Source File
v2_encode.go
Belonging Package
encoding/json
// 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.
//go:build goexperiment.jsonv2
// Package json 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
package json
import (
jsonv2
)
// Marshal returns the JSON encoding of v.
//
// Marshal traverses the value v recursively.
// If an encountered value implements [Marshaler]
// and is not a nil pointer, Marshal calls [Marshaler.MarshalJSON]
// to produce JSON. If no [Marshaler.MarshalJSON] method is present but the
// value implements [encoding.TextMarshaler] instead, Marshal calls
// [encoding.TextMarshaler.MarshalText] 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
// [Unmarshaler.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.
// NaN and +/-Inf values will return an [UnsupportedValueError].
//
// 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 [Encoder.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 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 omitted
// from 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 to
// determine 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 omitted
// if the value is either empty or zero (or both).
//
// 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.
//
// Embedded 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
// - keys that implement [encoding.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 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 ( any) ([]byte, error) {
return jsonv2.Marshal(, DefaultOptionsV1())
}
// 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 ( any, , string) ([]byte, error) {
, := Marshal()
if != nil {
return nil,
}
, = appendIndent(nil, , , )
if != nil {
return nil,
}
return , nil
}
// Marshaler is the interface implemented by types that
// can marshal themselves into valid JSON.
type Marshaler = jsonv2.Marshaler
// An UnsupportedTypeError is returned by [Marshal] when attempting
// to encode an unsupported value type.
type UnsupportedTypeError struct {
Type reflect.Type
}
func ( *UnsupportedTypeError) () string {
return "json: unsupported type: " + .Type.String()
}
// An UnsupportedValueError is returned by [Marshal] when attempting
// to encode an unsupported value.
type UnsupportedValueError struct {
Value reflect.Value
Str string
}
func ( *UnsupportedValueError) () string {
return "json: unsupported value: " + .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.
//
// Deprecated: No longer used; kept for compatibility.
type InvalidUTF8Error struct {
S string // the whole string value that caused the error
}
func ( *InvalidUTF8Error) () string {
return "json: invalid UTF-8 in string: " + strconv.Quote(.S)
}
// A MarshalerError represents an error from calling a
// [Marshaler.MarshalJSON] or [encoding.TextMarshaler.MarshalText] method.
type MarshalerError struct {
Type reflect.Type
Err error
sourceFunc string
}
func ( *MarshalerError) () string {
:= .sourceFunc
if == "" {
= "MarshalJSON"
}
return "json: error calling " + +
" for type " + .Type.String() +
": " + .Err.Error()
}
// Unwrap returns the underlying error.
func ( *MarshalerError) () error { return .Err }
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