funcCompact¶

func Compact(dst *bytes.Buffer, src []byte)error

Compact appends to dst the JSON-encoded src withinsignificant space characters elided.

funcHTMLEscape¶

func HTMLEscape(dst *bytes.Buffer, src []byte)

HTMLEscape appends to dst the JSON-encoded src with <, >, &, U+2028 and U+2029characters inside string literals changed to \u003c, \u003e, \u0026, \u2028, \u2029so that the JSON will be safe to embed inside HTML <script> tags.For historical reasons, web browsers don't honor standard HTMLescaping within <script> tags, so an alternative JSON encoding must be used.

package mainimport ("bytes""encoding/json""os")func main() {var out bytes.Bufferjson.HTMLEscape(&out, []byte(`{"Name":"<b>HTML content</b>"}`))out.WriteTo(os.Stdout)}

Output:{"Name":"\u003cb\u003eHTML content\u003c/b\u003e"}

funcIndent¶

func Indent(dst *bytes.Buffer, src []byte, prefix, indentstring)error

Indent appends to dst an indented form of the JSON-encoded src.Each element in a JSON object or array begins on a new,indented line beginning with prefix followed by one or morecopies of indent according to the indentation nesting.The data appended to dst does not begin with the prefix norany indentation, to make it easier to embed inside other formatted JSON data.Although leading space characters (space, tab, carriage return, newline)at the beginning of src are dropped, trailing space charactersat the end of src are preserved and copied to dst.For example, if src has no trailing spaces, neither will dst;if src ends in a trailing newline, so will dst.

package mainimport ("bytes""encoding/json""log""os")func main() {type Road struct {Name   stringNumber int}roads := []Road{{"Diamond Fork", 29},{"Sheep Creek", 51},}b, err := json.Marshal(roads)if err != nil {log.Fatal(err)}var out bytes.Bufferjson.Indent(&out, b, "=", "\t")out.WriteTo(os.Stdout)}

Output:[={="Name": "Diamond Fork",="Number": 29=},={="Name": "Sheep Creek",="Number": 51=}=]

funcMarshal¶

func Marshal(vany) ([]byte,error)

Marshal returns the JSON encoding of v.

Marshal traverses the value v recursively.If an encountered value implementsMarshalerand is not a nil pointer, Marshal calls [Marshaler.MarshalJSON]to produce JSON. If no [Marshaler.MarshalJSON] method is present but thevalue implementsencoding.TextMarshaler instead, Marshal callsencoding.TextMarshaler.MarshalText and encodes the result as a JSON string.The nil pointer exception is not strictly necessarybut mimics a similar, necessary exception in the behavior of[Unmarshaler.UnmarshalJSON].

Otherwise, Marshal uses the following type-dependent default encodings:

Boolean values encode as JSON booleans.

Floating point, integer, andNumber values encode as JSON numbers.NaN and +/-Inf values will return anUnsupportedValueError.

String values encode as JSON strings coerced to valid UTF-8,replacing invalid bytes with the Unicode replacement rune.So that the JSON will be safe to embed inside HTML <script> tags,the string is encoded usingHTMLEscape,which replaces "<", ">", "&", U+2028, and U+2029 are escapedto "\u003c","\u003e", "\u0026", "\u2028", and "\u2029".This replacement can be disabled when using anEncoder,by callingEncoder.SetEscapeHTML(false).

Array and slice values encode as JSON arrays, except that[]byte encodes as a base64-encoded string, and a nil sliceencodes as the null JSON value.

Struct values encode as JSON objects.Each exported struct field becomes a member of the object, using thefield name as the object key, unless the field is omitted for one of thereasons given below.

The encoding of each struct field can be customized by the format stringstored under the "json" key in the struct field's tag.The format string gives the name of the field, possibly followed by acomma-separated list of options. The name may be empty in order tospecify options without overriding the default field name.

The "omitempty" option specifies that the field should be omittedfrom the encoding if the field has an empty value, defined asfalse, 0, a nil pointer, a nil interface value, and any array,slice, map, or string of length zero.

As a special case, if the field tag is "-", the field is always omitted.Note that a field with name "-" can still be generated using the tag "-,".

Examples of struct field tags and their meanings:

// 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"`// Field is ignored by this package.Field int `json:"-"`// Field appears in JSON as key "-".Field int `json:"-,"`

The "omitzero" option specifies that the field should be omittedfrom the encoding if the field has a zero value, according to rules:

1) If the field type has an "IsZero() bool" method, that will be used todetermine whether the value is zero.

2) Otherwise, the value is zero if it is the zero value for its type.

If both "omitempty" and "omitzero" are specified, the field will be omittedif the value is either empty or zero (or both).

The "string" option signals that a field is stored as JSON inside aJSON-encoded string. It applies only to fields of string, floating point,integer, or boolean types. This extra level of encoding is sometimes usedwhen communicating with JavaScript programs:

Int64String int64 `json:",string"`

The key name will be used if it's a non-empty string consisting ofonly Unicode letters, digits, and ASCII punctuation except quotationmarks, backslash, and comma.

Embedded struct fields are usually marshaled as if their inner exported fieldswere fields in the outer struct, subject to the usual Go visibility rules amendedas described in the next paragraph.An anonymous struct field with a name given in its JSON tag is treated ashaving that name, rather than being anonymous.An anonymous struct field of interface type is treated the same as havingthat type as its name, rather than being anonymous.

The Go visibility rules for struct fields are amended for JSON whendeciding which field to marshal or unmarshal. If there aremultiple fields at the same level, and that level is the leastnested (and would therefore be the nesting level selected by theusual 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 ofan anonymous struct field in both current and earlier versions, give the fielda JSON tag of "-".

Map values encode as JSON objects. The map's key type must either be astring, an integer type, or implementencoding.TextMarshaler. The map keysare sorted and used as JSON object keys by applying the following rules,subject to the UTF-8 coercion described for string values above:

• keys of any string type are used directly
• keys that implementencoding.TextMarshaler are marshaled
• integer keys are converted to strings

Pointer values encode as the value pointed to.A nil pointer encodes as the null JSON value.

Interface values encode as the value contained in the interface.A nil interface value encodes as the null JSON value.

Channel, complex, and function values cannot be encoded in JSON.Attempting to encode such a value causes Marshal to returnanUnsupportedTypeError.

JSON cannot represent cyclic data structures and Marshal does nothandle them. Passing cyclic structures to Marshal will result inan error.

package mainimport ("encoding/json""fmt""os")func main() {type ColorGroup struct {ID     intName   stringColors []string}group := ColorGroup{ID:     1,Name:   "Reds",Colors: []string{"Crimson", "Red", "Ruby", "Maroon"},}b, err := json.Marshal(group)if err != nil {fmt.Println("error:", err)}os.Stdout.Write(b)}

Output:{"ID":1,"Name":"Reds","Colors":["Crimson","Red","Ruby","Maroon"]}

funcMarshalIndent¶

func MarshalIndent(vany, prefix, indentstring) ([]byte,error)

MarshalIndent is likeMarshal but appliesIndent to format the output.Each JSON element in the output will begin on a new line beginning with prefixfollowed by one or more copies of indent according to the indentation nesting.

package mainimport ("encoding/json""fmt""log")func main() {data := map[string]int{"a": 1,"b": 2,}b, err := json.MarshalIndent(data, "<prefix>", "<indent>")if err != nil {log.Fatal(err)}fmt.Println(string(b))}

Output:{<prefix><indent>"a": 1,<prefix><indent>"b": 2<prefix>}

funcUnmarshal¶

func Unmarshal(data []byte, vany)error

Unmarshal parses the JSON-encoded data and stores the resultin the value pointed to by v. If v is nil or not a pointer,Unmarshal returns anInvalidUnmarshalError.

Unmarshal uses the inverse of the encodings thatMarshal uses, allocating maps, slices, and pointers as necessary,with the following additional rules:

To unmarshal JSON into a pointer, Unmarshal first handles the case ofthe JSON being the JSON literal null. In that case, Unmarshal setsthe pointer to nil. Otherwise, Unmarshal unmarshals the JSON intothe value pointed at by the pointer. If the pointer is nil, Unmarshalallocates a new value for it to point to.

To unmarshal JSON into a value implementingUnmarshaler,Unmarshal calls that value's [Unmarshaler.UnmarshalJSON] method, includingwhen the input is a JSON null.Otherwise, if the value implementsencoding.TextUnmarshalerand the input is a JSON quoted string, Unmarshal callsencoding.TextUnmarshaler.UnmarshalText with the unquoted form of the string.

To unmarshal JSON into a struct, Unmarshal matches incoming object keys tothe keys used byMarshal (either the struct field name or its tag),ignoring case. If multiple struct fields match an object key, an exact casematch is preferred over a case-insensitive one.

Incoming object members are processed in the order observed. If an objectincludes duplicate keys, later duplicates will replace or be merged intoprior values.

To unmarshal JSON into an interface value,Unmarshal stores one of these in the interface value:

• bool, for JSON booleans
• float64, for JSON numbers
• string, for JSON strings
• []any, for JSON arrays
• map[string]any, for JSON objects
• nil for JSON null

To unmarshal a JSON array into a slice, Unmarshal resets the slice lengthto zero and then appends each element to the slice.As a special case, to unmarshal an empty JSON array into a slice,Unmarshal replaces the slice with a new empty slice.

To unmarshal a JSON array into a Go array, Unmarshal decodesJSON array elements into corresponding Go array elements.If the Go array is smaller than the JSON array,the additional JSON array elements are discarded.If the JSON array is smaller than the Go array,the additional Go array elements are set to zero values.

To unmarshal a JSON object into a map, Unmarshal first establishes a map touse. If the map is nil, Unmarshal allocates a new map. Otherwise Unmarshalreuses the existing map, keeping existing entries. Unmarshal then storeskey-value pairs from the JSON object into the map. The map's key type musteither be any string type, an integer, or implementencoding.TextUnmarshaler.

If the JSON-encoded data contain a syntax error, Unmarshal returns aSyntaxError.

If a JSON value is not appropriate for a given target type,or if a JSON number overflows the target type, Unmarshalskips that field and completes the unmarshaling as best it can.If no more serious errors are encountered, Unmarshal returnsanUnmarshalTypeError describing the earliest such error. In anycase, it's not guaranteed that all the remaining fields followingthe problematic one will be unmarshaled into the target object.

The JSON null value unmarshals into an interface, map, pointer, or sliceby setting that Go value to nil. Because null is often used in JSON to mean“not present,” unmarshaling a JSON null into any other Go type has no effecton the value and produces no error.

When unmarshaling quoted strings, invalid UTF-8 orinvalid UTF-16 surrogate pairs are not treated as an error.Instead, they are replaced by the Unicode replacementcharacter U+FFFD.

package mainimport ("encoding/json""fmt")func main() {var jsonBlob = []byte(`[{"Name": "Platypus", "Order": "Monotremata"},{"Name": "Quoll",    "Order": "Dasyuromorphia"}]`)type Animal struct {Name  stringOrder string}var animals []Animalerr := json.Unmarshal(jsonBlob, &animals)if err != nil {fmt.Println("error:", err)}fmt.Printf("%+v", animals)}

Output:[{Name:Platypus Order:Monotremata} {Name:Quoll Order:Dasyuromorphia}]

funcValid¶added ingo1.9

func Valid(data []byte)bool

Valid reports whether data is a valid JSON encoding.

package mainimport ("encoding/json""fmt")func main() {goodJSON := `{"example": 1}`badJSON := `{"example":2:]}}`fmt.Println(json.Valid([]byte(goodJSON)), json.Valid([]byte(badJSON)))}

Output:true false

typeDecoder¶

type Decoder struct {// contains filtered or unexported fields}

A Decoder reads and decodes JSON values from an input stream.

package mainimport ("encoding/json""fmt""io""log""strings")func main() {const jsonStream = `{"Name": "Ed", "Text": "Knock knock."}{"Name": "Sam", "Text": "Who's there?"}{"Name": "Ed", "Text": "Go fmt."}{"Name": "Sam", "Text": "Go fmt who?"}{"Name": "Ed", "Text": "Go fmt yourself!"}`type Message struct {Name, Text string}dec := json.NewDecoder(strings.NewReader(jsonStream))for {var m Messageif err := dec.Decode(&m); err == io.EOF {break} else if err != nil {log.Fatal(err)}fmt.Printf("%s: %s\n", m.Name, m.Text)}}

Output:Ed: Knock knock.Sam: Who's there?Ed: Go fmt.Sam: Go fmt who?Ed: Go fmt yourself!

func NewDecoder(rio.Reader) *Decoder

func (dec *Decoder) Buffered()io.Reader

func (dec *Decoder) Decode(vany)error

package mainimport ("encoding/json""fmt""log""strings")func main() {const jsonStream = `[{"Name": "Ed", "Text": "Knock knock."},{"Name": "Sam", "Text": "Who's there?"},{"Name": "Ed", "Text": "Go fmt."},{"Name": "Sam", "Text": "Go fmt who?"},{"Name": "Ed", "Text": "Go fmt yourself!"}]`type Message struct {Name, Text string}dec := json.NewDecoder(strings.NewReader(jsonStream))// read open brackett, err := dec.Token()if err != nil {log.Fatal(err)}fmt.Printf("%T: %v\n", t, t)// while the array contains valuesfor dec.More() {var m Message// decode an array value (Message)err := dec.Decode(&m)if err != nil {log.Fatal(err)}fmt.Printf("%v: %v\n", m.Name, m.Text)}// read closing brackett, err = dec.Token()if err != nil {log.Fatal(err)}fmt.Printf("%T: %v\n", t, t)}

Output:json.Delim: [Ed: Knock knock.Sam: Who's there?Ed: Go fmt.Sam: Go fmt who?Ed: Go fmt yourself!json.Delim: ]

func (dec *Decoder) DisallowUnknownFields()

func (dec *Decoder) InputOffset()int64

func (dec *Decoder) More()bool

func (dec *Decoder) Token() (Token,error)

package mainimport ("encoding/json""fmt""io""log""strings")func main() {const jsonStream = `{"Message": "Hello", "Array": [1, 2, 3], "Null": null, "Number": 1.234}`dec := json.NewDecoder(strings.NewReader(jsonStream))for {t, err := dec.Token()if err == io.EOF {break}if err != nil {log.Fatal(err)}fmt.Printf("%T: %v", t, t)if dec.More() {fmt.Printf(" (more)")}fmt.Printf("\n")}}

Output:json.Delim: { (more)string: Message (more)string: Hello (more)string: Array (more)json.Delim: [ (more)float64: 1 (more)float64: 2 (more)float64: 3json.Delim: ] (more)string: Null (more)<nil>: <nil> (more)string: Number (more)float64: 1.234json.Delim: }

func (dec *Decoder) UseNumber()

typeDelim¶added ingo1.5

type Delimrune

A Delim is a JSON array or object delimiter, one of [ ] { or }.

func (dDelim) String()string

typeEncoder¶

type Encoder struct {// contains filtered or unexported fields}

An Encoder writes JSON values to an output stream.

func NewEncoder(wio.Writer) *Encoder

func (enc *Encoder) Encode(vany)error

func (enc *Encoder) SetEscapeHTML(onbool)

func (enc *Encoder) SetIndent(prefix, indentstring)

typeInvalidUnmarshalError¶

type InvalidUnmarshalError struct {Typereflect.Type}

An InvalidUnmarshalError describes an invalid argument passed toUnmarshal.(The argument toUnmarshal must be a non-nil pointer.)

func (e *InvalidUnmarshalError) Error()string

typeMarshaler¶

type Marshaler interface {MarshalJSON() ([]byte,error)}

Marshaler is the interface implemented by types thatcan marshal themselves into valid JSON.

typeMarshalerError¶

type MarshalerError struct {Typereflect.TypeErrerror// contains filtered or unexported fields}

A MarshalerError represents an error from calling a[Marshaler.MarshalJSON] orencoding.TextMarshaler.MarshalText method.

func (e *MarshalerError) Error()string

func (e *MarshalerError) Unwrap()error

typeNumber¶added ingo1.1

type Numberstring

A Number represents a JSON number literal.

func (nNumber) Float64() (float64,error)

func (nNumber) Int64() (int64,error)

func (nNumber) String()string

typeRawMessage¶

type RawMessage []byte

RawMessage is a raw encoded JSON value.It implementsMarshaler andUnmarshaler and canbe used to delay JSON decoding or precompute a JSON encoding.

package mainimport ("encoding/json""fmt""os")func main() {h := json.RawMessage(`{"precomputed": true}`)c := struct {Header *json.RawMessage `json:"header"`Body   string           `json:"body"`}{Header: &h, Body: "Hello Gophers!"}b, err := json.MarshalIndent(&c, "", "\t")if err != nil {fmt.Println("error:", err)}os.Stdout.Write(b)}

Output:{"header": {"precomputed": true},"body": "Hello Gophers!"}

package mainimport ("encoding/json""fmt""log")func main() {type Color struct {Space stringPoint json.RawMessage // delay parsing until we know the color space}type RGB struct {R uint8G uint8B uint8}type YCbCr struct {Y  uint8Cb int8Cr int8}var j = []byte(`[{"Space": "YCbCr", "Point": {"Y": 255, "Cb": 0, "Cr": -10}},{"Space": "RGB",   "Point": {"R": 98, "G": 218, "B": 255}}]`)var colors []Colorerr := json.Unmarshal(j, &colors)if err != nil {log.Fatalln("error:", err)}for _, c := range colors {var dst anyswitch c.Space {case "RGB":dst = new(RGB)case "YCbCr":dst = new(YCbCr)}err := json.Unmarshal(c.Point, dst)if err != nil {log.Fatalln("error:", err)}fmt.Println(c.Space, dst)}}

Output:YCbCr &{255 0 -10}RGB &{98 218 255}

func (mRawMessage) MarshalJSON() ([]byte,error)

func (m *RawMessage) UnmarshalJSON(data []byte)error

typeSyntaxError¶

type SyntaxError struct {Offsetint64// error occurred after reading Offset bytes// contains filtered or unexported fields}

A SyntaxError is a description of a JSON syntax error.Unmarshal will return a SyntaxError if the JSON can't be parsed.

func (e *SyntaxError) Error()string

typeToken¶added ingo1.5

type Tokenany

A Token holds a value of one of these types:

• Delim, for the four JSON delimiters [ ] { }
• bool, for JSON booleans
• float64, for JSON numbers
• Number, for JSON numbers
• string, for JSON string literals
• nil, for JSON null

typeUnmarshalTypeError¶

type UnmarshalTypeError struct {Valuestring// description of JSON value - "bool", "array", "number -5"Typereflect.Type// type of Go value it could not be assigned toOffsetint64// error occurred after reading Offset bytesStructstring// name of the struct type containing the fieldFieldstring// the full path from root node to the field, include embedded struct}

An UnmarshalTypeError describes a JSON value that wasnot appropriate for a value of a specific Go type.

func (e *UnmarshalTypeError) Error()string

typeUnmarshaler¶

type Unmarshaler interface {UnmarshalJSON([]byte)error}

Unmarshaler is the interface implemented by typesthat can unmarshal a JSON description of themselves.The input can be assumed to be a valid encoding ofa JSON value. UnmarshalJSON must copy the JSON dataif it wishes to retain the data after returning.

typeUnsupportedTypeError¶

type UnsupportedTypeError struct {Typereflect.Type}

An UnsupportedTypeError is returned byMarshal when attemptingto encode an unsupported value type.

func (e *UnsupportedTypeError) Error()string

typeUnsupportedValueError¶

type UnsupportedValueError struct {Valuereflect.ValueStrstring}

An UnsupportedValueError is returned byMarshal when attemptingto encode an unsupported value.

func (e *UnsupportedValueError) Error()string