src/pkg/encoding/json/scanner.go - go - Git at Google

 // Copyright 2010 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 json

 // JSON value parser state machine.
 // Just about at the limit of what is reasonable to write by hand.
 // Some parts are a bit tedious, but overall it nicely factors out the
 // otherwise common code from the multiple scanning functions
 // in this package (Compact, Indent, checkValid, nextValue, etc).
 //
 // This file starts with two simple examples using the scanner
 // before diving into the scanner itself.

 import "strconv"

 // checkValid verifies that data is valid JSON-encoded data.
 // scan is passed in for use by checkValid to avoid an allocation.
 func checkValid(data []byte, scan *scanner) error {
 	scan.reset()
 	for _, c := range data {
 		scan.bytes++
 		if scan.step(scan, int(c)) == scanError {
 			return scan.err
 		}
 	}
 	if scan.eof() == scanError {
 		return scan.err
 	}
 	return nil
 }

 // nextValue splits data after the next whole JSON value,
 // returning that value and the bytes that follow it as separate slices.
 // scan is passed in for use by nextValue to avoid an allocation.
 func nextValue(data []byte, scan *scanner) (value, rest []byte, err error) {
 	scan.reset()
 	for i, c := range data {
 		v := scan.step(scan, int(c))
 		if v >= scanEnd {
 			switch v {
 			case scanError:
 				return nil, nil, scan.err
 			case scanEnd:
 				return data[0:i], data[i:], nil
 			}
 		}
 	}
 	if scan.eof() == scanError {
 		return nil, nil, scan.err
 	}
 	return data, nil, nil
 }

 // A SyntaxError is a description of a JSON syntax error.
 type SyntaxError struct {
 	msg    string // description of error
 	Offset int64  // error occurred after reading Offset bytes
 }

 func (e *SyntaxError) Error() string { return e.msg }

 // A scanner is a JSON scanning state machine.
 // Callers call scan.reset() and then pass bytes in one at a time
 // by calling scan.step(&scan, c) for each byte.
 // The return value, referred to as an opcode, tells the
 // caller about significant parsing events like beginning
 // and ending literals, objects, and arrays, so that the
 // caller can follow along if it wishes.
 // The return value scanEnd indicates that a single top-level
 // JSON value has been completed, *before* the byte that
 // just got passed in.  (The indication must be delayed in order
 // to recognize the end of numbers: is 123 a whole value or
 // the beginning of 12345e+6?).
 type scanner struct {
 	// The step is a func to be called to execute the next transition.
 	// Also tried using an integer constant and a single func
 	// with a switch, but using the func directly was 10% faster
 	// on a 64-bit Mac Mini, and it's nicer to read.
 	step func(*scanner, int) int

 	// Reached end of top-level value.
 	endTop bool

 	// Stack of what we're in the middle of - array values, object keys, object values.
 	parseState []int

 	// Error that happened, if any.
 	err error

 	// 1-byte redo (see undo method)
 	redo      bool
 	redoCode  int
 	redoState func(*scanner, int) int

 	// total bytes consumed, updated by decoder.Decode
 	bytes int64
 }

 // These values are returned by the state transition functions
 // assigned to scanner.state and the method scanner.eof.
 // They give details about the current state of the scan that
 // callers might be interested to know about.
 // It is okay to ignore the return value of any particular
 // call to scanner.state: if one call returns scanError,
 // every subsequent call will return scanError too.
 const (
 	// Continue.
 	scanContinue     = iota // uninteresting byte
 	scanBeginLiteral        // end implied by next result != scanContinue
 	scanBeginObject         // begin object
 	scanObjectKey           // just finished object key (string)
 	scanObjectValue         // just finished non-last object value
 	scanEndObject           // end object (implies scanObjectValue if possible)
 	scanBeginArray          // begin array
 	scanArrayValue          // just finished array value
 	scanEndArray            // end array (implies scanArrayValue if possible)
 	scanSkipSpace           // space byte; can skip; known to be last "continue" result

 	// Stop.
 	scanEnd   // top-level value ended *before* this byte; known to be first "stop" result
 	scanError // hit an error, scanner.err.
 )

 // These values are stored in the parseState stack.
 // They give the current state of a composite value
 // being scanned.  If the parser is inside a nested value
 // the parseState describes the nested state, outermost at entry 0.
 const (
 	parseObjectKey   = iota // parsing object key (before colon)
 	parseObjectValue        // parsing object value (after colon)
 	parseArrayValue         // parsing array value
 )

 // reset prepares the scanner for use.
 // It must be called before calling s.step.
 func (s *scanner) reset() {
 	s.step = stateBeginValue
 	s.parseState = s.parseState[0:0]
 	s.err = nil
 	s.redo = false
 	s.endTop = false
 }

 // eof tells the scanner that the end of input has been reached.
 // It returns a scan status just as s.step does.
 func (s *scanner) eof() int {
 	if s.err != nil {
 		return scanError
 	}
 	if s.endTop {
 		return scanEnd
 	}
 	s.step(s, ' ')
 	if s.endTop {
 		return scanEnd
 	}
 	if s.err == nil {
 		s.err = &SyntaxError{"unexpected end of JSON input", s.bytes}
 	}
 	return scanError
 }

 // pushParseState pushes a new parse state p onto the parse stack.
 func (s *scanner) pushParseState(p int) {
 	s.parseState = append(s.parseState, p)
 }

 // popParseState pops a parse state (already obtained) off the stack
 // and updates s.step accordingly.
 func (s *scanner) popParseState() {
 	n := len(s.parseState) - 1
 	s.parseState = s.parseState[0:n]
 	s.redo = false
 	if n == 0 {
 		s.step = stateEndTop
 		s.endTop = true
 	} else {
 		s.step = stateEndValue
 	}
 }

 func isSpace(c rune) bool {
 	return c == ' ' || c == '\t' || c == '\r' || c == '\n'
 }

 // stateBeginValueOrEmpty is the state after reading `[`.
 func stateBeginValueOrEmpty(s *scanner, c int) int {
 	if c <= ' ' && isSpace(rune(c)) {
 		return scanSkipSpace
 	}
 	if c == ']' {
 		return stateEndValue(s, c)
 	}
 	return stateBeginValue(s, c)
 }

 // stateBeginValue is the state at the beginning of the input.
 func stateBeginValue(s *scanner, c int) int {
 	if c <= ' ' && isSpace(rune(c)) {
 		return scanSkipSpace
 	}
 	switch c {
 	case '{':
 		s.step = stateBeginStringOrEmpty
 		s.pushParseState(parseObjectKey)
 		return scanBeginObject
 	case '[':
 		s.step = stateBeginValueOrEmpty
 		s.pushParseState(parseArrayValue)
 		return scanBeginArray
 	case '"':
 		s.step = stateInString
 		return scanBeginLiteral
 	case '-':
 		s.step = stateNeg
 		return scanBeginLiteral
 	case '0': // beginning of 0.123
 		s.step = state0
 		return scanBeginLiteral
 	case 't': // beginning of true
 		s.step = stateT
 		return scanBeginLiteral
 	case 'f': // beginning of false
 		s.step = stateF
 		return scanBeginLiteral
 	case 'n': // beginning of null
 		s.step = stateN
 		return scanBeginLiteral
 	}
 	if '1' <= c && c <= '9' { // beginning of 1234.5
 		s.step = state1
 		return scanBeginLiteral
 	}
 	return s.error(c, "looking for beginning of value")
 }

 // stateBeginStringOrEmpty is the state after reading `{`.
 func stateBeginStringOrEmpty(s *scanner, c int) int {
 	if c <= ' ' && isSpace(rune(c)) {
 		return scanSkipSpace
 	}
 	if c == '}' {
 		n := len(s.parseState)
 		s.parseState[n-1] = parseObjectValue
 		return stateEndValue(s, c)
 	}
 	return stateBeginString(s, c)
 }

 // stateBeginString is the state after reading `{"key": value,`.
 func stateBeginString(s *scanner, c int) int {
 	if c <= ' ' && isSpace(rune(c)) {
 		return scanSkipSpace
 	}
 	if c == '"' {
 		s.step = stateInString
 		return scanBeginLiteral
 	}
 	return s.error(c, "looking for beginning of object key string")
 }

 // stateEndValue is the state after completing a value,
 // such as after reading `{}` or `true` or `["x"`.
 func stateEndValue(s *scanner, c int) int {
 	n := len(s.parseState)
 	if n == 0 {
 		// Completed top-level before the current byte.
 		s.step = stateEndTop
 		s.endTop = true
 		return stateEndTop(s, c)
 	}
 	if c <= ' ' && isSpace(rune(c)) {
 		s.step = stateEndValue
 		return scanSkipSpace
 	}
 	ps := s.parseState[n-1]
 	switch ps {
 	case parseObjectKey:
 		if c == ':' {
 			s.parseState[n-1] = parseObjectValue
 			s.step = stateBeginValue
 			return scanObjectKey
 		}
 		return s.error(c, "after object key")
 	case parseObjectValue:
 		if c == ',' {
 			s.parseState[n-1] = parseObjectKey
 			s.step = stateBeginString
 			return scanObjectValue
 		}
 		if c == '}' {
 			s.popParseState()
 			return scanEndObject
 		}
 		return s.error(c, "after object key:value pair")
 	case parseArrayValue:
 		if c == ',' {
 			s.step = stateBeginValue
 			return scanArrayValue
 		}
 		if c == ']' {
 			s.popParseState()
 			return scanEndArray
 		}
 		return s.error(c, "after array element")
 	}
 	return s.error(c, "")
 }

 // stateEndTop is the state after finishing the top-level value,
 // such as after reading `{}` or `[1,2,3]`.
 // Only space characters should be seen now.
 func stateEndTop(s *scanner, c int) int {
 	if c != ' ' && c != '\t' && c != '\r' && c != '\n' {
 		// Complain about non-space byte on next call.
 		s.error(c, "after top-level value")
 	}
 	return scanEnd
 }

 // stateInString is the state after reading `"`.
 func stateInString(s *scanner, c int) int {
 	if c == '"' {
 		s.step = stateEndValue
 		return scanContinue
 	}
 	if c == '\\' {
 		s.step = stateInStringEsc
 		return scanContinue
 	}
 	if c < 0x20 {
 		return s.error(c, "in string literal")
 	}
 	return scanContinue
 }

 // stateInStringEsc is the state after reading `"\` during a quoted string.
 func stateInStringEsc(s *scanner, c int) int {
 	switch c {
 	case 'b', 'f', 'n', 'r', 't', '\\', '/', '"':
 		s.step = stateInString
 		return scanContinue
 	}
 	if c == 'u' {
 		s.step = stateInStringEscU
 		return scanContinue
 	}
 	return s.error(c, "in string escape code")
 }

 // stateInStringEscU is the state after reading `"\u` during a quoted string.
 func stateInStringEscU(s *scanner, c int) int {
 	if '0' <= c && c <= '9' || 'a' <= c && c <= 'f' || 'A' <= c && c <= 'F' {
 		s.step = stateInStringEscU1
 		return scanContinue
 	}
 	// numbers
 	return s.error(c, "in \\u hexadecimal character escape")
 }

 // stateInStringEscU1 is the state after reading `"\u1` during a quoted string.
 func stateInStringEscU1(s *scanner, c int) int {
 	if '0' <= c && c <= '9' || 'a' <= c && c <= 'f' || 'A' <= c && c <= 'F' {
 		s.step = stateInStringEscU12
 		return scanContinue
 	}
 	// numbers
 	return s.error(c, "in \\u hexadecimal character escape")
 }

 // stateInStringEscU12 is the state after reading `"\u12` during a quoted string.
 func stateInStringEscU12(s *scanner, c int) int {
 	if '0' <= c && c <= '9' || 'a' <= c && c <= 'f' || 'A' <= c && c <= 'F' {
 		s.step = stateInStringEscU123
 		return scanContinue
 	}
 	// numbers
 	return s.error(c, "in \\u hexadecimal character escape")
 }

 // stateInStringEscU123 is the state after reading `"\u123` during a quoted string.
 func stateInStringEscU123(s *scanner, c int) int {
 	if '0' <= c && c <= '9' || 'a' <= c && c <= 'f' || 'A' <= c && c <= 'F' {
 		s.step = stateInString
 		return scanContinue
 	}
 	// numbers
 	return s.error(c, "in \\u hexadecimal character escape")
 }

 // stateInStringEscU123 is the state after reading `-` during a number.
 func stateNeg(s *scanner, c int) int {
 	if c == '0' {
 		s.step = state0
 		return scanContinue
 	}
 	if '1' <= c && c <= '9' {
 		s.step = state1
 		return scanContinue
 	}
 	return s.error(c, "in numeric literal")
 }

 // state1 is the state after reading a non-zero integer during a number,
 // such as after reading `1` or `100` but not `0`.
 func state1(s *scanner, c int) int {
 	if '0' <= c && c <= '9' {
 		s.step = state1
 		return scanContinue
 	}
 	return state0(s, c)
 }

 // state0 is the state after reading `0` during a number.
 func state0(s *scanner, c int) int {
 	if c == '.' {
 		s.step = stateDot
 		return scanContinue
 	}
 	if c == 'e' || c == 'E' {
 		s.step = stateE
 		return scanContinue
 	}
 	return stateEndValue(s, c)
 }

 // stateDot is the state after reading the integer and decimal point in a number,
 // such as after reading `1.`.
 func stateDot(s *scanner, c int) int {
 	if '0' <= c && c <= '9' {
 		s.step = stateDot0
 		return scanContinue
 	}
 	return s.error(c, "after decimal point in numeric literal")
 }

 // stateDot0 is the state after reading the integer, decimal point, and subsequent
 // digits of a number, such as after reading `3.14`.
 func stateDot0(s *scanner, c int) int {
 	if '0' <= c && c <= '9' {
 		s.step = stateDot0
 		return scanContinue
 	}
 	if c == 'e' || c == 'E' {
 		s.step = stateE
 		return scanContinue
 	}
 	return stateEndValue(s, c)
 }

 // stateE is the state after reading the mantissa and e in a number,
 // such as after reading `314e` or `0.314e`.
 func stateE(s *scanner, c int) int {
 	if c == '+' {
 		s.step = stateESign
 		return scanContinue
 	}
 	if c == '-' {
 		s.step = stateESign
 		return scanContinue
 	}
 	return stateESign(s, c)
 }

 // stateESign is the state after reading the mantissa, e, and sign in a number,
 // such as after reading `314e-` or `0.314e+`.
 func stateESign(s *scanner, c int) int {
 	if '0' <= c && c <= '9' {
 		s.step = stateE0
 		return scanContinue
 	}
 	return s.error(c, "in exponent of numeric literal")
 }

 // stateE0 is the state after reading the mantissa, e, optional sign,
 // and at least one digit of the exponent in a number,
 // such as after reading `314e-2` or `0.314e+1` or `3.14e0`.
 func stateE0(s *scanner, c int) int {
 	if '0' <= c && c <= '9' {
 		s.step = stateE0
 		return scanContinue
 	}
 	return stateEndValue(s, c)
 }

 // stateT is the state after reading `t`.
 func stateT(s *scanner, c int) int {
 	if c == 'r' {
 		s.step = stateTr
 		return scanContinue
 	}
 	return s.error(c, "in literal true (expecting 'r')")
 }

 // stateTr is the state after reading `tr`.
 func stateTr(s *scanner, c int) int {
 	if c == 'u' {
 		s.step = stateTru
 		return scanContinue
 	}
 	return s.error(c, "in literal true (expecting 'u')")
 }

 // stateTru is the state after reading `tru`.
 func stateTru(s *scanner, c int) int {
 	if c == 'e' {
 		s.step = stateEndValue
 		return scanContinue
 	}
 	return s.error(c, "in literal true (expecting 'e')")
 }

 // stateF is the state after reading `f`.
 func stateF(s *scanner, c int) int {
 	if c == 'a' {
 		s.step = stateFa
 		return scanContinue
 	}
 	return s.error(c, "in literal false (expecting 'a')")
 }

 // stateFa is the state after reading `fa`.
 func stateFa(s *scanner, c int) int {
 	if c == 'l' {
 		s.step = stateFal
 		return scanContinue
 	}
 	return s.error(c, "in literal false (expecting 'l')")
 }

 // stateFal is the state after reading `fal`.
 func stateFal(s *scanner, c int) int {
 	if c == 's' {
 		s.step = stateFals
 		return scanContinue
 	}
 	return s.error(c, "in literal false (expecting 's')")
 }

 // stateFals is the state after reading `fals`.
 func stateFals(s *scanner, c int) int {
 	if c == 'e' {
 		s.step = stateEndValue
 		return scanContinue
 	}
 	return s.error(c, "in literal false (expecting 'e')")
 }

 // stateN is the state after reading `n`.
 func stateN(s *scanner, c int) int {
 	if c == 'u' {
 		s.step = stateNu
 		return scanContinue
 	}
 	return s.error(c, "in literal null (expecting 'u')")
 }

 // stateNu is the state after reading `nu`.
 func stateNu(s *scanner, c int) int {
 	if c == 'l' {
 		s.step = stateNul
 		return scanContinue
 	}
 	return s.error(c, "in literal null (expecting 'l')")
 }

 // stateNul is the state after reading `nul`.
 func stateNul(s *scanner, c int) int {
 	if c == 'l' {
 		s.step = stateEndValue
 		return scanContinue
 	}
 	return s.error(c, "in literal null (expecting 'l')")
 }

 // stateError is the state after reaching a syntax error,
 // such as after reading `[1}` or `5.1.2`.
 func stateError(s *scanner, c int) int {
 	return scanError
 }

 // error records an error and switches to the error state.
 func (s *scanner) error(c int, context string) int {
 	s.step = stateError
 	s.err = &SyntaxError{"invalid character " + quoteChar(c) + " " + context, s.bytes}
 	return scanError
 }

 // quoteChar formats c as a quoted character literal
 func quoteChar(c int) string {
 	// special cases - different from quoted strings
 	if c == '\'' {
 		return `'\''`
 	}
 	if c == '"' {
 		return `'"'`
 	}

 	// use quoted string with different quotation marks
 	s := strconv.Quote(string(c))
 	return "'" + s[1:len(s)-1] + "'"
 }

 // undo causes the scanner to return scanCode from the next state transition.
 // This gives callers a simple 1-byte undo mechanism.
 func (s *scanner) undo(scanCode int) {
 	if s.redo {
 		panic("json: invalid use of scanner")
 	}
 	s.redoCode = scanCode
 	s.redoState = s.step
 	s.step = stateRedo
 	s.redo = true
 }

 // stateRedo helps implement the scanner's 1-byte undo.
 func stateRedo(s *scanner, c int) int {
 	s.redo = false
 	s.step = s.redoState
 	return s.redoCode
 }
	// Copyright 2010 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 json

	// JSON value parser state machine.
	// Just about at the limit of what is reasonable to write by hand.
	// Some parts are a bit tedious, but overall it nicely factors out the
	// otherwise common code from the multiple scanning functions
	// in this package (Compact, Indent, checkValid, nextValue, etc).
	//
	// This file starts with two simple examples using the scanner
	// before diving into the scanner itself.

	import "strconv"

	// checkValid verifies that data is valid JSON-encoded data.
	// scan is passed in for use by checkValid to avoid an allocation.
	func checkValid(data []byte, scan *scanner) error {
	scan.reset()
	for _, c := range data {
	scan.bytes++
	if scan.step(scan, int(c)) == scanError {
	return scan.err
	}
	}
	if scan.eof() == scanError {
	return scan.err
	}
	return nil
	}

	// nextValue splits data after the next whole JSON value,
	// returning that value and the bytes that follow it as separate slices.
	// scan is passed in for use by nextValue to avoid an allocation.
	func nextValue(data []byte, scan *scanner) (value, rest []byte, err error) {
	scan.reset()
	for i, c := range data {
	v := scan.step(scan, int(c))
	if v >= scanEnd {
	switch v {
	case scanError:
	return nil, nil, scan.err
	case scanEnd:
	return data[0:i], data[i:], nil
	}
	}
	}
	if scan.eof() == scanError {
	return nil, nil, scan.err
	}
	return data, nil, nil
	}

	// A SyntaxError is a description of a JSON syntax error.
	type SyntaxError struct {
	msg string // description of error
	Offset int64 // error occurred after reading Offset bytes
	}

	func (e *SyntaxError) Error() string { return e.msg }

	// A scanner is a JSON scanning state machine.
	// Callers call scan.reset() and then pass bytes in one at a time
	// by calling scan.step(&scan, c) for each byte.
	// The return value, referred to as an opcode, tells the
	// caller about significant parsing events like beginning
	// and ending literals, objects, and arrays, so that the
	// caller can follow along if it wishes.
	// The return value scanEnd indicates that a single top-level
	// JSON value has been completed, before the byte that
	// just got passed in. (The indication must be delayed in order
	// to recognize the end of numbers: is 123 a whole value or
	// the beginning of 12345e+6?).
	type scanner struct {
	// The step is a func to be called to execute the next transition.
	// Also tried using an integer constant and a single func
	// with a switch, but using the func directly was 10% faster
	// on a 64-bit Mac Mini, and it's nicer to read.
	step func(*scanner, int) int

	// Reached end of top-level value.
	endTop bool

	// Stack of what we're in the middle of - array values, object keys, object values.
	parseState []int

	// Error that happened, if any.
	err error

	// 1-byte redo (see undo method)
	redo bool
	redoCode int
	redoState func(*scanner, int) int

	// total bytes consumed, updated by decoder.Decode
	bytes int64
	}

	// These values are returned by the state transition functions
	// assigned to scanner.state and the method scanner.eof.
	// They give details about the current state of the scan that
	// callers might be interested to know about.
	// It is okay to ignore the return value of any particular
	// call to scanner.state: if one call returns scanError,
	// every subsequent call will return scanError too.
	const (
	// Continue.
	scanContinue = iota // uninteresting byte
	scanBeginLiteral // end implied by next result != scanContinue
	scanBeginObject // begin object
	scanObjectKey // just finished object key (string)
	scanObjectValue // just finished non-last object value
	scanEndObject // end object (implies scanObjectValue if possible)
	scanBeginArray // begin array
	scanArrayValue // just finished array value
	scanEndArray // end array (implies scanArrayValue if possible)
	scanSkipSpace // space byte; can skip; known to be last "continue" result

	// Stop.
	scanEnd // top-level value ended before this byte; known to be first "stop" result
	scanError // hit an error, scanner.err.
	)

	// These values are stored in the parseState stack.
	// They give the current state of a composite value
	// being scanned. If the parser is inside a nested value
	// the parseState describes the nested state, outermost at entry 0.
	const (
	parseObjectKey = iota // parsing object key (before colon)
	parseObjectValue // parsing object value (after colon)
	parseArrayValue // parsing array value
	)

	// reset prepares the scanner for use.
	// It must be called before calling s.step.
	func (s *scanner) reset() {
	s.step = stateBeginValue
	s.parseState = s.parseState[0:0]
	s.err = nil
	s.redo = false
	s.endTop = false
	}

	// eof tells the scanner that the end of input has been reached.
	// It returns a scan status just as s.step does.
	func (s *scanner) eof() int {
	if s.err != nil {
	return scanError
	}
	if s.endTop {
	return scanEnd
	}
	s.step(s, ' ')
	if s.endTop {
	return scanEnd
	}
	if s.err == nil {
	s.err = &SyntaxError{"unexpected end of JSON input", s.bytes}
	}
	return scanError
	}

	// pushParseState pushes a new parse state p onto the parse stack.
	func (s *scanner) pushParseState(p int) {
	s.parseState = append(s.parseState, p)
	}

	// popParseState pops a parse state (already obtained) off the stack
	// and updates s.step accordingly.
	func (s *scanner) popParseState() {
	n := len(s.parseState) - 1
	s.parseState = s.parseState[0:n]
	s.redo = false
	if n == 0 {
	s.step = stateEndTop
	s.endTop = true
	} else {
	s.step = stateEndValue
	}
	}

	func isSpace(c rune) bool {
	return c == ' ' \|\| c == '\t' \|\| c == '\r' \|\| c == '\n'
	}

	// stateBeginValueOrEmpty is the state after reading `[`.
	func stateBeginValueOrEmpty(s *scanner, c int) int {
	if c <= ' ' && isSpace(rune(c)) {
	return scanSkipSpace
	}
	if c == ']' {
	return stateEndValue(s, c)
	}
	return stateBeginValue(s, c)
	}

	// stateBeginValue is the state at the beginning of the input.
	func stateBeginValue(s *scanner, c int) int {
	if c <= ' ' && isSpace(rune(c)) {
	return scanSkipSpace
	}
	switch c {
	case '{':
	s.step = stateBeginStringOrEmpty
	s.pushParseState(parseObjectKey)
	return scanBeginObject
	case '[':
	s.step = stateBeginValueOrEmpty
	s.pushParseState(parseArrayValue)
	return scanBeginArray
	case '"':
	s.step = stateInString
	return scanBeginLiteral
	case '-':
	s.step = stateNeg
	return scanBeginLiteral
	case '0': // beginning of 0.123
	s.step = state0
	return scanBeginLiteral
	case 't': // beginning of true
	s.step = stateT
	return scanBeginLiteral
	case 'f': // beginning of false
	s.step = stateF
	return scanBeginLiteral
	case 'n': // beginning of null
	s.step = stateN
	return scanBeginLiteral
	}
	if '1' <= c && c <= '9' { // beginning of 1234.5
	s.step = state1
	return scanBeginLiteral
	}
	return s.error(c, "looking for beginning of value")
	}

	// stateBeginStringOrEmpty is the state after reading `{`.
	func stateBeginStringOrEmpty(s *scanner, c int) int {
	if c <= ' ' && isSpace(rune(c)) {
	return scanSkipSpace
	}
	if c == '}' {
	n := len(s.parseState)
	s.parseState[n-1] = parseObjectValue
	return stateEndValue(s, c)
	}
	return stateBeginString(s, c)
	}

	// stateBeginString is the state after reading `{"key": value,`.
	func stateBeginString(s *scanner, c int) int {
	if c <= ' ' && isSpace(rune(c)) {
	return scanSkipSpace
	}
	if c == '"' {
	s.step = stateInString
	return scanBeginLiteral
	}
	return s.error(c, "looking for beginning of object key string")
	}

	// stateEndValue is the state after completing a value,
	// such as after reading `{}` or `true` or `["x"`.
	func stateEndValue(s *scanner, c int) int {
	n := len(s.parseState)
	if n == 0 {
	// Completed top-level before the current byte.
	s.step = stateEndTop
	s.endTop = true
	return stateEndTop(s, c)
	}
	if c <= ' ' && isSpace(rune(c)) {
	s.step = stateEndValue
	return scanSkipSpace
	}
	ps := s.parseState[n-1]
	switch ps {
	case parseObjectKey:
	if c == ':' {
	s.parseState[n-1] = parseObjectValue
	s.step = stateBeginValue
	return scanObjectKey
	}
	return s.error(c, "after object key")
	case parseObjectValue:
	if c == ',' {
	s.parseState[n-1] = parseObjectKey
	s.step = stateBeginString
	return scanObjectValue
	}
	if c == '}' {
	s.popParseState()
	return scanEndObject
	}
	return s.error(c, "after object key:value pair")
	case parseArrayValue:
	if c == ',' {
	s.step = stateBeginValue
	return scanArrayValue
	}
	if c == ']' {
	s.popParseState()
	return scanEndArray
	}
	return s.error(c, "after array element")
	}
	return s.error(c, "")
	}

	// stateEndTop is the state after finishing the top-level value,
	// such as after reading `{}` or `[1,2,3]`.
	// Only space characters should be seen now.
	func stateEndTop(s *scanner, c int) int {
	if c != ' ' && c != '\t' && c != '\r' && c != '\n' {
	// Complain about non-space byte on next call.
	s.error(c, "after top-level value")
	}
	return scanEnd
	}

	// stateInString is the state after reading `"`.
	func stateInString(s *scanner, c int) int {
	if c == '"' {
	s.step = stateEndValue
	return scanContinue
	}
	if c == '\\' {
	s.step = stateInStringEsc
	return scanContinue
	}
	if c < 0x20 {
	return s.error(c, "in string literal")
	}
	return scanContinue
	}

	// stateInStringEsc is the state after reading `"\` during a quoted string.
	func stateInStringEsc(s *scanner, c int) int {
	switch c {
	case 'b', 'f', 'n', 'r', 't', '\\', '/', '"':
	s.step = stateInString
	return scanContinue
	}
	if c == 'u' {
	s.step = stateInStringEscU
	return scanContinue
	}
	return s.error(c, "in string escape code")
	}

	// stateInStringEscU is the state after reading `"\u` during a quoted string.
	func stateInStringEscU(s *scanner, c int) int {
	if '0' <= c && c <= '9' \|\| 'a' <= c && c <= 'f' \|\| 'A' <= c && c <= 'F' {
	s.step = stateInStringEscU1
	return scanContinue
	}
	// numbers
	return s.error(c, "in \\u hexadecimal character escape")
	}

	// stateInStringEscU1 is the state after reading `"\u1` during a quoted string.
	func stateInStringEscU1(s *scanner, c int) int {
	if '0' <= c && c <= '9' \|\| 'a' <= c && c <= 'f' \|\| 'A' <= c && c <= 'F' {
	s.step = stateInStringEscU12
	return scanContinue
	}
	// numbers
	return s.error(c, "in \\u hexadecimal character escape")
	}

	// stateInStringEscU12 is the state after reading `"\u12` during a quoted string.
	func stateInStringEscU12(s *scanner, c int) int {
	if '0' <= c && c <= '9' \|\| 'a' <= c && c <= 'f' \|\| 'A' <= c && c <= 'F' {
	s.step = stateInStringEscU123
	return scanContinue
	}
	// numbers
	return s.error(c, "in \\u hexadecimal character escape")
	}

	// stateInStringEscU123 is the state after reading `"\u123` during a quoted string.
	func stateInStringEscU123(s *scanner, c int) int {
	if '0' <= c && c <= '9' \|\| 'a' <= c && c <= 'f' \|\| 'A' <= c && c <= 'F' {
	s.step = stateInString
	return scanContinue
	}
	// numbers
	return s.error(c, "in \\u hexadecimal character escape")
	}

	// stateInStringEscU123 is the state after reading `-` during a number.
	func stateNeg(s *scanner, c int) int {
	if c == '0' {
	s.step = state0
	return scanContinue
	}
	if '1' <= c && c <= '9' {
	s.step = state1
	return scanContinue
	}
	return s.error(c, "in numeric literal")
	}

	// state1 is the state after reading a non-zero integer during a number,
	// such as after reading `1` or `100` but not `0`.
	func state1(s *scanner, c int) int {
	if '0' <= c && c <= '9' {
	s.step = state1
	return scanContinue
	}
	return state0(s, c)
	}

	// state0 is the state after reading `0` during a number.
	func state0(s *scanner, c int) int {
	if c == '.' {
	s.step = stateDot
	return scanContinue
	}
	if c == 'e' \|\| c == 'E' {
	s.step = stateE
	return scanContinue
	}
	return stateEndValue(s, c)
	}

	// stateDot is the state after reading the integer and decimal point in a number,
	// such as after reading `1.`.
	func stateDot(s *scanner, c int) int {
	if '0' <= c && c <= '9' {
	s.step = stateDot0
	return scanContinue
	}
	return s.error(c, "after decimal point in numeric literal")
	}

	// stateDot0 is the state after reading the integer, decimal point, and subsequent
	// digits of a number, such as after reading `3.14`.
	func stateDot0(s *scanner, c int) int {
	if '0' <= c && c <= '9' {
	s.step = stateDot0
	return scanContinue
	}
	if c == 'e' \|\| c == 'E' {
	s.step = stateE
	return scanContinue
	}
	return stateEndValue(s, c)
	}

	// stateE is the state after reading the mantissa and e in a number,
	// such as after reading `314e` or `0.314e`.
	func stateE(s *scanner, c int) int {
	if c == '+' {
	s.step = stateESign
	return scanContinue
	}
	if c == '-' {
	s.step = stateESign
	return scanContinue
	}
	return stateESign(s, c)
	}

	// stateESign is the state after reading the mantissa, e, and sign in a number,
	// such as after reading `314e-` or `0.314e+`.
	func stateESign(s *scanner, c int) int {
	if '0' <= c && c <= '9' {
	s.step = stateE0
	return scanContinue
	}
	return s.error(c, "in exponent of numeric literal")
	}

	// stateE0 is the state after reading the mantissa, e, optional sign,
	// and at least one digit of the exponent in a number,
	// such as after reading `314e-2` or `0.314e+1` or `3.14e0`.
	func stateE0(s *scanner, c int) int {
	if '0' <= c && c <= '9' {
	s.step = stateE0
	return scanContinue
	}
	return stateEndValue(s, c)
	}

	// stateT is the state after reading `t`.
	func stateT(s *scanner, c int) int {
	if c == 'r' {
	s.step = stateTr
	return scanContinue
	}
	return s.error(c, "in literal true (expecting 'r')")
	}

	// stateTr is the state after reading `tr`.
	func stateTr(s *scanner, c int) int {
	if c == 'u' {
	s.step = stateTru
	return scanContinue
	}
	return s.error(c, "in literal true (expecting 'u')")
	}

	// stateTru is the state after reading `tru`.
	func stateTru(s *scanner, c int) int {
	if c == 'e' {
	s.step = stateEndValue
	return scanContinue
	}
	return s.error(c, "in literal true (expecting 'e')")
	}

	// stateF is the state after reading `f`.
	func stateF(s *scanner, c int) int {
	if c == 'a' {
	s.step = stateFa
	return scanContinue
	}
	return s.error(c, "in literal false (expecting 'a')")
	}

	// stateFa is the state after reading `fa`.
	func stateFa(s *scanner, c int) int {
	if c == 'l' {
	s.step = stateFal
	return scanContinue
	}
	return s.error(c, "in literal false (expecting 'l')")
	}

	// stateFal is the state after reading `fal`.
	func stateFal(s *scanner, c int) int {
	if c == 's' {
	s.step = stateFals
	return scanContinue
	}
	return s.error(c, "in literal false (expecting 's')")
	}

	// stateFals is the state after reading `fals`.
	func stateFals(s *scanner, c int) int {
	if c == 'e' {
	s.step = stateEndValue
	return scanContinue
	}
	return s.error(c, "in literal false (expecting 'e')")
	}

	// stateN is the state after reading `n`.
	func stateN(s *scanner, c int) int {
	if c == 'u' {
	s.step = stateNu
	return scanContinue
	}
	return s.error(c, "in literal null (expecting 'u')")
	}

	// stateNu is the state after reading `nu`.
	func stateNu(s *scanner, c int) int {
	if c == 'l' {
	s.step = stateNul
	return scanContinue
	}
	return s.error(c, "in literal null (expecting 'l')")
	}

	// stateNul is the state after reading `nul`.
	func stateNul(s *scanner, c int) int {
	if c == 'l' {
	s.step = stateEndValue
	return scanContinue
	}
	return s.error(c, "in literal null (expecting 'l')")
	}

	// stateError is the state after reaching a syntax error,
	// such as after reading `[1}` or `5.1.2`.
	func stateError(s *scanner, c int) int {
	return scanError
	}

	// error records an error and switches to the error state.
	func (s *scanner) error(c int, context string) int {
	s.step = stateError
	s.err = &SyntaxError{"invalid character " + quoteChar(c) + " " + context, s.bytes}
	return scanError
	}

	// quoteChar formats c as a quoted character literal
	func quoteChar(c int) string {
	// special cases - different from quoted strings
	if c == '\'' {
	return `'\''`
	}
	if c == '"' {
	return `'"'`
	}

	// use quoted string with different quotation marks
	s := strconv.Quote(string(c))
	return "'" + s[1:len(s)-1] + "'"
	}

	// undo causes the scanner to return scanCode from the next state transition.
	// This gives callers a simple 1-byte undo mechanism.
	func (s *scanner) undo(scanCode int) {
	if s.redo {
	panic("json: invalid use of scanner")
	}
	s.redoCode = scanCode
	s.redoState = s.step
	s.step = stateRedo
	s.redo = true
	}

	// stateRedo helps implement the scanner's 1-byte undo.
	func stateRedo(s *scanner, c int) int {
	s.redo = false
	s.step = s.redoState
	return s.redoCode
	}