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build.go
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build.go
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// Package jsonutil provides JSON serialization of AWS requests and responses.
package jsonutil
import (
"bytes"
"encoding/base64"
"fmt"
"reflect"
"sort"
"strconv"
"time"
"github.com/aws/aws-sdk-go/private/protocol"
)
var timeType = reflect.ValueOf(time.Time{}).Type()
var byteSliceType = reflect.ValueOf([]byte{}).Type()
// BuildJSON builds a JSON string for a given object v.
func BuildJSON(v interface{}) ([]byte, error) {
var buf bytes.Buffer
err := buildAny(reflect.ValueOf(v), &buf, "")
return buf.Bytes(), err
}
func buildAny(value reflect.Value, buf *bytes.Buffer, tag reflect.StructTag) error {
value = reflect.Indirect(value)
if !value.IsValid() {
return nil
}
vtype := value.Type()
t := tag.Get("type")
if t == "" {
switch vtype.Kind() {
case reflect.Struct:
// also it can't be a time object
if value.Type() != timeType {
t = "structure"
}
case reflect.Slice:
// also it can't be a byte slice
if _, ok := value.Interface().([]byte); !ok {
t = "list"
}
case reflect.Map:
t = "map"
}
}
switch t {
case "structure":
if field, ok := vtype.FieldByName("_"); ok {
tag = field.Tag
}
return buildStruct(value, buf, tag)
case "list":
return buildList(value, buf, tag)
case "map":
return buildMap(value, buf, tag)
default:
return buildScalar(value, buf, tag)
}
}
func buildStruct(value reflect.Value, buf *bytes.Buffer, tag reflect.StructTag) error {
if !value.IsValid() {
return nil
}
// unwrap payloads
if payload := tag.Get("payload"); payload != "" {
field, _ := value.Type().FieldByName(payload)
tag = field.Tag
value = elemOf(value.FieldByName(payload))
if !value.IsValid() {
return nil
}
}
buf.WriteByte('{')
t := value.Type()
first := true
for i := 0; i < t.NumField(); i++ {
member := value.Field(i)
field := t.Field(i)
if field.PkgPath != "" {
continue // ignore unexported fields
}
if field.Tag.Get("json") == "-" {
continue
}
if field.Tag.Get("location") != "" {
continue // ignore non-body elements
}
if protocol.CanSetIdempotencyToken(member, field) {
token := protocol.GetIdempotencyToken()
member = reflect.ValueOf(&token)
}
if (member.Kind() == reflect.Ptr || member.Kind() == reflect.Slice || member.Kind() == reflect.Map) && member.IsNil() {
continue // ignore unset fields
}
if first {
first = false
} else {
buf.WriteByte(',')
}
// figure out what this field is called
name := field.Name
if locName := field.Tag.Get("locationName"); locName != "" {
name = locName
}
writeString(name, buf)
buf.WriteString(`:`)
err := buildAny(member, buf, field.Tag)
if err != nil {
return err
}
}
buf.WriteString("}")
return nil
}
func buildList(value reflect.Value, buf *bytes.Buffer, tag reflect.StructTag) error {
buf.WriteString("[")
for i := 0; i < value.Len(); i++ {
buildAny(value.Index(i), buf, "")
if i < value.Len()-1 {
buf.WriteString(",")
}
}
buf.WriteString("]")
return nil
}
type sortedValues []reflect.Value
func (sv sortedValues) Len() int { return len(sv) }
func (sv sortedValues) Swap(i, j int) { sv[i], sv[j] = sv[j], sv[i] }
func (sv sortedValues) Less(i, j int) bool { return sv[i].String() < sv[j].String() }
func buildMap(value reflect.Value, buf *bytes.Buffer, tag reflect.StructTag) error {
buf.WriteString("{")
sv := sortedValues(value.MapKeys())
sort.Sort(sv)
for i, k := range sv {
if i > 0 {
buf.WriteByte(',')
}
writeString(k.String(), buf)
buf.WriteString(`:`)
buildAny(value.MapIndex(k), buf, "")
}
buf.WriteString("}")
return nil
}
func buildScalar(value reflect.Value, buf *bytes.Buffer, tag reflect.StructTag) error {
switch value.Kind() {
case reflect.String:
writeString(value.String(), buf)
case reflect.Bool:
buf.WriteString(strconv.FormatBool(value.Bool()))
case reflect.Int64:
buf.WriteString(strconv.FormatInt(value.Int(), 10))
case reflect.Float64:
buf.WriteString(strconv.FormatFloat(value.Float(), 'f', -1, 64))
default:
switch value.Type() {
case timeType:
converted := value.Interface().(time.Time)
buf.WriteString(strconv.FormatInt(converted.UTC().Unix(), 10))
case byteSliceType:
if !value.IsNil() {
converted := value.Interface().([]byte)
buf.WriteByte('"')
if len(converted) < 1024 {
// for small buffers, using Encode directly is much faster.
dst := make([]byte, base64.StdEncoding.EncodedLen(len(converted)))
base64.StdEncoding.Encode(dst, converted)
buf.Write(dst)
} else {
// for large buffers, avoid unnecessary extra temporary
// buffer space.
enc := base64.NewEncoder(base64.StdEncoding, buf)
enc.Write(converted)
enc.Close()
}
buf.WriteByte('"')
}
default:
return fmt.Errorf("unsupported JSON value %v (%s)", value.Interface(), value.Type())
}
}
return nil
}
func writeString(s string, buf *bytes.Buffer) {
buf.WriteByte('"')
for _, r := range s {
if r == '"' {
buf.WriteString(`\"`)
} else if r == '\\' {
buf.WriteString(`\\`)
} else if r == '\b' {
buf.WriteString(`\b`)
} else if r == '\f' {
buf.WriteString(`\f`)
} else if r == '\r' {
buf.WriteString(`\r`)
} else if r == '\t' {
buf.WriteString(`\t`)
} else if r == '\n' {
buf.WriteString(`\n`)
} else if r < 32 {
fmt.Fprintf(buf, "\\u%0.4x", r)
} else {
buf.WriteRune(r)
}
}
buf.WriteByte('"')
}
// Returns the reflection element of a value, if it is a pointer.
func elemOf(value reflect.Value) reflect.Value {
for value.Kind() == reflect.Ptr {
value = value.Elem()
}
return value
}