src/encoding/json/v2_encode.go

// 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
//
// # Security Considerations
//
// See the "Security Considerations" section in [encoding/json/v2].
//
// For historical reasons, the default behavior of v1 [encoding/json]
// unfortunately operates with less secure defaults.
// New usages of JSON in Go are encouraged to use [encoding/json/v2] instead.
package json

import (
	"reflect"
	"strconv"

	jsonv2 "encoding/json/v2"
)

// 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.
// JSON names containing commas or quotes, or names identical to "" or "-",
// can be specified using a single-quoted string literal, where the syntax
// is identical to the Go grammar for a double-quoted string literal,
// but instead uses single quotes as the delimiters.
//
// 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 Marshal(v any) ([]byte, error) {
	return jsonv2.Marshal(v, 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 MarshalIndent(v any, prefix, indent string) ([]byte, error) {
	b, err := Marshal(v)
	if err != nil {
		return nil, err
	}
	b, err = appendIndent(nil, b, prefix, indent)
	if err != nil {
		return nil, err
	}
	return b, 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 (e *UnsupportedTypeError) Error() string {
	return "json: unsupported type: " + e.Type.String()
}

// An UnsupportedValueError is returned by [Marshal] when attempting
// to encode an unsupported value.
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.
//
// Deprecated: No longer used; kept for compatibility.
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)
}

// 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 (e *MarshalerError) Error() string {
	srcFunc := e.sourceFunc
	if srcFunc == "" {
		srcFunc = "MarshalJSON"
	}
	return "json: error calling " + srcFunc +
		" for type " + e.Type.String() +
		": " + e.Err.Error()
}

// Unwrap returns the underlying error.
func (e *MarshalerError) Unwrap() error { return e.Err }