IsLetter(r) || unicode.IsNumber(r)
}