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decoder.go
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decoder.go
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package json
import (
"errors"
"unicode"
"unicode/utf16"
"unicode/utf8"
)
// Value types returned by Decoder.
const (
None = 0 // never returned in successful case
Null = 'n'
Bool = 'b'
String = 's'
Array = '['
Object = '{'
Number = 'N'
)
type (
// Decoder is a group of methods to parse JSON buffers.
// Decoder is stateless.
// All the needed state is passed though arguments and return values.
//
// Most of the methods take buffer with json and start position
// and return a value, end position and possible error.
Decoder struct{}
)
var ( // bitsets
whitespaces uint64
decimals uint64
hexdecimals uint64 // -64 offset
)
func init() {
for _, b := range []byte{'\n', '\r', '\t', ' '} {
whitespaces |= 1 << b
}
for b := '0'; b <= '9'; b++ {
decimals |= 1 << b
}
for b := 'a'; b <= 'z'; b++ {
hexdecimals |= 1 << b
hexdecimals |= 1 << (b - 'a' + 'A')
}
_, _ = isDigit1('f', true), isDigit2('f', true) // keep it used
}
// Errors returned by Decoder.
var (
ErrBadNumber = errors.New("bad number")
ErrBadRune = errors.New("bad rune")
ErrBadString = errors.New("bad string")
ErrEndOfBuffer = errors.New("unexpected end of buffer")
ErrNoSuchKey = errors.New("no such object key")
ErrOutOfBounds = errors.New("out of array bounds")
ErrSyntax = errors.New("syntax error")
ErrType = errors.New("incompatible type")
)
// Type finds the beginning of the next value and detects its type.
// It doesn't parse the value so it can't detect if it's incorrect.
func (d *Decoder) Type(b []byte, st int) (tp byte, i int, err error) {
for i = st; i < len(b); i++ {
if isWhitespace(b[i]) {
continue
}
switch b[i] {
case ',', ':':
continue
case 't', 'f':
return Bool, i, nil
case '"':
return String, i, nil
case Null, Array, Object:
return b[i], i, nil
case '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
'+', '-', '.',
'N', // NaN
'i', 'I': // Inf
return Number, i, nil
}
return None, i, ErrSyntax
}
return None, i, ErrEndOfBuffer
}
// Skip skips the next value.
func (d *Decoder) Skip(b []byte, st int) (i int, err error) {
return d.Break(b, st, 0)
}
// Raw skips the next value and returns subslice with the value trimming whitespaces.
func (d *Decoder) Raw(b []byte, st int) (v []byte, i int, err error) {
_, st, err = d.Type(b, st)
if err != nil {
return nil, st, err
}
i, err = d.Break(b, st, 0)
if err != nil {
return
}
return b[st:i], i, nil
}
// Break breaks from inside the object to the end of it on depth levels.
// As a special case with depth=0 it skips the next value.
// Skip and Raw do exactly that.
//
// It's intended for exiting out of arrays and objects when their content is not needed anymore
// (all the needed indexes or keys are already parsed) and we want to parse the next array or object.
func (d *Decoder) Break(b []byte, st, depth int) (i int, err error) {
i = st
for i < len(b) {
if isWhitespace(b[i]) {
i++
continue
}
switch b[i] {
case ',', ':':
i++
continue
case '"':
i, err = d.skipString(b, i)
case 'n', 't', 'f':
i, err = d.skipLit(b, i)
case '[', '{':
i++
depth++
case ']', '}':
i++
depth--
default:
i, err = d.skipNum(b, i)
}
if err != nil {
return
}
if depth == 0 {
return
}
}
return st, ErrEndOfBuffer
}
// Key reads the next string removing quotes but not decoding the string value.
// So escape sequences (\n, \uXXXX) are not decoded. They are returned as is.
// This is intended for object keys as they usually contain alpha-numeric symbols only.
// This is faster and does not require additional buffer for decoding.
func (d *Decoder) Key(b []byte, st int) (k []byte, i int, err error) {
tp, i, err := d.Type(b, st)
if err != nil {
return
}
if tp != String {
return nil, i, ErrType
}
raw, i, err := d.Raw(b, i)
if err != nil {
return
}
return raw[1 : len(raw)-1], i, nil
}
// DecodeString reads the next string, decodes escape sequences (\n, \uXXXX),
// and appends the result to the buf.
func (d *Decoder) DecodeString(b []byte, st int, buf []byte) (s []byte, i int, err error) {
tp, i, err := d.Type(b, st)
if err != nil {
return buf, i, err
}
if tp != String {
return buf, i, ErrType
}
if buf == nil {
buf = []byte{}
}
s, _, i, err = d.decodeString(b, i, buf)
return
}
// DecodedStringLength reads and decodes the next string but only return the result length.
// It doesn't allocate while DecodeString does.
func (d *Decoder) DecodedStringLength(b []byte, st int) (n, i int, err error) {
tp, i, err := d.Type(b, st)
if err != nil {
return
}
if tp != String {
return 0, i, ErrType
}
_, n, i, err = d.decodeString(b, i, nil)
return
}
// Enter enters an Array or an Object. typ is checked to match with the actual container type.
// Use More or, more convenient form, ForMore to iterate over container.
// See examples to understand the usage pattern more.
func (d *Decoder) Enter(b []byte, st int, typ byte) (i int, err error) {
tp, i, err := d.Type(b, st)
if err != nil {
return
}
if tp != typ || typ != Array && typ != Object {
return i, ErrType
}
i++
return
}
// More iterates over an Array or an Object elements entered by the Enter method.
func (d *Decoder) More(b []byte, st int, typ byte) (more bool, i int, err error) {
for i = st; i < len(b); i++ {
if isWhitespace(b[i]) || b[i] == ',' {
continue
}
break
}
if i == len(b) {
return false, i, ErrEndOfBuffer
}
if b[i] == typ+2 {
i++
return false, i, nil
}
if typ == Array {
return true, i, nil
}
tp, i, err := d.Type(b, i)
if err != nil {
return false, i, err
}
if tp != String {
return false, i, ErrSyntax
}
return true, i, nil
}
// ForMore is a convenient wrapper for More which makes iterating code shorter and simpler.
func (d *Decoder) ForMore(b []byte, i *int, typ byte, errp *error) bool { //nolint:gocritic
more, j, err := d.More(b, *i, typ)
*i = j
if errp != nil {
*errp = err
}
return more
}
// Length calculates number of elements in Array or Object.
func (d *Decoder) Length(b []byte, st int) (n, i int, err error) {
tp, i, err := d.Type(b, st)
if err != nil {
return 0, i, err
}
switch tp {
case Array, Object:
default:
return 0, i, ErrType
}
i, err = d.Enter(b, i, tp)
if err != nil {
return 0, i, err
}
for d.ForMore(b, &i, tp, &err) {
if tp == Object {
_, i, err = d.Key(b, i)
if err != nil {
return n, i, err
}
}
i, err = d.Skip(b, i)
if err != nil {
return n, i, err
}
n++
}
if err != nil {
return n, i, err
}
return n, i, nil
}
// SkipSpaces skips whitespaces.
func (d *Decoder) SkipSpaces(b []byte, i int) int {
for i < len(b) && isWhitespace(b[i]) {
i++
}
return i
}
func (d *Decoder) skipString(b []byte, st int) (i int, err error) {
i = st + 1 // opening "
for i < len(b) {
switch b[i] {
case '"':
return i + 1, nil
case '\\':
i++
if i == len(b) {
return st, ErrEndOfBuffer
}
size := 0
switch b[i] {
case '"', '\\', '/', 'n', 'r', 't', 'b', 'f':
case 'x':
size = 2
case 'u':
size = 4
case 'U':
size = 8
default:
return i, ErrBadString
}
i++
if i+size > len(b) {
return st, ErrEndOfBuffer
}
i += size
case '\n', '\r', '\b':
return i, ErrBadString
default:
if b[i] < utf8.RuneSelf {
i++
break
}
if !utf8.FullRune(b[i:]) {
return st, ErrEndOfBuffer
}
_, size := utf8.DecodeRune(b[i:])
// if r == utf8.RuneError && size == 1 {
// return i, ErrBadRune
// }
i += size
}
}
return st, ErrEndOfBuffer
}
func (d *Decoder) decodeString(b []byte, st int, w []byte) (_ []byte, n, i int, err error) {
i = st + 1 // opening "
done := i
add := func(d []byte, s ...byte) []byte {
n += len(s)
if w == nil {
return nil
}
return append(w, s...)
}
for i < len(b) {
switch b[i] {
case '"':
w = add(w, b[done:i]...)
i++
return w, n, i, nil
case '\\':
w = add(w, b[done:i]...)
i++
if i == len(b) {
return w, n, st, ErrEndOfBuffer
}
switch b[i] {
case '\\', '"', '/':
w = add(w, b[i])
case 'n':
w = add(w, '\n')
case 'r':
w = add(w, '\r')
case 't':
w = add(w, '\t')
case 'b':
w = add(w, '\b')
case 'f':
w = add(w, '\f')
case 'x', 'u', 'U':
w, i, err = decodeRune(w, b, i)
if err == ErrEndOfBuffer {
i = st
}
if err != nil {
return w, n, i, err
}
i--
default:
return w, n, i, ErrBadString
}
i++
done = i
case '\n', '\r', '\b':
return w, n, i, ErrBadString
default:
if b[i] < utf8.RuneSelf {
i++
break
}
if !utf8.FullRune(b[i:]) {
return w, n, st, ErrEndOfBuffer
}
r, size := utf8.DecodeRune(b[i:])
if r == utf8.RuneError && size == 1 {
w = add(w, b[done:i]...)
w = utf8.AppendRune(w, utf8.RuneError)
i += size
done = i
break
}
i += size
}
}
return w, n, st, ErrEndOfBuffer
}
func (d *Decoder) skipLit(b []byte, st int) (i int, err error) {
var lit string
switch b[st] {
case 't':
lit = "true"
case 'f':
lit = "false"
case 'n':
lit = "null"
}
return d.skipVal(b, st, lit)
}
func (d *Decoder) skipVal(b []byte, st int, val string) (i int, err error) {
end := st + len(val)
if end <= len(b) && string(b[st:end]) == val {
return end, nil
}
if end > len(b) && string(b[st:]) == val[:len(b)-st] {
return st, ErrEndOfBuffer
}
return st, ErrSyntax
}
func (d *Decoder) skipNum(b []byte, st int) (i int, err error) {
i = st
// NaN
if i+3 < len(b) && string(b[i:i+3]) == "NaN" {
return i + 3, nil
}
// sign
i = skipSign(b, i)
// Infinity
if i+3 < len(b) && (b[i] == 'i' || b[i] == 'I') && string(b[i+1:i+3]) == "nf" {
i += 3
if i+5 < len(b) && string(b[i:i+5]) == "inity" {
i += 5
}
return i, nil
}
// 0x
var hex bool
if i+2 < len(b) && b[i] == '0' && (b[i+1] == 'x' || b[i+1] == 'X') {
hex = true
i += 2
}
// integer
i, digit := skipInt(b, i, hex)
var dot bool
if dot = i < len(b) && b[i] == '.'; dot {
i++
i, _ = skipInt(b, i, hex)
}
var exp, exptail bool
if exp = i < len(b) && (b[i] == 'e' || b[i] == 'E'); exp {
i++
i = skipSign(b, i)
i, exptail = skipInt(b, i, false)
}
var pexp, pexptail bool
if pexp = i < len(b) && (b[i] == 'p' || b[i] == 'P'); pexp {
i++
i = skipSign(b, i)
i, pexptail = skipInt(b, i, false)
}
ok := (digit || dot) && (!exp || !pexp) && (hex || !pexp) && exp == exptail && pexp == pexptail
// log.Printf("parseNum %10q -> %5v ditdot %5v %5v hex %5v exp %5v %5v pexp %5v %5v", b[st:i], ok, digit, dot, hex, exp, exptail, pexp, pexptail)
if !ok {
return st, ErrBadNumber
}
return i, nil
}
// SkipSpaces skips whitespaces.
func SkipSpaces(b []byte, i int) int {
return (&Decoder{}).SkipSpaces(b, i)
}
func skipSign(b []byte, i int) int {
if i < len(b) && (b[i] == '+' || b[i] == '-') {
i++
}
return i
}
func skipInt(b []byte, i int, hex bool) (_ int, ok bool) {
for i < len(b) && (b[i] == '_' || isDigit1(b[i], hex)) {
ok = true
i++
}
return i, ok
}
func decodeRune(w, b []byte, st int) (_ []byte, i int, err error) {
i = st
var size int
switch b[i] {
case 'x':
size = 2
case 'u':
size = 4
case 'U':
size = 8
default:
panic(b[i])
}
i++
if i+size > len(b) {
return w, st - 1, ErrEndOfBuffer
}
decode := func(i, size int) (r rune) {
for j := 0; j < size; j++ {
c := b[i+j]
switch {
case c >= '0' && c <= '9':
c -= '0'
case c >= 'a' && c <= 'f':
c = 10 + c - 'a'
case c >= 'A' && c <= 'F':
c = 10 + c - 'A'
default:
return -1
}
r = r<<4 | rune(c)
}
return r
}
r := decode(i, size)
if r < 0 {
return w, st - 1, ErrBadRune
}
// we are after first \u
if b[i-1] == 'u' && utf16.IsSurrogate(r) &&
i+size+6 <= len(b) &&
b[i+4] == '\\' && b[i+5] == 'u' {
r1 := decode(i+6, size)
dec := utf16.DecodeRune(r, r1)
if dec != unicode.ReplacementChar {
r = dec
i += 6
}
}
w = utf8.AppendRune(w, r)
return w, i + size, nil
}
func isWhitespace(b byte) bool {
return b <= 0x20 && whitespaces&(1<<b) != 0
}
func isDigit1(b byte, hex bool) bool {
return b >= '0' && b <= '9' || hex && (b >= 'a' && b <= 'f' || b >= 'A' && b <= 'F')
}
func isDigit2(b byte, hex bool) bool {
return b < 64 && decimals&(1<<b) != 0 || b >= 64 && b < 128 && hexdecimals&(1<<b) != 0
}