jsonx

package module
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 Go to latest Published: Jan 24, 2020 License: BSD-3-Clause Imports: 15 Imported by: 0

README

jsonx

jsonx is an improved fork of the go standard library json package.

Features

Configurable field naming convention

Instead of struct tags, jsonx lets you specify a function that is applied to all field names automatically:

json := jsonx.New(jsonx.KeyEncodeFn(func(s string) string {
	r, z := utf8.DecodeRuneInString(s)
	return string(unicode.ToLower(r)) + s[z:]
}))

b, _ := json.Marshal(struct{
	FirstName string
	LastName  string
	Email     string
}{
	FirstName: "John",
	LastName:  "Doe",
	Email:     "jdoe@example.com",
})
fmt.Println(string(b))
// {"firstName":"John","lastName":"Doe","email":"jdoe@example.com"}
OmitEmpty

Instead of using the omitempty struct tag on all your fields, you can configure the json encoder to omit empty fields globally or for a single Marshal call:

user := struct {
	FirstName string
	LastName  string
	Email     string
	Nickname  string
}{
	FirstName: "John",
	LastName:  "Doe",
	Email:     "jdoe@example.com",
}
b, _ := jsonx.OmitEmpty().Marshal(user)
fmt.Println(string(b))
// {"FirstName":"John","LastName":"Doe","Email":"jdoe@example.com"}

// alternatively, with a JSON instance
json := jsonx.New(jsonx.KeyEncodeFn(func(s string) string {
	r, z := utf8.DecodeRuneInString(s)
	return string(unicode.ToLower(r)) + s[z:]
}))
b, _ = json.OmitEmpty().Marshal(user)
fmt.Println(string(b))
// {"firstName":"John","lastName":"Doe","email":"jdoe@example.com"}
Better API

If you want to unmarshal numbers as json.Number instead of float64 or if you want to get an error in case the json input contains a field that is not present in the destination struct, you have to create a json.Decoder and set its options. Aside from forcing you to use a different API using io.Reader, json.Decoder is designed for JSON streams, not single JSON objects.

jsonx allows you to set these options for Marshal and Unmarshal:

var v interface{}
jsonx.UseNumber().Unmarshal([]byte("2"), &v)
fmt.Printf("%T %[1]v\n", v)
// json.Number 2

var t struct{
	Foo int
}
err := jsonx.DisallowUnknownFields().Unmarshal([]byte(`{"foo": 1, "bar": 2}`), &t)
fmt.Println(err)
// json: unknown field "bar"
Compatibility

jsonx is not meant as a full replacement to encoding/json. It reuses as much of encoding/json as it can, including types such as json.Number and json.RawMessage, and does not duplicate json.Compact, json.Indent, json.Valid and json.HTMLEscape.

All errors are the same as encoding/json except json.SyntaxError and json.MarshalerError, which had unexported fields. jsonx uses jsonx.SyntaxError and jsonx.MarshalerError instead.

jsonx respects json struct tags, which can override both the key encoding function and OmitEmpty.

jsonx also respects UnmarshalJSON, MarshalJSON, UnmarshalText and MarshalText, but note that it cannot control what happens in those. Passing down options to a type's own Marshal or Unmarshal method is a complicated problem, and one that this package does not try to solve.

FAQ

Why yet another json package?

Most of the world uses camelCase or snake_case field names in JSON. Go defaults to PascalCase as a side effect of exported identifiers, and makes it difficult to use something else, forcing you to litter your code with struct tags, which make your code less readable and harder to maintain. The Go developers' suggestion is to fork off or use a tool to automatically litter your code with struct tags (which isn't really a solution). Hence this fork.

What about performance?

The standard library encoding/json package uses an internal cache of types, so it only needs to figure out how to encode a type once. This fork keeps that cache, but to fully benefit from it, you have to reuse the same JSON instance (or use the package-level functions, which are forwarded to a default instance). Methods like OmitEmpty create a new instance that shares the original's cache, so the performance impact of using those is minimal, but you can also reuse that instance to eliminate the overhead.

Performance is nearly identical to encoding/json, but slower than some of the fastest alternatives. See benchmarks.

Benchmarks

Benchmarks taken from jettison. Jettison encodes into a byte buffer to avoid allocating a byte slice, so the jsonx benchmarks include one with Marshal and one with Encoder.Encode.

BenchmarkSimplePayload

package time/op throughput bytes allocs
encoding/json 566ns ± 1% 239MB/s ± 1% 144 B/op 1 allocs/op
jsonx 566ns ± 0% 238MB/s ± 0% 144 B/op 1 allocs/op
jsonx encoder 529ns ± 0% 257MB/s ± 0% 0 B/op 0 allocs/op
jsoniter 598ns ± 1% 226MB/s ± 1% 152 B/op 2 allocs/op
gojay 375ns ± 2% 360MB/s ± 2% 512 B/op 1 allocs/op
jettison 459ns ± 1% 294MB/s ± 1% 0 B/op 0 allocs/op
jettison NoUTF8Coercion NoHTMLEscaping 397ns ± 0% 340MB/s ± 0% 0 B/op 0 allocs/op

BenchmarkComplexPayload

package time/op throughput bytes allocs
encoding/json 2170ns ± 1% 178MB/s ± 1% 416 B/op 1 allocs/op
jsonx 2200ns ± 1% 176MB/s ± 1% 416 B/op 1 allocs/op
jsonx encoder 2120ns ± 1% 183MB/s ± 1% 0 B/op 0 allocs/op
jsoniter 2010ns ± 1% 192MB/s ± 1% 472 B/op 3 allocs/op
jettison 1390ns ± 0% 279MB/s ± 0% 0 B/op 0 allocs/op

BenchmarkInterface

package time/op throughput bytes allocs
encoding/json 149ns ± 1% 53.5MB/s ± 2% 8 B/op 1 allocs/op
jsonx 152ns ± 0% 52.6MB/s ± 0% 8 B/op 1 allocs/op
jsonx encoder 130ns ± 0% 69.0MB/s ± 1% 0 B/op 0 allocs/op
jsoniter 131ns ± 5% 61.0MB/s ± 5% 8 B/op 1 allocs/op
jettison 65.3ns ± 1% 123MB/s ± 1% 0 B/op 0 allocs/op

BenchmarkMap

package time/op throughput bytes allocs
encoding/json 1030ns ± 2% 18.3MB/s ± 5% 536 B/op 13 allocs/op
jsonx 1030ns ± 2% 18.4MB/s ± 2% 536 B/op 13 allocs/op
jsonx encoder 1020ns ± 1% 19.6MB/s ± 1% 504 B/op 12 allocs/op
jsoniter 941ns ± 3% 20.2MB/s ± 3% 680 B/op 11 allocs/op
jettison sort 782ns ± 5% 24.3MB/s ± 5% 496 B/op 6 allocs/op
jettison nosort 328ns ± 2% 58.0MB/s ± 2% 128 B/op 2 allocs/op

Documentation

Overview

Package jsonx implements encoding and decoding of JSON as defined in RFC 7159. The mapping between JSON 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

Example (CustomMarshalJSON) 
package main

import (
	"fmt"
	"log"
	"strings"

	"github.com/nkovacs/jsonx"
)

type Animal int

const (
	Unknown Animal = iota
	Gopher
	Zebra
)

func (a *Animal) UnmarshalJSON(b []byte) error {
	var s string
	if err := jsonx.Unmarshal(b, &s); err != nil {
		return err
	}
	switch strings.ToLower(s) {
	default:
		*a = Unknown
	case "gopher":
		*a = Gopher
	case "zebra":
		*a = Zebra
	}

	return nil
}

func (a Animal) MarshalJSON() ([]byte, error) {
	var s string
	switch a {
	default:
		s = "unknown"
	case Gopher:
		s = "gopher"
	case Zebra:
		s = "zebra"
	}

	return jsonx.Marshal(s)
}

func main() {
	blob := `["gopher","armadillo","zebra","unknown","gopher","bee","gopher","zebra"]`
	var zoo []Animal
	if err := jsonx.Unmarshal([]byte(blob), &zoo); err != nil {
		log.Fatal(err)
	}

	census := make(map[Animal]int)
	for _, animal := range zoo {
		census[animal] += 1
	}

	fmt.Printf("Zoo Census:\n* Gophers: %d\n* Zebras:  %d\n* Unknown: %d\n",
		census[Gopher], census[Zebra], census[Unknown])

}

Output:

Zoo Census:
* Gophers: 3
* Zebras:  2
* Unknown: 3
Example (TextMarshalJSON) 
package main

import (
	"fmt"
	"log"
	"strings"

	"github.com/nkovacs/jsonx"
)

type Size int

const (
	Unrecognized Size = iota
	Small
	Large
)

func (s *Size) UnmarshalText(text []byte) error {
	switch strings.ToLower(string(text)) {
	default:
		*s = Unrecognized
	case "small":
		*s = Small
	case "large":
		*s = Large
	}
	return nil
}

func (s Size) MarshalText() ([]byte, error) {
	var name string
	switch s {
	default:
		name = "unrecognized"
	case Small:
		name = "small"
	case Large:
		name = "large"
	}
	return []byte(name), nil
}

func main() {
	blob := `["small","regular","large","unrecognized","small","normal","small","large"]`
	var inventory []Size
	if err := jsonx.Unmarshal([]byte(blob), &inventory); err != nil {
		log.Fatal(err)
	}

	counts := make(map[Size]int)
	for _, size := range inventory {
		counts[size] += 1
	}

	fmt.Printf("Inventory Counts:\n* Small:        %d\n* Large:        %d\n* Unrecognized: %d\n",
		counts[Small], counts[Large], counts[Unrecognized])

}

Output:

Inventory Counts:
* Small:        3
* Large:        2
* Unrecognized: 3

Index

Examples

Constants

This section is empty.

Variables

This section is empty.

Functions

func Marshal 

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

Marshal returns the JSON encoding of v using the default JSON encoder.

Example 
package main

import (
	"fmt"
	"os"

	"github.com/nkovacs/jsonx"
)

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

Output:

{"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. Each JSON element in the output will begin on a new line beginning with prefix followed by one or more copies of indent according to the indentation nesting.

Example 
package main

import (
	"fmt"
	"log"

	"github.com/nkovacs/jsonx"
)

func main() {
	data := map[string]int{
		"a": 1,
		"b": 2,
	}

	json, err := jsonx.MarshalIndent(data, "<prefix>", "<indent>")
	if err != nil {
		log.Fatal(err)
	}

	fmt.Println(string(json))
}

Output:

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

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 using the default JSON decoder.

Example 
package main

import (
	"fmt"

	"github.com/nkovacs/jsonx"
)

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

Output:

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

Types

type Decoder 

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

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

Example

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

package main

import (
	"fmt"
	"io"
	"log"
	"strings"

	"github.com/nkovacs/jsonx"
)

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 := jsonx.NewDecoder(strings.NewReader(jsonStream))
	for {
		var m Message
		if 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 

func NewDecoder(r io.Reader) *Decoder

NewDecoder returns a new decoder that reads from r using the default JSON encoder/decoder.

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.

Example (Stream)

This example uses a Decoder to decode a streaming array of JSON objects. 

package main

import (
	"fmt"
	"log"
	"strings"

	"github.com/nkovacs/jsonx"
)

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 := jsonx.NewDecoder(strings.NewReader(jsonStream))

	// read open bracket
	t, err := dec.Token()
	if err != nil {
		log.Fatal(err)
	}
	fmt.Printf("%T: %v\n", t, t)

	// while the array contains values
	for 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 bracket
	t, 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 (*Decoder) DisallowUnknownFields 

func (dec *Decoder) DisallowUnknownFields()

DisallowUnknownFields causes the Decoder to return an error when the destination is a struct and the input contains object keys which do not match any non-ignored, exported fields in the destination.

func (*Decoder) InputOffset added in v0.2.0 

func (dec *Decoder) InputOffset() int64

InputOffset returns the input stream byte offset of the current decoder position. The offset gives the location of the end of the most recently returned token and the beginning of the next token.

func (*Decoder) More 

func (dec *Decoder) More() bool

More reports whether there is another element in the current array or object being parsed.

func (*Decoder) Token 

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

Token returns the next JSON token in the input stream. At the end of the input stream, Token returns nil, io.EOF.

Token guarantees that the delimiters [ ] { } it returns are properly nested and matched: if Token encounters an unexpected delimiter in the input, it will return an error.

The input stream consists of basic JSON values—bool, string, number, and null—along with delimiters [ ] { } of type Delim to mark the start and end of arrays and objects. Commas and colons are elided.

Example

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

package main

import (
	"fmt"
	"io"
	"log"
	"strings"

	"github.com/nkovacs/jsonx"
)

func main() {
	const jsonStream = `
	{"Message": "Hello", "Array": [1, 2, 3], "Null": null, "Number": 1.234}
`
	dec := jsonx.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: 3
json.Delim: ] (more)
string: Null (more)
<nil>: <nil> (more)
string: Number (more)
float64: 1.234
json.Delim: }

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 values to an output stream.

func NewEncoder 

func NewEncoder(w io.Writer) *Encoder

NewEncoder returns a new encoder that writes to w using the default JSON encoder/decoder.

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.

func (*Encoder) SetEscapeHTML 

func (enc *Encoder) SetEscapeHTML(on bool)

SetEscapeHTML specifies whether problematic HTML characters should be escaped inside JSON quoted strings. The default behavior is to escape &, <, and > to \u0026, \u003c, and \u003e to avoid certain safety problems that can arise when embedding JSON in HTML.

In non-HTML settings where the escaping interferes with the readability of the output, SetEscapeHTML(false) disables this behavior.

func (*Encoder) SetIndent 

func (enc *Encoder) SetIndent(prefix, indent string)

SetIndent instructs the encoder to format each subsequent encoded value as if indented by the package-level function Indent(dst, src, prefix, indent). Calling SetIndent("", "") disables indentation.

type JSON 

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

JSON is a json encoder/decoder. It is safe for concurrent use by multiple goroutines.

func DisallowUnknownFields 

func DisallowUnknownFields() *JSON

DisallowUnknownFields causes the decoder to return an error when the destination is a struct and the input contains object keys which do not match any non-ignored, exported fields in the destination. It returns a copy of the default JSON encoder/decoder, sharing its cache.

func New 

func New(opts ...Option) *JSON

New creates a new JSON encoder/decoder.

The encoder has an internal cache, so it should be reused for best performance. Changing the key encoding function is not possible because it would require invalidating the cache.

func OmitEmpty 

func OmitEmpty() *JSON

OmitEmpty specifies that fields with an empty value should be omitted from encoding. It returns a copy of the default JSON encoder/decoder, sharing its cache.

func UseNumber 

func UseNumber() *JSON

UseNumber causes the decoder to unmarshal a number into an interface{} as a json.Number instead of as a float64. It returns a copy of the default JSON encoder/decoder, sharing its cache.

func (*JSON) DisallowUnknownFields 

func (j *JSON) DisallowUnknownFields() *JSON

DisallowUnknownFields causes the decoder to return an error when the destination is a struct and the input contains object keys which do not match any non-ignored, exported fields in the destination. It returns a copy of the original JSON encoder/decoder, sharing its cache.

func (*JSON) EscapeHTML 

func (j *JSON) EscapeHTML(on bool) *JSON

EscapeHTML specifies whether problematic HTML characters should be escaped inside JSON quoted strings. The default behavior is to escape &, <, and > to \u0026, \u003c, and \u003e to avoid certain safety problems that can arise when embedding JSON in HTML.

In non-HTML settings where the escaping interferes with the readability of the output, EscapeHTML(false) disables this behavior. It returns a copy of the original JSON encoder/decoder, sharing its cache.

func (*JSON) Marshal 

func (c *JSON) 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. If no MarshalJSON method is present but the value implements encoding.TextMarshaler instead, Marshal calls its MarshalText method and encodes the result as a JSON string. 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. So that the JSON will be safe to embed inside HTML <script> tags, the string is encoded using HTMLEscape, which replaces "<", ">", "&", U+2028, and U+2029 are escaped to "\u003c","\u003e", "\u0026", "\u2028", and "\u2029". This replacement can be disabled when using an Encoder, by calling SetEscapeHTML(false).

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 value.

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

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

The "omitempty" option specifies that the field should be omitted from the encoding if the field has an empty value, defined as false, 0, a nil pointer, a nil interface value, and any empty array, slice, map, or string.

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 "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, and ASCII punctuation except quotation marks, backslash, and comma.

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 either be a string, an integer type, or implement encoding.TextMarshaler. The map keys are 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
  • encoding.TextMarshalers 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 return an UnsupportedTypeError.

JSON cannot represent cyclic data structures and Marshal does not handle them. Passing cyclic structures to Marshal will result in an error.

func (*JSON) MarshalIndent 

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

MarshalIndent is like Marshal but applies Indent to format the output. Each JSON element in the output will begin on a new line beginning with prefix followed by one or more copies of indent according to the indentation nesting.

func (*JSON) NewDecoder 

func (c *JSON) 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 (*JSON) NewEncoder 

func (c *JSON) NewEncoder(w io.Writer) *Encoder

NewEncoder returns a new encoder that writes to w.

func (*JSON) OmitEmpty 

func (j *JSON) OmitEmpty() *JSON

OmitEmpty specifies that fields with an empty value should be omitted from encoding. It returns a copy of the original JSON encoder/decoder, sharing its cache.

func (*JSON) Unmarshal 

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

Unmarshal parses the JSON-encoded data and stores the result in the value pointed to by v. If v is nil or not a pointer, Unmarshal returns an json.InvalidUnmarshalError.

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 value implementing the Unmarshaler interface, Unmarshal calls that value's UnmarshalJSON method, including when the input is a JSON null. Otherwise, if the value implements encoding.TextUnmarshaler and the input is a JSON quoted string, Unmarshal calls that value's UnmarshalText method with the unquoted form of the string.

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. By default, object keys which don't have a corresponding struct field are ignored (see Decoder.DisallowUnknownFields for an alternative).

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

To unmarshal a JSON array into a slice, Unmarshal resets the slice length to 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 decodes JSON 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 to use. If the map is nil, Unmarshal allocates a new map. Otherwise Unmarshal reuses the existing map, keeping existing entries. Unmarshal then stores key-value pairs from the JSON object into the map. The map's key type must either be any string type, an integer, implement json.Unmarshaler, or implement encoding.TextUnmarshaler.

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 unmarshaling as best it can. If no more serious errors are encountered, Unmarshal returns an json.UnmarshalTypeError describing the earliest such error. In any case, it's not guaranteed that all the remaining fields following the problematic one will be unmarshaled into the target object.

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.

func (*JSON) UseNumber 

func (j *JSON) UseNumber() *JSON

UseNumber causes the decoder to unmarshal a number into an interface{} as a json.Number instead of as a float64. It returns a copy of the original JSON encoder/decoder, sharing its cache.

type MarshalerError added in v0.2.0 

type MarshalerError struct {
	Type reflect.Type
	Err  error
	// contains filtered or unexported fields
}

A MarshalerError represents an error from calling a MarshalJSON or MarshalText method.

func (*MarshalerError) Error added in v0.2.0 

func (e *MarshalerError) Error() string

func (*MarshalerError) Unwrap added in v0.2.0 

func (e *MarshalerError) Unwrap() error

Unwrap returns the underlying error.

type Option 

type Option func(Options)

Option is a JSON encoder/decoder option.

func KeyEncodeFn 

func KeyEncodeFn(fn func(string) string) Option

KeyEncodeFn sets the key encoding function when creating a new JSON encoder/decoder.

type Options 

type Options interface {
	// SetKeyEncodeFn sets the function that is applied to struct field names
	// to create object keys when marshaling.
	// It is also used to match incoming object keys to struct fields when unmarshaling,
	// by encoding the struct fields and then matching them case insensitively.
	SetKeyEncodeFn(func(string) string)
}

Options are used to customize a JSON encoder/decoder.

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

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