// Copyright 2009 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.
// Package asn1 implements parsing of DER-encoded ASN.1 data structures,
// as defined in ITU-T Rec X.690.
//
// See also ``A Layman's Guide to a Subset of ASN.1, BER, and DER,''
// http://luca.ntop.org/Teaching/Appunti/asn1.html.
package asn1
// ASN.1 is a syntax for specifying abstract objects and BER, DER, PER, XER etc
// are different encoding formats for those objects. Here, we'll be dealing
// with DER, the Distinguished Encoding Rules. DER is used in X.509 because
// it's fast to parse and, unlike BER, has a unique encoding for every object.
// When calculating hashes over objects, it's important that the resulting
// bytes be the same at both ends and DER removes this margin of error.
//
// ASN.1 is very complex and this package doesn't attempt to implement
// everything by any means.
import (
"errors"
"fmt"
"math"
"math/big"
"reflect"
"strconv"
"time"
"unicode/utf8"
)
// A StructuralError suggests that the ASN.1 data is valid, but the Go type
// which is receiving it doesn't match.
type StructuralError struct {
Msg string
}
func (e StructuralError) Error() string { return "asn1: structure error: " + e.Msg }
// A SyntaxError suggests that the ASN.1 data is invalid.
type SyntaxError struct {
Msg string
}
func (e SyntaxError) Error() string { return "asn1: syntax error: " + e.Msg }
// We start by dealing with each of the primitive types in turn.
// BOOLEAN
func parseBool(bytes []byte) (ret bool, err error) {
if len(bytes) != 1 {
err = SyntaxError{"invalid boolean"}
return
}
// DER demands that "If the encoding represents the boolean value TRUE,
// its single contents octet shall have all eight bits set to one."
// Thus only 0 and 255 are valid encoded values.
switch bytes[0] {
case 0:
ret = false
case 0xff:
ret = true
default:
err = SyntaxError{"invalid boolean"}
}
return
}
// INTEGER
// checkInteger returns nil if the given bytes are a valid DER-encoded
// INTEGER and an error otherwise.
func checkInteger(bytes []byte) error {
if len(bytes) == 0 {
return StructuralError{"empty integer"}
}
if len(bytes) == 1 {
return nil
}
if (bytes[0] == 0 && bytes[1]&0x80 == 0) || (bytes[0] == 0xff && bytes[1]&0x80 == 0x80) {
return StructuralError{"integer not minimally-encoded"}
}
return nil
}
// parseInt64 treats the given bytes as a big-endian, signed integer and
// returns the result.
func parseInt64(bytes []byte) (ret int64, err error) {
err = checkInteger(bytes)
if err != nil {
return
}
if len(bytes) > 8 {
// We'll overflow an int64 in this case.
err = StructuralError{"integer too large"}
return
}
for bytesRead := 0; bytesRead < len(bytes); bytesRead++ {
ret <<= 8
ret |= int64(bytes[bytesRead])
}
// Shift up and down in order to sign extend the result.
ret <<= 64 - uint8(len(bytes))*8
ret >>= 64 - uint8(len(bytes))*8
return
}
// parseInt treats the given bytes as a big-endian, signed integer and returns
// the result.
func parseInt32(bytes []byte) (int32, error) {
if err := checkInteger(bytes); err != nil {
return 0, err
}
ret64, err := parseInt64(bytes)
if err != nil {
return 0, err
}
if ret64 != int64(int32(ret64)) {
return 0, StructuralError{"integer too large"}
}
return int32(ret64), nil
}
var bigOne = big.NewInt(1)
// parseBigInt treats the given bytes as a big-endian, signed integer and returns
// the result.
func parseBigInt(bytes []byte) (*big.Int, error) {
if err := checkInteger(bytes); err != nil {
return nil, err
}
ret := new(big.Int)
if len(bytes) > 0 && bytes[0]&0x80 == 0x80 {
// This is a negative number.
notBytes := make([]byte, len(bytes))
for i := range notBytes {
notBytes[i] = ^bytes[i]
}
ret.SetBytes(notBytes)
ret.Add(ret, bigOne)
ret.Neg(ret)
return ret, nil
}
ret.SetBytes(bytes)
return ret, nil
}
// BIT STRING
// BitString is the structure to use when you want an ASN.1 BIT STRING type. A
// bit string is padded up to the nearest byte in memory and the number of
// valid bits is recorded. Padding bits will be zero.
type BitString struct {
Bytes []byte // bits packed into bytes.
BitLength int // length in bits.
}
// At returns the bit at the given index. If the index is out of range it
// returns false.
func (b BitString) At(i int) int {
if i < 0 || i >= b.BitLength {
return 0
}
x := i / 8
y := 7 - uint(i%8)
return int(b.Bytes[x]>>y) & 1
}
// RightAlign returns a slice where the padding bits are at the beginning. The
// slice may share memory with the BitString.
func (b BitString) RightAlign() []byte {
shift := uint(8 - (b.BitLength % 8))
if shift == 8 || len(b.Bytes) == 0 {
return b.Bytes
}
a := make([]byte, len(b.Bytes))
a[0] = b.Bytes[0] >> shift
for i := 1; i < len(b.Bytes); i++ {
a[i] = b.Bytes[i-1] << (8 - shift)
a[i] |= b.Bytes[i] >> shift
}
return a
}
// parseBitString parses an ASN.1 bit string from the given byte slice and returns it.
func parseBitString(bytes []byte) (ret BitString, err error) {
if len(bytes) == 0 {
err = SyntaxError{"zero length BIT STRING"}
return
}
paddingBits := int(bytes[0])
if paddingBits > 7 ||
len(bytes) == 1 && paddingBits > 0 ||
bytes[len(bytes)-1]&((1<<bytes[0])-1) != 0 {
err = SyntaxError{"invalid padding bits in BIT STRING"}
return
}
ret.BitLength = (len(bytes)-1)*8 - paddingBits
ret.Bytes = bytes[1:]
return
}
// NULL
// NullRawValue is a RawValue with its Tag set to the ASN.1 NULL type tag (5).
var NullRawValue = RawValue{Tag: TagNull}
// NullBytes contains bytes representing the DER-encoded ASN.1 NULL type.
var NullBytes = []byte{TagNull, 0}
// OBJECT IDENTIFIER
// An ObjectIdentifier represents an ASN.1 OBJECT IDENTIFIER.
type ObjectIdentifier []int
// Equal reports whether oi and other represent the same identifier.
func (oi ObjectIdentifier) Equal(other ObjectIdentifier) bool {
if len(oi) != len(other) {
return false
}
for i := 0; i < len(oi); i++ {
if oi[i] != other[i] {
return false
}
}
return true
}
func (oi ObjectIdentifier) String() string {
var s string
for i, v := range oi {
if i > 0 {
s += "."
}
s += strconv.Itoa(v)
}
return s
}
// parseObjectIdentifier parses an OBJECT IDENTIFIER from the given bytes and
// returns it. An object identifier is a sequence of variable length integers
// that are assigned in a hierarchy.
func parseObjectIdentifier(bytes []byte) (s ObjectIdentifier, err error) {
if len(bytes) == 0 {
err = SyntaxError{"zero length OBJECT IDENTIFIER"}
return
}
// In the worst case, we get two elements from the first byte (which is
// encoded differently) and then every varint is a single byte long.
s = make([]int, len(bytes)+1)
// The first varint is 40*value1 + value2:
// According to this packing, value1 can take the values 0, 1 and 2 only.
// When value1 = 0 or value1 = 1, then value2 is <= 39. When value1 = 2,
// then there are no restrictions on value2.
v, offset, err := parseBase128Int(bytes, 0)
if err != nil {
return
}
if v < 80 {
s[0] = v / 40
s[1] = v % 40
} else {
s[0] = 2
s[1] = v - 80
}
i := 2
for ; offset < len(bytes); i++ {
v, offset, err = parseBase128Int(bytes, offset)
if err != nil {
return
}
s[i] = v
}
s = s[0:i]
return
}
// ENUMERATED
// An Enumerated is represented as a plain int.
type Enumerated int
// FLAG
// A Flag accepts any data and is set to true if present.
type Flag bool
// parseBase128Int parses a base-128 encoded int from the given offset in the
// given byte slice. It returns the value and the new offset.
func parseBase128Int(bytes []byte, initOffset int) (ret, offset int, err error) {
offset = initOffset
var ret64 int64
for shifted := 0; offset < len(bytes); shifted++ {
// 5 * 7 bits per byte == 35 bits of data
// Thus the representation is either non-minimal or too large for an int32
if shifted == 5 {
err = StructuralError{"base 128 integer too large"}
return
}
ret64 <<= 7
b := bytes[offset]
ret64 |= int64(b & 0x7f)
offset++
if b&0x80 == 0 {
ret = int(ret64)
// Ensure that the returned value fits in an int on all platforms
if ret64 > math.MaxInt32 {
err = StructuralError{"base 128 integer too large"}
}
return
}
}
err = SyntaxError{"truncated base 128 integer"}
return
}
// UTCTime
func parseUTCTime(bytes []byte) (ret time.Time, err error) {
s := string(bytes)
formatStr := "0601021504Z0700"
ret, err = time.Parse(formatStr, s)
if err != nil {
formatStr = "060102150405Z0700"
ret, err = time.Parse(formatStr, s)
}
if err != nil {
return
}
if serialized := ret.Format(formatStr); serialized != s {
err = fmt.Errorf("asn1: time did not serialize back to the original value and may be invalid: given %q, but serialized as %q", s, serialized)
return
}
if ret.Year() >= 2050 {
// UTCTime only encodes times prior to 2050. See https://tools.ietf.org/html/rfc5280#section-4.1.2.5.1
ret = ret.AddDate(-100, 0, 0)
}
return
}
// parseGeneralizedTime parses the GeneralizedTime from the given byte slice
// and returns the resulting time.
func parseGeneralizedTime(bytes []byte) (ret time.Time, err error) {
const formatStr = "20060102150405Z0700"
s := string(bytes)
if ret, err = time.Parse(formatStr, s); err != nil {
return
}
if serialized := ret.Format(formatStr); serialized != s {
err = fmt.Errorf("asn1: time did not serialize back to the original value and may be invalid: given %q, but serialized as %q", s, serialized)
}
return
}
// NumericString
// parseNumericString parses an ASN.1 NumericString from the given byte array
// and returns it.
func parseNumericString(bytes []byte) (ret string, err error) {
for _, b := range bytes {
if !isNumeric(b) {
return "", SyntaxError{"NumericString contains invalid character"}
}
}
return string(bytes), nil
}
// isNumeric reports whether the given b is in the ASN.1 NumericString set.
func isNumeric(b byte) bool {
return '0' <= b && b <= '9' ||
b == ' '
}
// PrintableString
// parsePrintableString parses an ASN.1 PrintableString from the given byte
// array and returns it.
func parsePrintableString(bytes []byte) (ret string, err error) {
for _, b := range bytes {
if !isPrintable(b, allowAsterisk, allowAmpersand) {
err = SyntaxError{"PrintableString contains invalid character"}
return
}
}
ret = string(bytes)
return
}
type asteriskFlag bool
type ampersandFlag bool
const (
allowAsterisk asteriskFlag = true
rejectAsterisk asteriskFlag = false
allowAmpersand ampersandFlag = true
rejectAmpersand ampersandFlag = false
)
// isPrintable reports whether the given b is in the ASN.1 PrintableString set.
// If asterisk is allowAsterisk then '*' is also allowed, reflecting existing
// practice. If ampersand is allowAmpersand then '&' is allowed as well.
func isPrintable(b byte, asterisk asteriskFlag, ampersand ampersandFlag) bool {
return 'a' <= b && b <= 'z' ||
'A' <= b && b <= 'Z' ||
'0' <= b && b <= '9' ||
'\'' <= b && b <= ')' ||
'+' <= b && b <= '/' ||
b == ' ' ||
b == ':' ||
b == '=' ||
b == '?' ||
// This is technically not allowed in a PrintableString.
// However, x509 certificates with wildcard strings don't
// always use the correct string type so we permit it.
(bool(asterisk) && b == '*') ||
// This is not technically allowed either. However, not
// only is it relatively common, but there are also a
// handful of CA certificates that contain it. At least
// one of which will not expire until 2027.
(bool(ampersand) && b == '&')
}
// IA5String
// parseIA5String parses an ASN.1 IA5String (ASCII string) from the given
// byte slice and returns it.
func parseIA5String(bytes []byte) (ret string, err error) {
for _, b := range bytes {
if b >= utf8.RuneSelf {
err = SyntaxError{"IA5String contains invalid character"}
return
}
}
ret = string(bytes)
return
}
// T61String
// parseT61String parses an ASN.1 T61String (8-bit clean string) from the given
// byte slice and returns it.
func parseT61String(bytes []byte) (ret string, err error) {
return string(bytes), nil
}
// UTF8String
// parseUTF8String parses an ASN.1 UTF8String (raw UTF-8) from the given byte
// array and returns it.
func parseUTF8String(bytes []byte) (ret string, err error) {
if !utf8.Valid(bytes) {
return "", errors.New("asn1: invalid UTF-8 string")
}
return string(bytes), nil
}
// A RawValue represents an undecoded ASN.1 object.
type RawValue struct {
Class, Tag int
IsCompound bool
Bytes []byte
FullBytes []byte // includes the tag and length
}
// RawContent is used to signal that the undecoded, DER data needs to be
// preserved for a struct. To use it, the first field of the struct must have
// this type. It's an error for any of the other fields to have this type.
type RawContent []byte
// Tagging
// parseTagAndLength parses an ASN.1 tag and length pair from the given offset
// into a byte slice. It returns the parsed data and the new offset. SET and
// SET OF (tag 17) are mapped to SEQUENCE and SEQUENCE OF (tag 16) since we
// don't distinguish between ordered and unordered objects in this code.
func parseTagAndLength(bytes []byte, initOffset int) (ret tagAndLength, offset int, err error) {
offset = initOffset
// parseTagAndLength should not be called without at least a single
// byte to read. Thus this check is for robustness:
if offset >= len(bytes) {
err = errors.New("asn1: internal error in parseTagAndLength")
return
}
b := bytes[offset]
offset++
ret.class = int(b >> 6)
ret.isCompound = b&0x20 == 0x20
ret.tag = int(b & 0x1f)
// If the bottom five bits are set, then the tag number is actually base 128
// encoded afterwards
if ret.tag == 0x1f {
ret.tag, offset, err = parseBase128Int(bytes, offset)
if err != nil {
return
}
// Tags should be encoded in minimal form.
if ret.tag < 0x1f {
err = SyntaxError{"non-minimal tag"}
return
}
}
if offset >= len(bytes) {
err = SyntaxError{"truncated tag or length"}
return
}
b = bytes[offset]
offset++
if b&0x80 == 0 {
// The length is encoded in the bottom 7 bits.
ret.length = int(b & 0x7f)
} else {
// Bottom 7 bits give the number of length bytes to follow.
numBytes := int(b & 0x7f)
if numBytes == 0 {
err = SyntaxError{"indefinite length found (not DER)"}
return
}
ret.length = 0
for i := 0; i < numBytes; i++ {
if offset >= len(bytes) {
err = SyntaxError{"truncated tag or length"}
return
}
b = bytes[offset]
offset++
if ret.length >= 1<<23 {
// We can't shift ret.length up without
// overflowing.
err = StructuralError{"length too large"}
return
}
ret.length <<= 8
ret.length |= int(b)
if ret.length == 0 {
// DER requires that lengths be minimal.
err = StructuralError{"superfluous leading zeros in length"}
return
}
}
// Short lengths must be encoded in short form.
if ret.length < 0x80 {
err = StructuralError{"non-minimal length"}
return
}
}
return
}
// parseSequenceOf is used for SEQUENCE OF and SET OF values. It tries to parse
// a number of ASN.1 values from the given byte slice and returns them as a
// slice of Go values of the given type.
func parseSequenceOf(bytes []byte, sliceType reflect.Type, elemType reflect.Type) (ret reflect.Value, err error) {
matchAny, expectedTag, compoundType, ok := getUniversalType(elemType)
if !ok {
err = StructuralError{"unknown Go type for slice"}
return
}
// First we iterate over the input and count the number of elements,
// checking that the types are correct in each case.
numElements := 0
for offset := 0; offset < len(bytes); {
var t tagAndLength
t, offset, err = parseTagAndLength(bytes, offset)
if err != nil {
return
}
switch t.tag {
case TagIA5String, TagGeneralString, TagT61String, TagUTF8String, TagNumericString:
// We pretend that various other string types are
// PRINTABLE STRINGs so that a sequence of them can be
// parsed into a []string.
t.tag = TagPrintableString
case TagGeneralizedTime, TagUTCTime:
// Likewise, both time types are treated the same.
t.tag = TagUTCTime
}
if !matchAny && (t.class != ClassUniversal || t.isCompound != compoundType || t.tag != expectedTag) {
err = StructuralError{"sequence tag mismatch"}
return
}
if invalidLength(offset, t.length, len(bytes)) {
err = SyntaxError{"truncated sequence"}
return
}
offset += t.length
numElements++
}
ret = reflect.MakeSlice(sliceType, numElements, numElements)
params := fieldParameters{}
offset := 0
for i := 0; i < numElements; i++ {
offset, err = parseField(ret.Index(i), bytes, offset, params)
if err != nil {
return
}
}
return
}
var (
bitStringType = reflect.TypeOf(BitString{})
objectIdentifierType = reflect.TypeOf(ObjectIdentifier{})
enumeratedType = reflect.TypeOf(Enumerated(0))
flagType = reflect.TypeOf(Flag(false))
timeType = reflect.TypeOf(time.Time{})
rawValueType = reflect.TypeOf(RawValue{})
rawContentsType = reflect.TypeOf(RawContent(nil))
bigIntType = reflect.TypeOf(new(big.Int))
)
// invalidLength reports whether offset + length > sliceLength, or if the
// addition would overflow.
func invalidLength(offset, length, sliceLength int) bool {
return offset+length < offset || offset+length > sliceLength
}
// parseField is the main parsing function. Given a byte slice and an offset
// into the array, it will try to parse a suitable ASN.1 value out and store it
// in the given Value.
func parseField(v reflect.Value, bytes []byte, initOffset int, params fieldParameters) (offset int, err error) {
offset = initOffset
fieldType := v.Type()
// If we have run out of data, it may be that there are optional elements at the end.
if offset == len(bytes) {
if !setDefaultValue(v, params) {
err = SyntaxError{"sequence truncated"}
}
return
}
// Deal with the ANY type.
if ifaceType := fieldType; ifaceType.Kind() == reflect.Interface && ifaceType.NumMethod() == 0 {
var t tagAndLength
t, offset, err = parseTagAndLength(bytes, offset)
if err != nil {
return
}
if invalidLength(offset, t.length, len(bytes)) {
err = SyntaxError{"data truncated"}
return
}
var result interface{}
if !t.isCompound && t.class == ClassUniversal {
innerBytes := bytes[offset : offset+t.length]
switch t.tag {
case TagPrintableString:
result, err = parsePrintableString(innerBytes)
case TagNumericString:
result, err = parseNumericString(innerBytes)
case TagIA5String:
result, err = parseIA5String(innerBytes)
case TagT61String:
result, err = parseT61String(innerBytes)
case TagUTF8String:
result, err = parseUTF8String(innerBytes)
case TagInteger:
result, err = parseInt64(innerBytes)
case TagBitString:
result, err = parseBitString(innerBytes)
case TagOID:
result, err = parseObjectIdentifier(innerBytes)
case TagUTCTime:
result, err = parseUTCTime(innerBytes)
case TagGeneralizedTime:
result, err = parseGeneralizedTime(innerBytes)
case TagOctetString:
result = innerBytes
default:
// If we don't know how to handle the type, we just leave Value as nil.
}
}
offset += t.length
if err != nil {
return
}
if result != nil {
v.Set(reflect.ValueOf(result))
}
return
}
t, offset, err := parseTagAndLength(bytes, offset)
if err != nil {
return
}
if params.explicit {
expectedClass := ClassContextSpecific
if params.application {
expectedClass = ClassApplication
}
if offset == len(bytes) {
err = StructuralError{"explicit tag has no child"}
return
}
if t.class == expectedClass && t.tag == *params.tag && (t.length == 0 || t.isCompound) {
if fieldType == rawValueType {
// The inner element should not be parsed for RawValues.
} else if t.length > 0 {
t, offset, err = parseTagAndLength(bytes, offset)
if err != nil {
return
}
} else {
if fieldType != flagType {
err = StructuralError{"zero length explicit tag was not an asn1.Flag"}
return
}
v.SetBool(true)
return
}
} else {
// The tags didn't match, it might be an optional element.
ok := setDefaultValue(v, params)
if ok {
offset = initOffset
} else {
err = StructuralError{"explicitly tagged member didn't match"}
}
return
}
}
matchAny, universalTag, compoundType, ok1 := getUniversalType(fieldType)
if !ok1 {
err = StructuralError{fmt.Sprintf("unknown Go type: %v", fieldType)}
return
}
// Special case for strings: all the ASN.1 string types map to the Go
// type string. getUniversalType returns the tag for PrintableString
// when it sees a string, so if we see a different string type on the
// wire, we change the universal type to match.
if universalTag == TagPrintableString {
if t.class == ClassUniversal {
switch t.tag {
case TagIA5String, TagGeneralString, TagT61String, TagUTF8String, TagNumericString:
universalTag = t.tag
}
} else if params.stringType != 0 {
universalTag = params.stringType
}
}
// Special case for time: UTCTime and GeneralizedTime both map to the
// Go type time.Time.
if universalTag == TagUTCTime && t.tag == TagGeneralizedTime && t.class == ClassUniversal {
universalTag = TagGeneralizedTime
}
if params.set {
universalTag = TagSet
}
matchAnyClassAndTag := matchAny
expectedClass := ClassUniversal
expectedTag := universalTag
if !params.explicit && params.tag != nil {
expectedClass = ClassContextSpecific
expectedTag = *params.tag
matchAnyClassAndTag = false
}
if !params.explicit && params.application && params.tag != nil {
expectedClass = ClassApplication
expectedTag = *params.tag
matchAnyClassAndTag = false
}
if !params.explicit && params.private && params.tag != nil {
expectedClass = ClassPrivate
expectedTag = *params.tag
matchAnyClassAndTag = false
}
// We have unwrapped any explicit tagging at this point.
if !matchAnyClassAndTag && (t.class != expectedClass || t.tag != expectedTag) ||
(!matchAny && t.isCompound != compoundType) {
// Tags don't match. Again, it could be an optional element.
ok := setDefaultValue(v, params)
if ok {
offset = initOffset
} else {
err = StructuralError{fmt.Sprintf("tags don't match (%d vs %+v) %+v %s @%d", expectedTag, t, params, fieldType.Name(), offset)}
}
return
}
if invalidLength(offset, t.length, len(bytes)) {
err = SyntaxError{"data truncated"}
return
}
innerBytes := bytes[offset : offset+t.length]
offset += t.length
// We deal with the structures defined in this package first.
switch fieldType {
case rawValueType:
result := RawValue{t.class, t.tag, t.isCompound, innerBytes, bytes[initOffset:offset]}
v.Set(reflect.ValueOf(result))
return
case objectIdentifierType:
newSlice, err1 := parseObjectIdentifier(innerBytes)
v.Set(reflect.MakeSlice(v.Type(), len(newSlice), len(newSlice)))
if err1 == nil {
reflect.Copy(v, reflect.ValueOf(newSlice))
}
err = err1
return
case bitStringType:
bs, err1 := parseBitString(innerBytes)
if err1 == nil {
v.Set(reflect.ValueOf(bs))
}
err = err1
return
case timeType:
var time time.Time
var err1 error
if universalTag == TagUTCTime {
time, err1 = parseUTCTime(innerBytes)
} else {
time, err1 = parseGeneralizedTime(innerBytes)
}
if err1 == nil {
v.Set(reflect.ValueOf(time))
}
err = err1
return
case enumeratedType:
parsedInt, err1 := parseInt32(innerBytes)
if err1 == nil {
v.SetInt(int64(parsedInt))
}
err = err1
return
case flagType:
v.SetBool(true)
return
case bigIntType:
parsedInt, err1 := parseBigInt(innerBytes)
if err1 == nil {
v.Set(reflect.ValueOf(parsedInt))
}
err = err1
return
}
switch val := v; val.Kind() {
case reflect.Bool:
parsedBool, err1 := parseBool(innerBytes)
if err1 == nil {
val.SetBool(parsedBool)
}
err = err1
return
case reflect.Int, reflect.Int32, reflect.Int64:
if val.Type().Size() == 4 {
parsedInt, err1 := parseInt32(innerBytes)
if err1 == nil {
val.SetInt(int64(parsedInt))
}
err = err1
} else {
parsedInt, err1 := parseInt64(innerBytes)
if err1 == nil {
val.SetInt(parsedInt)
}
err = err1
}
return
// TODO(dfc) Add support for the remaining integer types
case reflect.Struct:
structType := fieldType
for i := 0; i < structType.NumField(); i++ {
if structType.Field(i).PkgPath != "" {
err = StructuralError{"struct contains unexported fields"}
return
}
}
if structType.NumField() > 0 &&
structType.Field(0).Type == rawContentsType {
bytes := bytes[initOffset:offset]
val.Field(0).Set(reflect.ValueOf(RawContent(bytes)))
}
innerOffset := 0
for i := 0; i < structType.NumField(); i++ {
field := structType.Field(i)
if i == 0 && field.Type == rawContentsType {
continue
}
innerOffset, err = parseField(val.Field(i), innerBytes, innerOffset, parseFieldParameters(field.Tag.Get("asn1")))
if err != nil {
return
}
}
// We allow extra bytes at the end of the SEQUENCE because
// adding elements to the end has been used in X.509 as the
// version numbers have increased.
return
case reflect.Slice:
sliceType := fieldType
if sliceType.Elem().Kind() == reflect.Uint8 {
val.Set(reflect.MakeSlice(sliceType, len(innerBytes), len(innerBytes)))
reflect.Copy(val, reflect.ValueOf(innerBytes))
return
}
newSlice, err1 := parseSequenceOf(innerBytes, sliceType, sliceType.Elem())
if err1 == nil {
val.Set(newSlice)
}
err = err1
return
case reflect.String:
var v string
switch universalTag {
case TagPrintableString:
v, err = parsePrintableString(innerBytes)
case TagNumericString:
v, err = parseNumericString(innerBytes)
case TagIA5String:
v, err = parseIA5String(innerBytes)
case TagT61String:
v, err = parseT61String(innerBytes)
case TagUTF8String:
v, err = parseUTF8String(innerBytes)
case TagGeneralString:
// GeneralString is specified in ISO-2022/ECMA-35,
// A brief review suggests that it includes structures
// that allow the encoding to change midstring and
// such. We give up and pass it as an 8-bit string.
v, err = parseT61String(innerBytes)
default:
err = SyntaxError{fmt.Sprintf("internal error: unknown string type %d", universalTag)}
}
if err == nil {
val.SetString(v)
}
return
}
err = StructuralError{"unsupported: " + v.Type().String()}
return
}
// canHaveDefaultValue reports whether k is a Kind that we will set a default
// value for. (A signed integer, essentially.)
func canHaveDefaultValue(k reflect.Kind) bool {
switch k {
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
return true
}
return false
}
// setDefaultValue is used to install a default value, from a tag string, into
// a Value. It is successful if the field was optional, even if a default value
// wasn't provided or it failed to install it into the Value.
func setDefaultValue(v reflect.Value, params fieldParameters) (ok bool) {
if !params.optional {
return
}
ok = true
if params.defaultValue == nil {
return
}
if canHaveDefaultValue(v.Kind()) {
v.SetInt(*params.defaultValue)
}
return
}
// Unmarshal parses the DER-encoded ASN.1 data structure b
// and uses the reflect package to fill in an arbitrary value pointed at by val.
// Because Unmarshal uses the reflect package, the structs
// being written to must use upper case field names.
//
// An ASN.1 INTEGER can be written to an int, int32, int64,
// or *big.Int (from the math/big package).
// If the encoded value does not fit in the Go type,
// Unmarshal returns a parse error.
//
// An ASN.1 BIT STRING can be written to a BitString.
//
// An ASN.1 OCTET STRING can be written to a []byte.
//
// An ASN.1 OBJECT IDENTIFIER can be written to an
// ObjectIdentifier.
//
// An ASN.1 ENUMERATED can be written to an Enumerated.
//
// An ASN.1 UTCTIME or GENERALIZEDTIME can be written to a time.Time.
//
// An ASN.1 PrintableString, IA5String, or NumericString can be written to a string.
//
// Any of the above ASN.1 values can be written to an interface{}.
// The value stored in the interface has the corresponding Go type.
// For integers, that type is int64.
//
// An ASN.1 SEQUENCE OF x or SET OF x can be written
// to a slice if an x can be written to the slice's element type.
//
// An ASN.1 SEQUENCE or SET can be written to a struct
// if each of the elements in the sequence can be
// written to the corresponding element in the struct.
//
// The following tags on struct fields have special meaning to Unmarshal:
//
// application specifies that an APPLICATION tag is used
// private specifies that a PRIVATE tag is used
// default:x sets the default value for optional integer fields (only used if optional is also present)
// explicit specifies that an additional, explicit tag wraps the implicit one
// optional marks the field as ASN.1 OPTIONAL
// set causes a SET, rather than a SEQUENCE type to be expected
// tag:x specifies the ASN.1 tag number; implies ASN.1 CONTEXT SPECIFIC
//
// If the type of the first field of a structure is RawContent then the raw
// ASN1 contents of the struct will be stored in it.
//
// If the type name of a slice element ends with "SET" then it's treated as if
// the "set" tag was set on it. This can be used with nested slices where a
// struct tag cannot be given.
//
// Other ASN.1 types are not supported; if it encounters them,
// Unmarshal returns a parse error.
func Unmarshal(b []byte, val interface{}) (rest []byte, err error) {
return UnmarshalWithParams(b, val, "")
}
// UnmarshalWithParams allows field parameters to be specified for the
// top-level element. The form of the params is the same as the field tags.
func UnmarshalWithParams(b []byte, val interface{}, params string) (rest []byte, err error) {
v := reflect.ValueOf(val).Elem()
offset, err := parseField(v, b, 0, parseFieldParameters(params))
if err != nil {
return nil, err
}
return b[offset:], nil
}
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