Source file src/encoding/json/encode.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  // Package json implements encoding and decoding of JSON as defined in
     6  // RFC 7159. The mapping between JSON and Go values is described
     7  // in the documentation for the Marshal and Unmarshal functions.
     8  //
     9  // See "JSON and Go" for an introduction to this package:
    10  // https://golang.org/doc/articles/json_and_go.html
    11  package json
    12  
    13  import (
    14  	"bytes"
    15  	"encoding"
    16  	"encoding/base64"
    17  	"fmt"
    18  	"math"
    19  	"reflect"
    20  	"sort"
    21  	"strconv"
    22  	"strings"
    23  	"sync"
    24  	"unicode"
    25  	"unicode/utf8"
    26  )
    27  
    28  // Marshal returns the JSON encoding of v.
    29  //
    30  // Marshal traverses the value v recursively.
    31  // If an encountered value implements the Marshaler interface
    32  // and is not a nil pointer, Marshal calls its MarshalJSON method
    33  // to produce JSON. If no MarshalJSON method is present but the
    34  // value implements encoding.TextMarshaler instead, Marshal calls
    35  // its MarshalText method and encodes the result as a JSON string.
    36  // The nil pointer exception is not strictly necessary
    37  // but mimics a similar, necessary exception in the behavior of
    38  // UnmarshalJSON.
    39  //
    40  // Otherwise, Marshal uses the following type-dependent default encodings:
    41  //
    42  // Boolean values encode as JSON booleans.
    43  //
    44  // Floating point, integer, and Number values encode as JSON numbers.
    45  //
    46  // String values encode as JSON strings coerced to valid UTF-8,
    47  // replacing invalid bytes with the Unicode replacement rune.
    48  // So that the JSON will be safe to embed inside HTML <script> tags,
    49  // the string is encoded using HTMLEscape,
    50  // which replaces "<", ">", "&", U+2028, and U+2029 are escaped
    51  // to "\u003c","\u003e", "\u0026", "\u2028", and "\u2029".
    52  // This replacement can be disabled when using an Encoder,
    53  // by calling SetEscapeHTML(false).
    54  //
    55  // Array and slice values encode as JSON arrays, except that
    56  // []byte encodes as a base64-encoded string, and a nil slice
    57  // encodes as the null JSON value.
    58  //
    59  // Struct values encode as JSON objects.
    60  // Each exported struct field becomes a member of the object, using the
    61  // field name as the object key, unless the field is omitted for one of the
    62  // reasons given below.
    63  //
    64  // The encoding of each struct field can be customized by the format string
    65  // stored under the "json" key in the struct field's tag.
    66  // The format string gives the name of the field, possibly followed by a
    67  // comma-separated list of options. The name may be empty in order to
    68  // specify options without overriding the default field name.
    69  //
    70  // The "omitempty" option specifies that the field should be omitted
    71  // from the encoding if the field has an empty value, defined as
    72  // false, 0, a nil pointer, a nil interface value, and any empty array,
    73  // slice, map, or string.
    74  //
    75  // As a special case, if the field tag is "-", the field is always omitted.
    76  // Note that a field with name "-" can still be generated using the tag "-,".
    77  //
    78  // Examples of struct field tags and their meanings:
    79  //
    80  //   // Field appears in JSON as key "myName".
    81  //   Field int `json:"myName"`
    82  //
    83  //   // Field appears in JSON as key "myName" and
    84  //   // the field is omitted from the object if its value is empty,
    85  //   // as defined above.
    86  //   Field int `json:"myName,omitempty"`
    87  //
    88  //   // Field appears in JSON as key "Field" (the default), but
    89  //   // the field is skipped if empty.
    90  //   // Note the leading comma.
    91  //   Field int `json:",omitempty"`
    92  //
    93  //   // Field is ignored by this package.
    94  //   Field int `json:"-"`
    95  //
    96  //   // Field appears in JSON as key "-".
    97  //   Field int `json:"-,"`
    98  //
    99  // The "string" option signals that a field is stored as JSON inside a
   100  // JSON-encoded string. It applies only to fields of string, floating point,
   101  // integer, or boolean types. This extra level of encoding is sometimes used
   102  // when communicating with JavaScript programs:
   103  //
   104  //    Int64String int64 `json:",string"`
   105  //
   106  // The key name will be used if it's a non-empty string consisting of
   107  // only Unicode letters, digits, and ASCII punctuation except quotation
   108  // marks, backslash, and comma.
   109  //
   110  // Anonymous struct fields are usually marshaled as if their inner exported fields
   111  // were fields in the outer struct, subject to the usual Go visibility rules amended
   112  // as described in the next paragraph.
   113  // An anonymous struct field with a name given in its JSON tag is treated as
   114  // having that name, rather than being anonymous.
   115  // An anonymous struct field of interface type is treated the same as having
   116  // that type as its name, rather than being anonymous.
   117  //
   118  // The Go visibility rules for struct fields are amended for JSON when
   119  // deciding which field to marshal or unmarshal. If there are
   120  // multiple fields at the same level, and that level is the least
   121  // nested (and would therefore be the nesting level selected by the
   122  // usual Go rules), the following extra rules apply:
   123  //
   124  // 1) Of those fields, if any are JSON-tagged, only tagged fields are considered,
   125  // even if there are multiple untagged fields that would otherwise conflict.
   126  //
   127  // 2) If there is exactly one field (tagged or not according to the first rule), that is selected.
   128  //
   129  // 3) Otherwise there are multiple fields, and all are ignored; no error occurs.
   130  //
   131  // Handling of anonymous struct fields is new in Go 1.1.
   132  // Prior to Go 1.1, anonymous struct fields were ignored. To force ignoring of
   133  // an anonymous struct field in both current and earlier versions, give the field
   134  // a JSON tag of "-".
   135  //
   136  // Map values encode as JSON objects. The map's key type must either be a
   137  // string, an integer type, or implement encoding.TextMarshaler. The map keys
   138  // are sorted and used as JSON object keys by applying the following rules,
   139  // subject to the UTF-8 coercion described for string values above:
   140  //   - keys of any string type are used directly
   141  //   - encoding.TextMarshalers are marshaled
   142  //   - integer keys are converted to strings
   143  //
   144  // Pointer values encode as the value pointed to.
   145  // A nil pointer encodes as the null JSON value.
   146  //
   147  // Interface values encode as the value contained in the interface.
   148  // A nil interface value encodes as the null JSON value.
   149  //
   150  // Channel, complex, and function values cannot be encoded in JSON.
   151  // Attempting to encode such a value causes Marshal to return
   152  // an UnsupportedTypeError.
   153  //
   154  // JSON cannot represent cyclic data structures and Marshal does not
   155  // handle them. Passing cyclic structures to Marshal will result in
   156  // an infinite recursion.
   157  //
   158  func Marshal(v interface{}) ([]byte, error) {
   159  	e := newEncodeState()
   160  
   161  	err := e.marshal(v, encOpts{escapeHTML: true})
   162  	if err != nil {
   163  		return nil, err
   164  	}
   165  	buf := append([]byte(nil), e.Bytes()...)
   166  
   167  	e.Reset()
   168  	encodeStatePool.Put(e)
   169  
   170  	return buf, nil
   171  }
   172  
   173  // MarshalIndent is like Marshal but applies Indent to format the output.
   174  // Each JSON element in the output will begin on a new line beginning with prefix
   175  // followed by one or more copies of indent according to the indentation nesting.
   176  func MarshalIndent(v interface{}, prefix, indent string) ([]byte, error) {
   177  	b, err := Marshal(v)
   178  	if err != nil {
   179  		return nil, err
   180  	}
   181  	var buf bytes.Buffer
   182  	err = Indent(&buf, b, prefix, indent)
   183  	if err != nil {
   184  		return nil, err
   185  	}
   186  	return buf.Bytes(), nil
   187  }
   188  
   189  // HTMLEscape appends to dst the JSON-encoded src with <, >, &, U+2028 and U+2029
   190  // characters inside string literals changed to \u003c, \u003e, \u0026, \u2028, \u2029
   191  // so that the JSON will be safe to embed inside HTML <script> tags.
   192  // For historical reasons, web browsers don't honor standard HTML
   193  // escaping within <script> tags, so an alternative JSON encoding must
   194  // be used.
   195  func HTMLEscape(dst *bytes.Buffer, src []byte) {
   196  	// The characters can only appear in string literals,
   197  	// so just scan the string one byte at a time.
   198  	start := 0
   199  	for i, c := range src {
   200  		if c == '<' || c == '>' || c == '&' {
   201  			if start < i {
   202  				dst.Write(src[start:i])
   203  			}
   204  			dst.WriteString(`\u00`)
   205  			dst.WriteByte(hex[c>>4])
   206  			dst.WriteByte(hex[c&0xF])
   207  			start = i + 1
   208  		}
   209  		// Convert U+2028 and U+2029 (E2 80 A8 and E2 80 A9).
   210  		if c == 0xE2 && i+2 < len(src) && src[i+1] == 0x80 && src[i+2]&^1 == 0xA8 {
   211  			if start < i {
   212  				dst.Write(src[start:i])
   213  			}
   214  			dst.WriteString(`\u202`)
   215  			dst.WriteByte(hex[src[i+2]&0xF])
   216  			start = i + 3
   217  		}
   218  	}
   219  	if start < len(src) {
   220  		dst.Write(src[start:])
   221  	}
   222  }
   223  
   224  // Marshaler is the interface implemented by types that
   225  // can marshal themselves into valid JSON.
   226  type Marshaler interface {
   227  	MarshalJSON() ([]byte, error)
   228  }
   229  
   230  // An UnsupportedTypeError is returned by Marshal when attempting
   231  // to encode an unsupported value type.
   232  type UnsupportedTypeError struct {
   233  	Type reflect.Type
   234  }
   235  
   236  func (e *UnsupportedTypeError) Error() string {
   237  	return "json: unsupported type: " + e.Type.String()
   238  }
   239  
   240  type UnsupportedValueError struct {
   241  	Value reflect.Value
   242  	Str   string
   243  }
   244  
   245  func (e *UnsupportedValueError) Error() string {
   246  	return "json: unsupported value: " + e.Str
   247  }
   248  
   249  // Before Go 1.2, an InvalidUTF8Error was returned by Marshal when
   250  // attempting to encode a string value with invalid UTF-8 sequences.
   251  // As of Go 1.2, Marshal instead coerces the string to valid UTF-8 by
   252  // replacing invalid bytes with the Unicode replacement rune U+FFFD.
   253  //
   254  // Deprecated: No longer used; kept for compatibility.
   255  type InvalidUTF8Error struct {
   256  	S string // the whole string value that caused the error
   257  }
   258  
   259  func (e *InvalidUTF8Error) Error() string {
   260  	return "json: invalid UTF-8 in string: " + strconv.Quote(e.S)
   261  }
   262  
   263  // A MarshalerError represents an error from calling a MarshalJSON or MarshalText method.
   264  type MarshalerError struct {
   265  	Type reflect.Type
   266  	Err  error
   267  }
   268  
   269  func (e *MarshalerError) Error() string {
   270  	return "json: error calling MarshalJSON for type " + e.Type.String() + ": " + e.Err.Error()
   271  }
   272  
   273  func (e *MarshalerError) Unwrap() error { return e.Err }
   274  
   275  var hex = "0123456789abcdef"
   276  
   277  // An encodeState encodes JSON into a bytes.Buffer.
   278  type encodeState struct {
   279  	bytes.Buffer // accumulated output
   280  	scratch      [64]byte
   281  }
   282  
   283  var encodeStatePool sync.Pool
   284  
   285  func newEncodeState() *encodeState {
   286  	if v := encodeStatePool.Get(); v != nil {
   287  		e := v.(*encodeState)
   288  		e.Reset()
   289  		return e
   290  	}
   291  	return new(encodeState)
   292  }
   293  
   294  // jsonError is an error wrapper type for internal use only.
   295  // Panics with errors are wrapped in jsonError so that the top-level recover
   296  // can distinguish intentional panics from this package.
   297  type jsonError struct{ error }
   298  
   299  func (e *encodeState) marshal(v interface{}, opts encOpts) (err error) {
   300  	defer func() {
   301  		if r := recover(); r != nil {
   302  			if je, ok := r.(jsonError); ok {
   303  				err = je.error
   304  			} else {
   305  				panic(r)
   306  			}
   307  		}
   308  	}()
   309  	e.reflectValue(reflect.ValueOf(v), opts)
   310  	return nil
   311  }
   312  
   313  // error aborts the encoding by panicking with err wrapped in jsonError.
   314  func (e *encodeState) error(err error) {
   315  	panic(jsonError{err})
   316  }
   317  
   318  func isEmptyValue(v reflect.Value) bool {
   319  	switch v.Kind() {
   320  	case reflect.Array, reflect.Map, reflect.Slice, reflect.String:
   321  		return v.Len() == 0
   322  	case reflect.Bool:
   323  		return !v.Bool()
   324  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   325  		return v.Int() == 0
   326  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   327  		return v.Uint() == 0
   328  	case reflect.Float32, reflect.Float64:
   329  		return v.Float() == 0
   330  	case reflect.Interface, reflect.Ptr:
   331  		return v.IsNil()
   332  	}
   333  	return false
   334  }
   335  
   336  func (e *encodeState) reflectValue(v reflect.Value, opts encOpts) {
   337  	valueEncoder(v)(e, v, opts)
   338  }
   339  
   340  type encOpts struct {
   341  	// quoted causes primitive fields to be encoded inside JSON strings.
   342  	quoted bool
   343  	// escapeHTML causes '<', '>', and '&' to be escaped in JSON strings.
   344  	escapeHTML bool
   345  }
   346  
   347  type encoderFunc func(e *encodeState, v reflect.Value, opts encOpts)
   348  
   349  var encoderCache sync.Map // map[reflect.Type]encoderFunc
   350  
   351  func valueEncoder(v reflect.Value) encoderFunc {
   352  	if !v.IsValid() {
   353  		return invalidValueEncoder
   354  	}
   355  	return typeEncoder(v.Type())
   356  }
   357  
   358  func typeEncoder(t reflect.Type) encoderFunc {
   359  	if fi, ok := encoderCache.Load(t); ok {
   360  		return fi.(encoderFunc)
   361  	}
   362  
   363  	// To deal with recursive types, populate the map with an
   364  	// indirect func before we build it. This type waits on the
   365  	// real func (f) to be ready and then calls it. This indirect
   366  	// func is only used for recursive types.
   367  	var (
   368  		wg sync.WaitGroup
   369  		f  encoderFunc
   370  	)
   371  	wg.Add(1)
   372  	fi, loaded := encoderCache.LoadOrStore(t, encoderFunc(func(e *encodeState, v reflect.Value, opts encOpts) {
   373  		wg.Wait()
   374  		f(e, v, opts)
   375  	}))
   376  	if loaded {
   377  		return fi.(encoderFunc)
   378  	}
   379  
   380  	// Compute the real encoder and replace the indirect func with it.
   381  	f = newTypeEncoder(t, true)
   382  	wg.Done()
   383  	encoderCache.Store(t, f)
   384  	return f
   385  }
   386  
   387  var (
   388  	marshalerType     = reflect.TypeOf((*Marshaler)(nil)).Elem()
   389  	textMarshalerType = reflect.TypeOf((*encoding.TextMarshaler)(nil)).Elem()
   390  )
   391  
   392  // newTypeEncoder constructs an encoderFunc for a type.
   393  // The returned encoder only checks CanAddr when allowAddr is true.
   394  func newTypeEncoder(t reflect.Type, allowAddr bool) encoderFunc {
   395  	if t.Implements(marshalerType) {
   396  		return marshalerEncoder
   397  	}
   398  	if t.Kind() != reflect.Ptr && allowAddr && reflect.PtrTo(t).Implements(marshalerType) {
   399  		return newCondAddrEncoder(addrMarshalerEncoder, newTypeEncoder(t, false))
   400  	}
   401  
   402  	if t.Implements(textMarshalerType) {
   403  		return textMarshalerEncoder
   404  	}
   405  	if t.Kind() != reflect.Ptr && allowAddr && reflect.PtrTo(t).Implements(textMarshalerType) {
   406  		return newCondAddrEncoder(addrTextMarshalerEncoder, newTypeEncoder(t, false))
   407  	}
   408  
   409  	switch t.Kind() {
   410  	case reflect.Bool:
   411  		return boolEncoder
   412  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   413  		return intEncoder
   414  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   415  		return uintEncoder
   416  	case reflect.Float32:
   417  		return float32Encoder
   418  	case reflect.Float64:
   419  		return float64Encoder
   420  	case reflect.String:
   421  		return stringEncoder
   422  	case reflect.Interface:
   423  		return interfaceEncoder
   424  	case reflect.Struct:
   425  		return newStructEncoder(t)
   426  	case reflect.Map:
   427  		return newMapEncoder(t)
   428  	case reflect.Slice:
   429  		return newSliceEncoder(t)
   430  	case reflect.Array:
   431  		return newArrayEncoder(t)
   432  	case reflect.Ptr:
   433  		return newPtrEncoder(t)
   434  	default:
   435  		return unsupportedTypeEncoder
   436  	}
   437  }
   438  
   439  func invalidValueEncoder(e *encodeState, v reflect.Value, _ encOpts) {
   440  	e.WriteString("null")
   441  }
   442  
   443  func marshalerEncoder(e *encodeState, v reflect.Value, opts encOpts) {
   444  	if v.Kind() == reflect.Ptr && v.IsNil() {
   445  		e.WriteString("null")
   446  		return
   447  	}
   448  	m, ok := v.Interface().(Marshaler)
   449  	if !ok {
   450  		e.WriteString("null")
   451  		return
   452  	}
   453  	b, err := m.MarshalJSON()
   454  	if err == nil {
   455  		// copy JSON into buffer, checking validity.
   456  		err = compact(&e.Buffer, b, opts.escapeHTML)
   457  	}
   458  	if err != nil {
   459  		e.error(&MarshalerError{v.Type(), err})
   460  	}
   461  }
   462  
   463  func addrMarshalerEncoder(e *encodeState, v reflect.Value, opts encOpts) {
   464  	va := v.Addr()
   465  	if va.IsNil() {
   466  		e.WriteString("null")
   467  		return
   468  	}
   469  	m := va.Interface().(Marshaler)
   470  	b, err := m.MarshalJSON()
   471  	if err == nil {
   472  		// copy JSON into buffer, checking validity.
   473  		err = compact(&e.Buffer, b, opts.escapeHTML)
   474  	}
   475  	if err != nil {
   476  		e.error(&MarshalerError{v.Type(), err})
   477  	}
   478  }
   479  
   480  func textMarshalerEncoder(e *encodeState, v reflect.Value, opts encOpts) {
   481  	if v.Kind() == reflect.Ptr && v.IsNil() {
   482  		e.WriteString("null")
   483  		return
   484  	}
   485  	m := v.Interface().(encoding.TextMarshaler)
   486  	b, err := m.MarshalText()
   487  	if err != nil {
   488  		e.error(&MarshalerError{v.Type(), err})
   489  	}
   490  	e.stringBytes(b, opts.escapeHTML)
   491  }
   492  
   493  func addrTextMarshalerEncoder(e *encodeState, v reflect.Value, opts encOpts) {
   494  	va := v.Addr()
   495  	if va.IsNil() {
   496  		e.WriteString("null")
   497  		return
   498  	}
   499  	m := va.Interface().(encoding.TextMarshaler)
   500  	b, err := m.MarshalText()
   501  	if err != nil {
   502  		e.error(&MarshalerError{v.Type(), err})
   503  	}
   504  	e.stringBytes(b, opts.escapeHTML)
   505  }
   506  
   507  func boolEncoder(e *encodeState, v reflect.Value, opts encOpts) {
   508  	if opts.quoted {
   509  		e.WriteByte('"')
   510  	}
   511  	if v.Bool() {
   512  		e.WriteString("true")
   513  	} else {
   514  		e.WriteString("false")
   515  	}
   516  	if opts.quoted {
   517  		e.WriteByte('"')
   518  	}
   519  }
   520  
   521  func intEncoder(e *encodeState, v reflect.Value, opts encOpts) {
   522  	b := strconv.AppendInt(e.scratch[:0], v.Int(), 10)
   523  	if opts.quoted {
   524  		e.WriteByte('"')
   525  	}
   526  	e.Write(b)
   527  	if opts.quoted {
   528  		e.WriteByte('"')
   529  	}
   530  }
   531  
   532  func uintEncoder(e *encodeState, v reflect.Value, opts encOpts) {
   533  	b := strconv.AppendUint(e.scratch[:0], v.Uint(), 10)
   534  	if opts.quoted {
   535  		e.WriteByte('"')
   536  	}
   537  	e.Write(b)
   538  	if opts.quoted {
   539  		e.WriteByte('"')
   540  	}
   541  }
   542  
   543  type floatEncoder int // number of bits
   544  
   545  func (bits floatEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) {
   546  	f := v.Float()
   547  	if math.IsInf(f, 0) || math.IsNaN(f) {
   548  		e.error(&UnsupportedValueError{v, strconv.FormatFloat(f, 'g', -1, int(bits))})
   549  	}
   550  
   551  	// Convert as if by ES6 number to string conversion.
   552  	// This matches most other JSON generators.
   553  	// See golang.org/issue/6384 and golang.org/issue/14135.
   554  	// Like fmt %g, but the exponent cutoffs are different
   555  	// and exponents themselves are not padded to two digits.
   556  	b := e.scratch[:0]
   557  	abs := math.Abs(f)
   558  	fmt := byte('f')
   559  	// Note: Must use float32 comparisons for underlying float32 value to get precise cutoffs right.
   560  	if abs != 0 {
   561  		if bits == 64 && (abs < 1e-6 || abs >= 1e21) || bits == 32 && (float32(abs) < 1e-6 || float32(abs) >= 1e21) {
   562  			fmt = 'e'
   563  		}
   564  	}
   565  	b = strconv.AppendFloat(b, f, fmt, -1, int(bits))
   566  	if fmt == 'e' {
   567  		// clean up e-09 to e-9
   568  		n := len(b)
   569  		if n >= 4 && b[n-4] == 'e' && b[n-3] == '-' && b[n-2] == '0' {
   570  			b[n-2] = b[n-1]
   571  			b = b[:n-1]
   572  		}
   573  	}
   574  
   575  	if opts.quoted {
   576  		e.WriteByte('"')
   577  	}
   578  	e.Write(b)
   579  	if opts.quoted {
   580  		e.WriteByte('"')
   581  	}
   582  }
   583  
   584  var (
   585  	float32Encoder = (floatEncoder(32)).encode
   586  	float64Encoder = (floatEncoder(64)).encode
   587  )
   588  
   589  func stringEncoder(e *encodeState, v reflect.Value, opts encOpts) {
   590  	if v.Type() == numberType {
   591  		numStr := v.String()
   592  		// In Go1.5 the empty string encodes to "0", while this is not a valid number literal
   593  		// we keep compatibility so check validity after this.
   594  		if numStr == "" {
   595  			numStr = "0" // Number's zero-val
   596  		}
   597  		if !isValidNumber(numStr) {
   598  			e.error(fmt.Errorf("json: invalid number literal %q", numStr))
   599  		}
   600  		e.WriteString(numStr)
   601  		return
   602  	}
   603  	if opts.quoted {
   604  		sb, err := Marshal(v.String())
   605  		if err != nil {
   606  			e.error(err)
   607  		}
   608  		e.string(string(sb), opts.escapeHTML)
   609  	} else {
   610  		e.string(v.String(), opts.escapeHTML)
   611  	}
   612  }
   613  
   614  func interfaceEncoder(e *encodeState, v reflect.Value, opts encOpts) {
   615  	if v.IsNil() {
   616  		e.WriteString("null")
   617  		return
   618  	}
   619  	e.reflectValue(v.Elem(), opts)
   620  }
   621  
   622  func unsupportedTypeEncoder(e *encodeState, v reflect.Value, _ encOpts) {
   623  	e.error(&UnsupportedTypeError{v.Type()})
   624  }
   625  
   626  type structEncoder struct {
   627  	fields structFields
   628  }
   629  
   630  type structFields struct {
   631  	list      []field
   632  	nameIndex map[string]int
   633  }
   634  
   635  func (se structEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) {
   636  	next := byte('{')
   637  FieldLoop:
   638  	for i := range se.fields.list {
   639  		f := &se.fields.list[i]
   640  
   641  		// Find the nested struct field by following f.index.
   642  		fv := v
   643  		for _, i := range f.index {
   644  			if fv.Kind() == reflect.Ptr {
   645  				if fv.IsNil() {
   646  					continue FieldLoop
   647  				}
   648  				fv = fv.Elem()
   649  			}
   650  			fv = fv.Field(i)
   651  		}
   652  
   653  		if f.omitEmpty && isEmptyValue(fv) {
   654  			continue
   655  		}
   656  		e.WriteByte(next)
   657  		next = ','
   658  		if opts.escapeHTML {
   659  			e.WriteString(f.nameEscHTML)
   660  		} else {
   661  			e.WriteString(f.nameNonEsc)
   662  		}
   663  		opts.quoted = f.quoted
   664  		f.encoder(e, fv, opts)
   665  	}
   666  	if next == '{' {
   667  		e.WriteString("{}")
   668  	} else {
   669  		e.WriteByte('}')
   670  	}
   671  }
   672  
   673  func newStructEncoder(t reflect.Type) encoderFunc {
   674  	se := structEncoder{fields: cachedTypeFields(t)}
   675  	return se.encode
   676  }
   677  
   678  type mapEncoder struct {
   679  	elemEnc encoderFunc
   680  }
   681  
   682  func (me mapEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) {
   683  	if v.IsNil() {
   684  		e.WriteString("null")
   685  		return
   686  	}
   687  	e.WriteByte('{')
   688  
   689  	// Extract and sort the keys.
   690  	keys := v.MapKeys()
   691  	sv := make([]reflectWithString, len(keys))
   692  	for i, v := range keys {
   693  		sv[i].v = v
   694  		if err := sv[i].resolve(); err != nil {
   695  			e.error(&MarshalerError{v.Type(), err})
   696  		}
   697  	}
   698  	sort.Slice(sv, func(i, j int) bool { return sv[i].s < sv[j].s })
   699  
   700  	for i, kv := range sv {
   701  		if i > 0 {
   702  			e.WriteByte(',')
   703  		}
   704  		e.string(kv.s, opts.escapeHTML)
   705  		e.WriteByte(':')
   706  		me.elemEnc(e, v.MapIndex(kv.v), opts)
   707  	}
   708  	e.WriteByte('}')
   709  }
   710  
   711  func newMapEncoder(t reflect.Type) encoderFunc {
   712  	switch t.Key().Kind() {
   713  	case reflect.String,
   714  		reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
   715  		reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   716  	default:
   717  		if !t.Key().Implements(textMarshalerType) {
   718  			return unsupportedTypeEncoder
   719  		}
   720  	}
   721  	me := mapEncoder{typeEncoder(t.Elem())}
   722  	return me.encode
   723  }
   724  
   725  func encodeByteSlice(e *encodeState, v reflect.Value, _ encOpts) {
   726  	if v.IsNil() {
   727  		e.WriteString("null")
   728  		return
   729  	}
   730  	s := v.Bytes()
   731  	e.WriteByte('"')
   732  	encodedLen := base64.StdEncoding.EncodedLen(len(s))
   733  	if encodedLen <= len(e.scratch) {
   734  		// If the encoded bytes fit in e.scratch, avoid an extra
   735  		// allocation and use the cheaper Encoding.Encode.
   736  		dst := e.scratch[:encodedLen]
   737  		base64.StdEncoding.Encode(dst, s)
   738  		e.Write(dst)
   739  	} else if encodedLen <= 1024 {
   740  		// The encoded bytes are short enough to allocate for, and
   741  		// Encoding.Encode is still cheaper.
   742  		dst := make([]byte, encodedLen)
   743  		base64.StdEncoding.Encode(dst, s)
   744  		e.Write(dst)
   745  	} else {
   746  		// The encoded bytes are too long to cheaply allocate, and
   747  		// Encoding.Encode is no longer noticeably cheaper.
   748  		enc := base64.NewEncoder(base64.StdEncoding, e)
   749  		enc.Write(s)
   750  		enc.Close()
   751  	}
   752  	e.WriteByte('"')
   753  }
   754  
   755  // sliceEncoder just wraps an arrayEncoder, checking to make sure the value isn't nil.
   756  type sliceEncoder struct {
   757  	arrayEnc encoderFunc
   758  }
   759  
   760  func (se sliceEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) {
   761  	if v.IsNil() {
   762  		e.WriteString("null")
   763  		return
   764  	}
   765  	se.arrayEnc(e, v, opts)
   766  }
   767  
   768  func newSliceEncoder(t reflect.Type) encoderFunc {
   769  	// Byte slices get special treatment; arrays don't.
   770  	if t.Elem().Kind() == reflect.Uint8 {
   771  		p := reflect.PtrTo(t.Elem())
   772  		if !p.Implements(marshalerType) && !p.Implements(textMarshalerType) {
   773  			return encodeByteSlice
   774  		}
   775  	}
   776  	enc := sliceEncoder{newArrayEncoder(t)}
   777  	return enc.encode
   778  }
   779  
   780  type arrayEncoder struct {
   781  	elemEnc encoderFunc
   782  }
   783  
   784  func (ae arrayEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) {
   785  	e.WriteByte('[')
   786  	n := v.Len()
   787  	for i := 0; i < n; i++ {
   788  		if i > 0 {
   789  			e.WriteByte(',')
   790  		}
   791  		ae.elemEnc(e, v.Index(i), opts)
   792  	}
   793  	e.WriteByte(']')
   794  }
   795  
   796  func newArrayEncoder(t reflect.Type) encoderFunc {
   797  	enc := arrayEncoder{typeEncoder(t.Elem())}
   798  	return enc.encode
   799  }
   800  
   801  type ptrEncoder struct {
   802  	elemEnc encoderFunc
   803  }
   804  
   805  func (pe ptrEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) {
   806  	if v.IsNil() {
   807  		e.WriteString("null")
   808  		return
   809  	}
   810  	pe.elemEnc(e, v.Elem(), opts)
   811  }
   812  
   813  func newPtrEncoder(t reflect.Type) encoderFunc {
   814  	enc := ptrEncoder{typeEncoder(t.Elem())}
   815  	return enc.encode
   816  }
   817  
   818  type condAddrEncoder struct {
   819  	canAddrEnc, elseEnc encoderFunc
   820  }
   821  
   822  func (ce condAddrEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) {
   823  	if v.CanAddr() {
   824  		ce.canAddrEnc(e, v, opts)
   825  	} else {
   826  		ce.elseEnc(e, v, opts)
   827  	}
   828  }
   829  
   830  // newCondAddrEncoder returns an encoder that checks whether its value
   831  // CanAddr and delegates to canAddrEnc if so, else to elseEnc.
   832  func newCondAddrEncoder(canAddrEnc, elseEnc encoderFunc) encoderFunc {
   833  	enc := condAddrEncoder{canAddrEnc: canAddrEnc, elseEnc: elseEnc}
   834  	return enc.encode
   835  }
   836  
   837  func isValidTag(s string) bool {
   838  	if s == "" {
   839  		return false
   840  	}
   841  	for _, c := range s {
   842  		switch {
   843  		case strings.ContainsRune("!#$%&()*+-./:<=>?@[]^_{|}~ ", c):
   844  			// Backslash and quote chars are reserved, but
   845  			// otherwise any punctuation chars are allowed
   846  			// in a tag name.
   847  		case !unicode.IsLetter(c) && !unicode.IsDigit(c):
   848  			return false
   849  		}
   850  	}
   851  	return true
   852  }
   853  
   854  func typeByIndex(t reflect.Type, index []int) reflect.Type {
   855  	for _, i := range index {
   856  		if t.Kind() == reflect.Ptr {
   857  			t = t.Elem()
   858  		}
   859  		t = t.Field(i).Type
   860  	}
   861  	return t
   862  }
   863  
   864  type reflectWithString struct {
   865  	v reflect.Value
   866  	s string
   867  }
   868  
   869  func (w *reflectWithString) resolve() error {
   870  	if w.v.Kind() == reflect.String {
   871  		w.s = w.v.String()
   872  		return nil
   873  	}
   874  	if tm, ok := w.v.Interface().(encoding.TextMarshaler); ok {
   875  		buf, err := tm.MarshalText()
   876  		w.s = string(buf)
   877  		return err
   878  	}
   879  	switch w.v.Kind() {
   880  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   881  		w.s = strconv.FormatInt(w.v.Int(), 10)
   882  		return nil
   883  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   884  		w.s = strconv.FormatUint(w.v.Uint(), 10)
   885  		return nil
   886  	}
   887  	panic("unexpected map key type")
   888  }
   889  
   890  // NOTE: keep in sync with stringBytes below.
   891  func (e *encodeState) string(s string, escapeHTML bool) {
   892  	e.WriteByte('"')
   893  	start := 0
   894  	for i := 0; i < len(s); {
   895  		if b := s[i]; b < utf8.RuneSelf {
   896  			if htmlSafeSet[b] || (!escapeHTML && safeSet[b]) {
   897  				i++
   898  				continue
   899  			}
   900  			if start < i {
   901  				e.WriteString(s[start:i])
   902  			}
   903  			e.WriteByte('\\')
   904  			switch b {
   905  			case '\\', '"':
   906  				e.WriteByte(b)
   907  			case '\n':
   908  				e.WriteByte('n')
   909  			case '\r':
   910  				e.WriteByte('r')
   911  			case '\t':
   912  				e.WriteByte('t')
   913  			default:
   914  				// This encodes bytes < 0x20 except for \t, \n and \r.
   915  				// If escapeHTML is set, it also escapes <, >, and &
   916  				// because they can lead to security holes when
   917  				// user-controlled strings are rendered into JSON
   918  				// and served to some browsers.
   919  				e.WriteString(`u00`)
   920  				e.WriteByte(hex[b>>4])
   921  				e.WriteByte(hex[b&0xF])
   922  			}
   923  			i++
   924  			start = i
   925  			continue
   926  		}
   927  		c, size := utf8.DecodeRuneInString(s[i:])
   928  		if c == utf8.RuneError && size == 1 {
   929  			if start < i {
   930  				e.WriteString(s[start:i])
   931  			}
   932  			e.WriteString(`\ufffd`)
   933  			i += size
   934  			start = i
   935  			continue
   936  		}
   937  		// U+2028 is LINE SEPARATOR.
   938  		// U+2029 is PARAGRAPH SEPARATOR.
   939  		// They are both technically valid characters in JSON strings,
   940  		// but don't work in JSONP, which has to be evaluated as JavaScript,
   941  		// and can lead to security holes there. It is valid JSON to
   942  		// escape them, so we do so unconditionally.
   943  		// See http://timelessrepo.com/json-isnt-a-javascript-subset for discussion.
   944  		if c == '\u2028' || c == '\u2029' {
   945  			if start < i {
   946  				e.WriteString(s[start:i])
   947  			}
   948  			e.WriteString(`\u202`)
   949  			e.WriteByte(hex[c&0xF])
   950  			i += size
   951  			start = i
   952  			continue
   953  		}
   954  		i += size
   955  	}
   956  	if start < len(s) {
   957  		e.WriteString(s[start:])
   958  	}
   959  	e.WriteByte('"')
   960  }
   961  
   962  // NOTE: keep in sync with string above.
   963  func (e *encodeState) stringBytes(s []byte, escapeHTML bool) {
   964  	e.WriteByte('"')
   965  	start := 0
   966  	for i := 0; i < len(s); {
   967  		if b := s[i]; b < utf8.RuneSelf {
   968  			if htmlSafeSet[b] || (!escapeHTML && safeSet[b]) {
   969  				i++
   970  				continue
   971  			}
   972  			if start < i {
   973  				e.Write(s[start:i])
   974  			}
   975  			e.WriteByte('\\')
   976  			switch b {
   977  			case '\\', '"':
   978  				e.WriteByte(b)
   979  			case '\n':
   980  				e.WriteByte('n')
   981  			case '\r':
   982  				e.WriteByte('r')
   983  			case '\t':
   984  				e.WriteByte('t')
   985  			default:
   986  				// This encodes bytes < 0x20 except for \t, \n and \r.
   987  				// If escapeHTML is set, it also escapes <, >, and &
   988  				// because they can lead to security holes when
   989  				// user-controlled strings are rendered into JSON
   990  				// and served to some browsers.
   991  				e.WriteString(`u00`)
   992  				e.WriteByte(hex[b>>4])
   993  				e.WriteByte(hex[b&0xF])
   994  			}
   995  			i++
   996  			start = i
   997  			continue
   998  		}
   999  		c, size := utf8.DecodeRune(s[i:])
  1000  		if c == utf8.RuneError && size == 1 {
  1001  			if start < i {
  1002  				e.Write(s[start:i])
  1003  			}
  1004  			e.WriteString(`\ufffd`)
  1005  			i += size
  1006  			start = i
  1007  			continue
  1008  		}
  1009  		// U+2028 is LINE SEPARATOR.
  1010  		// U+2029 is PARAGRAPH SEPARATOR.
  1011  		// They are both technically valid characters in JSON strings,
  1012  		// but don't work in JSONP, which has to be evaluated as JavaScript,
  1013  		// and can lead to security holes there. It is valid JSON to
  1014  		// escape them, so we do so unconditionally.
  1015  		// See http://timelessrepo.com/json-isnt-a-javascript-subset for discussion.
  1016  		if c == '\u2028' || c == '\u2029' {
  1017  			if start < i {
  1018  				e.Write(s[start:i])
  1019  			}
  1020  			e.WriteString(`\u202`)
  1021  			e.WriteByte(hex[c&0xF])
  1022  			i += size
  1023  			start = i
  1024  			continue
  1025  		}
  1026  		i += size
  1027  	}
  1028  	if start < len(s) {
  1029  		e.Write(s[start:])
  1030  	}
  1031  	e.WriteByte('"')
  1032  }
  1033  
  1034  // A field represents a single field found in a struct.
  1035  type field struct {
  1036  	name      string
  1037  	nameBytes []byte                 // []byte(name)
  1038  	equalFold func(s, t []byte) bool // bytes.EqualFold or equivalent
  1039  
  1040  	nameNonEsc  string // `"` + name + `":`
  1041  	nameEscHTML string // `"` + HTMLEscape(name) + `":`
  1042  
  1043  	tag       bool
  1044  	index     []int
  1045  	typ       reflect.Type
  1046  	omitEmpty bool
  1047  	quoted    bool
  1048  
  1049  	encoder encoderFunc
  1050  }
  1051  
  1052  // byIndex sorts field by index sequence.
  1053  type byIndex []field
  1054  
  1055  func (x byIndex) Len() int { return len(x) }
  1056  
  1057  func (x byIndex) Swap(i, j int) { x[i], x[j] = x[j], x[i] }
  1058  
  1059  func (x byIndex) Less(i, j int) bool {
  1060  	for k, xik := range x[i].index {
  1061  		if k >= len(x[j].index) {
  1062  			return false
  1063  		}
  1064  		if xik != x[j].index[k] {
  1065  			return xik < x[j].index[k]
  1066  		}
  1067  	}
  1068  	return len(x[i].index) < len(x[j].index)
  1069  }
  1070  
  1071  // typeFields returns a list of fields that JSON should recognize for the given type.
  1072  // The algorithm is breadth-first search over the set of structs to include - the top struct
  1073  // and then any reachable anonymous structs.
  1074  func typeFields(t reflect.Type) structFields {
  1075  	// Anonymous fields to explore at the current level and the next.
  1076  	current := []field{}
  1077  	next := []field{{typ: t}}
  1078  
  1079  	// Count of queued names for current level and the next.
  1080  	var count, nextCount map[reflect.Type]int
  1081  
  1082  	// Types already visited at an earlier level.
  1083  	visited := map[reflect.Type]bool{}
  1084  
  1085  	// Fields found.
  1086  	var fields []field
  1087  
  1088  	// Buffer to run HTMLEscape on field names.
  1089  	var nameEscBuf bytes.Buffer
  1090  
  1091  	for len(next) > 0 {
  1092  		current, next = next, current[:0]
  1093  		count, nextCount = nextCount, map[reflect.Type]int{}
  1094  
  1095  		for _, f := range current {
  1096  			if visited[f.typ] {
  1097  				continue
  1098  			}
  1099  			visited[f.typ] = true
  1100  
  1101  			// Scan f.typ for fields to include.
  1102  			for i := 0; i < f.typ.NumField(); i++ {
  1103  				sf := f.typ.Field(i)
  1104  				isUnexported := sf.PkgPath != ""
  1105  				if sf.Anonymous {
  1106  					t := sf.Type
  1107  					if t.Kind() == reflect.Ptr {
  1108  						t = t.Elem()
  1109  					}
  1110  					if isUnexported && t.Kind() != reflect.Struct {
  1111  						// Ignore embedded fields of unexported non-struct types.
  1112  						continue
  1113  					}
  1114  					// Do not ignore embedded fields of unexported struct types
  1115  					// since they may have exported fields.
  1116  				} else if isUnexported {
  1117  					// Ignore unexported non-embedded fields.
  1118  					continue
  1119  				}
  1120  				tag := sf.Tag.Get("json")
  1121  				if tag == "-" {
  1122  					continue
  1123  				}
  1124  				name, opts := parseTag(tag)
  1125  				if !isValidTag(name) {
  1126  					name = ""
  1127  				}
  1128  				index := make([]int, len(f.index)+1)
  1129  				copy(index, f.index)
  1130  				index[len(f.index)] = i
  1131  
  1132  				ft := sf.Type
  1133  				if ft.Name() == "" && ft.Kind() == reflect.Ptr {
  1134  					// Follow pointer.
  1135  					ft = ft.Elem()
  1136  				}
  1137  
  1138  				// Only strings, floats, integers, and booleans can be quoted.
  1139  				quoted := false
  1140  				if opts.Contains("string") {
  1141  					switch ft.Kind() {
  1142  					case reflect.Bool,
  1143  						reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
  1144  						reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr,
  1145  						reflect.Float32, reflect.Float64,
  1146  						reflect.String:
  1147  						quoted = true
  1148  					}
  1149  				}
  1150  
  1151  				// Record found field and index sequence.
  1152  				if name != "" || !sf.Anonymous || ft.Kind() != reflect.Struct {
  1153  					tagged := name != ""
  1154  					if name == "" {
  1155  						name = sf.Name
  1156  					}
  1157  					field := field{
  1158  						name:      name,
  1159  						tag:       tagged,
  1160  						index:     index,
  1161  						typ:       ft,
  1162  						omitEmpty: opts.Contains("omitempty"),
  1163  						quoted:    quoted,
  1164  					}
  1165  					field.nameBytes = []byte(field.name)
  1166  					field.equalFold = foldFunc(field.nameBytes)
  1167  
  1168  					// Build nameEscHTML and nameNonEsc ahead of time.
  1169  					nameEscBuf.Reset()
  1170  					nameEscBuf.WriteString(`"`)
  1171  					HTMLEscape(&nameEscBuf, field.nameBytes)
  1172  					nameEscBuf.WriteString(`":`)
  1173  					field.nameEscHTML = nameEscBuf.String()
  1174  					field.nameNonEsc = `"` + field.name + `":`
  1175  
  1176  					fields = append(fields, field)
  1177  					if count[f.typ] > 1 {
  1178  						// If there were multiple instances, add a second,
  1179  						// so that the annihilation code will see a duplicate.
  1180  						// It only cares about the distinction between 1 or 2,
  1181  						// so don't bother generating any more copies.
  1182  						fields = append(fields, fields[len(fields)-1])
  1183  					}
  1184  					continue
  1185  				}
  1186  
  1187  				// Record new anonymous struct to explore in next round.
  1188  				nextCount[ft]++
  1189  				if nextCount[ft] == 1 {
  1190  					next = append(next, field{name: ft.Name(), index: index, typ: ft})
  1191  				}
  1192  			}
  1193  		}
  1194  	}
  1195  
  1196  	sort.Slice(fields, func(i, j int) bool {
  1197  		x := fields
  1198  		// sort field by name, breaking ties with depth, then
  1199  		// breaking ties with "name came from json tag", then
  1200  		// breaking ties with index sequence.
  1201  		if x[i].name != x[j].name {
  1202  			return x[i].name < x[j].name
  1203  		}
  1204  		if len(x[i].index) != len(x[j].index) {
  1205  			return len(x[i].index) < len(x[j].index)
  1206  		}
  1207  		if x[i].tag != x[j].tag {
  1208  			return x[i].tag
  1209  		}
  1210  		return byIndex(x).Less(i, j)
  1211  	})
  1212  
  1213  	// Delete all fields that are hidden by the Go rules for embedded fields,
  1214  	// except that fields with JSON tags are promoted.
  1215  
  1216  	// The fields are sorted in primary order of name, secondary order
  1217  	// of field index length. Loop over names; for each name, delete
  1218  	// hidden fields by choosing the one dominant field that survives.
  1219  	out := fields[:0]
  1220  	for advance, i := 0, 0; i < len(fields); i += advance {
  1221  		// One iteration per name.
  1222  		// Find the sequence of fields with the name of this first field.
  1223  		fi := fields[i]
  1224  		name := fi.name
  1225  		for advance = 1; i+advance < len(fields); advance++ {
  1226  			fj := fields[i+advance]
  1227  			if fj.name != name {
  1228  				break
  1229  			}
  1230  		}
  1231  		if advance == 1 { // Only one field with this name
  1232  			out = append(out, fi)
  1233  			continue
  1234  		}
  1235  		dominant, ok := dominantField(fields[i : i+advance])
  1236  		if ok {
  1237  			out = append(out, dominant)
  1238  		}
  1239  	}
  1240  
  1241  	fields = out
  1242  	sort.Sort(byIndex(fields))
  1243  
  1244  	for i := range fields {
  1245  		f := &fields[i]
  1246  		f.encoder = typeEncoder(typeByIndex(t, f.index))
  1247  	}
  1248  	nameIndex := make(map[string]int, len(fields))
  1249  	for i, field := range fields {
  1250  		nameIndex[field.name] = i
  1251  	}
  1252  	return structFields{fields, nameIndex}
  1253  }
  1254  
  1255  // dominantField looks through the fields, all of which are known to
  1256  // have the same name, to find the single field that dominates the
  1257  // others using Go's embedding rules, modified by the presence of
  1258  // JSON tags. If there are multiple top-level fields, the boolean
  1259  // will be false: This condition is an error in Go and we skip all
  1260  // the fields.
  1261  func dominantField(fields []field) (field, bool) {
  1262  	// The fields are sorted in increasing index-length order, then by presence of tag.
  1263  	// That means that the first field is the dominant one. We need only check
  1264  	// for error cases: two fields at top level, either both tagged or neither tagged.
  1265  	if len(fields) > 1 && len(fields[0].index) == len(fields[1].index) && fields[0].tag == fields[1].tag {
  1266  		return field{}, false
  1267  	}
  1268  	return fields[0], true
  1269  }
  1270  
  1271  var fieldCache sync.Map // map[reflect.Type]structFields
  1272  
  1273  // cachedTypeFields is like typeFields but uses a cache to avoid repeated work.
  1274  func cachedTypeFields(t reflect.Type) structFields {
  1275  	if f, ok := fieldCache.Load(t); ok {
  1276  		return f.(structFields)
  1277  	}
  1278  	f, _ := fieldCache.LoadOrStore(t, typeFields(t))
  1279  	return f.(structFields)
  1280  }
  1281  

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