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encode.go
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encode.go
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package asn1
import (
"bytes"
"fmt"
"reflect"
"time"
)
const (
tagKey = "asn1"
)
func Marshal(v interface{}) ([]byte, error) {
return MarshalWithOptions(v, "")
}
func MarshalWithOptions(v interface{}, optionsString string) ([]byte, error) {
options, err := parseOptions(optionsString)
if err != nil {
return nil, err
}
enc := NewEncoder(v, options)
b, err := enc.encode()
if err != nil {
return nil, err
}
return b, nil
}
type encoder interface {
encode() ([]byte, error)
}
func NewEncoder(v interface{}, opts *options) Encoder {
buf := new(bytes.Buffer)
return Encoder{buf, v, opts}
}
type Encoder struct {
buf *bytes.Buffer
v interface{}
opts *options
}
func getChoiceIndex(val reflect.Value) (int, error) {
kind := val.Kind()
if kind != reflect.Struct {
return -1, fmt.Errorf("invalid 'choice' type '%s', must be struct", kind.String())
}
choiceIndex := 0
choiceFound := false
for i := 0; i < val.NumField(); i++ {
choice := val.Field(i).Interface()
if !reflect.DeepEqual(choice, reflect.Zero(val.Field(i).Type()).Interface()) {
if choiceFound {
return -1, fmt.Errorf("choice value has multiple fields set")
}
choiceIndex = i
choiceFound = true
}
}
return choiceIndex, nil
}
func (e Encoder) encode() (encodedContents []byte, err error) {
val := reflect.ValueOf(e.v)
// handle interface type
if val.Kind() == reflect.Interface {
val = val.Elem()
}
if !val.IsValid() {
return nil, fmt.Errorf("asn1: cannot marshal nil value")
}
var contentsEncoder encoder
if val.Kind() == reflect.Slice && val.Len() == 0 && e.opts.omitEmpty {
fmt.Println("omit empty!")
return []byte(nil), nil
}
id := identifier{
isConstructed: false,
class: TagClassUniversal,
}
empty := isEmpty(val)
if empty && e.opts.optional {
return []byte(nil), nil
}
if e.opts.defaultValue != nil {
if canHaveDefaultValue(val.Kind()) {
defaultValue := reflect.New(val.Type()).Elem()
defaultValue.SetInt(*e.opts.defaultValue)
if reflect.DeepEqual(val.Interface(), defaultValue.Interface()) {
return []byte(nil), nil
}
}
}
if e.opts.choice {
choiceIndex, err := getChoiceIndex(val)
if err != nil {
return nil, err
}
if e.opts.tag != nil {
tag := val.Type().Field(choiceIndex).Tag.Get(tagKey)
tagOpts, err := parseOptions(tag)
if err != nil {
return nil, err
}
encodedContents, err = NewEncoder(val.Field(choiceIndex).Interface(), tagOpts).encode()
if err != nil {
return nil, err
}
} else {
choiceTag := val.Type().Field(choiceIndex).Tag.Get(tagKey)
e.opts, err = parseOptions(choiceTag)
if err != nil {
return nil, err
}
val = reflect.ValueOf(val.Field(choiceIndex).Interface())
}
}
switch val.Type() {
case timeType:
id.tag = e.opts.timeType
switch e.opts.timeType {
case TagUtcTime:
contentsEncoder = stringEncoder(makeUTCTime(val.Interface().(time.Time)))
default:
contentsEncoder = stringEncoder(makeGeneralizedTime(val.Interface().(time.Time)))
}
case bitStringType:
id.tag = TagBitString
contentsEncoder = bitStringEncoder(val.Interface().(BitString))
case objectIdentifierType:
id.tag = TagObjectIdentifier
contentsEncoder = objectIdentifierEncoder(val.Interface().(ObjectIdentifier))
case nullType:
id.tag = TagNull
contentsEncoder = nullEncoder(val.Interface().(Null))
}
if contentsEncoder == nil {
switch val.Kind() {
case reflect.Bool:
id.tag = TagBoolean
contentsEncoder = boolEncoder(val.Bool())
case reflect.String:
id.tag = e.opts.stringType
switch e.opts.stringType {
case TagPrintableString:
printableString, err := makePrintableString(val.String())
if err != nil {
return nil, err
}
contentsEncoder = stringEncoder(printableString)
case TagIa5String:
ia5String, err := makeIA5String(val.String())
if err != nil {
return nil, err
}
contentsEncoder = stringEncoder(ia5String)
case TagOctetString:
contentsEncoder = bytesEncoder(val.String())
case TagNumericString:
numericString, err := makeNumericString(val.String())
if err != nil {
return nil, err
}
contentsEncoder = stringEncoder(numericString)
default:
contentsEncoder = stringEncoder(val.String())
}
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
if e.opts.enumerated {
id.tag = TagEnumerated
} else {
id.tag = TagInteger
}
contentsEncoder = intEncoder(val.Int())
case reflect.Float32, reflect.Float64:
id.tag = TagReal
contentsEncoder = realEncoder(val.Float())
case reflect.Struct:
id.isConstructed = true
if e.opts.set {
id.tag = TagSet
} else {
id.tag = TagSequence
}
var encoders multiEncoder
for i := 0; i < val.NumField(); i++ {
fieldVal := val.Field(i)
fieldStruct := val.Type().Field(i)
if fieldVal.CanInterface() {
tag := fieldStruct.Tag.Get(tagKey)
tagOpts, err := parseOptions(tag)
if err != nil {
return nil, err
}
fieldEncoder := NewEncoder(fieldVal.Interface(), tagOpts)
encoders = append(encoders, fieldEncoder)
}
}
contentsEncoder = encoders
case reflect.Array, reflect.Slice:
if val.Type().Elem().Kind() == reflect.Uint8 {
id.tag = TagOctetString
contentsEncoder = bytesEncoder(val.Interface().([]byte))
} else {
id.isConstructed = true
if e.opts.set {
id.tag = TagSetOf
} else {
id.tag = TagSequenceOf
}
var encoders multiEncoder
for i := 0; i < val.Len(); i++ {
encoder := NewEncoder(val.Index(i).Interface(), e.opts)
encoders = append(encoders, encoder)
}
contentsEncoder = encoders
}
default:
return nil, &UnsupportedTypeError{val.Type()}
}
}
if encodedContents == nil {
encodedContents, err = contentsEncoder.encode()
if err != nil {
return nil, err
}
}
encodedLength := encodeLength(len(encodedContents))
if e.opts.tag != nil {
if e.opts.application {
id.class = TagClassApplication
} else if e.opts.private {
id.class = TagClassPrivate
} else {
id.class = TagClassContextSpecific
}
if e.opts.explicit {
if e.opts.tag == nil {
return nil, fmt.Errorf("'explicit' flag requires 'tag' to be set")
}
innerId := identifier{
class: TagClassUniversal,
tag: id.tag,
isConstructed: false,
}
innerBuf := new(bytes.Buffer)
innerBuf.Write(innerId.encode())
innerBuf.Write(encodedLength)
innerBuf.Write(encodedContents)
encodedContents = innerBuf.Bytes()
encodedLength = encodeLength(len(encodedContents))
id.isConstructed = true
}
// implicit
id.tag = *e.opts.tag
}
encodedIdentifier := id.encode()
e.buf.Write(encodedIdentifier)
e.buf.Write(encodedLength)
e.buf.Write(encodedContents)
return e.buf.Bytes(), nil
}
type identifier struct {
class TagClass
isConstructed bool
tag Tag
}
func (i identifier) encode() []byte {
b := []byte{0x00}
// class
b[0] |= byte(i.class << 6)
if i.isConstructed {
b[0] |= byte(1 << 5)
} else {
b[0] |= byte(0 << 5)
}
if i.tag <= 30 {
// short form
b[0] |= byte(i.tag)
} else {
// long form
b[0] |= byte(0x1f) // set bits 1-5 to 1
// encoded tag in next octet
b = append(b, encodeBase128(uint(i.tag))...)
}
return b
}
func encodeLength(length int) []byte {
lengthBytes := encodeUint(uint(length))
// short form
if length <= 0x7f {
return lengthBytes
}
// long form
b := new(bytes.Buffer)
header := len(lengthBytes) | 0x80
b.Write(encodeUint(uint(header)))
b.Write(lengthBytes)
return b.Bytes()
}
type multiEncoder []encoder
func (e multiEncoder) encode() ([]byte, error) {
buf := new(bytes.Buffer)
for _, encoder := range e {
encoding, err := encoder.encode()
if err != nil {
return nil, err
}
buf.Write(encoding)
}
return buf.Bytes(), nil
}
type bytesEncoder []byte
func (e bytesEncoder) encode() ([]byte, error) {
return e, nil
}
func isEmpty(value reflect.Value) bool {
if value.Type() == nullType {
return false
}
defaultValue := reflect.Zero(value.Type())
return reflect.DeepEqual(value.Interface(), defaultValue.Interface())
// if value.Interface() == nil {
// return true
// }
// return false
}
func canHaveDefaultValue(k reflect.Kind) bool {
switch k {
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
return true
}
return false
}