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// 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.
// The json package implements encoding and decoding of JSON objects as
// defined in RFC 4627.
package json
import (
"bytes"
"encoding/base64"
"os"
"reflect"
"runtime"
"sort"
"strconv"
"unicode"
"utf8"
)
// Marshal returns the JSON encoding of v.
//
// Marshal traverses the value v recursively.
// If an encountered value implements the Marshaler interface,
// Marshal calls its MarshalJSON method to produce JSON.
//
// Otherwise, Marshal uses the following type-dependent default encodings:
//
// Boolean values encode as JSON booleans.
//
// Floating point and integer values encode as JSON numbers.
//
// String values encode as JSON strings, with each invalid UTF-8 sequence
// replaced by the encoding of the Unicode replacement character U+FFFD.
//
// Array and slice values encode as JSON arrays, except that
// []byte encodes as a base64-encoded string.
//
// Struct values encode as JSON objects. Each struct field becomes
// a member of the object. By default the object's key name is the
// struct field name. If the struct field has a non-empty tag consisting
// of only Unicode letters, digits, and underscores, that tag will be used
// as the name instead. Only exported fields will be encoded.
//
// 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 InvalidTypeError.
//
// JSON cannot represent cyclic data structures and Marshal does not
// handle them. Passing cyclic structures to Marshal will result in
// an infinite recursion.
//
func Marshal(v interface{}) ([]byte, os.Error) {
e := &encodeState{}
err := e.marshal(v)
if err != nil {
return nil, err
}
return e.Bytes(), nil
}
// MarshalIndent is like Marshal but applies Indent to format the output.
func MarshalIndent(v interface{}, prefix, indent string) ([]byte, os.Error) {
b, err := Marshal(v)
if err != nil {
return nil, err
}
var buf bytes.Buffer
err = Indent(&buf, b, prefix, indent)
if err != nil {
return nil, err
}
return buf.Bytes(), nil
}
// MarshalForHTML is like Marshal but applies HTMLEscape to the output.
func MarshalForHTML(v interface{}) ([]byte, os.Error) {
b, err := Marshal(v)
if err != nil {
return nil, err
}
var buf bytes.Buffer
HTMLEscape(&buf, b)
return buf.Bytes(), nil
}
// HTMLEscape appends to dst the JSON-encoded src with <, >, and &
// characters inside string literals changed to \u003c, \u003e, \u0026
// 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 HTMLEscape(dst *bytes.Buffer, src []byte) {
// < > & can only appear in string literals,
// so just scan the string one byte at a time.
start := 0
for i, c := range src {
if c == '<' || c == '>' || c == '&' {
if start < i {
dst.Write(src[start:i])
}
dst.WriteString(`\u00`)
dst.WriteByte(hex[c>>4])
dst.WriteByte(hex[c&0xF])
start = i + 1
}
}
if start < len(src) {
dst.Write(src[start:])
}
}
// Marshaler is the interface implemented by objects that
// can marshal themselves into valid JSON.
type Marshaler interface {
MarshalJSON() ([]byte, os.Error)
}
type UnsupportedTypeError struct {
Type reflect.Type
}
func (e *UnsupportedTypeError) String() string {
return "json: unsupported type: " + e.Type.String()
}
type InvalidUTF8Error struct {
S string
}
func (e *InvalidUTF8Error) String() string {
return "json: invalid UTF-8 in string: " + strconv.Quote(e.S)
}
type MarshalerError struct {
Type reflect.Type
Error os.Error
}
func (e *MarshalerError) String() string {
return "json: error calling MarshalJSON for type " + e.Type.String() + ": " + e.Error.String()
}
type interfaceOrPtrValue interface {
IsNil() bool
Elem() reflect.Value
}
var hex = "0123456789abcdef"
// An encodeState encodes JSON into a bytes.Buffer.
type encodeState struct {
bytes.Buffer // accumulated output
}
func (e *encodeState) marshal(v interface{}) (err os.Error) {
defer func() {
if r := recover(); r != nil {
if _, ok := r.(runtime.Error); ok {
panic(r)
}
err = r.(os.Error)
}
}()
e.reflectValue(reflect.ValueOf(v))
return nil
}
func (e *encodeState) error(err os.Error) {
panic(err)
}
var byteSliceType = reflect.TypeOf([]byte(nil))
func (e *encodeState) reflectValue(v reflect.Value) {
if !v.IsValid() {
e.WriteString("null")
return
}
if j, ok := v.Interface().(Marshaler); ok {
b, err := j.MarshalJSON()
if err == nil {
// copy JSON into buffer, checking validity.
err = Compact(&e.Buffer, b)
}
if err != nil {
e.error(&MarshalerError{v.Type(), err})
}
return
}
switch v.Kind() {
case reflect.Bool:
x := v.Bool()
if x {
e.WriteString("true")
} else {
e.WriteString("false")
}
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
e.WriteString(strconv.Itoa64(v.Int()))
case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
e.WriteString(strconv.Uitoa64(v.Uint()))
case reflect.Float32, reflect.Float64:
e.WriteString(strconv.FtoaN(v.Float(), 'g', -1, v.Type().Bits()))
case reflect.String:
e.string(v.String())
case reflect.Struct:
e.WriteByte('{')
t := v.Type()
n := v.NumField()
first := true
for i := 0; i < n; i++ {
f := t.Field(i)
if f.PkgPath != "" {
continue
}
if first {
first = false
} else {
e.WriteByte(',')
}
if isValidTag(f.Tag) {
e.string(f.Tag)
} else {
e.string(f.Name)
}
e.WriteByte(':')
e.reflectValue(v.Field(i))
}
e.WriteByte('}')
case reflect.Map:
if v.Type().Key().Kind() != reflect.String {
e.error(&UnsupportedTypeError{v.Type()})
}
if v.IsNil() {
e.WriteString("null")
break
}
e.WriteByte('{')
var sv stringValues = v.MapKeys()
sort.Sort(sv)
for i, k := range sv {
if i > 0 {
e.WriteByte(',')
}
e.string(k.String())
e.WriteByte(':')
e.reflectValue(v.MapIndex(k))
}
e.WriteByte('}')
case reflect.Array, reflect.Slice:
if v.Type() == byteSliceType {
e.WriteByte('"')
s := v.Interface().([]byte)
if len(s) < 1024 {
// for small buffers, using Encode directly is much faster.
dst := make([]byte, base64.StdEncoding.EncodedLen(len(s)))
base64.StdEncoding.Encode(dst, s)
e.Write(dst)
} else {
// for large buffers, avoid unnecessary extra temporary
// buffer space.
enc := base64.NewEncoder(base64.StdEncoding, e)
enc.Write(s)
enc.Close()
}
e.WriteByte('"')
break
}
e.WriteByte('[')
n := v.Len()
for i := 0; i < n; i++ {
if i > 0 {
e.WriteByte(',')
}
e.reflectValue(v.Index(i))
}
e.WriteByte(']')
case interfaceOrPtrValue:
if v.IsNil() {
e.WriteString("null")
return
}
e.reflectValue(v.Elem())
default:
e.error(&UnsupportedTypeError{v.Type()})
}
return
}
func isValidTag(s string) bool {
if s == "" {
return false
}
for _, c := range s {
if c != '_' && !unicode.IsLetter(c) && !unicode.IsDigit(c) {
return false
}
}
return true
}
// stringValues is a slice of reflect.Value holding *reflect.StringValue.
// It implements the methods to sort by string.
type stringValues []reflect.Value
func (sv stringValues) Len() int { return len(sv) }
func (sv stringValues) Swap(i, j int) { sv[i], sv[j] = sv[j], sv[i] }
func (sv stringValues) Less(i, j int) bool { return sv.get(i) < sv.get(j) }
func (sv stringValues) get(i int) string { return sv[i].String() }
func (e *encodeState) string(s string) {
e.WriteByte('"')
start := 0
for i := 0; i < len(s); {
if b := s[i]; b < utf8.RuneSelf {
if 0x20 <= b && b != '\\' && b != '"' {
i++
continue
}
if start < i {
e.WriteString(s[start:i])
}
if b == '\\' || b == '"' {
e.WriteByte('\\')
e.WriteByte(b)
} else {
e.WriteString(`\u00`)
e.WriteByte(hex[b>>4])
e.WriteByte(hex[b&0xF])
}
i++
start = i
continue
}
c, size := utf8.DecodeRuneInString(s[i:])
if c == utf8.RuneError && size == 1 {
e.error(&InvalidUTF8Error{s})
}
i += size
}
if start < len(s) {
e.WriteString(s[start:])
}
e.WriteByte('"')
}