mox!

tlsrpt/lookup.go

@@ -0,0 +1,91 @@
+package tlsrpt
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+
+	"github.com/mjl-/mox/dns"
+	"github.com/mjl-/mox/mlog"
+)
+
+var xlog = mlog.New("tlsrpt")
+
+var (
+	metricLookup = promauto.NewHistogramVec(
+		prometheus.HistogramOpts{
+			Name:    "mox_tlsrpt_lookup_duration_seconds",
+			Help:    "TLSRPT lookups with result.",
+			Buckets: []float64{0.001, 0.005, 0.01, 0.05, 0.100, 0.5, 1, 5, 10, 20, 30},
+		},
+		[]string{"result"},
+	)
+)
+
+var (
+	ErrNoRecord        = errors.New("tlsrpt: no tlsrpt dns txt record")
+	ErrMultipleRecords = errors.New("tlsrpt: multiple tlsrpt records") // Must be treated as if domain does not implement TLSRPT.
+	ErrDNS             = errors.New("tlsrpt: temporary error")
+	ErrRecordSyntax    = errors.New("tlsrpt: record syntax error")
+)
+
+// Lookup looks up a TLSRPT DNS TXT record for domain at "_smtp._tls.<domain>" and
+// parses it.
+func Lookup(ctx context.Context, resolver dns.Resolver, domain dns.Domain) (rrecord *Record, rtxt string, rerr error) {
+	log := xlog.WithContext(ctx)
+	start := time.Now()
+	defer func() {
+		result := "ok"
+		if rerr != nil {
+			if errors.Is(rerr, ErrNoRecord) {
+				result = "notfound"
+			} else if errors.Is(rerr, ErrMultipleRecords) {
+				result = "multiple"
+			} else if errors.Is(rerr, ErrDNS) {
+				result = "temperror"
+			} else if errors.Is(rerr, ErrRecordSyntax) {
+				result = "malformed"
+			} else {
+				result = "error"
+			}
+		}
+		metricLookup.WithLabelValues(result).Observe(float64(time.Since(start)) / float64(time.Second))
+		log.Debugx("tlsrpt lookup result", rerr, mlog.Field("domain", domain), mlog.Field("record", rrecord), mlog.Field("duration", time.Since(start)))
+	}()
+
+	name := "_smtp._tls." + domain.ASCII + "."
+	txts, err := dns.WithPackage(resolver, "tlsrpt").LookupTXT(ctx, name)
+	if dns.IsNotFound(err) {
+		return nil, "", ErrNoRecord
+	} else if err != nil {
+		return nil, "", fmt.Errorf("%w: %s", ErrDNS, err)
+	}
+
+	var text string
+	var record *Record
+	for _, txt := range txts {
+		r, istlsrpt, err := ParseRecord(txt)
+		if !istlsrpt {
+			// This is a loose but probably reasonable interpretation of ../rfc/8460:375 which
+			// wants us to discard otherwise valid records that start with e.g. "v=TLSRPTv1 ;"
+			// (note the space before the ";") when multiple TXT records were returned.
+			continue
+		}
+		if err != nil {
+			return nil, "", fmt.Errorf("parsing record: %w", err)
+		}
+		if record != nil {
+			return nil, "", ErrMultipleRecords
+		}
+		record = r
+		text = txt
+	}
+	if record == nil {
+		return nil, "", ErrNoRecord
+	}
+	return record, text, nil
+}