question.go

package dns

import (
	"bytes"
	"encoding/binary"
	"errors"
)

// Question holds single dns questions
type Question struct {
	Domain          string
	Type            Type
	Class           Class
	UnicastResponse bool
}

// UnicastResponseBit holds the bit for the mDNS unicast response
const UnicastResponseBit = 0x8000

// ParseQuestion parses DNS question records
func ParseQuestion(buf *bytes.Buffer, pointer int, domains *Domains) (Question, error) {
	q := Question{}
	dom, err := ParseName(buf, pointer, domains)
	if err != nil {
		return Question{}, err
	}
	q.Domain = dom
	if err := binary.Read(buf, binary.BigEndian, &q.Type); err != nil {
		return Question{}, err
	}
	if err := binary.Read(buf, binary.BigEndian, &q.Class); err != nil {
		return Question{}, err
	}

	// Read and filter out mDNS unicast UnicastResponse bit
	q.UnicastResponse = (q.Class & UnicastResponseBit) == UnicastResponseBit
	q.Class = q.Class & 0x7fff

	return q, nil
}

// Build builds a DNS question record
func (q *Question) Build(buf *bytes.Buffer, domains *Domains) error {
	if q.Domain == "" || q.Type == 0 || q.Class == 0 {
		return errors.New("domain or query type unset")
	}

	name := BuildName(q.Domain, domains)
	domains.SetBuild(buf.Len(), q.Domain)
	buf.WriteString(name)
	err := binary.Write(buf, binary.BigEndian, q.Type)
	if err != nil {
		return err
	}
	if q.UnicastResponse {
		err = binary.Write(buf, binary.BigEndian, q.Class|UnicastResponseBit)
	} else {
		err = binary.Write(buf, binary.BigEndian, q.Class)
	}
	if err != nil {
		return err
	}
	return nil
}