// Copyright 2010 The Go Authors. All rights reserved. // Use of this source code is governed by a BSD-style // license that can be found in the LICENSE file. // Package json implements encoding and decoding of JSON objects as defined in // RFC 4627. The mapping between JSON objects and Go values is described // in the documentation for the Marshal and Unmarshal functions. // // See "JSON and Go" for an introduction to this package: // https://golang.org/doc/articles/json_and_go.html package json import ( "bytes" "encoding" "encoding/base64" "fmt" "math" "reflect" "runtime" "sort" "strconv" "strings" "sync" "unicode" "unicode/utf8" ) // Marshal returns the JSON encoding of v. // // Marshal traverses the value v recursively. // If an encountered value implements the Marshaler interface // and is not a nil pointer, Marshal calls its MarshalJSON method // to produce JSON. If no MarshalJSON method is present but the // value implements encoding.TextMarshaler instead, Marshal calls // its MarshalText method. // The nil pointer exception is not strictly necessary // but mimics a similar, necessary exception in the behavior of // UnmarshalJSON. // // Otherwise, Marshal uses the following type-dependent default encodings: // // Boolean values encode as JSON booleans. // // Floating point, integer, and Number values encode as JSON numbers. // // String values encode as JSON strings coerced to valid UTF-8, // replacing invalid bytes with the Unicode replacement rune. // The angle brackets "<" and ">" are escaped to "\u003c" and "\u003e" // to keep some browsers from misinterpreting JSON output as HTML. // Ampersand "&" is also escaped to "\u0026" for the same reason. // // Array and slice values encode as JSON arrays, except that // []byte encodes as a base64-encoded string, and a nil slice // encodes as the null JSON object. // // Struct values encode as JSON objects. Each exported struct field // becomes a member of the object unless // - the field's tag is "-", or // - the field is empty and its tag specifies the "omitempty" option. // The empty values are false, 0, any // nil pointer or interface value, and any array, slice, map, or string of // length zero. The object's default key string is the struct field name // but can be specified in the struct field's tag value. The "json" key in // the struct field's tag value is the key name, followed by an optional comma // and options. Examples: // // // Field is ignored by this package. // Field int `json:"-"` // // // Field appears in JSON as key "myName". // Field int `json:"myName"` // // // Field appears in JSON as key "myName" and // // the field is omitted from the object if its value is empty, // // as defined above. // Field int `json:"myName,omitempty"` // // // Field appears in JSON as key "Field" (the default), but // // the field is skipped if empty. // // Note the leading comma. // Field int `json:",omitempty"` // // The "string" option signals that a field is stored as JSON inside a // JSON-encoded string. It applies only to fields of string, floating point, // integer, or boolean types. This extra level of encoding is sometimes used // when communicating with JavaScript programs: // // Int64String int64 `json:",string"` // // The key name will be used if it's a non-empty string consisting of // only Unicode letters, digits, dollar signs, percent signs, hyphens, // underscores and slashes. // // Anonymous struct fields are usually marshaled as if their inner exported fields // were fields in the outer struct, subject to the usual Go visibility rules amended // as described in the next paragraph. // An anonymous struct field with a name given in its JSON tag is treated as // having that name, rather than being anonymous. // An anonymous struct field of interface type is treated the same as having // that type as its name, rather than being anonymous. // // The Go visibility rules for struct fields are amended for JSON when // deciding which field to marshal or unmarshal. If there are // multiple fields at the same level, and that level is the least // nested (and would therefore be the nesting level selected by the // usual Go rules), the following extra rules apply: // // 1) Of those fields, if any are JSON-tagged, only tagged fields are considered, // even if there are multiple untagged fields that would otherwise conflict. // 2) If there is exactly one field (tagged or not according to the first rule), that is selected. // 3) Otherwise there are multiple fields, and all are ignored; no error occurs. // // Handling of anonymous struct fields is new in Go 1.1. // Prior to Go 1.1, anonymous struct fields were ignored. To force ignoring of // an anonymous struct field in both current and earlier versions, give the field // a JSON tag of "-". // // Map values encode as JSON objects. // The map's key type must be string; the map keys are used as JSON object // keys, subject to the UTF-8 coercion described for string values above. // // Pointer values encode as the value pointed to. // A nil pointer encodes as the null JSON object. // // Interface values encode as the value contained in the interface. // A nil interface value encodes as the null JSON object. // // Channel, complex, and function values cannot be encoded in JSON. // Attempting to encode such a value causes Marshal to return // an UnsupportedTypeError. // // JSON cannot represent cyclic data structures and Marshal does not // handle them. Passing cyclic structures to Marshal will result in // an infinite recursion. // func Marshal(v interface{}) ([]byte, error) { e := &encodeState{} err := e.marshal(v) if err != nil { return nil, err } return e.Bytes(), nil } // MarshalIndent is like Marshal but applies Indent to format the output. func MarshalIndent(v interface{}, prefix, indent string) ([]byte, error) { b, err := Marshal(v) if err != nil { return nil, err } var buf bytes.Buffer err = Indent(&buf, b, prefix, indent) if err != nil { return nil, err } return buf.Bytes(), nil } // HTMLEscape appends to dst the JSON-encoded src with <, >, &, U+2028 and U+2029 // characters inside string literals changed to \u003c, \u003e, \u0026, \u2028, \u2029 // so that the JSON will be safe to embed inside HTML <script> tags. // For historical reasons, web browsers don't honor standard HTML // escaping within <script> tags, so an alternative JSON encoding must // be used. func HTMLEscape(dst *bytes.Buffer, src []byte) { // The characters can only appear in string literals, // so just scan the string one byte at a time. start := 0 for i, c := range src { if c == '<' || c == '>' || c == '&' { if start < i { dst.Write(src[start:i]) } dst.WriteString(`\u00`) dst.WriteByte(hex[c>>4]) dst.WriteByte(hex[c&0xF]) start = i + 1 } // Convert U+2028 and U+2029 (E2 80 A8 and E2 80 A9). if c == 0xE2 && i+2 < len(src) && src[i+1] == 0x80 && src[i+2]&^1 == 0xA8 { if start < i { dst.Write(src[start:i]) } dst.WriteString(`\u202`) dst.WriteByte(hex[src[i+2]&0xF]) start = i + 3 } } if start < len(src) { dst.Write(src[start:]) } } // Marshaler is the interface implemented by objects that // can marshal themselves into valid JSON. type Marshaler interface { MarshalJSON() ([]byte, error) } // An UnsupportedTypeError is returned by Marshal when attempting // to encode an unsupported value type. type UnsupportedTypeError struct { Type reflect.Type } func (e *UnsupportedTypeError) Error() string { return "json: unsupported type: " + e.Type.String() } type UnsupportedValueError struct { Value reflect.Value Str string } func (e *UnsupportedValueError) Error() string { return "json: unsupported value: " + e.Str } // Before Go 1.2, an InvalidUTF8Error was returned by Marshal when // attempting to encode a string value with invalid UTF-8 sequences. // As of Go 1.2, Marshal instead coerces the string to valid UTF-8 by // replacing invalid bytes with the Unicode replacement rune U+FFFD. // This error is no longer generated but is kept for backwards compatibility // with programs that might mention it. type InvalidUTF8Error struct { S string // the whole string value that caused the error } func (e *InvalidUTF8Error) Error() string { return "json: invalid UTF-8 in string: " + strconv.Quote(e.S) } type MarshalerError struct { Type reflect.Type Err error } func (e *MarshalerError) Error() string { return "json: error calling MarshalJSON for type " + e.Type.String() + ": " + e.Err.Error() } var hex = "0123456789abcdef" // An encodeState encodes JSON into a bytes.Buffer. type encodeState struct { bytes.Buffer // accumulated output scratch [64]byte } var encodeStatePool sync.Pool func newEncodeState() *encodeState { if v := encodeStatePool.Get(); v != nil { e := v.(*encodeState) e.Reset() return e } return new(encodeState) } func (e *encodeState) marshal(v interface{}) (err error) { defer func() { if r := recover(); r != nil { if _, ok := r.(runtime.Error); ok { panic(r) } if s, ok := r.(string); ok { panic(s) } err = r.(error) } }() e.reflectValue(reflect.ValueOf(v)) return nil } func (e *encodeState) error(err error) { panic(err) } func isEmptyValue(v reflect.Value) bool { switch v.Kind() { case reflect.Array, reflect.Map, reflect.Slice, reflect.String: return v.Len() == 0 case reflect.Bool: return !v.Bool() case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64: return v.Int() == 0 case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr: return v.Uint() == 0 case reflect.Float32, reflect.Float64: return v.Float() == 0 case reflect.Interface, reflect.Ptr: return v.IsNil() } return false } func (e *encodeState) reflectValue(v reflect.Value) { valueEncoder(v)(e, v, false) } type encoderFunc func(e *encodeState, v reflect.Value, quoted bool) var encoderCache struct { sync.RWMutex m map[reflect.Type]encoderFunc } func valueEncoder(v reflect.Value) encoderFunc { if !v.IsValid() { return invalidValueEncoder } return typeEncoder(v.Type()) } func typeEncoder(t reflect.Type) encoderFunc { encoderCache.RLock() f := encoderCache.m[t] encoderCache.RUnlock() if f != nil { return f } // To deal with recursive types, populate the map with an // indirect func before we build it. This type waits on the // real func (f) to be ready and then calls it. This indirect // func is only used for recursive types. encoderCache.Lock() if encoderCache.m == nil { encoderCache.m = make(map[reflect.Type]encoderFunc) } var wg sync.WaitGroup wg.Add(1) encoderCache.m[t] = func(e *encodeState, v reflect.Value, quoted bool) { wg.Wait() f(e, v, quoted) } encoderCache.Unlock() // Compute fields without lock. // Might duplicate effort but won't hold other computations back. f = newTypeEncoder(t, true) wg.Done() encoderCache.Lock() encoderCache.m[t] = f encoderCache.Unlock() return f } var ( marshalerType = reflect.TypeOf(new(Marshaler)).Elem() textMarshalerType = reflect.TypeOf(new(encoding.TextMarshaler)).Elem() ) // newTypeEncoder constructs an encoderFunc for a type. // The returned encoder only checks CanAddr when allowAddr is true. func newTypeEncoder(t reflect.Type, allowAddr bool) encoderFunc { if t.Implements(marshalerType) { return marshalerEncoder } if t.Kind() != reflect.Ptr && allowAddr { if reflect.PtrTo(t).Implements(marshalerType) { return newCondAddrEncoder(addrMarshalerEncoder, newTypeEncoder(t, false)) } } if t.Implements(textMarshalerType) { return textMarshalerEncoder } if t.Kind() != reflect.Ptr && allowAddr { if reflect.PtrTo(t).Implements(textMarshalerType) { return newCondAddrEncoder(addrTextMarshalerEncoder, newTypeEncoder(t, false)) } } switch t.Kind() { case reflect.Bool: return boolEncoder case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64: return intEncoder case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr: return uintEncoder case reflect.Float32: return float32Encoder case reflect.Float64: return float64Encoder case reflect.String: return stringEncoder case reflect.Interface: return interfaceEncoder case reflect.Struct: return newStructEncoder(t) case reflect.Map: return newMapEncoder(t) case reflect.Slice: return newSliceEncoder(t) case reflect.Array: return newArrayEncoder(t) case reflect.Ptr: return newPtrEncoder(t) default: return unsupportedTypeEncoder } } func invalidValueEncoder(e *encodeState, v reflect.Value, quoted bool) { e.WriteString("null") } func marshalerEncoder(e *encodeState, v reflect.Value, quoted bool) { if v.Kind() == reflect.Ptr && v.IsNil() { e.WriteString("null") return } m := v.Interface().(Marshaler) b, err := m.MarshalJSON() if err == nil { // copy JSON into buffer, checking validity. err = compact(&e.Buffer, b, true) } if err != nil { e.error(&MarshalerError{v.Type(), err}) } } func addrMarshalerEncoder(e *encodeState, v reflect.Value, quoted bool) { va := v.Addr() if va.IsNil() { e.WriteString("null") return } m := va.Interface().(Marshaler) b, err := m.MarshalJSON() if err == nil { // copy JSON into buffer, checking validity. err = compact(&e.Buffer, b, true) } if err != nil { e.error(&MarshalerError{v.Type(), err}) } } func textMarshalerEncoder(e *encodeState, v reflect.Value, quoted bool) { if v.Kind() == reflect.Ptr && v.IsNil() { e.WriteString("null") return } m := v.Interface().(encoding.TextMarshaler) b, err := m.MarshalText() if err != nil { e.error(&MarshalerError{v.Type(), err}) } e.stringBytes(b) } func addrTextMarshalerEncoder(e *encodeState, v reflect.Value, quoted bool) { va := v.Addr() if va.IsNil() { e.WriteString("null") return } m := va.Interface().(encoding.TextMarshaler) b, err := m.MarshalText() if err != nil { e.error(&MarshalerError{v.Type(), err}) } e.stringBytes(b) } func boolEncoder(e *encodeState, v reflect.Value, quoted bool) { if quoted { e.WriteByte('"') } if v.Bool() { e.WriteString("true") } else { e.WriteString("false") } if quoted { e.WriteByte('"') } } func intEncoder(e *encodeState, v reflect.Value, quoted bool) { b := strconv.AppendInt(e.scratch[:0], v.Int(), 10) if quoted { e.WriteByte('"') } e.Write(b) if quoted { e.WriteByte('"') } } func uintEncoder(e *encodeState, v reflect.Value, quoted bool) { b := strconv.AppendUint(e.scratch[:0], v.Uint(), 10) if quoted { e.WriteByte('"') } e.Write(b) if quoted { e.WriteByte('"') } } type floatEncoder int // number of bits func (bits floatEncoder) encode(e *encodeState, v reflect.Value, quoted bool) { f := v.Float() if math.IsInf(f, 0) || math.IsNaN(f) { e.error(&UnsupportedValueError{v, strconv.FormatFloat(f, 'g', -1, int(bits))}) } b := strconv.AppendFloat(e.scratch[:0], f, 'g', -1, int(bits)) if quoted { e.WriteByte('"') } e.Write(b) if quoted { e.WriteByte('"') } } var ( float32Encoder = (floatEncoder(32)).encode float64Encoder = (floatEncoder(64)).encode ) func stringEncoder(e *encodeState, v reflect.Value, quoted bool) { if v.Type() == numberType { numStr := v.String() // In Go1.5 the empty string encodes to "0", while this is not a valid number literal // we keep compatibility so check validity after this. if numStr == "" { numStr = "0" // Number's zero-val } if !isValidNumber(numStr) { e.error(fmt.Errorf("json: invalid number literal %q", numStr)) } e.WriteString(numStr) return } if quoted { sb, err := Marshal(v.String()) if err != nil { e.error(err) } e.string(string(sb)) } else { e.string(v.String()) } } func interfaceEncoder(e *encodeState, v reflect.Value, quoted bool) { if v.IsNil() { e.WriteString("null") return } e.reflectValue(v.Elem()) } func unsupportedTypeEncoder(e *encodeState, v reflect.Value, quoted bool) { e.error(&UnsupportedTypeError{v.Type()}) } type structEncoder struct { fields []field fieldEncs []encoderFunc } func (se *structEncoder) encode(e *encodeState, v reflect.Value, quoted bool) { e.WriteByte('{') first := true for i, f := range se.fields { fv := fieldByIndex(v, f.index) if !fv.IsValid() || f.omitEmpty && isEmptyValue(fv) { continue } if first { first = false } else { e.WriteByte(',') } e.string(f.name) e.WriteByte(':') se.fieldEncs[i](e, fv, f.quoted) } e.WriteByte('}') } func newStructEncoder(t reflect.Type) encoderFunc { fields := cachedTypeFields(t) se := &structEncoder{ fields: fields, fieldEncs: make([]encoderFunc, len(fields)), } for i, f := range fields { se.fieldEncs[i] = typeEncoder(typeByIndex(t, f.index)) } return se.encode } type mapEncoder struct { elemEnc encoderFunc } func (me *mapEncoder) encode(e *encodeState, v reflect.Value, _ bool) { if v.IsNil() { e.WriteString("null") return } e.WriteByte('{') var sv stringValues = v.MapKeys() sort.Sort(sv) for i, k := range sv { if i > 0 { e.WriteByte(',') } e.string(k.String()) e.WriteByte(':') me.elemEnc(e, v.MapIndex(k), false) } e.WriteByte('}') } func newMapEncoder(t reflect.Type) encoderFunc { if t.Key().Kind() != reflect.String { return unsupportedTypeEncoder } me := &mapEncoder{typeEncoder(t.Elem())} return me.encode } func encodeByteSlice(e *encodeState, v reflect.Value, _ bool) { if v.IsNil() { e.WriteString("null") return } s := v.Bytes() e.WriteByte('"') if len(s) < 1024 { // for small buffers, using Encode directly is much faster. dst := make([]byte, base64.StdEncoding.EncodedLen(len(s))) base64.StdEncoding.Encode(dst, s) e.Write(dst) } else { // for large buffers, avoid unnecessary extra temporary // buffer space. enc := base64.NewEncoder(base64.StdEncoding, e) enc.Write(s) enc.Close() } e.WriteByte('"') } // sliceEncoder just wraps an arrayEncoder, checking to make sure the value isn't nil. type sliceEncoder struct { arrayEnc encoderFunc } func (se *sliceEncoder) encode(e *encodeState, v reflect.Value, _ bool) { if v.IsNil() { e.WriteString("null") return } se.arrayEnc(e, v, false) } func newSliceEncoder(t reflect.Type) encoderFunc { // Byte slices get special treatment; arrays don't. if t.Elem().Kind() == reflect.Uint8 { return encodeByteSlice } enc := &sliceEncoder{newArrayEncoder(t)} return enc.encode } type arrayEncoder struct { elemEnc encoderFunc } func (ae *arrayEncoder) encode(e *encodeState, v reflect.Value, _ bool) { e.WriteByte('[') n := v.Len() for i := 0; i < n; i++ { if i > 0 { e.WriteByte(',') } ae.elemEnc(e, v.Index(i), false) } e.WriteByte(']') } func newArrayEncoder(t reflect.Type) encoderFunc { enc := &arrayEncoder{typeEncoder(t.Elem())} return enc.encode } type ptrEncoder struct { elemEnc encoderFunc } func (pe *ptrEncoder) encode(e *encodeState, v reflect.Value, quoted bool) { if v.IsNil() { e.WriteString("null") return } pe.elemEnc(e, v.Elem(), quoted) } func newPtrEncoder(t reflect.Type) encoderFunc { enc := &ptrEncoder{typeEncoder(t.Elem())} return enc.encode } type condAddrEncoder struct { canAddrEnc, elseEnc encoderFunc } func (ce *condAddrEncoder) encode(e *encodeState, v reflect.Value, quoted bool) { if v.CanAddr() { ce.canAddrEnc(e, v, quoted) } else { ce.elseEnc(e, v, quoted) } } // newCondAddrEncoder returns an encoder that checks whether its value // CanAddr and delegates to canAddrEnc if so, else to elseEnc. func newCondAddrEncoder(canAddrEnc, elseEnc encoderFunc) encoderFunc { enc := &condAddrEncoder{canAddrEnc: canAddrEnc, elseEnc: elseEnc} return enc.encode } func isValidTag(s string) bool { if s == "" { return false } for _, c := range s { switch { case strings.ContainsRune("!#$%&()*+-./:<=>?@[]^_{|}~ ", c): // Backslash and quote chars are reserved, but // otherwise any punctuation chars are allowed // in a tag name. default: if !unicode.IsLetter(c) && !unicode.IsDigit(c) { return false } } } return true } func fieldByIndex(v reflect.Value, index []int) reflect.Value { for _, i := range index { if v.Kind() == reflect.Ptr { if v.IsNil() { return reflect.Value{} } v = v.Elem() } v = v.Field(i) } return v } func typeByIndex(t reflect.Type, index []int) reflect.Type { for _, i := range index { if t.Kind() == reflect.Ptr { t = t.Elem() } t = t.Field(i).Type } return t } // stringValues is a slice of reflect.Value holding *reflect.StringValue. // It implements the methods to sort by string. type stringValues []reflect.Value func (sv stringValues) Len() int { return len(sv) } func (sv stringValues) Swap(i, j int) { sv[i], sv[j] = sv[j], sv[i] } func (sv stringValues) Less(i, j int) bool { return sv.get(i) < sv.get(j) } func (sv stringValues) get(i int) string { return sv[i].String() } // NOTE: keep in sync with stringBytes below. func (e *encodeState) string(s string) int { len0 := e.Len() e.WriteByte('"') start := 0 for i := 0; i < len(s); { if b := s[i]; b < utf8.RuneSelf { if 0x20 <= b && b != '\\' && b != '"' && b != '<' && b != '>' && b != '&' { i++ continue } if start < i { e.WriteString(s[start:i]) } switch b { case '\\', '"': e.WriteByte('\\') e.WriteByte(b) case '\n': e.WriteByte('\\') e.WriteByte('n') case '\r': e.WriteByte('\\') e.WriteByte('r') case '\t': e.WriteByte('\\') e.WriteByte('t') default: // This encodes bytes < 0x20 except for \n and \r, // as well as <, > and &. The latter are escaped because they // can lead to security holes when user-controlled strings // are rendered into JSON and served to some browsers. e.WriteString(`\u00`) e.WriteByte(hex[b>>4]) e.WriteByte(hex[b&0xF]) } i++ start = i continue } c, size := utf8.DecodeRuneInString(s[i:]) if c == utf8.RuneError && size == 1 { if start < i { e.WriteString(s[start:i]) } e.WriteString(`\ufffd`) i += size start = i continue } // U+2028 is LINE SEPARATOR. // U+2029 is PARAGRAPH SEPARATOR. // They are both technically valid characters in JSON strings, // but don't work in JSONP, which has to be evaluated as JavaScript, // and can lead to security holes there. It is valid JSON to // escape them, so we do so unconditionally. // See http://timelessrepo.com/json-isnt-a-javascript-subset for discussion. if c == '\u2028' || c == '\u2029' { if start < i { e.WriteString(s[start:i]) } e.WriteString(`\u202`) e.WriteByte(hex[c&0xF]) i += size start = i continue } i += size } if start < len(s) { e.WriteString(s[start:]) } e.WriteByte('"') return e.Len() - len0 } // NOTE: keep in sync with string above. func (e *encodeState) stringBytes(s []byte) int { len0 := e.Len() e.WriteByte('"') start := 0 for i := 0; i < len(s); { if b := s[i]; b < utf8.RuneSelf { if 0x20 <= b && b != '\\' && b != '"' && b != '<' && b != '>' && b != '&' { i++ continue } if start < i { e.Write(s[start:i]) } switch b { case '\\', '"': e.WriteByte('\\') e.WriteByte(b) case '\n': e.WriteByte('\\') e.WriteByte('n') case '\r': e.WriteByte('\\') e.WriteByte('r') case '\t': e.WriteByte('\\') e.WriteByte('t') default: // This encodes bytes < 0x20 except for \n and \r, // as well as <, >, and &. The latter are escaped because they // can lead to security holes when user-controlled strings // are rendered into JSON and served to some browsers. e.WriteString(`\u00`) e.WriteByte(hex[b>>4]) e.WriteByte(hex[b&0xF]) } i++ start = i continue } c, size := utf8.DecodeRune(s[i:]) if c == utf8.RuneError && size == 1 { if start < i { e.Write(s[start:i]) } e.WriteString(`\ufffd`) i += size start = i continue } // U+2028 is LINE SEPARATOR. // U+2029 is PARAGRAPH SEPARATOR. // They are both technically valid characters in JSON strings, // but don't work in JSONP, which has to be evaluated as JavaScript, // and can lead to security holes there. It is valid JSON to // escape them, so we do so unconditionally. // See http://timelessrepo.com/json-isnt-a-javascript-subset for discussion. if c == '\u2028' || c == '\u2029' { if start < i { e.Write(s[start:i]) } e.WriteString(`\u202`) e.WriteByte(hex[c&0xF]) i += size start = i continue } i += size } if start < len(s) { e.Write(s[start:]) } e.WriteByte('"') return e.Len() - len0 } // A field represents a single field found in a struct. type field struct { name string nameBytes []byte // []byte(name) tag bool index []int typ reflect.Type omitEmpty bool quoted bool } func fillField(f field) field { f.nameBytes = []byte(f.name) return f } // byName sorts field by name, breaking ties with depth, // then breaking ties with "name came from json tag", then // breaking ties with index sequence. type byName []field func (x byName) Len() int { return len(x) } func (x byName) Swap(i, j int) { x[i], x[j] = x[j], x[i] } func (x byName) Less(i, j int) bool { if x[i].name != x[j].name { return x[i].name < x[j].name } if len(x[i].index) != len(x[j].index) { return len(x[i].index) < len(x[j].index) } if x[i].tag != x[j].tag { return x[i].tag } return byIndex(x).Less(i, j) } // byIndex sorts field by index sequence. type byIndex []field func (x byIndex) Len() int { return len(x) } func (x byIndex) Swap(i, j int) { x[i], x[j] = x[j], x[i] } func (x byIndex) Less(i, j int) bool { for k, xik := range x[i].index { if k >= len(x[j].index) { return false } if xik != x[j].index[k] { return xik < x[j].index[k] } } return len(x[i].index) < len(x[j].index) } // typeFields returns a list of fields that JSON should recognize for the given type. // The algorithm is breadth-first search over the set of structs to include - the top struct // and then any reachable anonymous structs. func typeFields(t reflect.Type) []field { // Anonymous fields to explore at the current level and the next. current := []field{} next := []field{{typ: t}} // Count of queued names for current level and the next. count := map[reflect.Type]int{} nextCount := map[reflect.Type]int{} // Types already visited at an earlier level. visited := map[reflect.Type]bool{} // Fields found. var fields []field for len(next) > 0 { current, next = next, current[:0] count, nextCount = nextCount, map[reflect.Type]int{} for _, f := range current { if visited[f.typ] { continue } visited[f.typ] = true // Scan f.typ for fields to include. for i := 0; i < f.typ.NumField(); i++ { sf := f.typ.Field(i) if sf.PkgPath != "" && !sf.Anonymous { // unexported continue } tag := sf.Tag.Get("json") if tag == "-" { continue } name, opts := parseTag(tag) if !isValidTag(name) { name = "" } index := make([]int, len(f.index)+1) copy(index, f.index) index[len(f.index)] = i ft := sf.Type if ft.Name() == "" && ft.Kind() == reflect.Ptr { // Follow pointer. ft = ft.Elem() } // Only strings, floats, integers, and booleans can be quoted. quoted := false if opts.Contains("string") { switch ft.Kind() { case reflect.Bool, reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64, reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Float32, reflect.Float64, reflect.String: quoted = true } } // Record found field and index sequence. if name != "" || !sf.Anonymous || ft.Kind() != reflect.Struct { tagged := name != "" if name == "" { name = sf.Name } fields = append(fields, fillField(field{ name: name, tag: tagged, index: index, typ: ft, omitEmpty: opts.Contains("omitempty"), quoted: quoted, })) if count[f.typ] > 1 { // If there were multiple instances, add a second, // so that the annihilation code will see a duplicate. // It only cares about the distinction between 1 or 2, // so don't bother generating any more copies. fields = append(fields, fields[len(fields)-1]) } continue } // Record new anonymous struct to explore in next round. nextCount[ft]++ if nextCount[ft] == 1 { next = append(next, fillField(field{name: ft.Name(), index: index, typ: ft})) } } } } sort.Sort(byName(fields)) // Delete all fields that are hidden by the Go rules for embedded fields, // except that fields with JSON tags are promoted. // The fields are sorted in primary order of name, secondary order // of field index length. Loop over names; for each name, delete // hidden fields by choosing the one dominant field that survives. out := fields[:0] for advance, i := 0, 0; i < len(fields); i += advance { // One iteration per name. // Find the sequence of fields with the name of this first field. fi := fields[i] name := fi.name for advance = 1; i+advance < len(fields); advance++ { fj := fields[i+advance] if fj.name != name { break } } if advance == 1 { // Only one field with this name out = append(out, fi) continue } dominant, ok := dominantField(fields[i : i+advance]) if ok { out = append(out, dominant) } } fields = out sort.Sort(byIndex(fields)) return fields } // dominantField looks through the fields, all of which are known to // have the same name, to find the single field that dominates the // others using Go's embedding rules, modified by the presence of // JSON tags. If there are multiple top-level fields, the boolean // will be false: This condition is an error in Go and we skip all // the fields. func dominantField(fields []field) (field, bool) { // The fields are sorted in increasing index-length order. The winner // must therefore be one with the shortest index length. Drop all // longer entries, which is easy: just truncate the slice. length := len(fields[0].index) tagged := -1 // Index of first tagged field. for i, f := range fields { if len(f.index) > length { fields = fields[:i] break } if f.tag { if tagged >= 0 { // Multiple tagged fields at the same level: conflict. // Return no field. return field{}, false } tagged = i } } if tagged >= 0 { return fields[tagged], true } // All remaining fields have the same length. If there's more than one, // we have a conflict (two fields named "X" at the same level) and we // return no field. if len(fields) > 1 { return field{}, false } return fields[0], true } var fieldCache struct { sync.RWMutex m map[reflect.Type][]field } // cachedTypeFields is like typeFields but uses a cache to avoid repeated work. func cachedTypeFields(t reflect.Type) []field { fieldCache.RLock() f := fieldCache.m[t] fieldCache.RUnlock() if f != nil { return f } // Compute fields without lock. // Might duplicate effort but won't hold other computations back. f = typeFields(t) if f == nil { f = []field{} } fieldCache.Lock() if fieldCache.m == nil { fieldCache.m = map[reflect.Type][]field{} } fieldCache.m[t] = f fieldCache.Unlock() return f }