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// 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.
// Represents JSON data structure using native Go types: booleans, floats,
// strings, arrays, and maps.
package json
import (
"encoding/base64"
"errors"
"fmt"
"reflect"
"runtime"
"strconv"
"strings"
"unicode"
"unicode/utf16"
"unicode/utf8"
)
// Unmarshal parses the JSON-encoded data and stores the result
// in the value pointed to by v.
//
// Unmarshal uses the inverse of the encodings that
// Marshal uses, allocating maps, slices, and pointers as necessary,
// with the following additional rules:
//
// To unmarshal JSON into a pointer, Unmarshal first handles the case of
// the JSON being the JSON literal null. In that case, Unmarshal sets
// the pointer to nil. Otherwise, Unmarshal unmarshals the JSON into
// the value pointed at by the pointer. If the pointer is nil, Unmarshal
// allocates a new value for it to point to.
//
// To unmarshal JSON into an interface value, Unmarshal unmarshals
// the JSON into the concrete value contained in the interface value.
// If the interface value is nil, that is, has no concrete value stored in it,
// Unmarshal stores one of these in the interface value:
//
// bool, for JSON booleans
// float64, for JSON numbers
// string, for JSON strings
// []interface{}, for JSON arrays
// map[string]interface{}, for JSON objects
// nil for JSON null
//
// If a JSON value is not appropriate for a given target type,
// or if a JSON number overflows the target type, Unmarshal
// skips that field and completes the unmarshalling as best it can.
// If no more serious errors are encountered, Unmarshal returns
// an UnmarshalTypeError describing the earliest such error.
//
func Unmarshal(data []byte, v interface{}) error {
d := new(decodeState).init(data)
// Quick check for well-formedness.
// Avoids filling out half a data structure
// before discovering a JSON syntax error.
err := checkValid(data, &d.scan)
if err != nil {
return err
}
return d.unmarshal(v)
}
// Unmarshaler is the interface implemented by objects
// that can unmarshal a JSON description of themselves.
// The input can be assumed to be a valid JSON object
// encoding. UnmarshalJSON must copy the JSON data
// if it wishes to retain the data after returning.
type Unmarshaler interface {
UnmarshalJSON([]byte) error
}
// An UnmarshalTypeError describes a JSON value that was
// not appropriate for a value of a specific Go type.
type UnmarshalTypeError struct {
Value string // description of JSON value - "bool", "array", "number -5"
Type reflect.Type // type of Go value it could not be assigned to
}
func (e *UnmarshalTypeError) Error() string {
return "json: cannot unmarshal " + e.Value + " into Go value of type " + e.Type.String()
}
// An UnmarshalFieldError describes a JSON object key that
// led to an unexported (and therefore unwritable) struct field.
type UnmarshalFieldError struct {
Key string
Type reflect.Type
Field reflect.StructField
}
func (e *UnmarshalFieldError) Error() string {
return "json: cannot unmarshal object key " + strconv.Quote(e.Key) + " into unexported field " + e.Field.Name + " of type " + e.Type.String()
}
// An InvalidUnmarshalError describes an invalid argument passed to Unmarshal.
// (The argument to Unmarshal must be a non-nil pointer.)
type InvalidUnmarshalError struct {
Type reflect.Type
}
func (e *InvalidUnmarshalError) Error() string {
if e.Type == nil {
return "json: Unmarshal(nil)"
}
if e.Type.Kind() != reflect.Ptr {
return "json: Unmarshal(non-pointer " + e.Type.String() + ")"
}
return "json: Unmarshal(nil " + e.Type.String() + ")"
}
func (d *decodeState) unmarshal(v interface{}) (err error) {
defer func() {
if r := recover(); r != nil {
if _, ok := r.(runtime.Error); ok {
panic(r)
}
err = r.(error)
}
}()
rv := reflect.ValueOf(v)
pv := rv
if pv.Kind() != reflect.Ptr || pv.IsNil() {
return &InvalidUnmarshalError{reflect.TypeOf(v)}
}
d.scan.reset()
// We decode rv not pv.Elem because the Unmarshaler interface
// test must be applied at the top level of the value.
d.value(rv)
return d.savedError
}
// decodeState represents the state while decoding a JSON value.
type decodeState struct {
data []byte
off int // read offset in data
scan scanner
nextscan scanner // for calls to nextValue
savedError error
tempstr string // scratch space to avoid some allocations
}
// errPhase is used for errors that should not happen unless
// there is a bug in the JSON decoder or something is editing
// the data slice while the decoder executes.
var errPhase = errors.New("JSON decoder out of sync - data changing underfoot?")
func (d *decodeState) init(data []byte) *decodeState {
d.data = data
d.off = 0
d.savedError = nil
return d
}
// error aborts the decoding by panicking with err.
func (d *decodeState) error(err error) {
panic(err)
}
// saveError saves the first err it is called with,
// for reporting at the end of the unmarshal.
func (d *decodeState) saveError(err error) {
if d.savedError == nil {
d.savedError = err
}
}
// next cuts off and returns the next full JSON value in d.data[d.off:].
// The next value is known to be an object or array, not a literal.
func (d *decodeState) next() []byte {
c := d.data[d.off]
item, rest, err := nextValue(d.data[d.off:], &d.nextscan)
if err != nil {
d.error(err)
}
d.off = len(d.data) - len(rest)
// Our scanner has seen the opening brace/bracket
// and thinks we're still in the middle of the object.
// invent a closing brace/bracket to get it out.
if c == '{' {
d.scan.step(&d.scan, '}')
} else {
d.scan.step(&d.scan, ']')
}
return item
}
// scanWhile processes bytes in d.data[d.off:] until it
// receives a scan code not equal to op.
// It updates d.off and returns the new scan code.
func (d *decodeState) scanWhile(op int) int {
var newOp int
for {
if d.off >= len(d.data) {
newOp = d.scan.eof()
d.off = len(d.data) + 1 // mark processed EOF with len+1
} else {
c := int(d.data[d.off])
d.off++
newOp = d.scan.step(&d.scan, c)
}
if newOp != op {
break
}
}
return newOp
}
// value decodes a JSON value from d.data[d.off:] into the value.
// it updates d.off to point past the decoded value.
func (d *decodeState) value(v reflect.Value) {
if !v.IsValid() {
_, rest, err := nextValue(d.data[d.off:], &d.nextscan)
if err != nil {
d.error(err)
}
d.off = len(d.data) - len(rest)
// d.scan thinks we're still at the beginning of the item.
// Feed in an empty string - the shortest, simplest value -
// so that it knows we got to the end of the value.
if d.scan.redo {
// rewind.
d.scan.redo = false
d.scan.step = stateBeginValue
}
d.scan.step(&d.scan, '"')
d.scan.step(&d.scan, '"')
return
}
switch op := d.scanWhile(scanSkipSpace); op {
default:
d.error(errPhase)
case scanBeginArray:
d.array(v)
case scanBeginObject:
d.object(v)
case scanBeginLiteral:
d.literal(v)
}
}
// indirect walks down v allocating pointers as needed,
// until it gets to a non-pointer.
// if it encounters an Unmarshaler, indirect stops and returns that.
// if decodingNull is true, indirect stops at the last pointer so it can be set to nil.
func (d *decodeState) indirect(v reflect.Value, decodingNull bool) (Unmarshaler, reflect.Value) {
// If v is a named type and is addressable,
// start with its address, so that if the type has pointer methods,
// we find them.
if v.Kind() != reflect.Ptr && v.Type().Name() != "" && v.CanAddr() {
v = v.Addr()
}
for {
var isUnmarshaler bool
if v.Type().NumMethod() > 0 {
// Remember that this is an unmarshaler,
// but wait to return it until after allocating
// the pointer (if necessary).
_, isUnmarshaler = v.Interface().(Unmarshaler)
}
if iv := v; iv.Kind() == reflect.Interface && !iv.IsNil() {
v = iv.Elem()
continue
}
pv := v
if pv.Kind() != reflect.Ptr {
break
}
if pv.Elem().Kind() != reflect.Ptr && decodingNull && pv.CanSet() {
return nil, pv
}
if pv.IsNil() {
pv.Set(reflect.New(pv.Type().Elem()))
}
if isUnmarshaler {
// Using v.Interface().(Unmarshaler)
// here means that we have to use a pointer
// as the struct field. We cannot use a value inside
// a pointer to a struct, because in that case
// v.Interface() is the value (x.f) not the pointer (&x.f).
// This is an unfortunate consequence of reflect.
// An alternative would be to look up the
// UnmarshalJSON method and return a FuncValue.
return v.Interface().(Unmarshaler), reflect.Value{}
}
v = pv.Elem()
}
return nil, v
}
// array consumes an array from d.data[d.off-1:], decoding into the value v.
// the first byte of the array ('[') has been read already.
func (d *decodeState) array(v reflect.Value) {
// Check for unmarshaler.
unmarshaler, pv := d.indirect(v, false)
if unmarshaler != nil {
d.off--
err := unmarshaler.UnmarshalJSON(d.next())
if err != nil {
d.error(err)
}
return
}
v = pv
// Check type of target.
switch v.Kind() {
default:
d.saveError(&UnmarshalTypeError{"array", v.Type()})
d.off--
d.next()
return
case reflect.Interface:
// Decoding into nil interface? Switch to non-reflect code.
v.Set(reflect.ValueOf(d.arrayInterface()))
return
case reflect.Array:
case reflect.Slice:
break
}
i := 0
for {
// Look ahead for ] - can only happen on first iteration.
op := d.scanWhile(scanSkipSpace)
if op == scanEndArray {
break
}
// Back up so d.value can have the byte we just read.
d.off--
d.scan.undo(op)
// Get element of array, growing if necessary.
if v.Kind() == reflect.Slice {
// Grow slice if necessary
if i >= v.Cap() {
newcap := v.Cap() + v.Cap()/2
if newcap < 4 {
newcap = 4
}
newv := reflect.MakeSlice(v.Type(), v.Len(), newcap)
reflect.Copy(newv, v)
v.Set(newv)
}
if i >= v.Len() {
v.SetLen(i + 1)
}
}
if i < v.Len() {
// Decode into element.
d.value(v.Index(i))
} else {
// Ran out of fixed array: skip.
d.value(reflect.Value{})
}
i++
// Next token must be , or ].
op = d.scanWhile(scanSkipSpace)
if op == scanEndArray {
break
}
if op != scanArrayValue {
d.error(errPhase)
}
}
if i < v.Len() {
if v.Kind() == reflect.Array {
// Array. Zero the rest.
z := reflect.Zero(v.Type().Elem())
for ; i < v.Len(); i++ {
v.Index(i).Set(z)
}
} else {
v.SetLen(i)
}
}
if i == 0 && v.Kind() == reflect.Slice {
v.Set(reflect.MakeSlice(v.Type(), 0, 0))
}
}
// object consumes an object from d.data[d.off-1:], decoding into the value v.
// the first byte of the object ('{') has been read already.
func (d *decodeState) object(v reflect.Value) {
// Check for unmarshaler.
unmarshaler, pv := d.indirect(v, false)
if unmarshaler != nil {
d.off--
err := unmarshaler.UnmarshalJSON(d.next())
if err != nil {
d.error(err)
}
return
}
v = pv
// Decoding into nil interface? Switch to non-reflect code.
iv := v
if iv.Kind() == reflect.Interface {
iv.Set(reflect.ValueOf(d.objectInterface()))
return
}
// Check type of target: struct or map[string]T
var (
mv reflect.Value
sv reflect.Value
)
switch v.Kind() {
case reflect.Map:
// map must have string type
t := v.Type()
if t.Key() != reflect.TypeOf("") {
d.saveError(&UnmarshalTypeError{"object", v.Type()})
break
}
mv = v
if mv.IsNil() {
mv.Set(reflect.MakeMap(t))
}
case reflect.Struct:
sv = v
default:
d.saveError(&UnmarshalTypeError{"object", v.Type()})
}
if !mv.IsValid() && !sv.IsValid() {
d.off--
d.next() // skip over { } in input
return
}
var mapElem reflect.Value
for {
// Read opening " of string key or closing }.
op := d.scanWhile(scanSkipSpace)
if op == scanEndObject {
// closing } - can only happen on first iteration.
break
}
if op != scanBeginLiteral {
d.error(errPhase)
}
// Read string key.
start := d.off - 1
op = d.scanWhile(scanContinue)
item := d.data[start : d.off-1]
key, ok := unquote(item)
if !ok {
d.error(errPhase)
}
// Figure out field corresponding to key.
var subv reflect.Value
destring := false // whether the value is wrapped in a string to be decoded first
if mv.IsValid() {
elemType := mv.Type().Elem()
if !mapElem.IsValid() {
mapElem = reflect.New(elemType).Elem()
} else {
mapElem.Set(reflect.Zero(elemType))
}
subv = mapElem
} else {
var f reflect.StructField
var ok bool
st := sv.Type()
for i := 0; i < sv.NumField(); i++ {
sf := st.Field(i)
tag := sf.Tag.Get("json")
if tag == "-" {
// Pretend this field doesn't exist.
continue
}
// First, tag match
tagName, _ := parseTag(tag)
if tagName == key {
f = sf
ok = true
break // no better match possible
}
// Second, exact field name match
if sf.Name == key {
f = sf
ok = true
}
// Third, case-insensitive field name match,
// but only if a better match hasn't already been seen
if !ok && strings.EqualFold(sf.Name, key) {
f = sf
ok = true
}
}
// Extract value; name must be exported.
if ok {
if f.PkgPath != "" {
d.saveError(&UnmarshalFieldError{key, st, f})
} else {
subv = sv.FieldByIndex(f.Index)
}
_, opts := parseTag(f.Tag.Get("json"))
destring = opts.Contains("string")
}
}
// Read : before value.
if op == scanSkipSpace {
op = d.scanWhile(scanSkipSpace)
}
if op != scanObjectKey {
d.error(errPhase)
}
// Read value.
if destring {
d.value(reflect.ValueOf(&d.tempstr))
d.literalStore([]byte(d.tempstr), subv, true)
} else {
d.value(subv)
}
// Write value back to map;
// if using struct, subv points into struct already.
if mv.IsValid() {
mv.SetMapIndex(reflect.ValueOf(key), subv)
}
// Next token must be , or }.
op = d.scanWhile(scanSkipSpace)
if op == scanEndObject {
break
}
if op != scanObjectValue {
d.error(errPhase)
}
}
}
// literal consumes a literal from d.data[d.off-1:], decoding into the value v.
// The first byte of the literal has been read already
// (that's how the caller knows it's a literal).
func (d *decodeState) literal(v reflect.Value) {
// All bytes inside literal return scanContinue op code.
start := d.off - 1
op := d.scanWhile(scanContinue)
// Scan read one byte too far; back up.
d.off--
d.scan.undo(op)
d.literalStore(d.data[start:d.off], v, false)
}
// literalStore decodes a literal stored in item into v.
//
// fromQuoted indicates whether this literal came from unwrapping a
// string from the ",string" struct tag option. this is used only to
// produce more helpful error messages.
func (d *decodeState) literalStore(item []byte, v reflect.Value, fromQuoted bool) {
// Check for unmarshaler.
wantptr := item[0] == 'n' // null
unmarshaler, pv := d.indirect(v, wantptr)
if unmarshaler != nil {
err := unmarshaler.UnmarshalJSON(item)
if err != nil {
d.error(err)
}
return
}
v = pv
switch c := item[0]; c {
case 'n': // null
switch v.Kind() {
default:
d.saveError(&UnmarshalTypeError{"null", v.Type()})
case reflect.Interface, reflect.Ptr, reflect.Map, reflect.Slice:
v.Set(reflect.Zero(v.Type()))
}
case 't', 'f': // true, false
value := c == 't'
switch v.Kind() {
default:
if fromQuoted {
d.saveError(fmt.Errorf("json: invalid use of ,string struct tag, trying to unmarshal %q into %v", item, v.Type()))
} else {
d.saveError(&UnmarshalTypeError{"bool", v.Type()})
}
case reflect.Bool:
v.SetBool(value)
case reflect.Interface:
v.Set(reflect.ValueOf(value))
}
case '"': // string
s, ok := unquoteBytes(item)
if !ok {
if fromQuoted {
d.error(fmt.Errorf("json: invalid use of ,string struct tag, trying to unmarshal %q into %v", item, v.Type()))
} else {
d.error(errPhase)
}
}
switch v.Kind() {
default:
d.saveError(&UnmarshalTypeError{"string", v.Type()})
case reflect.Slice:
if v.Type() != byteSliceType {
d.saveError(&UnmarshalTypeError{"string", v.Type()})
break
}
b := make([]byte, base64.StdEncoding.DecodedLen(len(s)))
n, err := base64.StdEncoding.Decode(b, s)
if err != nil {
d.saveError(err)
break
}
v.Set(reflect.ValueOf(b[0:n]))
case reflect.String:
v.SetString(string(s))
case reflect.Interface:
v.Set(reflect.ValueOf(string(s)))
}
default: // number
if c != '-' && (c < '0' || c > '9') {
if fromQuoted {
d.error(fmt.Errorf("json: invalid use of ,string struct tag, trying to unmarshal %q into %v", item, v.Type()))
} else {
d.error(errPhase)
}
}
s := string(item)
switch v.Kind() {
default:
if fromQuoted {
d.error(fmt.Errorf("json: invalid use of ,string struct tag, trying to unmarshal %q into %v", item, v.Type()))
} else {
d.error(&UnmarshalTypeError{"number", v.Type()})
}
case reflect.Interface:
n, err := strconv.ParseFloat(s, 64)
if err != nil {
d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
break
}
v.Set(reflect.ValueOf(n))
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
n, err := strconv.ParseInt(s, 10, 64)
if err != nil || v.OverflowInt(n) {
d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
break
}
v.SetInt(n)
case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
n, err := strconv.ParseUint(s, 10, 64)
if err != nil || v.OverflowUint(n) {
d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
break
}
v.SetUint(n)
case reflect.Float32, reflect.Float64:
n, err := strconv.ParseFloat(s, v.Type().Bits())
if err != nil || v.OverflowFloat(n) {
d.saveError(&UnmarshalTypeError{"number " + s, v.Type()})
break
}
v.SetFloat(n)
}
}
}
// The xxxInterface routines build up a value to be stored
// in an empty interface. They are not strictly necessary,
// but they avoid the weight of reflection in this common case.
// valueInterface is like value but returns interface{}
func (d *decodeState) valueInterface() interface{} {
switch d.scanWhile(scanSkipSpace) {
default:
d.error(errPhase)
case scanBeginArray:
return d.arrayInterface()
case scanBeginObject:
return d.objectInterface()
case scanBeginLiteral:
return d.literalInterface()
}
panic("unreachable")
}
// arrayInterface is like array but returns []interface{}.
func (d *decodeState) arrayInterface() []interface{} {
var v []interface{}
for {
// Look ahead for ] - can only happen on first iteration.
op := d.scanWhile(scanSkipSpace)
if op == scanEndArray {
break
}
// Back up so d.value can have the byte we just read.
d.off--
d.scan.undo(op)
v = append(v, d.valueInterface())
// Next token must be , or ].
op = d.scanWhile(scanSkipSpace)
if op == scanEndArray {
break
}
if op != scanArrayValue {
d.error(errPhase)
}
}
return v
}
// objectInterface is like object but returns map[string]interface{}.
func (d *decodeState) objectInterface() map[string]interface{} {
m := make(map[string]interface{})
for {
// Read opening " of string key or closing }.
op := d.scanWhile(scanSkipSpace)
if op == scanEndObject {
// closing } - can only happen on first iteration.
break
}
if op != scanBeginLiteral {
d.error(errPhase)
}
// Read string key.
start := d.off - 1
op = d.scanWhile(scanContinue)
item := d.data[start : d.off-1]
key, ok := unquote(item)
if !ok {
d.error(errPhase)
}
// Read : before value.
if op == scanSkipSpace {
op = d.scanWhile(scanSkipSpace)
}
if op != scanObjectKey {
d.error(errPhase)
}
// Read value.
m[key] = d.valueInterface()
// Next token must be , or }.
op = d.scanWhile(scanSkipSpace)
if op == scanEndObject {
break
}
if op != scanObjectValue {
d.error(errPhase)
}
}
return m
}
// literalInterface is like literal but returns an interface value.
func (d *decodeState) literalInterface() interface{} {
// All bytes inside literal return scanContinue op code.
start := d.off - 1
op := d.scanWhile(scanContinue)
// Scan read one byte too far; back up.
d.off--
d.scan.undo(op)
item := d.data[start:d.off]
switch c := item[0]; c {
case 'n': // null
return nil
case 't', 'f': // true, false
return c == 't'
case '"': // string
s, ok := unquote(item)
if !ok {
d.error(errPhase)
}
return s
default: // number
if c != '-' && (c < '0' || c > '9') {
d.error(errPhase)
}
n, err := strconv.ParseFloat(string(item), 64)
if err != nil {
d.saveError(&UnmarshalTypeError{"number " + string(item), reflect.TypeOf(0.0)})
}
return n
}
panic("unreachable")
}
// getu4 decodes \uXXXX from the beginning of s, returning the hex value,
// or it returns -1.
func getu4(s []byte) rune {
if len(s) < 6 || s[0] != '\\' || s[1] != 'u' {
return -1
}
r, err := strconv.ParseUint(string(s[2:6]), 16, 64)
if err != nil {
return -1
}
return rune(r)
}
// unquote converts a quoted JSON string literal s into an actual string t.
// The rules are different than for Go, so cannot use strconv.Unquote.
func unquote(s []byte) (t string, ok bool) {
s, ok = unquoteBytes(s)
t = string(s)
return
}
func unquoteBytes(s []byte) (t []byte, ok bool) {
if len(s) < 2 || s[0] != '"' || s[len(s)-1] != '"' {
return
}
s = s[1 : len(s)-1]
// Check for unusual characters. If there are none,
// then no unquoting is needed, so return a slice of the
// original bytes.
r := 0
for r < len(s) {
c := s[r]
if c == '\\' || c == '"' || c < ' ' {
break
}
if c < utf8.RuneSelf {
r++
continue
}
rr, size := utf8.DecodeRune(s[r:])
if rr == utf8.RuneError && size == 1 {
break
}
r += size
}
if r == len(s) {
return s, true
}
b := make([]byte, len(s)+2*utf8.UTFMax)
w := copy(b, s[0:r])
for r < len(s) {
// Out of room? Can only happen if s is full of
// malformed UTF-8 and we're replacing each
// byte with RuneError.
if w >= len(b)-2*utf8.UTFMax {
nb := make([]byte, (len(b)+utf8.UTFMax)*2)
copy(nb, b[0:w])
b = nb
}
switch c := s[r]; {
case c == '\\':
r++
if r >= len(s) {
return
}
switch s[r] {
default:
return
case '"', '\\', '/', '\'':
b[w] = s[r]
r++
w++
case 'b':
b[w] = '\b'
r++
w++
case 'f':
b[w] = '\f'
r++
w++
case 'n':
b[w] = '\n'
r++
w++
case 'r':
b[w] = '\r'
r++
w++
case 't':
b[w] = '\t'
r++
w++
case 'u':
r--
rr := getu4(s[r:])
if rr < 0 {
return
}
r += 6
if utf16.IsSurrogate(rr) {
rr1 := getu4(s[r:])
if dec := utf16.DecodeRune(rr, rr1); dec != unicode.ReplacementChar {
// A valid pair; consume.
r += 6
w += utf8.EncodeRune(b[w:], dec)
break
}
// Invalid surrogate; fall back to replacement rune.
rr = unicode.ReplacementChar
}
w += utf8.EncodeRune(b[w:], rr)
}
// Quote, control characters are invalid.
case c == '"', c < ' ':
return
// ASCII
case c < utf8.RuneSelf:
b[w] = c
r++
w++
// Coerce to well-formed UTF-8.
default:
rr, size := utf8.DecodeRune(s[r:])
r += size
w += utf8.EncodeRune(b[w:], rr)
}
}
return b[0:w], true
}