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.
ASN.1 tags represent the type of the following object.
const (
TagBoolean = 1
TagInteger = 2
TagBitString = 3
TagOctetString = 4
TagNull = 5
TagOID = 6
TagEnum = 10
TagUTF8String = 12
TagSequence = 16
TagSet = 17
TagNumericString = 18
TagPrintableString = 19
TagT61String = 20
TagIA5String = 22
TagUTCTime = 23
TagGeneralizedTime = 24
TagGeneralString = 27
TagBMPString = 30
) ASN.1 class types represent the namespace of the tag.
const (
ClassUniversal = 0
ClassApplication = 1
ClassContextSpecific = 2
ClassPrivate = 3
) NullBytes contains bytes representing the DER-encoded ASN.1 NULL type.
var NullBytes = []byte{TagNull, 0} NullRawValue is a RawValue with its Tag set to the ASN.1 NULL type tag (5).
var NullRawValue = RawValue{Tag: TagNull} func Marshal(val interface{}) ([]byte, error) Marshal returns the ASN.1 encoding of val.
In addition to the struct tags recognised by Unmarshal, the following can be used:
ia5: causes strings to be marshaled as ASN.1, IA5String values omitempty: causes empty slices to be skipped printable: causes strings to be marshaled as ASN.1, PrintableString values utf8: causes strings to be marshaled as ASN.1, UTF8String values utc: causes time.Time to be marshaled as ASN.1, UTCTime values generalized: causes time.Time to be marshaled as ASN.1, GeneralizedTime values
func MarshalWithParams(val interface{}, params string) ([]byte, error) MarshalWithParams allows field parameters to be specified for the top-level element. The form of the params is the same as the field tags.
func Unmarshal(b []byte, val interface{}) (rest []byte, err error) 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.
After parsing b, any bytes that were leftover and not used to fill val will be returned in rest. When parsing a SEQUENCE into a struct, any trailing elements of the SEQUENCE that do not have matching fields in val will not be included in rest, as these are considered valid elements of the SEQUENCE and not trailing data.
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 UnmarshalWithParams(b []byte, val interface{}, params string) (rest []byte, err error) UnmarshalWithParams allows field parameters to be specified for the top-level element. The form of the params is the same as the field tags.
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.
}
func (b BitString) At(i int) int
At returns the bit at the given index. If the index is out of range it returns false.
func (b BitString) RightAlign() []byte
RightAlign returns a slice where the padding bits are at the beginning. The slice may share memory with the BitString.
An Enumerated is represented as a plain int.
type Enumerated int
A Flag accepts any data and is set to true if present.
type Flag bool
An ObjectIdentifier represents an ASN.1 OBJECT IDENTIFIER.
type ObjectIdentifier []int
func (oi ObjectIdentifier) Equal(other ObjectIdentifier) bool
Equal reports whether oi and other represent the same identifier.
func (oi ObjectIdentifier) String() string
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
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
}
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
A SyntaxError suggests that the ASN.1 data is invalid.
type SyntaxError struct {
Msg string
}
func (e SyntaxError) Error() string
© Google, Inc.
Licensed under the Creative Commons Attribution License 3.0.
https://golang.org/pkg/encoding/asn1/