package smtpserver

import (

"context"

"errors"

"sync"

"time"

"github.com/mjl-/mox/dns"

"github.com/mjl-/mox/dnsbl"

"github.com/mjl-/mox/mlog"

)

var dnsblHealth = struct {

sync.Mutex

zones map[dns.Domain]dnsblStatus

}{

zones: map[dns.Domain]dnsblStatus{},

}

type dnsblStatus struct {

last time.Time

err error // nil, dnsbl.ErrDNS or other

}

// checkDNSBLHealth checks healthiness of DNSBL "zone", keeping the result cached for 4 hours.

func checkDNSBLHealth(ctx context.Context, log mlog.Log, resolver dns.Resolver, zone dns.Domain) (rok bool) {

dnsblHealth.Lock()

defer dnsblHealth.Unlock()

status, ok := dnsblHealth.zones[zone]

if !ok || time.Since(status.last) > 4*time.Hour {

status.err = dnsbl.CheckHealth(ctx, log.Logger, resolver, zone)

status.last = time.Now()

dnsblHealth.zones[zone] = status

}

return status.err == nil || errors.Is(status.err, dnsbl.ErrDNS)

}