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// Copyright 2018 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
import (
"bytes"
"fmt"
"io"
"regexp"
"unicode/utf8"
"google.golang.org/protobuf/internal/errors"
)
// call specifies which Decoder method was invoked.
type call uint8
const (
readCall call = iota
peekCall
)
const unexpectedFmt = "unexpected token %s"
// ErrUnexpectedEOF means that EOF was encountered in the middle of the input.
var ErrUnexpectedEOF = errors.New("%v", io.ErrUnexpectedEOF)
// Decoder is a token-based JSON decoder.
type Decoder struct {
// lastCall is last method called, either readCall or peekCall.
// Initial value is readCall.
lastCall call
// lastToken contains the last read token.
lastToken Token
// lastErr contains the last read error.
lastErr error
// openStack is a stack containing ObjectOpen and ArrayOpen values. The
// top of stack represents the object or the array the current value is
// directly located in.
openStack []Kind
// orig is used in reporting line and column.
orig []byte
// in contains the unconsumed input.
in []byte
}
// NewDecoder returns a Decoder to read the given []byte.
func NewDecoder(b []byte) *Decoder {
return &Decoder{orig: b, in: b}
}
// Peek looks ahead and returns the next token kind without advancing a read.
func (d *Decoder) Peek() (Token, error) {
defer func() { d.lastCall = peekCall }()
if d.lastCall == readCall {
d.lastToken, d.lastErr = d.Read()
}
return d.lastToken, d.lastErr
}
// Read returns the next JSON token.
// It will return an error if there is no valid token.
func (d *Decoder) Read() (Token, error) {
const scalar = Null | Bool | Number | String
defer func() { d.lastCall = readCall }()
if d.lastCall == peekCall {
return d.lastToken, d.lastErr
}
tok, err := d.parseNext()
if err != nil {
return Token{}, err
}
switch tok.kind {
case EOF:
if len(d.openStack) != 0 ||
d.lastToken.kind&scalar|ObjectClose|ArrayClose == 0 {
return Token{}, ErrUnexpectedEOF
}
case Null:
if !d.isValueNext() {
return Token{}, d.newSyntaxError(tok.pos, unexpectedFmt, tok.RawString())
}
case Bool, Number:
if !d.isValueNext() {
return Token{}, d.newSyntaxError(tok.pos, unexpectedFmt, tok.RawString())
}
case String:
if d.isValueNext() {
break
}
// This string token should only be for a field name.
if d.lastToken.kind&(ObjectOpen|comma) == 0 {
return Token{}, d.newSyntaxError(tok.pos, unexpectedFmt, tok.RawString())
}
if len(d.in) == 0 {
return Token{}, ErrUnexpectedEOF
}
if c := d.in[0]; c != ':' {
return Token{}, d.newSyntaxError(d.currPos(), `unexpected character %s, missing ":" after field name`, string(c))
}
tok.kind = Name
d.consume(1)
case ObjectOpen, ArrayOpen:
if !d.isValueNext() {
return Token{}, d.newSyntaxError(tok.pos, unexpectedFmt, tok.RawString())
}
d.openStack = append(d.openStack, tok.kind)
case ObjectClose:
if len(d.openStack) == 0 ||
d.lastToken.kind == comma ||
d.openStack[len(d.openStack)-1] != ObjectOpen {
return Token{}, d.newSyntaxError(tok.pos, unexpectedFmt, tok.RawString())
}
d.openStack = d.openStack[:len(d.openStack)-1]
case ArrayClose:
if len(d.openStack) == 0 ||
d.lastToken.kind == comma ||
d.openStack[len(d.openStack)-1] != ArrayOpen {
return Token{}, d.newSyntaxError(tok.pos, unexpectedFmt, tok.RawString())
}
d.openStack = d.openStack[:len(d.openStack)-1]
case comma:
if len(d.openStack) == 0 ||
d.lastToken.kind&(scalar|ObjectClose|ArrayClose) == 0 {
return Token{}, d.newSyntaxError(tok.pos, unexpectedFmt, tok.RawString())
}
}
// Update d.lastToken only after validating token to be in the right sequence.
d.lastToken = tok
if d.lastToken.kind == comma {
return d.Read()
}
return tok, nil
}
// Any sequence that looks like a non-delimiter (for error reporting).
var errRegexp = regexp.MustCompile(`^([-+._a-zA-Z0-9]{1,32}|.)`)
// parseNext parses for the next JSON token. It returns a Token object for
// different types, except for Name. It does not handle whether the next token
// is in a valid sequence or not.
func (d *Decoder) parseNext() (Token, error) {
// Trim leading spaces.
d.consume(0)
in := d.in
if len(in) == 0 {
return d.consumeToken(EOF, 0), nil
}
switch in[0] {
case 'n':
if n := matchWithDelim("null", in); n != 0 {
return d.consumeToken(Null, n), nil
}
case 't':
if n := matchWithDelim("true", in); n != 0 {
return d.consumeBoolToken(true, n), nil
}
case 'f':
if n := matchWithDelim("false", in); n != 0 {
return d.consumeBoolToken(false, n), nil
}
case '-', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
if n, ok := parseNumber(in); ok {
return d.consumeToken(Number, n), nil
}
case '"':
s, n, err := d.parseString(in)
if err != nil {
return Token{}, err
}
return d.consumeStringToken(s, n), nil
case '{':
return d.consumeToken(ObjectOpen, 1), nil
case '}':
return d.consumeToken(ObjectClose, 1), nil
case '[':
return d.consumeToken(ArrayOpen, 1), nil
case ']':
return d.consumeToken(ArrayClose, 1), nil
case ',':
return d.consumeToken(comma, 1), nil
}
return Token{}, d.newSyntaxError(d.currPos(), "invalid value %s", errRegexp.Find(in))
}
// newSyntaxError returns an error with line and column information useful for
// syntax errors.
func (d *Decoder) newSyntaxError(pos int, f string, x ...interface{}) error {
e := errors.New(f, x...)
line, column := d.Position(pos)
return errors.New("syntax error (line %d:%d): %v", line, column, e)
}
// Position returns line and column number of given index of the original input.
// It will panic if index is out of range.
func (d *Decoder) Position(idx int) (line int, column int) {
b := d.orig[:idx]
line = bytes.Count(b, []byte("\n")) + 1
if i := bytes.LastIndexByte(b, '\n'); i >= 0 {
b = b[i+1:]
}
column = utf8.RuneCount(b) + 1 // ignore multi-rune characters
return line, column
}
// currPos returns the current index position of d.in from d.orig.
func (d *Decoder) currPos() int {
return len(d.orig) - len(d.in)
}
// matchWithDelim matches s with the input b and verifies that the match
// terminates with a delimiter of some form (e.g., r"[^-+_.a-zA-Z0-9]").
// As a special case, EOF is considered a delimiter. It returns the length of s
// if there is a match, else 0.
func matchWithDelim(s string, b []byte) int {
if !bytes.HasPrefix(b, []byte(s)) {
return 0
}
n := len(s)
if n < len(b) && isNotDelim(b[n]) {
return 0
}
return n
}
// isNotDelim returns true if given byte is a not delimiter character.
func isNotDelim(c byte) bool {
return (c == '-' || c == '+' || c == '.' || c == '_' ||
('a' <= c && c <= 'z') ||
('A' <= c && c <= 'Z') ||
('0' <= c && c <= '9'))
}
// consume consumes n bytes of input and any subsequent whitespace.
func (d *Decoder) consume(n int) {
d.in = d.in[n:]
for len(d.in) > 0 {
switch d.in[0] {
case ' ', '\n', '\r', '\t':
d.in = d.in[1:]
default:
return
}
}
}
// isValueNext returns true if next type should be a JSON value: Null,
// Number, String or Bool.
func (d *Decoder) isValueNext() bool {
if len(d.openStack) == 0 {
return d.lastToken.kind == 0
}
start := d.openStack[len(d.openStack)-1]
switch start {
case ObjectOpen:
return d.lastToken.kind&Name != 0
case ArrayOpen:
return d.lastToken.kind&(ArrayOpen|comma) != 0
}
panic(fmt.Sprintf(
"unreachable logic in Decoder.isValueNext, lastToken.kind: %v, openStack: %v",
d.lastToken.kind, start))
}
// consumeToken constructs a Token for given Kind with raw value derived from
// current d.in and given size, and consumes the given size-lenght of it.
func (d *Decoder) consumeToken(kind Kind, size int) Token {
tok := Token{
kind: kind,
raw: d.in[:size],
pos: len(d.orig) - len(d.in),
}
d.consume(size)
return tok
}
// consumeBoolToken constructs a Token for a Bool kind with raw value derived from
// current d.in and given size.
func (d *Decoder) consumeBoolToken(b bool, size int) Token {
tok := Token{
kind: Bool,
raw: d.in[:size],
pos: len(d.orig) - len(d.in),
boo: b,
}
d.consume(size)
return tok
}
// consumeStringToken constructs a Token for a String kind with raw value derived
// from current d.in and given size.
func (d *Decoder) consumeStringToken(s string, size int) Token {
tok := Token{
kind: String,
raw: d.in[:size],
pos: len(d.orig) - len(d.in),
str: s,
}
d.consume(size)
return tok
}
// Clone returns a copy of the Decoder for use in reading ahead the next JSON
// object, array or other values without affecting current Decoder.
func (d *Decoder) Clone() *Decoder {
ret := *d
ret.openStack = append([]Kind(nil), ret.openStack...)
return &ret
}