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Package json

import "encoding/json"
Overview
Index
Examples

Overview ▾

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: http://golang.org/doc/articles/json_and_go.html

Index ▾

func Compact(dst *bytes.Buffer, src []byte) error
func HTMLEscape(dst *bytes.Buffer, src []byte)
func Indent(dst *bytes.Buffer, src []byte, prefix, indent string) error
func Marshal(v interface{}) ([]byte, error)
func MarshalIndent(v interface{}, prefix, indent string) ([]byte, error)
func Unmarshal(data []byte, v interface{}) error
type Decoder
    func NewDecoder(r io.Reader) *Decoder
    func (dec *Decoder) Buffered() io.Reader
    func (dec *Decoder) Decode(v interface{}) error
    func (dec *Decoder) UseNumber()
type Encoder
    func NewEncoder(w io.Writer) *Encoder
    func (enc *Encoder) Encode(v interface{}) error
type InvalidUTF8Error
    func (e *InvalidUTF8Error) Error() string
type InvalidUnmarshalError
    func (e *InvalidUnmarshalError) Error() string
type Marshaler
type MarshalerError
    func (e *MarshalerError) Error() string
type Number
    func (n Number) Float64() (float64, error)
    func (n Number) Int64() (int64, error)
    func (n Number) String() string
type RawMessage
    func (m *RawMessage) MarshalJSON() ([]byte, error)
    func (m *RawMessage) UnmarshalJSON(data []byte) error
type SyntaxError
    func (e *SyntaxError) Error() string
type UnmarshalFieldError
    func (e *UnmarshalFieldError) Error() string
type UnmarshalTypeError
    func (e *UnmarshalTypeError) Error() string
type Unmarshaler
type UnsupportedTypeError
    func (e *UnsupportedTypeError) Error() string
type UnsupportedValueError
    func (e *UnsupportedValueError) Error() string

Package files

decode.go encode.go fold.go indent.go scanner.go stream.go tags.go

func Compact

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

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

func HTMLEscape

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

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 Indent

func Indent(dst *bytes.Buffer, src []byte, prefix, indent string) 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 more copies of indent according to the indentation nesting. The data appended to dst does not begin with the prefix nor any indentation, and has no trailing newline, to make it easier to embed inside other formatted JSON data.

Example

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

func Marshal

func Marshal(v interface{}) ([]byte, error)

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. 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. InvalidUTF8Error will be returned if an invalid UTF-8 sequence is encountered. 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, or integer 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.

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 object keys are used directly as map keys.

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.

Example

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

func MarshalIndent

func MarshalIndent(v interface{}, prefix, indent string) ([]byte, error)

MarshalIndent is like Marshal but applies Indent to format the output.

func Unmarshal

func Unmarshal(data []byte, v interface{}) error

Unmarshal parses the JSON-encoded data and stores the result in the value pointed to by v.

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

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

To unmarshal JSON into a struct, Unmarshal matches incoming object keys to the keys used by Marshal (either the struct field name or its tag), preferring an exact match but also accepting a case-insensitive match.

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
[]interface{}, for JSON arrays
map[string]interface{}, for JSON objects
nil for JSON null

If a JSON value is not appropriate for a given target type, or if a JSON number overflows the target type, Unmarshal skips that field and completes the unmarshalling as best it can. If no more serious errors are encountered, Unmarshal returns an UnmarshalTypeError describing the earliest such error.

The JSON null value unmarshals into an interface, map, pointer, or slice by 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 effect on the value and produces no error.

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

Example

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

type Decoder

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

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

Example

This example uses a Decoder to decode a stream of distinct JSON values.

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

func NewDecoder

func NewDecoder(r io.Reader) *Decoder

NewDecoder returns a new decoder that reads from r.

The decoder introduces its own buffering and may read data from r beyond the JSON values requested.

func (*Decoder) Buffered

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

Buffered returns a reader of the data remaining in the Decoder's buffer. The reader is valid until the next call to Decode.

func (*Decoder) Decode

func (dec *Decoder) Decode(v interface{}) error

Decode reads the next JSON-encoded value from its input and stores it in the value pointed to by v.

See the documentation for Unmarshal for details about the conversion of JSON into a Go value.

func (*Decoder) UseNumber

func (dec *Decoder) UseNumber()

UseNumber causes the Decoder to unmarshal a number into an interface{} as a Number instead of as a float64.

type Encoder

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

An Encoder writes JSON objects to an output stream.

func NewEncoder

func NewEncoder(w io.Writer) *Encoder

NewEncoder returns a new encoder that writes to w.

func (*Encoder) Encode

func (enc *Encoder) Encode(v interface{}) error

Encode writes the JSON encoding of v to the stream, followed by a newline character.

See the documentation for Marshal for details about the conversion of Go values to JSON.

type InvalidUTF8Error

type InvalidUTF8Error struct {
        S string // the whole string value that caused the error
}

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.

func (*InvalidUTF8Error) Error

func (e *InvalidUTF8Error) Error() string

type InvalidUnmarshalError

type InvalidUnmarshalError struct {
        Type reflect.Type
}

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

func (*InvalidUnmarshalError) Error

func (e *InvalidUnmarshalError) Error() string

type Marshaler

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

Marshaler is the interface implemented by objects that can marshal themselves into valid JSON.

type MarshalerError

type MarshalerError struct {
        Type reflect.Type
        Err  error
}

func (*MarshalerError) Error

func (e *MarshalerError) Error() string

type Number

type Number string

A Number represents a JSON number literal.

func (Number) Float64

func (n Number) Float64() (float64, error)

Float64 returns the number as a float64.

func (Number) Int64

func (n Number) Int64() (int64, error)

Int64 returns the number as an int64.

func (Number) String

func (n Number) String() string

String returns the literal text of the number.

type RawMessage

type RawMessage []byte

RawMessage is a raw encoded JSON object. It implements Marshaler and Unmarshaler and can be used to delay JSON decoding or precompute a JSON encoding.

Example

This example uses RawMessage to delay parsing part of a JSON message.

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

func (*RawMessage) MarshalJSON

func (m *RawMessage) MarshalJSON() ([]byte, error)

MarshalJSON returns *m as the JSON encoding of m.

func (*RawMessage) UnmarshalJSON

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

UnmarshalJSON sets *m to a copy of data.

type SyntaxError

type SyntaxError struct {
        Offset int64 // error occurred after reading Offset bytes
        // contains filtered or unexported fields
}

A SyntaxError is a description of a JSON syntax error.

func (*SyntaxError) Error

func (e *SyntaxError) Error() string

type UnmarshalFieldError

type UnmarshalFieldError struct {
        Key   string
        Type  reflect.Type
        Field reflect.StructField
}

An UnmarshalFieldError describes a JSON object key that led to an unexported (and therefore unwritable) struct field. (No longer used; kept for compatibility.)

func (*UnmarshalFieldError) Error

func (e *UnmarshalFieldError) Error() string

type UnmarshalTypeError

type UnmarshalTypeError struct {
        Value string       // description of JSON value - "bool", "array", "number -5"
        Type  reflect.Type // type of Go value it could not be assigned to
}

An UnmarshalTypeError describes a JSON value that was not appropriate for a value of a specific Go type.

func (*UnmarshalTypeError) Error

func (e *UnmarshalTypeError) Error() string

type Unmarshaler

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

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

type UnsupportedTypeError

type UnsupportedTypeError struct {
        Type reflect.Type
}

An UnsupportedTypeError is returned by Marshal when attempting to encode an unsupported value type.

func (*UnsupportedTypeError) Error

func (e *UnsupportedTypeError) Error() string

type UnsupportedValueError

type UnsupportedValueError struct {
        Value reflect.Value
        Str   string
}

func (*UnsupportedValueError) Error

func (e *UnsupportedValueError) Error() string