Source file src/encoding/json/encode.go

     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  	"cmp"
    16  	"encoding"
    17  	"encoding/base64"
    18  	"fmt"
    19  	"math"
    20  	"reflect"
    21  	"slices"
    22  	"strconv"
    23  	"strings"
    24  	"sync"
    25  	"unicode"
    26  	"unicode/utf8"
    27  	_ "unsafe" // for linkname
    28  )
    29  
    30  // Marshal returns the JSON encoding of v.
    31  //
    32  // Marshal traverses the value v recursively.
    33  // If an encountered value implements [Marshaler]
    34  // and is not a nil pointer, Marshal calls [Marshaler.MarshalJSON]
    35  // to produce JSON. If no [Marshaler.MarshalJSON] method is present but the
    36  // value implements [encoding.TextMarshaler] instead, Marshal calls
    37  // [encoding.TextMarshaler.MarshalText] and encodes the result as a JSON string.
    38  // The nil pointer exception is not strictly necessary
    39  // but mimics a similar, necessary exception in the behavior of
    40  // [Unmarshaler.UnmarshalJSON].
    41  //
    42  // Otherwise, Marshal uses the following type-dependent default encodings:
    43  //
    44  // Boolean values encode as JSON booleans.
    45  //
    46  // Floating point, integer, and [Number] values encode as JSON numbers.
    47  // NaN and +/-Inf values will return an [UnsupportedValueError].
    48  //
    49  // String values encode as JSON strings coerced to valid UTF-8,
    50  // replacing invalid bytes with the Unicode replacement rune.
    51  // So that the JSON will be safe to embed inside HTML <script> tags,
    52  // the string is encoded using [HTMLEscape],
    53  // which replaces "<", ">", "&", U+2028, and U+2029 are escaped
    54  // to "\u003c","\u003e", "\u0026", "\u2028", and "\u2029".
    55  // This replacement can be disabled when using an [Encoder],
    56  // by calling [Encoder.SetEscapeHTML](false).
    57  //
    58  // Array and slice values encode as JSON arrays, except that
    59  // []byte encodes as a base64-encoded string, and a nil slice
    60  // encodes as the null JSON value.
    61  //
    62  // Struct values encode as JSON objects.
    63  // Each exported struct field becomes a member of the object, using the
    64  // field name as the object key, unless the field is omitted for one of the
    65  // reasons given below.
    66  //
    67  // The encoding of each struct field can be customized by the format string
    68  // stored under the "json" key in the struct field's tag.
    69  // The format string gives the name of the field, possibly followed by a
    70  // comma-separated list of options. The name may be empty in order to
    71  // specify options without overriding the default field name.
    72  //
    73  // The "omitempty" option specifies that the field should be omitted
    74  // from the encoding if the field has an empty value, defined as
    75  // false, 0, a nil pointer, a nil interface value, and any array,
    76  // slice, map, or string of length zero.
    77  //
    78  // As a special case, if the field tag is "-", the field is always omitted.
    79  // Note that a field with name "-" can still be generated using the tag "-,".
    80  //
    81  // Examples of struct field tags and their meanings:
    82  //
    83  //	// Field appears in JSON as key "myName".
    84  //	Field int `json:"myName"`
    85  //
    86  //	// Field appears in JSON as key "myName" and
    87  //	// the field is omitted from the object if its value is empty,
    88  //	// as defined above.
    89  //	Field int `json:"myName,omitempty"`
    90  //
    91  //	// Field appears in JSON as key "Field" (the default), but
    92  //	// the field is skipped if empty.
    93  //	// Note the leading comma.
    94  //	Field int `json:",omitempty"`
    95  //
    96  //	// Field is ignored by this package.
    97  //	Field int `json:"-"`
    98  //
    99  //	// Field appears in JSON as key "-".
   100  //	Field int `json:"-,"`
   101  //
   102  // The "omitzero" option specifies that the field should be omitted
   103  // from the encoding if the field has a zero value, according to rules:
   104  //
   105  // 1) If the field type has an "IsZero() bool" method, that will be used to
   106  // determine whether the value is zero.
   107  //
   108  // 2) Otherwise, the value is zero if it is the zero value for its type.
   109  //
   110  // If both "omitempty" and "omitzero" are specified, the field will be omitted
   111  // if the value is either empty or zero (or both).
   112  //
   113  // The "string" option signals that a field is stored as JSON inside a
   114  // JSON-encoded string. It applies only to fields of string, floating point,
   115  // integer, or boolean types. This extra level of encoding is sometimes used
   116  // when communicating with JavaScript programs:
   117  //
   118  //	Int64String int64 `json:",string"`
   119  //
   120  // The key name will be used if it's a non-empty string consisting of
   121  // only Unicode letters, digits, and ASCII punctuation except quotation
   122  // marks, backslash, and comma.
   123  //
   124  // Embedded struct fields are usually marshaled as if their inner exported fields
   125  // were fields in the outer struct, subject to the usual Go visibility rules amended
   126  // as described in the next paragraph.
   127  // An anonymous struct field with a name given in its JSON tag is treated as
   128  // having that name, rather than being anonymous.
   129  // An anonymous struct field of interface type is treated the same as having
   130  // that type as its name, rather than being anonymous.
   131  //
   132  // The Go visibility rules for struct fields are amended for JSON when
   133  // deciding which field to marshal or unmarshal. If there are
   134  // multiple fields at the same level, and that level is the least
   135  // nested (and would therefore be the nesting level selected by the
   136  // usual Go rules), the following extra rules apply:
   137  //
   138  // 1) Of those fields, if any are JSON-tagged, only tagged fields are considered,
   139  // even if there are multiple untagged fields that would otherwise conflict.
   140  //
   141  // 2) If there is exactly one field (tagged or not according to the first rule), that is selected.
   142  //
   143  // 3) Otherwise there are multiple fields, and all are ignored; no error occurs.
   144  //
   145  // Handling of anonymous struct fields is new in Go 1.1.
   146  // Prior to Go 1.1, anonymous struct fields were ignored. To force ignoring of
   147  // an anonymous struct field in both current and earlier versions, give the field
   148  // a JSON tag of "-".
   149  //
   150  // Map values encode as JSON objects. The map's key type must either be a
   151  // string, an integer type, or implement [encoding.TextMarshaler]. The map keys
   152  // are sorted and used as JSON object keys by applying the following rules,
   153  // subject to the UTF-8 coercion described for string values above:
   154  //   - keys of any string type are used directly
   155  //   - keys that implement [encoding.TextMarshaler] are marshaled
   156  //   - integer keys are converted to strings
   157  //
   158  // Pointer values encode as the value pointed to.
   159  // A nil pointer encodes as the null JSON value.
   160  //
   161  // Interface values encode as the value contained in the interface.
   162  // A nil interface value encodes as the null JSON value.
   163  //
   164  // Channel, complex, and function values cannot be encoded in JSON.
   165  // Attempting to encode such a value causes Marshal to return
   166  // an [UnsupportedTypeError].
   167  //
   168  // JSON cannot represent cyclic data structures and Marshal does not
   169  // handle them. Passing cyclic structures to Marshal will result in
   170  // an error.
   171  func Marshal(v any) ([]byte, error) {
   172  	e := newEncodeState()
   173  	defer encodeStatePool.Put(e)
   174  
   175  	err := e.marshal(v, encOpts{escapeHTML: true})
   176  	if err != nil {
   177  		return nil, err
   178  	}
   179  	buf := append([]byte(nil), e.Bytes()...)
   180  
   181  	return buf, nil
   182  }
   183  
   184  // MarshalIndent is like [Marshal] but applies [Indent] to format the output.
   185  // Each JSON element in the output will begin on a new line beginning with prefix
   186  // followed by one or more copies of indent according to the indentation nesting.
   187  func MarshalIndent(v any, prefix, indent string) ([]byte, error) {
   188  	b, err := Marshal(v)
   189  	if err != nil {
   190  		return nil, err
   191  	}
   192  	b2 := make([]byte, 0, indentGrowthFactor*len(b))
   193  	b2, err = appendIndent(b2, b, prefix, indent)
   194  	if err != nil {
   195  		return nil, err
   196  	}
   197  	return b2, nil
   198  }
   199  
   200  // Marshaler is the interface implemented by types that
   201  // can marshal themselves into valid JSON.
   202  type Marshaler interface {
   203  	MarshalJSON() ([]byte, error)
   204  }
   205  
   206  // An UnsupportedTypeError is returned by [Marshal] when attempting
   207  // to encode an unsupported value type.
   208  type UnsupportedTypeError struct {
   209  	Type reflect.Type
   210  }
   211  
   212  func (e *UnsupportedTypeError) Error() string {
   213  	return "json: unsupported type: " + e.Type.String()
   214  }
   215  
   216  // An UnsupportedValueError is returned by [Marshal] when attempting
   217  // to encode an unsupported value.
   218  type UnsupportedValueError struct {
   219  	Value reflect.Value
   220  	Str   string
   221  }
   222  
   223  func (e *UnsupportedValueError) Error() string {
   224  	return "json: unsupported value: " + e.Str
   225  }
   226  
   227  // Before Go 1.2, an InvalidUTF8Error was returned by [Marshal] when
   228  // attempting to encode a string value with invalid UTF-8 sequences.
   229  // As of Go 1.2, [Marshal] instead coerces the string to valid UTF-8 by
   230  // replacing invalid bytes with the Unicode replacement rune U+FFFD.
   231  //
   232  // Deprecated: No longer used; kept for compatibility.
   233  type InvalidUTF8Error struct {
   234  	S string // the whole string value that caused the error
   235  }
   236  
   237  func (e *InvalidUTF8Error) Error() string {
   238  	return "json: invalid UTF-8 in string: " + strconv.Quote(e.S)
   239  }
   240  
   241  // A MarshalerError represents an error from calling a
   242  // [Marshaler.MarshalJSON] or [encoding.TextMarshaler.MarshalText] method.
   243  type MarshalerError struct {
   244  	Type       reflect.Type
   245  	Err        error
   246  	sourceFunc string
   247  }
   248  
   249  func (e *MarshalerError) Error() string {
   250  	srcFunc := e.sourceFunc
   251  	if srcFunc == "" {
   252  		srcFunc = "MarshalJSON"
   253  	}
   254  	return "json: error calling " + srcFunc +
   255  		" for type " + e.Type.String() +
   256  		": " + e.Err.Error()
   257  }
   258  
   259  // Unwrap returns the underlying error.
   260  func (e *MarshalerError) Unwrap() error { return e.Err }
   261  
   262  const hex = "0123456789abcdef"
   263  
   264  // An encodeState encodes JSON into a bytes.Buffer.
   265  type encodeState struct {
   266  	bytes.Buffer // accumulated output
   267  
   268  	// Keep track of what pointers we've seen in the current recursive call
   269  	// path, to avoid cycles that could lead to a stack overflow. Only do
   270  	// the relatively expensive map operations if ptrLevel is larger than
   271  	// startDetectingCyclesAfter, so that we skip the work if we're within a
   272  	// reasonable amount of nested pointers deep.
   273  	ptrLevel uint
   274  	ptrSeen  map[any]struct{}
   275  }
   276  
   277  const startDetectingCyclesAfter = 1000
   278  
   279  var encodeStatePool sync.Pool
   280  
   281  func newEncodeState() *encodeState {
   282  	if v := encodeStatePool.Get(); v != nil {
   283  		e := v.(*encodeState)
   284  		e.Reset()
   285  		if len(e.ptrSeen) > 0 {
   286  			panic("ptrEncoder.encode should have emptied ptrSeen via defers")
   287  		}
   288  		e.ptrLevel = 0
   289  		return e
   290  	}
   291  	return &encodeState{ptrSeen: make(map[any]struct{})}
   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 any, 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  		reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
   324  		reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr,
   325  		reflect.Float32, reflect.Float64,
   326  		reflect.Interface, reflect.Pointer:
   327  		return v.IsZero()
   328  	}
   329  	return false
   330  }
   331  
   332  func (e *encodeState) reflectValue(v reflect.Value, opts encOpts) {
   333  	valueEncoder(v)(e, v, opts)
   334  }
   335  
   336  type encOpts struct {
   337  	// quoted causes primitive fields to be encoded inside JSON strings.
   338  	quoted bool
   339  	// escapeHTML causes '<', '>', and '&' to be escaped in JSON strings.
   340  	escapeHTML bool
   341  }
   342  
   343  type encoderFunc func(e *encodeState, v reflect.Value, opts encOpts)
   344  
   345  var encoderCache sync.Map // map[reflect.Type]encoderFunc
   346  
   347  func valueEncoder(v reflect.Value) encoderFunc {
   348  	if !v.IsValid() {
   349  		return invalidValueEncoder
   350  	}
   351  	return typeEncoder(v.Type())
   352  }
   353  
   354  func typeEncoder(t reflect.Type) encoderFunc {
   355  	if fi, ok := encoderCache.Load(t); ok {
   356  		return fi.(encoderFunc)
   357  	}
   358  
   359  	// To deal with recursive types, populate the map with an
   360  	// indirect func before we build it. This type waits on the
   361  	// real func (f) to be ready and then calls it. This indirect
   362  	// func is only used for recursive types.
   363  	var (
   364  		wg sync.WaitGroup
   365  		f  encoderFunc
   366  	)
   367  	wg.Add(1)
   368  	fi, loaded := encoderCache.LoadOrStore(t, encoderFunc(func(e *encodeState, v reflect.Value, opts encOpts) {
   369  		wg.Wait()
   370  		f(e, v, opts)
   371  	}))
   372  	if loaded {
   373  		return fi.(encoderFunc)
   374  	}
   375  
   376  	// Compute the real encoder and replace the indirect func with it.
   377  	f = newTypeEncoder(t, true)
   378  	wg.Done()
   379  	encoderCache.Store(t, f)
   380  	return f
   381  }
   382  
   383  var (
   384  	marshalerType     = reflect.TypeFor[Marshaler]()
   385  	textMarshalerType = reflect.TypeFor[encoding.TextMarshaler]()
   386  )
   387  
   388  // newTypeEncoder constructs an encoderFunc for a type.
   389  // The returned encoder only checks CanAddr when allowAddr is true.
   390  func newTypeEncoder(t reflect.Type, allowAddr bool) encoderFunc {
   391  	// If we have a non-pointer value whose type implements
   392  	// Marshaler with a value receiver, then we're better off taking
   393  	// the address of the value - otherwise we end up with an
   394  	// allocation as we cast the value to an interface.
   395  	if t.Kind() != reflect.Pointer && allowAddr && reflect.PointerTo(t).Implements(marshalerType) {
   396  		return newCondAddrEncoder(addrMarshalerEncoder, newTypeEncoder(t, false))
   397  	}
   398  	if t.Implements(marshalerType) {
   399  		return marshalerEncoder
   400  	}
   401  	if t.Kind() != reflect.Pointer && allowAddr && reflect.PointerTo(t).Implements(textMarshalerType) {
   402  		return newCondAddrEncoder(addrTextMarshalerEncoder, newTypeEncoder(t, false))
   403  	}
   404  	if t.Implements(textMarshalerType) {
   405  		return textMarshalerEncoder
   406  	}
   407  
   408  	switch t.Kind() {
   409  	case reflect.Bool:
   410  		return boolEncoder
   411  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   412  		return intEncoder
   413  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   414  		return uintEncoder
   415  	case reflect.Float32:
   416  		return float32Encoder
   417  	case reflect.Float64:
   418  		return float64Encoder
   419  	case reflect.String:
   420  		return stringEncoder
   421  	case reflect.Interface:
   422  		return interfaceEncoder
   423  	case reflect.Struct:
   424  		return newStructEncoder(t)
   425  	case reflect.Map:
   426  		return newMapEncoder(t)
   427  	case reflect.Slice:
   428  		return newSliceEncoder(t)
   429  	case reflect.Array:
   430  		return newArrayEncoder(t)
   431  	case reflect.Pointer:
   432  		return newPtrEncoder(t)
   433  	default:
   434  		return unsupportedTypeEncoder
   435  	}
   436  }
   437  
   438  func invalidValueEncoder(e *encodeState, v reflect.Value, _ encOpts) {
   439  	e.WriteString("null")
   440  }
   441  
   442  func marshalerEncoder(e *encodeState, v reflect.Value, opts encOpts) {
   443  	if v.Kind() == reflect.Pointer && v.IsNil() {
   444  		e.WriteString("null")
   445  		return
   446  	}
   447  	m, ok := v.Interface().(Marshaler)
   448  	if !ok {
   449  		e.WriteString("null")
   450  		return
   451  	}
   452  	b, err := m.MarshalJSON()
   453  	if err == nil {
   454  		e.Grow(len(b))
   455  		out := e.AvailableBuffer()
   456  		out, err = appendCompact(out, b, opts.escapeHTML)
   457  		e.Buffer.Write(out)
   458  	}
   459  	if err != nil {
   460  		e.error(&MarshalerError{v.Type(), err, "MarshalJSON"})
   461  	}
   462  }
   463  
   464  func addrMarshalerEncoder(e *encodeState, v reflect.Value, opts encOpts) {
   465  	va := v.Addr()
   466  	if va.IsNil() {
   467  		e.WriteString("null")
   468  		return
   469  	}
   470  	m := va.Interface().(Marshaler)
   471  	b, err := m.MarshalJSON()
   472  	if err == nil {
   473  		e.Grow(len(b))
   474  		out := e.AvailableBuffer()
   475  		out, err = appendCompact(out, b, opts.escapeHTML)
   476  		e.Buffer.Write(out)
   477  	}
   478  	if err != nil {
   479  		e.error(&MarshalerError{v.Type(), err, "MarshalJSON"})
   480  	}
   481  }
   482  
   483  func textMarshalerEncoder(e *encodeState, v reflect.Value, opts encOpts) {
   484  	if v.Kind() == reflect.Pointer && v.IsNil() {
   485  		e.WriteString("null")
   486  		return
   487  	}
   488  	m, ok := v.Interface().(encoding.TextMarshaler)
   489  	if !ok {
   490  		e.WriteString("null")
   491  		return
   492  	}
   493  	b, err := m.MarshalText()
   494  	if err != nil {
   495  		e.error(&MarshalerError{v.Type(), err, "MarshalText"})
   496  	}
   497  	e.Write(appendString(e.AvailableBuffer(), b, opts.escapeHTML))
   498  }
   499  
   500  func addrTextMarshalerEncoder(e *encodeState, v reflect.Value, opts encOpts) {
   501  	va := v.Addr()
   502  	if va.IsNil() {
   503  		e.WriteString("null")
   504  		return
   505  	}
   506  	m := va.Interface().(encoding.TextMarshaler)
   507  	b, err := m.MarshalText()
   508  	if err != nil {
   509  		e.error(&MarshalerError{v.Type(), err, "MarshalText"})
   510  	}
   511  	e.Write(appendString(e.AvailableBuffer(), b, opts.escapeHTML))
   512  }
   513  
   514  func boolEncoder(e *encodeState, v reflect.Value, opts encOpts) {
   515  	b := e.AvailableBuffer()
   516  	b = mayAppendQuote(b, opts.quoted)
   517  	b = strconv.AppendBool(b, v.Bool())
   518  	b = mayAppendQuote(b, opts.quoted)
   519  	e.Write(b)
   520  }
   521  
   522  func intEncoder(e *encodeState, v reflect.Value, opts encOpts) {
   523  	b := e.AvailableBuffer()
   524  	b = mayAppendQuote(b, opts.quoted)
   525  	b = strconv.AppendInt(b, v.Int(), 10)
   526  	b = mayAppendQuote(b, opts.quoted)
   527  	e.Write(b)
   528  }
   529  
   530  func uintEncoder(e *encodeState, v reflect.Value, opts encOpts) {
   531  	b := e.AvailableBuffer()
   532  	b = mayAppendQuote(b, opts.quoted)
   533  	b = strconv.AppendUint(b, v.Uint(), 10)
   534  	b = mayAppendQuote(b, opts.quoted)
   535  	e.Write(b)
   536  }
   537  
   538  type floatEncoder int // number of bits
   539  
   540  func (bits floatEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) {
   541  	f := v.Float()
   542  	if math.IsInf(f, 0) || math.IsNaN(f) {
   543  		e.error(&UnsupportedValueError{v, strconv.FormatFloat(f, 'g', -1, int(bits))})
   544  	}
   545  
   546  	// Convert as if by ES6 number to string conversion.
   547  	// This matches most other JSON generators.
   548  	// See golang.org/issue/6384 and golang.org/issue/14135.
   549  	// Like fmt %g, but the exponent cutoffs are different
   550  	// and exponents themselves are not padded to two digits.
   551  	b := e.AvailableBuffer()
   552  	b = mayAppendQuote(b, opts.quoted)
   553  	abs := math.Abs(f)
   554  	fmt := byte('f')
   555  	// Note: Must use float32 comparisons for underlying float32 value to get precise cutoffs right.
   556  	if abs != 0 {
   557  		if bits == 64 && (abs < 1e-6 || abs >= 1e21) || bits == 32 && (float32(abs) < 1e-6 || float32(abs) >= 1e21) {
   558  			fmt = 'e'
   559  		}
   560  	}
   561  	b = strconv.AppendFloat(b, f, fmt, -1, int(bits))
   562  	if fmt == 'e' {
   563  		// clean up e-09 to e-9
   564  		n := len(b)
   565  		if n >= 4 && b[n-4] == 'e' && b[n-3] == '-' && b[n-2] == '0' {
   566  			b[n-2] = b[n-1]
   567  			b = b[:n-1]
   568  		}
   569  	}
   570  	b = mayAppendQuote(b, opts.quoted)
   571  	e.Write(b)
   572  }
   573  
   574  var (
   575  	float32Encoder = (floatEncoder(32)).encode
   576  	float64Encoder = (floatEncoder(64)).encode
   577  )
   578  
   579  func stringEncoder(e *encodeState, v reflect.Value, opts encOpts) {
   580  	if v.Type() == numberType {
   581  		numStr := v.String()
   582  		// In Go1.5 the empty string encodes to "0", while this is not a valid number literal
   583  		// we keep compatibility so check validity after this.
   584  		if numStr == "" {
   585  			numStr = "0" // Number's zero-val
   586  		}
   587  		if !isValidNumber(numStr) {
   588  			e.error(fmt.Errorf("json: invalid number literal %q", numStr))
   589  		}
   590  		b := e.AvailableBuffer()
   591  		b = mayAppendQuote(b, opts.quoted)
   592  		b = append(b, numStr...)
   593  		b = mayAppendQuote(b, opts.quoted)
   594  		e.Write(b)
   595  		return
   596  	}
   597  	if opts.quoted {
   598  		b := appendString(nil, v.String(), opts.escapeHTML)
   599  		e.Write(appendString(e.AvailableBuffer(), b, false)) // no need to escape again since it is already escaped
   600  	} else {
   601  		e.Write(appendString(e.AvailableBuffer(), v.String(), opts.escapeHTML))
   602  	}
   603  }
   604  
   605  // isValidNumber reports whether s is a valid JSON number literal.
   606  //
   607  // isValidNumber should be an internal detail,
   608  // but widely used packages access it using linkname.
   609  // Notable members of the hall of shame include:
   610  //   - github.com/bytedance/sonic
   611  //
   612  // Do not remove or change the type signature.
   613  // See go.dev/issue/67401.
   614  //
   615  //go:linkname isValidNumber
   616  func isValidNumber(s string) bool {
   617  	// This function implements the JSON numbers grammar.
   618  	// See https://tools.ietf.org/html/rfc7159#section-6
   619  	// and https://www.json.org/img/number.png
   620  
   621  	if s == "" {
   622  		return false
   623  	}
   624  
   625  	// Optional -
   626  	if s[0] == '-' {
   627  		s = s[1:]
   628  		if s == "" {
   629  			return false
   630  		}
   631  	}
   632  
   633  	// Digits
   634  	switch {
   635  	default:
   636  		return false
   637  
   638  	case s[0] == '0':
   639  		s = s[1:]
   640  
   641  	case '1' <= s[0] && s[0] <= '9':
   642  		s = s[1:]
   643  		for len(s) > 0 && '0' <= s[0] && s[0] <= '9' {
   644  			s = s[1:]
   645  		}
   646  	}
   647  
   648  	// . followed by 1 or more digits.
   649  	if len(s) >= 2 && s[0] == '.' && '0' <= s[1] && s[1] <= '9' {
   650  		s = s[2:]
   651  		for len(s) > 0 && '0' <= s[0] && s[0] <= '9' {
   652  			s = s[1:]
   653  		}
   654  	}
   655  
   656  	// e or E followed by an optional - or + and
   657  	// 1 or more digits.
   658  	if len(s) >= 2 && (s[0] == 'e' || s[0] == 'E') {
   659  		s = s[1:]
   660  		if s[0] == '+' || s[0] == '-' {
   661  			s = s[1:]
   662  			if s == "" {
   663  				return false
   664  			}
   665  		}
   666  		for len(s) > 0 && '0' <= s[0] && s[0] <= '9' {
   667  			s = s[1:]
   668  		}
   669  	}
   670  
   671  	// Make sure we are at the end.
   672  	return s == ""
   673  }
   674  
   675  func interfaceEncoder(e *encodeState, v reflect.Value, opts encOpts) {
   676  	if v.IsNil() {
   677  		e.WriteString("null")
   678  		return
   679  	}
   680  	e.reflectValue(v.Elem(), opts)
   681  }
   682  
   683  func unsupportedTypeEncoder(e *encodeState, v reflect.Value, _ encOpts) {
   684  	e.error(&UnsupportedTypeError{v.Type()})
   685  }
   686  
   687  type structEncoder struct {
   688  	fields structFields
   689  }
   690  
   691  type structFields struct {
   692  	list         []field
   693  	byExactName  map[string]*field
   694  	byFoldedName map[string]*field
   695  }
   696  
   697  func (se structEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) {
   698  	next := byte('{')
   699  FieldLoop:
   700  	for i := range se.fields.list {
   701  		f := &se.fields.list[i]
   702  
   703  		// Find the nested struct field by following f.index.
   704  		fv := v
   705  		for _, i := range f.index {
   706  			if fv.Kind() == reflect.Pointer {
   707  				if fv.IsNil() {
   708  					continue FieldLoop
   709  				}
   710  				fv = fv.Elem()
   711  			}
   712  			fv = fv.Field(i)
   713  		}
   714  
   715  		if (f.omitEmpty && isEmptyValue(fv)) ||
   716  			(f.omitZero && (f.isZero == nil && fv.IsZero() || (f.isZero != nil && f.isZero(fv)))) {
   717  			continue
   718  		}
   719  		e.WriteByte(next)
   720  		next = ','
   721  		if opts.escapeHTML {
   722  			e.WriteString(f.nameEscHTML)
   723  		} else {
   724  			e.WriteString(f.nameNonEsc)
   725  		}
   726  		opts.quoted = f.quoted
   727  		f.encoder(e, fv, opts)
   728  	}
   729  	if next == '{' {
   730  		e.WriteString("{}")
   731  	} else {
   732  		e.WriteByte('}')
   733  	}
   734  }
   735  
   736  func newStructEncoder(t reflect.Type) encoderFunc {
   737  	se := structEncoder{fields: cachedTypeFields(t)}
   738  	return se.encode
   739  }
   740  
   741  type mapEncoder struct {
   742  	elemEnc encoderFunc
   743  }
   744  
   745  func (me mapEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) {
   746  	if v.IsNil() {
   747  		e.WriteString("null")
   748  		return
   749  	}
   750  	if e.ptrLevel++; e.ptrLevel > startDetectingCyclesAfter {
   751  		// We're a large number of nested ptrEncoder.encode calls deep;
   752  		// start checking if we've run into a pointer cycle.
   753  		ptr := v.UnsafePointer()
   754  		if _, ok := e.ptrSeen[ptr]; ok {
   755  			e.error(&UnsupportedValueError{v, fmt.Sprintf("encountered a cycle via %s", v.Type())})
   756  		}
   757  		e.ptrSeen[ptr] = struct{}{}
   758  		defer delete(e.ptrSeen, ptr)
   759  	}
   760  	e.WriteByte('{')
   761  
   762  	// Extract and sort the keys.
   763  	var (
   764  		sv  = make([]reflectWithString, v.Len())
   765  		mi  = v.MapRange()
   766  		err error
   767  	)
   768  	for i := 0; mi.Next(); i++ {
   769  		if sv[i].ks, err = resolveKeyName(mi.Key()); err != nil {
   770  			e.error(fmt.Errorf("json: encoding error for type %q: %q", v.Type().String(), err.Error()))
   771  		}
   772  		sv[i].v = mi.Value()
   773  	}
   774  	slices.SortFunc(sv, func(i, j reflectWithString) int {
   775  		return strings.Compare(i.ks, j.ks)
   776  	})
   777  
   778  	for i, kv := range sv {
   779  		if i > 0 {
   780  			e.WriteByte(',')
   781  		}
   782  		e.Write(appendString(e.AvailableBuffer(), kv.ks, opts.escapeHTML))
   783  		e.WriteByte(':')
   784  		me.elemEnc(e, kv.v, opts)
   785  	}
   786  	e.WriteByte('}')
   787  	e.ptrLevel--
   788  }
   789  
   790  func newMapEncoder(t reflect.Type) encoderFunc {
   791  	switch t.Key().Kind() {
   792  	case reflect.String,
   793  		reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
   794  		reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   795  	default:
   796  		if !t.Key().Implements(textMarshalerType) {
   797  			return unsupportedTypeEncoder
   798  		}
   799  	}
   800  	me := mapEncoder{typeEncoder(t.Elem())}
   801  	return me.encode
   802  }
   803  
   804  func encodeByteSlice(e *encodeState, v reflect.Value, _ encOpts) {
   805  	if v.IsNil() {
   806  		e.WriteString("null")
   807  		return
   808  	}
   809  
   810  	s := v.Bytes()
   811  	b := e.AvailableBuffer()
   812  	b = append(b, '"')
   813  	b = base64.StdEncoding.AppendEncode(b, s)
   814  	b = append(b, '"')
   815  	e.Write(b)
   816  }
   817  
   818  // sliceEncoder just wraps an arrayEncoder, checking to make sure the value isn't nil.
   819  type sliceEncoder struct {
   820  	arrayEnc encoderFunc
   821  }
   822  
   823  func (se sliceEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) {
   824  	if v.IsNil() {
   825  		e.WriteString("null")
   826  		return
   827  	}
   828  	if e.ptrLevel++; e.ptrLevel > startDetectingCyclesAfter {
   829  		// We're a large number of nested ptrEncoder.encode calls deep;
   830  		// start checking if we've run into a pointer cycle.
   831  		// Here we use a struct to memorize the pointer to the first element of the slice
   832  		// and its length.
   833  		ptr := struct {
   834  			ptr any // always an unsafe.Pointer, but avoids a dependency on package unsafe
   835  			len int
   836  		}{v.UnsafePointer(), v.Len()}
   837  		if _, ok := e.ptrSeen[ptr]; ok {
   838  			e.error(&UnsupportedValueError{v, fmt.Sprintf("encountered a cycle via %s", v.Type())})
   839  		}
   840  		e.ptrSeen[ptr] = struct{}{}
   841  		defer delete(e.ptrSeen, ptr)
   842  	}
   843  	se.arrayEnc(e, v, opts)
   844  	e.ptrLevel--
   845  }
   846  
   847  func newSliceEncoder(t reflect.Type) encoderFunc {
   848  	// Byte slices get special treatment; arrays don't.
   849  	if t.Elem().Kind() == reflect.Uint8 {
   850  		p := reflect.PointerTo(t.Elem())
   851  		if !p.Implements(marshalerType) && !p.Implements(textMarshalerType) {
   852  			return encodeByteSlice
   853  		}
   854  	}
   855  	enc := sliceEncoder{newArrayEncoder(t)}
   856  	return enc.encode
   857  }
   858  
   859  type arrayEncoder struct {
   860  	elemEnc encoderFunc
   861  }
   862  
   863  func (ae arrayEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) {
   864  	e.WriteByte('[')
   865  	n := v.Len()
   866  	for i := 0; i < n; i++ {
   867  		if i > 0 {
   868  			e.WriteByte(',')
   869  		}
   870  		ae.elemEnc(e, v.Index(i), opts)
   871  	}
   872  	e.WriteByte(']')
   873  }
   874  
   875  func newArrayEncoder(t reflect.Type) encoderFunc {
   876  	enc := arrayEncoder{typeEncoder(t.Elem())}
   877  	return enc.encode
   878  }
   879  
   880  type ptrEncoder struct {
   881  	elemEnc encoderFunc
   882  }
   883  
   884  func (pe ptrEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) {
   885  	if v.IsNil() {
   886  		e.WriteString("null")
   887  		return
   888  	}
   889  	if e.ptrLevel++; e.ptrLevel > startDetectingCyclesAfter {
   890  		// We're a large number of nested ptrEncoder.encode calls deep;
   891  		// start checking if we've run into a pointer cycle.
   892  		ptr := v.Interface()
   893  		if _, ok := e.ptrSeen[ptr]; ok {
   894  			e.error(&UnsupportedValueError{v, fmt.Sprintf("encountered a cycle via %s", v.Type())})
   895  		}
   896  		e.ptrSeen[ptr] = struct{}{}
   897  		defer delete(e.ptrSeen, ptr)
   898  	}
   899  	pe.elemEnc(e, v.Elem(), opts)
   900  	e.ptrLevel--
   901  }
   902  
   903  func newPtrEncoder(t reflect.Type) encoderFunc {
   904  	enc := ptrEncoder{typeEncoder(t.Elem())}
   905  	return enc.encode
   906  }
   907  
   908  type condAddrEncoder struct {
   909  	canAddrEnc, elseEnc encoderFunc
   910  }
   911  
   912  func (ce condAddrEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) {
   913  	if v.CanAddr() {
   914  		ce.canAddrEnc(e, v, opts)
   915  	} else {
   916  		ce.elseEnc(e, v, opts)
   917  	}
   918  }
   919  
   920  // newCondAddrEncoder returns an encoder that checks whether its value
   921  // CanAddr and delegates to canAddrEnc if so, else to elseEnc.
   922  func newCondAddrEncoder(canAddrEnc, elseEnc encoderFunc) encoderFunc {
   923  	enc := condAddrEncoder{canAddrEnc: canAddrEnc, elseEnc: elseEnc}
   924  	return enc.encode
   925  }
   926  
   927  func isValidTag(s string) bool {
   928  	if s == "" {
   929  		return false
   930  	}
   931  	for _, c := range s {
   932  		switch {
   933  		case strings.ContainsRune("!#$%&()*+-./:;<=>?@[]^_{|}~ ", c):
   934  			// Backslash and quote chars are reserved, but
   935  			// otherwise any punctuation chars are allowed
   936  			// in a tag name.
   937  		case !unicode.IsLetter(c) && !unicode.IsDigit(c):
   938  			return false
   939  		}
   940  	}
   941  	return true
   942  }
   943  
   944  func typeByIndex(t reflect.Type, index []int) reflect.Type {
   945  	for _, i := range index {
   946  		if t.Kind() == reflect.Pointer {
   947  			t = t.Elem()
   948  		}
   949  		t = t.Field(i).Type
   950  	}
   951  	return t
   952  }
   953  
   954  type reflectWithString struct {
   955  	v  reflect.Value
   956  	ks string
   957  }
   958  
   959  func resolveKeyName(k reflect.Value) (string, error) {
   960  	if k.Kind() == reflect.String {
   961  		return k.String(), nil
   962  	}
   963  	if tm, ok := k.Interface().(encoding.TextMarshaler); ok {
   964  		if k.Kind() == reflect.Pointer && k.IsNil() {
   965  			return "", nil
   966  		}
   967  		buf, err := tm.MarshalText()
   968  		return string(buf), err
   969  	}
   970  	switch k.Kind() {
   971  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   972  		return strconv.FormatInt(k.Int(), 10), nil
   973  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   974  		return strconv.FormatUint(k.Uint(), 10), nil
   975  	}
   976  	panic("unexpected map key type")
   977  }
   978  
   979  func appendString[Bytes []byte | string](dst []byte, src Bytes, escapeHTML bool) []byte {
   980  	dst = append(dst, '"')
   981  	start := 0
   982  	for i := 0; i < len(src); {
   983  		if b := src[i]; b < utf8.RuneSelf {
   984  			if htmlSafeSet[b] || (!escapeHTML && safeSet[b]) {
   985  				i++
   986  				continue
   987  			}
   988  			dst = append(dst, src[start:i]...)
   989  			switch b {
   990  			case '\\', '"':
   991  				dst = append(dst, '\\', b)
   992  			case '\b':
   993  				dst = append(dst, '\\', 'b')
   994  			case '\f':
   995  				dst = append(dst, '\\', 'f')
   996  			case '\n':
   997  				dst = append(dst, '\\', 'n')
   998  			case '\r':
   999  				dst = append(dst, '\\', 'r')
  1000  			case '\t':
  1001  				dst = append(dst, '\\', 't')
  1002  			default:
  1003  				// This encodes bytes < 0x20 except for \b, \f, \n, \r and \t.
  1004  				// If escapeHTML is set, it also escapes <, >, and &
  1005  				// because they can lead to security holes when
  1006  				// user-controlled strings are rendered into JSON
  1007  				// and served to some browsers.
  1008  				dst = append(dst, '\\', 'u', '0', '0', hex[b>>4], hex[b&0xF])
  1009  			}
  1010  			i++
  1011  			start = i
  1012  			continue
  1013  		}
  1014  		// TODO(https://go.dev/issue/56948): Use generic utf8 functionality.
  1015  		// For now, cast only a small portion of byte slices to a string
  1016  		// so that it can be stack allocated. This slows down []byte slightly
  1017  		// due to the extra copy, but keeps string performance roughly the same.
  1018  		n := min(len(src)-i, utf8.UTFMax)
  1019  		c, size := utf8.DecodeRuneInString(string(src[i : i+n]))
  1020  		if c == utf8.RuneError && size == 1 {
  1021  			dst = append(dst, src[start:i]...)
  1022  			dst = append(dst, `\ufffd`...)
  1023  			i += size
  1024  			start = i
  1025  			continue
  1026  		}
  1027  		// U+2028 is LINE SEPARATOR.
  1028  		// U+2029 is PARAGRAPH SEPARATOR.
  1029  		// They are both technically valid characters in JSON strings,
  1030  		// but don't work in JSONP, which has to be evaluated as JavaScript,
  1031  		// and can lead to security holes there. It is valid JSON to
  1032  		// escape them, so we do so unconditionally.
  1033  		// See https://en.wikipedia.org/wiki/JSON#Safety.
  1034  		if c == '\u2028' || c == '\u2029' {
  1035  			dst = append(dst, src[start:i]...)
  1036  			dst = append(dst, '\\', 'u', '2', '0', '2', hex[c&0xF])
  1037  			i += size
  1038  			start = i
  1039  			continue
  1040  		}
  1041  		i += size
  1042  	}
  1043  	dst = append(dst, src[start:]...)
  1044  	dst = append(dst, '"')
  1045  	return dst
  1046  }
  1047  
  1048  // A field represents a single field found in a struct.
  1049  type field struct {
  1050  	name      string
  1051  	nameBytes []byte // []byte(name)
  1052  
  1053  	nameNonEsc  string // `"` + name + `":`
  1054  	nameEscHTML string // `"` + HTMLEscape(name) + `":`
  1055  
  1056  	tag       bool
  1057  	index     []int
  1058  	typ       reflect.Type
  1059  	omitEmpty bool
  1060  	omitZero  bool
  1061  	isZero    func(reflect.Value) bool
  1062  	quoted    bool
  1063  
  1064  	encoder encoderFunc
  1065  }
  1066  
  1067  type isZeroer interface {
  1068  	IsZero() bool
  1069  }
  1070  
  1071  var isZeroerType = reflect.TypeFor[isZeroer]()
  1072  
  1073  // typeFields returns a list of fields that JSON should recognize for the given type.
  1074  // The algorithm is breadth-first search over the set of structs to include - the top struct
  1075  // and then any reachable anonymous structs.
  1076  //
  1077  // typeFields should be an internal detail,
  1078  // but widely used packages access it using linkname.
  1079  // Notable members of the hall of shame include:
  1080  //   - github.com/bytedance/sonic
  1081  //
  1082  // Do not remove or change the type signature.
  1083  // See go.dev/issue/67401.
  1084  //
  1085  //go:linkname typeFields
  1086  func typeFields(t reflect.Type) structFields {
  1087  	// Anonymous fields to explore at the current level and the next.
  1088  	current := []field{}
  1089  	next := []field{{typ: t}}
  1090  
  1091  	// Count of queued names for current level and the next.
  1092  	var count, nextCount map[reflect.Type]int
  1093  
  1094  	// Types already visited at an earlier level.
  1095  	visited := map[reflect.Type]bool{}
  1096  
  1097  	// Fields found.
  1098  	var fields []field
  1099  
  1100  	// Buffer to run appendHTMLEscape on field names.
  1101  	var nameEscBuf []byte
  1102  
  1103  	for len(next) > 0 {
  1104  		current, next = next, current[:0]
  1105  		count, nextCount = nextCount, map[reflect.Type]int{}
  1106  
  1107  		for _, f := range current {
  1108  			if visited[f.typ] {
  1109  				continue
  1110  			}
  1111  			visited[f.typ] = true
  1112  
  1113  			// Scan f.typ for fields to include.
  1114  			for i := 0; i < f.typ.NumField(); i++ {
  1115  				sf := f.typ.Field(i)
  1116  				if sf.Anonymous {
  1117  					t := sf.Type
  1118  					if t.Kind() == reflect.Pointer {
  1119  						t = t.Elem()
  1120  					}
  1121  					if !sf.IsExported() && t.Kind() != reflect.Struct {
  1122  						// Ignore embedded fields of unexported non-struct types.
  1123  						continue
  1124  					}
  1125  					// Do not ignore embedded fields of unexported struct types
  1126  					// since they may have exported fields.
  1127  				} else if !sf.IsExported() {
  1128  					// Ignore unexported non-embedded fields.
  1129  					continue
  1130  				}
  1131  				tag := sf.Tag.Get("json")
  1132  				if tag == "-" {
  1133  					continue
  1134  				}
  1135  				name, opts := parseTag(tag)
  1136  				if !isValidTag(name) {
  1137  					name = ""
  1138  				}
  1139  				index := make([]int, len(f.index)+1)
  1140  				copy(index, f.index)
  1141  				index[len(f.index)] = i
  1142  
  1143  				ft := sf.Type
  1144  				if ft.Name() == "" && ft.Kind() == reflect.Pointer {
  1145  					// Follow pointer.
  1146  					ft = ft.Elem()
  1147  				}
  1148  
  1149  				// Only strings, floats, integers, and booleans can be quoted.
  1150  				quoted := false
  1151  				if opts.Contains("string") {
  1152  					switch ft.Kind() {
  1153  					case reflect.Bool,
  1154  						reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
  1155  						reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr,
  1156  						reflect.Float32, reflect.Float64,
  1157  						reflect.String:
  1158  						quoted = true
  1159  					}
  1160  				}
  1161  
  1162  				// Record found field and index sequence.
  1163  				if name != "" || !sf.Anonymous || ft.Kind() != reflect.Struct {
  1164  					tagged := name != ""
  1165  					if name == "" {
  1166  						name = sf.Name
  1167  					}
  1168  					field := field{
  1169  						name:      name,
  1170  						tag:       tagged,
  1171  						index:     index,
  1172  						typ:       ft,
  1173  						omitEmpty: opts.Contains("omitempty"),
  1174  						omitZero:  opts.Contains("omitzero"),
  1175  						quoted:    quoted,
  1176  					}
  1177  					field.nameBytes = []byte(field.name)
  1178  
  1179  					// Build nameEscHTML and nameNonEsc ahead of time.
  1180  					nameEscBuf = appendHTMLEscape(nameEscBuf[:0], field.nameBytes)
  1181  					field.nameEscHTML = `"` + string(nameEscBuf) + `":`
  1182  					field.nameNonEsc = `"` + field.name + `":`
  1183  
  1184  					if field.omitZero {
  1185  						t := sf.Type
  1186  						// Provide a function that uses a type's IsZero method.
  1187  						switch {
  1188  						case t.Kind() == reflect.Interface && t.Implements(isZeroerType):
  1189  							field.isZero = func(v reflect.Value) bool {
  1190  								// Avoid panics calling IsZero on a nil interface or
  1191  								// non-nil interface with nil pointer.
  1192  								return v.IsNil() ||
  1193  									(v.Elem().Kind() == reflect.Pointer && v.Elem().IsNil()) ||
  1194  									v.Interface().(isZeroer).IsZero()
  1195  							}
  1196  						case t.Kind() == reflect.Pointer && t.Implements(isZeroerType):
  1197  							field.isZero = func(v reflect.Value) bool {
  1198  								// Avoid panics calling IsZero on nil pointer.
  1199  								return v.IsNil() || v.Interface().(isZeroer).IsZero()
  1200  							}
  1201  						case t.Implements(isZeroerType):
  1202  							field.isZero = func(v reflect.Value) bool {
  1203  								return v.Interface().(isZeroer).IsZero()
  1204  							}
  1205  						case reflect.PointerTo(t).Implements(isZeroerType):
  1206  							field.isZero = func(v reflect.Value) bool {
  1207  								if !v.CanAddr() {
  1208  									// Temporarily box v so we can take the address.
  1209  									v2 := reflect.New(v.Type()).Elem()
  1210  									v2.Set(v)
  1211  									v = v2
  1212  								}
  1213  								return v.Addr().Interface().(isZeroer).IsZero()
  1214  							}
  1215  						}
  1216  					}
  1217  
  1218  					fields = append(fields, field)
  1219  					if count[f.typ] > 1 {
  1220  						// If there were multiple instances, add a second,
  1221  						// so that the annihilation code will see a duplicate.
  1222  						// It only cares about the distinction between 1 and 2,
  1223  						// so don't bother generating any more copies.
  1224  						fields = append(fields, fields[len(fields)-1])
  1225  					}
  1226  					continue
  1227  				}
  1228  
  1229  				// Record new anonymous struct to explore in next round.
  1230  				nextCount[ft]++
  1231  				if nextCount[ft] == 1 {
  1232  					next = append(next, field{name: ft.Name(), index: index, typ: ft})
  1233  				}
  1234  			}
  1235  		}
  1236  	}
  1237  
  1238  	slices.SortFunc(fields, func(a, b field) int {
  1239  		// sort field by name, breaking ties with depth, then
  1240  		// breaking ties with "name came from json tag", then
  1241  		// breaking ties with index sequence.
  1242  		if c := strings.Compare(a.name, b.name); c != 0 {
  1243  			return c
  1244  		}
  1245  		if c := cmp.Compare(len(a.index), len(b.index)); c != 0 {
  1246  			return c
  1247  		}
  1248  		if a.tag != b.tag {
  1249  			if a.tag {
  1250  				return -1
  1251  			}
  1252  			return +1
  1253  		}
  1254  		return slices.Compare(a.index, b.index)
  1255  	})
  1256  
  1257  	// Delete all fields that are hidden by the Go rules for embedded fields,
  1258  	// except that fields with JSON tags are promoted.
  1259  
  1260  	// The fields are sorted in primary order of name, secondary order
  1261  	// of field index length. Loop over names; for each name, delete
  1262  	// hidden fields by choosing the one dominant field that survives.
  1263  	out := fields[:0]
  1264  	for advance, i := 0, 0; i < len(fields); i += advance {
  1265  		// One iteration per name.
  1266  		// Find the sequence of fields with the name of this first field.
  1267  		fi := fields[i]
  1268  		name := fi.name
  1269  		for advance = 1; i+advance < len(fields); advance++ {
  1270  			fj := fields[i+advance]
  1271  			if fj.name != name {
  1272  				break
  1273  			}
  1274  		}
  1275  		if advance == 1 { // Only one field with this name
  1276  			out = append(out, fi)
  1277  			continue
  1278  		}
  1279  		dominant, ok := dominantField(fields[i : i+advance])
  1280  		if ok {
  1281  			out = append(out, dominant)
  1282  		}
  1283  	}
  1284  
  1285  	fields = out
  1286  	slices.SortFunc(fields, func(i, j field) int {
  1287  		return slices.Compare(i.index, j.index)
  1288  	})
  1289  
  1290  	for i := range fields {
  1291  		f := &fields[i]
  1292  		f.encoder = typeEncoder(typeByIndex(t, f.index))
  1293  	}
  1294  	exactNameIndex := make(map[string]*field, len(fields))
  1295  	foldedNameIndex := make(map[string]*field, len(fields))
  1296  	for i, field := range fields {
  1297  		exactNameIndex[field.name] = &fields[i]
  1298  		// For historical reasons, first folded match takes precedence.
  1299  		if _, ok := foldedNameIndex[string(foldName(field.nameBytes))]; !ok {
  1300  			foldedNameIndex[string(foldName(field.nameBytes))] = &fields[i]
  1301  		}
  1302  	}
  1303  	return structFields{fields, exactNameIndex, foldedNameIndex}
  1304  }
  1305  
  1306  // dominantField looks through the fields, all of which are known to
  1307  // have the same name, to find the single field that dominates the
  1308  // others using Go's embedding rules, modified by the presence of
  1309  // JSON tags. If there are multiple top-level fields, the boolean
  1310  // will be false: This condition is an error in Go and we skip all
  1311  // the fields.
  1312  func dominantField(fields []field) (field, bool) {
  1313  	// The fields are sorted in increasing index-length order, then by presence of tag.
  1314  	// That means that the first field is the dominant one. We need only check
  1315  	// for error cases: two fields at top level, either both tagged or neither tagged.
  1316  	if len(fields) > 1 && len(fields[0].index) == len(fields[1].index) && fields[0].tag == fields[1].tag {
  1317  		return field{}, false
  1318  	}
  1319  	return fields[0], true
  1320  }
  1321  
  1322  var fieldCache sync.Map // map[reflect.Type]structFields
  1323  
  1324  // cachedTypeFields is like typeFields but uses a cache to avoid repeated work.
  1325  func cachedTypeFields(t reflect.Type) structFields {
  1326  	if f, ok := fieldCache.Load(t); ok {
  1327  		return f.(structFields)
  1328  	}
  1329  	f, _ := fieldCache.LoadOrStore(t, typeFields(t))
  1330  	return f.(structFields)
  1331  }
  1332  
  1333  func mayAppendQuote(b []byte, quoted bool) []byte {
  1334  	if quoted {
  1335  		b = append(b, '"')
  1336  	}
  1337  	return b
  1338  }
  1339  

View as plain text