Luzilla/dnsbl_exporter

package dns

import (
    "net"
    "strings"
    "time"

    x "github.com/miekg/dns"
    "golang.org/x/exp/slog"
)

type DNSUtil struct {
    client   *x.Client
    resolver struct {
        host string
        port string
    }
    logger *slog.Logger
}

func New(client *x.Client, resolver string, logger *slog.Logger) (*DNSUtil, error) {
    host, port, err := net.SplitHostPort(resolver)
    if err != nil {
        addrErr, ok := err.(*net.AddrError)
        if !ok {
            return nil, err
        }

        if !strings.Contains(addrErr.Error(), "missing port in address") {
            return nil, err
        }

        // default to port 53
        host = resolver
        port = "53"
    }

    // set timeouts
    client.DialTimeout = (2 * time.Second)
    client.ReadTimeout = (2 * time.Second)
    client.WriteTimeout = (2 * time.Second)

    return &DNSUtil{
        client: client,
        resolver: struct {
            host string
            port string
        }{
            host, port,
        },
        logger: logger,
    }, nil
}

// leaving this note for future me: maybe asking for As is not enough?
// what about CNAMEs, or AAAAs, etc..
func (d *DNSUtil) GetARecords(target string) (list []string, err error) {
    msg := createQuestion(target, x.TypeA)

    result, err := d.makeQuery(msg)
    if err != nil {
        return
    }

    if len(result.Answer) == 0 {
        return
    }

    for _, ans := range result.Answer {
        if t, ok := ans.(*x.A); ok {
            d.logger.Debug("we have an A-record", slog.String("target", target), slog.String("v", t.A.String()))
            list = append(list, t.A.String())
        }
    }

    return
}

func (d *DNSUtil) GetTxtRecords(target string) (list []string, err error) {
    msg := createQuestion(target, x.TypeTXT)

    result, err := d.makeQuery(msg)
    if err != nil {
        return
    }

    if len(result.Answer) == 0 {
        return
    }

    for _, ans := range result.Answer {
        if t, ok := ans.(*x.TXT); ok {
            list = append(list, t.Txt...)
        }
    }

    return
}

func (d *DNSUtil) makeQuery(msg *x.Msg) (*x.Msg, error) {
    result, rt, err := d.client.Exchange(msg, net.JoinHostPort(d.resolver.host, d.resolver.port))
    d.logger.Debug("roundtrip",
        slog.String("question", msg.Question[0].String()),
        slog.Float64("seconds", rt.Seconds())) // fixme -> histogram

    return result, err
}

func createQuestion(target string, record uint16) *x.Msg {
    msg := new(x.Msg)
    msg.SetQuestion(x.Fqdn(target), record)

    return msg
}