Source file src/encoding/json/decode.go

Documentation: encoding/json

     1  // Copyright 2010 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Represents JSON data structure using native Go types: booleans, floats,
     6  // strings, arrays, and maps.
     7  
     8  package json
     9  
    10  import (
    11  	"encoding"
    12  	"encoding/base64"
    13  	"fmt"
    14  	"reflect"
    15  	"strconv"
    16  	"strings"
    17  	"unicode"
    18  	"unicode/utf16"
    19  	"unicode/utf8"
    20  )
    21  
    22  // Unmarshal parses the JSON-encoded data and stores the result
    23  // in the value pointed to by v. If v is nil or not a pointer,
    24  // Unmarshal returns an InvalidUnmarshalError.
    25  //
    26  // Unmarshal uses the inverse of the encodings that
    27  // Marshal uses, allocating maps, slices, and pointers as necessary,
    28  // with the following additional rules:
    29  //
    30  // To unmarshal JSON into a pointer, Unmarshal first handles the case of
    31  // the JSON being the JSON literal null. In that case, Unmarshal sets
    32  // the pointer to nil. Otherwise, Unmarshal unmarshals the JSON into
    33  // the value pointed at by the pointer. If the pointer is nil, Unmarshal
    34  // allocates a new value for it to point to.
    35  //
    36  // To unmarshal JSON into a value implementing the Unmarshaler interface,
    37  // Unmarshal calls that value's UnmarshalJSON method, including
    38  // when the input is a JSON null.
    39  // Otherwise, if the value implements encoding.TextUnmarshaler
    40  // and the input is a JSON quoted string, Unmarshal calls that value's
    41  // UnmarshalText method with the unquoted form of the string.
    42  //
    43  // To unmarshal JSON into a struct, Unmarshal matches incoming object
    44  // keys to the keys used by Marshal (either the struct field name or its tag),
    45  // preferring an exact match but also accepting a case-insensitive match. By
    46  // default, object keys which don't have a corresponding struct field are
    47  // ignored (see Decoder.DisallowUnknownFields for an alternative).
    48  //
    49  // To unmarshal JSON into an interface value,
    50  // Unmarshal stores one of these in the interface value:
    51  //
    52  //	bool, for JSON booleans
    53  //	float64, for JSON numbers
    54  //	string, for JSON strings
    55  //	[]interface{}, for JSON arrays
    56  //	map[string]interface{}, for JSON objects
    57  //	nil for JSON null
    58  //
    59  // To unmarshal a JSON array into a slice, Unmarshal resets the slice length
    60  // to zero and then appends each element to the slice.
    61  // As a special case, to unmarshal an empty JSON array into a slice,
    62  // Unmarshal replaces the slice with a new empty slice.
    63  //
    64  // To unmarshal a JSON array into a Go array, Unmarshal decodes
    65  // JSON array elements into corresponding Go array elements.
    66  // If the Go array is smaller than the JSON array,
    67  // the additional JSON array elements are discarded.
    68  // If the JSON array is smaller than the Go array,
    69  // the additional Go array elements are set to zero values.
    70  //
    71  // To unmarshal a JSON object into a map, Unmarshal first establishes a map to
    72  // use. If the map is nil, Unmarshal allocates a new map. Otherwise Unmarshal
    73  // reuses the existing map, keeping existing entries. Unmarshal then stores
    74  // key-value pairs from the JSON object into the map. The map's key type must
    75  // either be any string type, an integer, implement json.Unmarshaler, or
    76  // implement encoding.TextUnmarshaler.
    77  //
    78  // If a JSON value is not appropriate for a given target type,
    79  // or if a JSON number overflows the target type, Unmarshal
    80  // skips that field and completes the unmarshaling as best it can.
    81  // If no more serious errors are encountered, Unmarshal returns
    82  // an UnmarshalTypeError describing the earliest such error. In any
    83  // case, it's not guaranteed that all the remaining fields following
    84  // the problematic one will be unmarshaled into the target object.
    85  //
    86  // The JSON null value unmarshals into an interface, map, pointer, or slice
    87  // by setting that Go value to nil. Because null is often used in JSON to mean
    88  // ``not present,'' unmarshaling a JSON null into any other Go type has no effect
    89  // on the value and produces no error.
    90  //
    91  // When unmarshaling quoted strings, invalid UTF-8 or
    92  // invalid UTF-16 surrogate pairs are not treated as an error.
    93  // Instead, they are replaced by the Unicode replacement
    94  // character U+FFFD.
    95  //
    96  func Unmarshal(data []byte, v interface{}) error {
    97  	// Check for well-formedness.
    98  	// Avoids filling out half a data structure
    99  	// before discovering a JSON syntax error.
   100  	var d decodeState
   101  	err := checkValid(data, &d.scan)
   102  	if err != nil {
   103  		return err
   104  	}
   105  
   106  	d.init(data)
   107  	return d.unmarshal(v)
   108  }
   109  
   110  // Unmarshaler is the interface implemented by types
   111  // that can unmarshal a JSON description of themselves.
   112  // The input can be assumed to be a valid encoding of
   113  // a JSON value. UnmarshalJSON must copy the JSON data
   114  // if it wishes to retain the data after returning.
   115  //
   116  // By convention, to approximate the behavior of Unmarshal itself,
   117  // Unmarshalers implement UnmarshalJSON([]byte("null")) as a no-op.
   118  type Unmarshaler interface {
   119  	UnmarshalJSON([]byte) error
   120  }
   121  
   122  // An UnmarshalTypeError describes a JSON value that was
   123  // not appropriate for a value of a specific Go type.
   124  type UnmarshalTypeError struct {
   125  	Value  string       // description of JSON value - "bool", "array", "number -5"
   126  	Type   reflect.Type // type of Go value it could not be assigned to
   127  	Offset int64        // error occurred after reading Offset bytes
   128  	Struct string       // name of the struct type containing the field
   129  	Field  string       // the full path from root node to the field
   130  }
   131  
   132  func (e *UnmarshalTypeError) Error() string {
   133  	if e.Struct != "" || e.Field != "" {
   134  		return "json: cannot unmarshal " + e.Value + " into Go struct field " + e.Struct + "." + e.Field + " of type " + e.Type.String()
   135  	}
   136  	return "json: cannot unmarshal " + e.Value + " into Go value of type " + e.Type.String()
   137  }
   138  
   139  // An UnmarshalFieldError describes a JSON object key that
   140  // led to an unexported (and therefore unwritable) struct field.
   141  //
   142  // Deprecated: No longer used; kept for compatibility.
   143  type UnmarshalFieldError struct {
   144  	Key   string
   145  	Type  reflect.Type
   146  	Field reflect.StructField
   147  }
   148  
   149  func (e *UnmarshalFieldError) Error() string {
   150  	return "json: cannot unmarshal object key " + strconv.Quote(e.Key) + " into unexported field " + e.Field.Name + " of type " + e.Type.String()
   151  }
   152  
   153  // An InvalidUnmarshalError describes an invalid argument passed to Unmarshal.
   154  // (The argument to Unmarshal must be a non-nil pointer.)
   155  type InvalidUnmarshalError struct {
   156  	Type reflect.Type
   157  }
   158  
   159  func (e *InvalidUnmarshalError) Error() string {
   160  	if e.Type == nil {
   161  		return "json: Unmarshal(nil)"
   162  	}
   163  
   164  	if e.Type.Kind() != reflect.Ptr {
   165  		return "json: Unmarshal(non-pointer " + e.Type.String() + ")"
   166  	}
   167  	return "json: Unmarshal(nil " + e.Type.String() + ")"
   168  }
   169  
   170  func (d *decodeState) unmarshal(v interface{}) error {
   171  	rv := reflect.ValueOf(v)
   172  	if rv.Kind() != reflect.Ptr || rv.IsNil() {
   173  		return &InvalidUnmarshalError{reflect.TypeOf(v)}
   174  	}
   175  
   176  	d.scan.reset()
   177  	d.scanWhile(scanSkipSpace)
   178  	// We decode rv not rv.Elem because the Unmarshaler interface
   179  	// test must be applied at the top level of the value.
   180  	err := d.value(rv)
   181  	if err != nil {
   182  		return d.addErrorContext(err)
   183  	}
   184  	return d.savedError
   185  }
   186  
   187  // A Number represents a JSON number literal.
   188  type Number string
   189  
   190  // String returns the literal text of the number.
   191  func (n Number) String() string { return string(n) }
   192  
   193  // Float64 returns the number as a float64.
   194  func (n Number) Float64() (float64, error) {
   195  	return strconv.ParseFloat(string(n), 64)
   196  }
   197  
   198  // Int64 returns the number as an int64.
   199  func (n Number) Int64() (int64, error) {
   200  	return strconv.ParseInt(string(n), 10, 64)
   201  }
   202  
   203  // decodeState represents the state while decoding a JSON value.
   204  type decodeState struct {
   205  	data         []byte
   206  	off          int // next read offset in data
   207  	opcode       int // last read result
   208  	scan         scanner
   209  	errorContext struct { // provides context for type errors
   210  		Struct     reflect.Type
   211  		FieldStack []string
   212  	}
   213  	savedError            error
   214  	useNumber             bool
   215  	disallowUnknownFields bool
   216  }
   217  
   218  // readIndex returns the position of the last byte read.
   219  func (d *decodeState) readIndex() int {
   220  	return d.off - 1
   221  }
   222  
   223  // phasePanicMsg is used as a panic message when we end up with something that
   224  // shouldn't happen. It can indicate a bug in the JSON decoder, or that
   225  // something is editing the data slice while the decoder executes.
   226  const phasePanicMsg = "JSON decoder out of sync - data changing underfoot?"
   227  
   228  func (d *decodeState) init(data []byte) *decodeState {
   229  	d.data = data
   230  	d.off = 0
   231  	d.savedError = nil
   232  	d.errorContext.Struct = nil
   233  
   234  	// Reuse the allocated space for the FieldStack slice.
   235  	d.errorContext.FieldStack = d.errorContext.FieldStack[:0]
   236  	return d
   237  }
   238  
   239  // saveError saves the first err it is called with,
   240  // for reporting at the end of the unmarshal.
   241  func (d *decodeState) saveError(err error) {
   242  	if d.savedError == nil {
   243  		d.savedError = d.addErrorContext(err)
   244  	}
   245  }
   246  
   247  // addErrorContext returns a new error enhanced with information from d.errorContext
   248  func (d *decodeState) addErrorContext(err error) error {
   249  	if d.errorContext.Struct != nil || len(d.errorContext.FieldStack) > 0 {
   250  		switch err := err.(type) {
   251  		case *UnmarshalTypeError:
   252  			err.Struct = d.errorContext.Struct.Name()
   253  			err.Field = strings.Join(d.errorContext.FieldStack, ".")
   254  			return err
   255  		}
   256  	}
   257  	return err
   258  }
   259  
   260  // skip scans to the end of what was started.
   261  func (d *decodeState) skip() {
   262  	s, data, i := &d.scan, d.data, d.off
   263  	depth := len(s.parseState)
   264  	for {
   265  		op := s.step(s, data[i])
   266  		i++
   267  		if len(s.parseState) < depth {
   268  			d.off = i
   269  			d.opcode = op
   270  			return
   271  		}
   272  	}
   273  }
   274  
   275  // scanNext processes the byte at d.data[d.off].
   276  func (d *decodeState) scanNext() {
   277  	if d.off < len(d.data) {
   278  		d.opcode = d.scan.step(&d.scan, d.data[d.off])
   279  		d.off++
   280  	} else {
   281  		d.opcode = d.scan.eof()
   282  		d.off = len(d.data) + 1 // mark processed EOF with len+1
   283  	}
   284  }
   285  
   286  // scanWhile processes bytes in d.data[d.off:] until it
   287  // receives a scan code not equal to op.
   288  func (d *decodeState) scanWhile(op int) {
   289  	s, data, i := &d.scan, d.data, d.off
   290  	for i < len(data) {
   291  		newOp := s.step(s, data[i])
   292  		i++
   293  		if newOp != op {
   294  			d.opcode = newOp
   295  			d.off = i
   296  			return
   297  		}
   298  	}
   299  
   300  	d.off = len(data) + 1 // mark processed EOF with len+1
   301  	d.opcode = d.scan.eof()
   302  }
   303  
   304  // rescanLiteral is similar to scanWhile(scanContinue), but it specialises the
   305  // common case where we're decoding a literal. The decoder scans the input
   306  // twice, once for syntax errors and to check the length of the value, and the
   307  // second to perform the decoding.
   308  //
   309  // Only in the second step do we use decodeState to tokenize literals, so we
   310  // know there aren't any syntax errors. We can take advantage of that knowledge,
   311  // and scan a literal's bytes much more quickly.
   312  func (d *decodeState) rescanLiteral() {
   313  	data, i := d.data, d.off
   314  Switch:
   315  	switch data[i-1] {
   316  	case '"': // string
   317  		for ; i < len(data); i++ {
   318  			switch data[i] {
   319  			case '\\':
   320  				i++ // escaped char
   321  			case '"':
   322  				i++ // tokenize the closing quote too
   323  				break Switch
   324  			}
   325  		}
   326  	case '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '-': // number
   327  		for ; i < len(data); i++ {
   328  			switch data[i] {
   329  			case '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
   330  				'.', 'e', 'E', '+', '-':
   331  			default:
   332  				break Switch
   333  			}
   334  		}
   335  	case 't': // true
   336  		i += len("rue")
   337  	case 'f': // false
   338  		i += len("alse")
   339  	case 'n': // null
   340  		i += len("ull")
   341  	}
   342  	if i < len(data) {
   343  		d.opcode = stateEndValue(&d.scan, data[i])
   344  	} else {
   345  		d.opcode = scanEnd
   346  	}
   347  	d.off = i + 1
   348  }
   349  
   350  // value consumes a JSON value from d.data[d.off-1:], decoding into v, and
   351  // reads the following byte ahead. If v is invalid, the value is discarded.
   352  // The first byte of the value has been read already.
   353  func (d *decodeState) value(v reflect.Value) error {
   354  	switch d.opcode {
   355  	default:
   356  		panic(phasePanicMsg)
   357  
   358  	case scanBeginArray:
   359  		if v.IsValid() {
   360  			if err := d.array(v); err != nil {
   361  				return err
   362  			}
   363  		} else {
   364  			d.skip()
   365  		}
   366  		d.scanNext()
   367  
   368  	case scanBeginObject:
   369  		if v.IsValid() {
   370  			if err := d.object(v); err != nil {
   371  				return err
   372  			}
   373  		} else {
   374  			d.skip()
   375  		}
   376  		d.scanNext()
   377  
   378  	case scanBeginLiteral:
   379  		// All bytes inside literal return scanContinue op code.
   380  		start := d.readIndex()
   381  		d.rescanLiteral()
   382  
   383  		if v.IsValid() {
   384  			if err := d.literalStore(d.data[start:d.readIndex()], v, false); err != nil {
   385  				return err
   386  			}
   387  		}
   388  	}
   389  	return nil
   390  }
   391  
   392  type unquotedValue struct{}
   393  
   394  // valueQuoted is like value but decodes a
   395  // quoted string literal or literal null into an interface value.
   396  // If it finds anything other than a quoted string literal or null,
   397  // valueQuoted returns unquotedValue{}.
   398  func (d *decodeState) valueQuoted() interface{} {
   399  	switch d.opcode {
   400  	default:
   401  		panic(phasePanicMsg)
   402  
   403  	case scanBeginArray, scanBeginObject:
   404  		d.skip()
   405  		d.scanNext()
   406  
   407  	case scanBeginLiteral:
   408  		v := d.literalInterface()
   409  		switch v.(type) {
   410  		case nil, string:
   411  			return v
   412  		}
   413  	}
   414  	return unquotedValue{}
   415  }
   416  
   417  // indirect walks down v allocating pointers as needed,
   418  // until it gets to a non-pointer.
   419  // If it encounters an Unmarshaler, indirect stops and returns that.
   420  // If decodingNull is true, indirect stops at the first settable pointer so it
   421  // can be set to nil.
   422  func indirect(v reflect.Value, decodingNull bool) (Unmarshaler, encoding.TextUnmarshaler, reflect.Value) {
   423  	// Issue #24153 indicates that it is generally not a guaranteed property
   424  	// that you may round-trip a reflect.Value by calling Value.Addr().Elem()
   425  	// and expect the value to still be settable for values derived from
   426  	// unexported embedded struct fields.
   427  	//
   428  	// The logic below effectively does this when it first addresses the value
   429  	// (to satisfy possible pointer methods) and continues to dereference
   430  	// subsequent pointers as necessary.
   431  	//
   432  	// After the first round-trip, we set v back to the original value to
   433  	// preserve the original RW flags contained in reflect.Value.
   434  	v0 := v
   435  	haveAddr := false
   436  
   437  	// If v is a named type and is addressable,
   438  	// start with its address, so that if the type has pointer methods,
   439  	// we find them.
   440  	if v.Kind() != reflect.Ptr && v.Type().Name() != "" && v.CanAddr() {
   441  		haveAddr = true
   442  		v = v.Addr()
   443  	}
   444  	for {
   445  		// Load value from interface, but only if the result will be
   446  		// usefully addressable.
   447  		if v.Kind() == reflect.Interface && !v.IsNil() {
   448  			e := v.Elem()
   449  			if e.Kind() == reflect.Ptr && !e.IsNil() && (!decodingNull || e.Elem().Kind() == reflect.Ptr) {
   450  				haveAddr = false
   451  				v = e
   452  				continue
   453  			}
   454  		}
   455  
   456  		if v.Kind() != reflect.Ptr {
   457  			break
   458  		}
   459  
   460  		if decodingNull && v.CanSet() {
   461  			break
   462  		}
   463  
   464  		// Prevent infinite loop if v is an interface pointing to its own address:
   465  		//     var v interface{}
   466  		//     v = &v
   467  		if v.Elem().Kind() == reflect.Interface && v.Elem().Elem() == v {
   468  			v = v.Elem()
   469  			break
   470  		}
   471  		if v.IsNil() {
   472  			v.Set(reflect.New(v.Type().Elem()))
   473  		}
   474  		if v.Type().NumMethod() > 0 && v.CanInterface() {
   475  			if u, ok := v.Interface().(Unmarshaler); ok {
   476  				return u, nil, reflect.Value{}
   477  			}
   478  			if !decodingNull {
   479  				if u, ok := v.Interface().(encoding.TextUnmarshaler); ok {
   480  					return nil, u, reflect.Value{}
   481  				}
   482  			}
   483  		}
   484  
   485  		if haveAddr {
   486  			v = v0 // restore original value after round-trip Value.Addr().Elem()
   487  			haveAddr = false
   488  		} else {
   489  			v = v.Elem()
   490  		}
   491  	}
   492  	return nil, nil, v
   493  }
   494  
   495  // array consumes an array from d.data[d.off-1:], decoding into v.
   496  // The first byte of the array ('[') has been read already.
   497  func (d *decodeState) array(v reflect.Value) error {
   498  	// Check for unmarshaler.
   499  	u, ut, pv := indirect(v, false)
   500  	if u != nil {
   501  		start := d.readIndex()
   502  		d.skip()
   503  		return u.UnmarshalJSON(d.data[start:d.off])
   504  	}
   505  	if ut != nil {
   506  		d.saveError(&UnmarshalTypeError{Value: "array", Type: v.Type(), Offset: int64(d.off)})
   507  		d.skip()
   508  		return nil
   509  	}
   510  	v = pv
   511  
   512  	// Check type of target.
   513  	switch v.Kind() {
   514  	case reflect.Interface:
   515  		if v.NumMethod() == 0 {
   516  			// Decoding into nil interface? Switch to non-reflect code.
   517  			ai := d.arrayInterface()
   518  			v.Set(reflect.ValueOf(ai))
   519  			return nil
   520  		}
   521  		// Otherwise it's invalid.
   522  		fallthrough
   523  	default:
   524  		d.saveError(&UnmarshalTypeError{Value: "array", Type: v.Type(), Offset: int64(d.off)})
   525  		d.skip()
   526  		return nil
   527  	case reflect.Array, reflect.Slice:
   528  		break
   529  	}
   530  
   531  	i := 0
   532  	for {
   533  		// Look ahead for ] - can only happen on first iteration.
   534  		d.scanWhile(scanSkipSpace)
   535  		if d.opcode == scanEndArray {
   536  			break
   537  		}
   538  
   539  		// Get element of array, growing if necessary.
   540  		if v.Kind() == reflect.Slice {
   541  			// Grow slice if necessary
   542  			if i >= v.Cap() {
   543  				newcap := v.Cap() + v.Cap()/2
   544  				if newcap < 4 {
   545  					newcap = 4
   546  				}
   547  				newv := reflect.MakeSlice(v.Type(), v.Len(), newcap)
   548  				reflect.Copy(newv, v)
   549  				v.Set(newv)
   550  			}
   551  			if i >= v.Len() {
   552  				v.SetLen(i + 1)
   553  			}
   554  		}
   555  
   556  		if i < v.Len() {
   557  			// Decode into element.
   558  			if err := d.value(v.Index(i)); err != nil {
   559  				return err
   560  			}
   561  		} else {
   562  			// Ran out of fixed array: skip.
   563  			if err := d.value(reflect.Value{}); err != nil {
   564  				return err
   565  			}
   566  		}
   567  		i++
   568  
   569  		// Next token must be , or ].
   570  		if d.opcode == scanSkipSpace {
   571  			d.scanWhile(scanSkipSpace)
   572  		}
   573  		if d.opcode == scanEndArray {
   574  			break
   575  		}
   576  		if d.opcode != scanArrayValue {
   577  			panic(phasePanicMsg)
   578  		}
   579  	}
   580  
   581  	if i < v.Len() {
   582  		if v.Kind() == reflect.Array {
   583  			// Array. Zero the rest.
   584  			z := reflect.Zero(v.Type().Elem())
   585  			for ; i < v.Len(); i++ {
   586  				v.Index(i).Set(z)
   587  			}
   588  		} else {
   589  			v.SetLen(i)
   590  		}
   591  	}
   592  	if i == 0 && v.Kind() == reflect.Slice {
   593  		v.Set(reflect.MakeSlice(v.Type(), 0, 0))
   594  	}
   595  	return nil
   596  }
   597  
   598  var nullLiteral = []byte("null")
   599  var textUnmarshalerType = reflect.TypeOf((*encoding.TextUnmarshaler)(nil)).Elem()
   600  
   601  // object consumes an object from d.data[d.off-1:], decoding into v.
   602  // The first byte ('{') of the object has been read already.
   603  func (d *decodeState) object(v reflect.Value) error {
   604  	// Check for unmarshaler.
   605  	u, ut, pv := indirect(v, false)
   606  	if u != nil {
   607  		start := d.readIndex()
   608  		d.skip()
   609  		return u.UnmarshalJSON(d.data[start:d.off])
   610  	}
   611  	if ut != nil {
   612  		d.saveError(&UnmarshalTypeError{Value: "object", Type: v.Type(), Offset: int64(d.off)})
   613  		d.skip()
   614  		return nil
   615  	}
   616  	v = pv
   617  	t := v.Type()
   618  
   619  	// Decoding into nil interface? Switch to non-reflect code.
   620  	if v.Kind() == reflect.Interface && v.NumMethod() == 0 {
   621  		oi := d.objectInterface()
   622  		v.Set(reflect.ValueOf(oi))
   623  		return nil
   624  	}
   625  
   626  	var fields structFields
   627  
   628  	// Check type of target:
   629  	//   struct or
   630  	//   map[T1]T2 where T1 is string, an integer type,
   631  	//             or an encoding.TextUnmarshaler
   632  	switch v.Kind() {
   633  	case reflect.Map:
   634  		// Map key must either have string kind, have an integer kind,
   635  		// or be an encoding.TextUnmarshaler.
   636  		switch t.Key().Kind() {
   637  		case reflect.String,
   638  			reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
   639  			reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   640  		default:
   641  			if !reflect.PtrTo(t.Key()).Implements(textUnmarshalerType) {
   642  				d.saveError(&UnmarshalTypeError{Value: "object", Type: t, Offset: int64(d.off)})
   643  				d.skip()
   644  				return nil
   645  			}
   646  		}
   647  		if v.IsNil() {
   648  			v.Set(reflect.MakeMap(t))
   649  		}
   650  	case reflect.Struct:
   651  		fields = cachedTypeFields(t)
   652  		// ok
   653  	default:
   654  		d.saveError(&UnmarshalTypeError{Value: "object", Type: t, Offset: int64(d.off)})
   655  		d.skip()
   656  		return nil
   657  	}
   658  
   659  	var mapElem reflect.Value
   660  	origErrorContext := d.errorContext
   661  
   662  	for {
   663  		// Read opening " of string key or closing }.
   664  		d.scanWhile(scanSkipSpace)
   665  		if d.opcode == scanEndObject {
   666  			// closing } - can only happen on first iteration.
   667  			break
   668  		}
   669  		if d.opcode != scanBeginLiteral {
   670  			panic(phasePanicMsg)
   671  		}
   672  
   673  		// Read key.
   674  		start := d.readIndex()
   675  		d.rescanLiteral()
   676  		item := d.data[start:d.readIndex()]
   677  		key, ok := unquoteBytes(item)
   678  		if !ok {
   679  			panic(phasePanicMsg)
   680  		}
   681  
   682  		// Figure out field corresponding to key.
   683  		var subv reflect.Value
   684  		destring := false // whether the value is wrapped in a string to be decoded first
   685  
   686  		if v.Kind() == reflect.Map {
   687  			elemType := t.Elem()
   688  			if !mapElem.IsValid() {
   689  				mapElem = reflect.New(elemType).Elem()
   690  			} else {
   691  				mapElem.Set(reflect.Zero(elemType))
   692  			}
   693  			subv = mapElem
   694  		} else {
   695  			var f *field
   696  			if i, ok := fields.nameIndex[string(key)]; ok {
   697  				// Found an exact name match.
   698  				f = &fields.list[i]
   699  			} else {
   700  				// Fall back to the expensive case-insensitive
   701  				// linear search.
   702  				for i := range fields.list {
   703  					ff := &fields.list[i]
   704  					if ff.equalFold(ff.nameBytes, key) {
   705  						f = ff
   706  						break
   707  					}
   708  				}
   709  			}
   710  			if f != nil {
   711  				subv = v
   712  				destring = f.quoted
   713  				for _, i := range f.index {
   714  					if subv.Kind() == reflect.Ptr {
   715  						if subv.IsNil() {
   716  							// If a struct embeds a pointer to an unexported type,
   717  							// it is not possible to set a newly allocated value
   718  							// since the field is unexported.
   719  							//
   720  							// See https://golang.org/issue/21357
   721  							if !subv.CanSet() {
   722  								d.saveError(fmt.Errorf("json: cannot set embedded pointer to unexported struct: %v", subv.Type().Elem()))
   723  								// Invalidate subv to ensure d.value(subv) skips over
   724  								// the JSON value without assigning it to subv.
   725  								subv = reflect.Value{}
   726  								destring = false
   727  								break
   728  							}
   729  							subv.Set(reflect.New(subv.Type().Elem()))
   730  						}
   731  						subv = subv.Elem()
   732  					}
   733  					subv = subv.Field(i)
   734  				}
   735  				d.errorContext.FieldStack = append(d.errorContext.FieldStack, f.name)
   736  				d.errorContext.Struct = t
   737  			} else if d.disallowUnknownFields {
   738  				d.saveError(fmt.Errorf("json: unknown field %q", key))
   739  			}
   740  		}
   741  
   742  		// Read : before value.
   743  		if d.opcode == scanSkipSpace {
   744  			d.scanWhile(scanSkipSpace)
   745  		}
   746  		if d.opcode != scanObjectKey {
   747  			panic(phasePanicMsg)
   748  		}
   749  		d.scanWhile(scanSkipSpace)
   750  
   751  		if destring {
   752  			switch qv := d.valueQuoted().(type) {
   753  			case nil:
   754  				if err := d.literalStore(nullLiteral, subv, false); err != nil {
   755  					return err
   756  				}
   757  			case string:
   758  				if err := d.literalStore([]byte(qv), subv, true); err != nil {
   759  					return err
   760  				}
   761  			default:
   762  				d.saveError(fmt.Errorf("json: invalid use of ,string struct tag, trying to unmarshal unquoted value into %v", subv.Type()))
   763  			}
   764  		} else {
   765  			if err := d.value(subv); err != nil {
   766  				return err
   767  			}
   768  		}
   769  
   770  		// Write value back to map;
   771  		// if using struct, subv points into struct already.
   772  		if v.Kind() == reflect.Map {
   773  			kt := t.Key()
   774  			var kv reflect.Value
   775  			switch {
   776  			case reflect.PtrTo(kt).Implements(textUnmarshalerType):
   777  				kv = reflect.New(kt)
   778  				if err := d.literalStore(item, kv, true); err != nil {
   779  					return err
   780  				}
   781  				kv = kv.Elem()
   782  			case kt.Kind() == reflect.String:
   783  				kv = reflect.ValueOf(key).Convert(kt)
   784  			default:
   785  				switch kt.Kind() {
   786  				case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   787  					s := string(key)
   788  					n, err := strconv.ParseInt(s, 10, 64)
   789  					if err != nil || reflect.Zero(kt).OverflowInt(n) {
   790  						d.saveError(&UnmarshalTypeError{Value: "number " + s, Type: kt, Offset: int64(start + 1)})
   791  						break
   792  					}
   793  					kv = reflect.ValueOf(n).Convert(kt)
   794  				case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   795  					s := string(key)
   796  					n, err := strconv.ParseUint(s, 10, 64)
   797  					if err != nil || reflect.Zero(kt).OverflowUint(n) {
   798  						d.saveError(&UnmarshalTypeError{Value: "number " + s, Type: kt, Offset: int64(start + 1)})
   799  						break
   800  					}
   801  					kv = reflect.ValueOf(n).Convert(kt)
   802  				default:
   803  					panic("json: Unexpected key type") // should never occur
   804  				}
   805  			}
   806  			if kv.IsValid() {
   807  				v.SetMapIndex(kv, subv)
   808  			}
   809  		}
   810  
   811  		// Next token must be , or }.
   812  		if d.opcode == scanSkipSpace {
   813  			d.scanWhile(scanSkipSpace)
   814  		}
   815  		// Reset errorContext to its original state.
   816  		// Keep the same underlying array for FieldStack, to reuse the
   817  		// space and avoid unnecessary allocs.
   818  		d.errorContext.FieldStack = d.errorContext.FieldStack[:len(origErrorContext.FieldStack)]
   819  		d.errorContext.Struct = origErrorContext.Struct
   820  		if d.opcode == scanEndObject {
   821  			break
   822  		}
   823  		if d.opcode != scanObjectValue {
   824  			panic(phasePanicMsg)
   825  		}
   826  	}
   827  	return nil
   828  }
   829  
   830  // convertNumber converts the number literal s to a float64 or a Number
   831  // depending on the setting of d.useNumber.
   832  func (d *decodeState) convertNumber(s string) (interface{}, error) {
   833  	if d.useNumber {
   834  		return Number(s), nil
   835  	}
   836  	f, err := strconv.ParseFloat(s, 64)
   837  	if err != nil {
   838  		return nil, &UnmarshalTypeError{Value: "number " + s, Type: reflect.TypeOf(0.0), Offset: int64(d.off)}
   839  	}
   840  	return f, nil
   841  }
   842  
   843  var numberType = reflect.TypeOf(Number(""))
   844  
   845  // literalStore decodes a literal stored in item into v.
   846  //
   847  // fromQuoted indicates whether this literal came from unwrapping a
   848  // string from the ",string" struct tag option. this is used only to
   849  // produce more helpful error messages.
   850  func (d *decodeState) literalStore(item []byte, v reflect.Value, fromQuoted bool) error {
   851  	// Check for unmarshaler.
   852  	if len(item) == 0 {
   853  		//Empty string given
   854  		d.saveError(fmt.Errorf("json: invalid use of ,string struct tag, trying to unmarshal %q into %v", item, v.Type()))
   855  		return nil
   856  	}
   857  	isNull := item[0] == 'n' // null
   858  	u, ut, pv := indirect(v, isNull)
   859  	if u != nil {
   860  		return u.UnmarshalJSON(item)
   861  	}
   862  	if ut != nil {
   863  		if item[0] != '"' {
   864  			if fromQuoted {
   865  				d.saveError(fmt.Errorf("json: invalid use of ,string struct tag, trying to unmarshal %q into %v", item, v.Type()))
   866  				return nil
   867  			}
   868  			val := "number"
   869  			switch item[0] {
   870  			case 'n':
   871  				val = "null"
   872  			case 't', 'f':
   873  				val = "bool"
   874  			}
   875  			d.saveError(&UnmarshalTypeError{Value: val, Type: v.Type(), Offset: int64(d.readIndex())})
   876  			return nil
   877  		}
   878  		s, ok := unquoteBytes(item)
   879  		if !ok {
   880  			if fromQuoted {
   881  				return fmt.Errorf("json: invalid use of ,string struct tag, trying to unmarshal %q into %v", item, v.Type())
   882  			}
   883  			panic(phasePanicMsg)
   884  		}
   885  		return ut.UnmarshalText(s)
   886  	}
   887  
   888  	v = pv
   889  
   890  	switch c := item[0]; c {
   891  	case 'n': // null
   892  		// The main parser checks that only true and false can reach here,
   893  		// but if this was a quoted string input, it could be anything.
   894  		if fromQuoted && string(item) != "null" {
   895  			d.saveError(fmt.Errorf("json: invalid use of ,string struct tag, trying to unmarshal %q into %v", item, v.Type()))
   896  			break
   897  		}
   898  		switch v.Kind() {
   899  		case reflect.Interface, reflect.Ptr, reflect.Map, reflect.Slice:
   900  			v.Set(reflect.Zero(v.Type()))
   901  			// otherwise, ignore null for primitives/string
   902  		}
   903  	case 't', 'f': // true, false
   904  		value := item[0] == 't'
   905  		// The main parser checks that only true and false can reach here,
   906  		// but if this was a quoted string input, it could be anything.
   907  		if fromQuoted && string(item) != "true" && string(item) != "false" {
   908  			d.saveError(fmt.Errorf("json: invalid use of ,string struct tag, trying to unmarshal %q into %v", item, v.Type()))
   909  			break
   910  		}
   911  		switch v.Kind() {
   912  		default:
   913  			if fromQuoted {
   914  				d.saveError(fmt.Errorf("json: invalid use of ,string struct tag, trying to unmarshal %q into %v", item, v.Type()))
   915  			} else {
   916  				d.saveError(&UnmarshalTypeError{Value: "bool", Type: v.Type(), Offset: int64(d.readIndex())})
   917  			}
   918  		case reflect.Bool:
   919  			v.SetBool(value)
   920  		case reflect.Interface:
   921  			if v.NumMethod() == 0 {
   922  				v.Set(reflect.ValueOf(value))
   923  			} else {
   924  				d.saveError(&UnmarshalTypeError{Value: "bool", Type: v.Type(), Offset: int64(d.readIndex())})
   925  			}
   926  		}
   927  
   928  	case '"': // string
   929  		s, ok := unquoteBytes(item)
   930  		if !ok {
   931  			if fromQuoted {
   932  				return fmt.Errorf("json: invalid use of ,string struct tag, trying to unmarshal %q into %v", item, v.Type())
   933  			}
   934  			panic(phasePanicMsg)
   935  		}
   936  		switch v.Kind() {
   937  		default:
   938  			d.saveError(&UnmarshalTypeError{Value: "string", Type: v.Type(), Offset: int64(d.readIndex())})
   939  		case reflect.Slice:
   940  			if v.Type().Elem().Kind() != reflect.Uint8 {
   941  				d.saveError(&UnmarshalTypeError{Value: "string", Type: v.Type(), Offset: int64(d.readIndex())})
   942  				break
   943  			}
   944  			b := make([]byte, base64.StdEncoding.DecodedLen(len(s)))
   945  			n, err := base64.StdEncoding.Decode(b, s)
   946  			if err != nil {
   947  				d.saveError(err)
   948  				break
   949  			}
   950  			v.SetBytes(b[:n])
   951  		case reflect.String:
   952  			if v.Type() == numberType && !isValidNumber(string(s)) {
   953  				return fmt.Errorf("json: invalid number literal, trying to unmarshal %q into Number", item)
   954  			}
   955  			v.SetString(string(s))
   956  		case reflect.Interface:
   957  			if v.NumMethod() == 0 {
   958  				v.Set(reflect.ValueOf(string(s)))
   959  			} else {
   960  				d.saveError(&UnmarshalTypeError{Value: "string", Type: v.Type(), Offset: int64(d.readIndex())})
   961  			}
   962  		}
   963  
   964  	default: // number
   965  		if c != '-' && (c < '0' || c > '9') {
   966  			if fromQuoted {
   967  				return fmt.Errorf("json: invalid use of ,string struct tag, trying to unmarshal %q into %v", item, v.Type())
   968  			}
   969  			panic(phasePanicMsg)
   970  		}
   971  		s := string(item)
   972  		switch v.Kind() {
   973  		default:
   974  			if v.Kind() == reflect.String && v.Type() == numberType {
   975  				// s must be a valid number, because it's
   976  				// already been tokenized.
   977  				v.SetString(s)
   978  				break
   979  			}
   980  			if fromQuoted {
   981  				return fmt.Errorf("json: invalid use of ,string struct tag, trying to unmarshal %q into %v", item, v.Type())
   982  			}
   983  			d.saveError(&UnmarshalTypeError{Value: "number", Type: v.Type(), Offset: int64(d.readIndex())})
   984  		case reflect.Interface:
   985  			n, err := d.convertNumber(s)
   986  			if err != nil {
   987  				d.saveError(err)
   988  				break
   989  			}
   990  			if v.NumMethod() != 0 {
   991  				d.saveError(&UnmarshalTypeError{Value: "number", Type: v.Type(), Offset: int64(d.readIndex())})
   992  				break
   993  			}
   994  			v.Set(reflect.ValueOf(n))
   995  
   996  		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   997  			n, err := strconv.ParseInt(s, 10, 64)
   998  			if err != nil || v.OverflowInt(n) {
   999  				d.saveError(&UnmarshalTypeError{Value: "number " + s, Type: v.Type(), Offset: int64(d.readIndex())})
  1000  				break
  1001  			}
  1002  			v.SetInt(n)
  1003  
  1004  		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
  1005  			n, err := strconv.ParseUint(s, 10, 64)
  1006  			if err != nil || v.OverflowUint(n) {
  1007  				d.saveError(&UnmarshalTypeError{Value: "number " + s, Type: v.Type(), Offset: int64(d.readIndex())})
  1008  				break
  1009  			}
  1010  			v.SetUint(n)
  1011  
  1012  		case reflect.Float32, reflect.Float64:
  1013  			n, err := strconv.ParseFloat(s, v.Type().Bits())
  1014  			if err != nil || v.OverflowFloat(n) {
  1015  				d.saveError(&UnmarshalTypeError{Value: "number " + s, Type: v.Type(), Offset: int64(d.readIndex())})
  1016  				break
  1017  			}
  1018  			v.SetFloat(n)
  1019  		}
  1020  	}
  1021  	return nil
  1022  }
  1023  
  1024  // The xxxInterface routines build up a value to be stored
  1025  // in an empty interface. They are not strictly necessary,
  1026  // but they avoid the weight of reflection in this common case.
  1027  
  1028  // valueInterface is like value but returns interface{}
  1029  func (d *decodeState) valueInterface() (val interface{}) {
  1030  	switch d.opcode {
  1031  	default:
  1032  		panic(phasePanicMsg)
  1033  	case scanBeginArray:
  1034  		val = d.arrayInterface()
  1035  		d.scanNext()
  1036  	case scanBeginObject:
  1037  		val = d.objectInterface()
  1038  		d.scanNext()
  1039  	case scanBeginLiteral:
  1040  		val = d.literalInterface()
  1041  	}
  1042  	return
  1043  }
  1044  
  1045  // arrayInterface is like array but returns []interface{}.
  1046  func (d *decodeState) arrayInterface() []interface{} {
  1047  	var v = make([]interface{}, 0)
  1048  	for {
  1049  		// Look ahead for ] - can only happen on first iteration.
  1050  		d.scanWhile(scanSkipSpace)
  1051  		if d.opcode == scanEndArray {
  1052  			break
  1053  		}
  1054  
  1055  		v = append(v, d.valueInterface())
  1056  
  1057  		// Next token must be , or ].
  1058  		if d.opcode == scanSkipSpace {
  1059  			d.scanWhile(scanSkipSpace)
  1060  		}
  1061  		if d.opcode == scanEndArray {
  1062  			break
  1063  		}
  1064  		if d.opcode != scanArrayValue {
  1065  			panic(phasePanicMsg)
  1066  		}
  1067  	}
  1068  	return v
  1069  }
  1070  
  1071  // objectInterface is like object but returns map[string]interface{}.
  1072  func (d *decodeState) objectInterface() map[string]interface{} {
  1073  	m := make(map[string]interface{})
  1074  	for {
  1075  		// Read opening " of string key or closing }.
  1076  		d.scanWhile(scanSkipSpace)
  1077  		if d.opcode == scanEndObject {
  1078  			// closing } - can only happen on first iteration.
  1079  			break
  1080  		}
  1081  		if d.opcode != scanBeginLiteral {
  1082  			panic(phasePanicMsg)
  1083  		}
  1084  
  1085  		// Read string key.
  1086  		start := d.readIndex()
  1087  		d.rescanLiteral()
  1088  		item := d.data[start:d.readIndex()]
  1089  		key, ok := unquote(item)
  1090  		if !ok {
  1091  			panic(phasePanicMsg)
  1092  		}
  1093  
  1094  		// Read : before value.
  1095  		if d.opcode == scanSkipSpace {
  1096  			d.scanWhile(scanSkipSpace)
  1097  		}
  1098  		if d.opcode != scanObjectKey {
  1099  			panic(phasePanicMsg)
  1100  		}
  1101  		d.scanWhile(scanSkipSpace)
  1102  
  1103  		// Read value.
  1104  		m[key] = d.valueInterface()
  1105  
  1106  		// Next token must be , or }.
  1107  		if d.opcode == scanSkipSpace {
  1108  			d.scanWhile(scanSkipSpace)
  1109  		}
  1110  		if d.opcode == scanEndObject {
  1111  			break
  1112  		}
  1113  		if d.opcode != scanObjectValue {
  1114  			panic(phasePanicMsg)
  1115  		}
  1116  	}
  1117  	return m
  1118  }
  1119  
  1120  // literalInterface consumes and returns a literal from d.data[d.off-1:] and
  1121  // it reads the following byte ahead. The first byte of the literal has been
  1122  // read already (that's how the caller knows it's a literal).
  1123  func (d *decodeState) literalInterface() interface{} {
  1124  	// All bytes inside literal return scanContinue op code.
  1125  	start := d.readIndex()
  1126  	d.rescanLiteral()
  1127  
  1128  	item := d.data[start:d.readIndex()]
  1129  
  1130  	switch c := item[0]; c {
  1131  	case 'n': // null
  1132  		return nil
  1133  
  1134  	case 't', 'f': // true, false
  1135  		return c == 't'
  1136  
  1137  	case '"': // string
  1138  		s, ok := unquote(item)
  1139  		if !ok {
  1140  			panic(phasePanicMsg)
  1141  		}
  1142  		return s
  1143  
  1144  	default: // number
  1145  		if c != '-' && (c < '0' || c > '9') {
  1146  			panic(phasePanicMsg)
  1147  		}
  1148  		n, err := d.convertNumber(string(item))
  1149  		if err != nil {
  1150  			d.saveError(err)
  1151  		}
  1152  		return n
  1153  	}
  1154  }
  1155  
  1156  // getu4 decodes \uXXXX from the beginning of s, returning the hex value,
  1157  // or it returns -1.
  1158  func getu4(s []byte) rune {
  1159  	if len(s) < 6 || s[0] != '\\' || s[1] != 'u' {
  1160  		return -1
  1161  	}
  1162  	var r rune
  1163  	for _, c := range s[2:6] {
  1164  		switch {
  1165  		case '0' <= c && c <= '9':
  1166  			c = c - '0'
  1167  		case 'a' <= c && c <= 'f':
  1168  			c = c - 'a' + 10
  1169  		case 'A' <= c && c <= 'F':
  1170  			c = c - 'A' + 10
  1171  		default:
  1172  			return -1
  1173  		}
  1174  		r = r*16 + rune(c)
  1175  	}
  1176  	return r
  1177  }
  1178  
  1179  // unquote converts a quoted JSON string literal s into an actual string t.
  1180  // The rules are different than for Go, so cannot use strconv.Unquote.
  1181  func unquote(s []byte) (t string, ok bool) {
  1182  	s, ok = unquoteBytes(s)
  1183  	t = string(s)
  1184  	return
  1185  }
  1186  
  1187  func unquoteBytes(s []byte) (t []byte, ok bool) {
  1188  	if len(s) < 2 || s[0] != '"' || s[len(s)-1] != '"' {
  1189  		return
  1190  	}
  1191  	s = s[1 : len(s)-1]
  1192  
  1193  	// Check for unusual characters. If there are none,
  1194  	// then no unquoting is needed, so return a slice of the
  1195  	// original bytes.
  1196  	r := 0
  1197  	for r < len(s) {
  1198  		c := s[r]
  1199  		if c == '\\' || c == '"' || c < ' ' {
  1200  			break
  1201  		}
  1202  		if c < utf8.RuneSelf {
  1203  			r++
  1204  			continue
  1205  		}
  1206  		rr, size := utf8.DecodeRune(s[r:])
  1207  		if rr == utf8.RuneError && size == 1 {
  1208  			break
  1209  		}
  1210  		r += size
  1211  	}
  1212  	if r == len(s) {
  1213  		return s, true
  1214  	}
  1215  
  1216  	b := make([]byte, len(s)+2*utf8.UTFMax)
  1217  	w := copy(b, s[0:r])
  1218  	for r < len(s) {
  1219  		// Out of room? Can only happen if s is full of
  1220  		// malformed UTF-8 and we're replacing each
  1221  		// byte with RuneError.
  1222  		if w >= len(b)-2*utf8.UTFMax {
  1223  			nb := make([]byte, (len(b)+utf8.UTFMax)*2)
  1224  			copy(nb, b[0:w])
  1225  			b = nb
  1226  		}
  1227  		switch c := s[r]; {
  1228  		case c == '\\':
  1229  			r++
  1230  			if r >= len(s) {
  1231  				return
  1232  			}
  1233  			switch s[r] {
  1234  			default:
  1235  				return
  1236  			case '"', '\\', '/', '\'':
  1237  				b[w] = s[r]
  1238  				r++
  1239  				w++
  1240  			case 'b':
  1241  				b[w] = '\b'
  1242  				r++
  1243  				w++
  1244  			case 'f':
  1245  				b[w] = '\f'
  1246  				r++
  1247  				w++
  1248  			case 'n':
  1249  				b[w] = '\n'
  1250  				r++
  1251  				w++
  1252  			case 'r':
  1253  				b[w] = '\r'
  1254  				r++
  1255  				w++
  1256  			case 't':
  1257  				b[w] = '\t'
  1258  				r++
  1259  				w++
  1260  			case 'u':
  1261  				r--
  1262  				rr := getu4(s[r:])
  1263  				if rr < 0 {
  1264  					return
  1265  				}
  1266  				r += 6
  1267  				if utf16.IsSurrogate(rr) {
  1268  					rr1 := getu4(s[r:])
  1269  					if dec := utf16.DecodeRune(rr, rr1); dec != unicode.ReplacementChar {
  1270  						// A valid pair; consume.
  1271  						r += 6
  1272  						w += utf8.EncodeRune(b[w:], dec)
  1273  						break
  1274  					}
  1275  					// Invalid surrogate; fall back to replacement rune.
  1276  					rr = unicode.ReplacementChar
  1277  				}
  1278  				w += utf8.EncodeRune(b[w:], rr)
  1279  			}
  1280  
  1281  		// Quote, control characters are invalid.
  1282  		case c == '"', c < ' ':
  1283  			return
  1284  
  1285  		// ASCII
  1286  		case c < utf8.RuneSelf:
  1287  			b[w] = c
  1288  			r++
  1289  			w++
  1290  
  1291  		// Coerce to well-formed UTF-8.
  1292  		default:
  1293  			rr, size := utf8.DecodeRune(s[r:])
  1294  			r += size
  1295  			w += utf8.EncodeRune(b[w:], rr)
  1296  		}
  1297  	}
  1298  	return b[0:w], true
  1299  }
  1300  

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