mox!

smtpserver/dnsbl.go

@@ -0,0 +1,36 @@
+package smtpserver
+
+import (
+	"context"
+	"errors"
+	"sync"
+	"time"
+
+	"github.com/mjl-/mox/dns"
+	"github.com/mjl-/mox/dnsbl"
+)
+
+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, 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, resolver, zone)
+		status.last = time.Now()
+		dnsblHealth.zones[zone] = status
+	}
+	return status.err == nil || errors.Is(status.err, dnsbl.ErrDNS)
+}