Description

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 or IA5String 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 a APPLICATION tag is used
default:x	sets the default value for optional integer fields
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.