bitstring.go

package asn1

import (
	"fmt"
	"reflect"
)

type BitString struct {
	Bytes       []byte
	PaddingBits int
}

var bitStringType = reflect.TypeOf(BitString{})

func NewBitString(b []byte, paddingBits int) (BitString, error) {
	bitString := BitString{
		Bytes: b,
	}

	if paddingBits > 7 {
		return bitString, fmt.Errorf("too many padding bits: expecting <= 7, got: %d", paddingBits)
	}

	if len(b) == 0 && paddingBits != 0 {
		return bitString, fmt.Errorf("empty bit string, but got %d padding bits", paddingBits)
	}

	// ber does not require padding to be zero-valued
	// if paddingBits > 0 && b[len(b) - 1] & ((1 << paddingBits) - 1) != 0 {
	// 	return bitString, fmt.Errorf("Padded bits not zero")
	// }

	bitString.PaddingBits = paddingBits

	return bitString, nil
}

type bitStringEncoder BitString

func (e bitStringEncoder) encode() ([]byte, error) {
	buf := make([]byte, len(e.Bytes)+1)
	buf[0] = byte(e.PaddingBits)
	copy(buf[1:], e.Bytes)
	return buf, nil
}