Fix internal cache TTL computation for dnsx responses

intra/dnsx/alg.go

@@ -1927,6 +1927,19 @@ func (t *dnsgateway) ptrLocked(maybeAlg netip.Addr, uid, tid string, useptr bool
 	return copyUniq(domains)
 }
 
+func minNonZeroDuration(curr, next time.Duration) time.Duration {
+	if curr == 0 {
+		return next
+	}
+	if next == 0 {
+		return curr
+	}
+	if next < curr {
+		return next
+	}
+	return curr
+}
+
 // resolvLocked returns IPs and related targets for domain
 // depending on typ.
 // If typ is typalg, returns all algips for domain.
@@ -1950,7 +1963,7 @@ func (t *dnsgateway) resolvLocked(domain string, typ iptype, tid, uid string) (i
 				if life, fresh := ans.fresh(); fresh { // not stale
 					ip4s = append(ip4s, ans.algip)
 					targets = append(targets, domainsFor(ans.baseans, tid, uid, ans.algip, xalive)...)
-					until = min(until, life)
+					until = minNonZeroDuration(until, life)
 				} else {
 					staleips = append(staleips, ans.algip)
 				}
@@ -1964,7 +1977,7 @@ func (t *dnsgateway) resolvLocked(domain string, typ iptype, tid, uid string) (i
 				if life, fresh := ans.fresh(); fresh { // not stale
 					ip6s = append(ip6s, ans.algip)
 					targets = append(targets, domainsFor(ans.baseans, tid, uid, ans.algip, xalive)...)
-					until = min(until, life)
+					until = minNonZeroDuration(until, life)
 				} else {
 					staleips = append(staleips, ans.algip)
 				}
@@ -1984,7 +1997,7 @@ func (t *dnsgateway) resolvLocked(domain string, typ iptype, tid, uid string) (i
 					all4s := v4only(ans.ips.realipsFor(tid, uid, xalive))
 					ip4s = append(ip4s, all4s...)
 					targets = append(targets, domainsFor(ans.baseans, tid, uid, core.FirstOf(all4s), xalive)...)
-					until = min(until, life)
+					until = minNonZeroDuration(until, life)
 				} else {
 					staleips = append(staleips, ans.ips.realipsFor(tid, uid, xall)...)
 				}
@@ -1999,7 +2012,7 @@ func (t *dnsgateway) resolvLocked(domain string, typ iptype, tid, uid string) (i
 					all6s := v6only(ans.ips.realipsFor(tid, uid, xalive))
 					ip6s = append(ip6s, all6s...)
 					targets = append(targets, domainsFor(ans.baseans, tid, uid, core.FirstOf(all6s), xalive)...)
-					until = min(until, life)
+					until = minNonZeroDuration(until, life)
 				} else {
 					staleips = append(staleips, ans.ips.realipsFor(tid, uid, xall)...)
 				}
@@ -2019,7 +2032,7 @@ func (t *dnsgateway) resolvLocked(domain string, typ iptype, tid, uid string) (i
 					all4s := v4only(ans.ips.secipsFor(tid, uid))
 					ip4s = append(ip4s, all4s...)
 					targets = append(targets, domainsFor(ans.baseans, tid, uid, core.FirstOf(all4s), xalive)...)
-					until = min(until, life)
+					until = minNonZeroDuration(until, life)
 				} else {
 					staleips = append(staleips, ans.ips.secips(xall)...)
 				}
@@ -2034,7 +2047,7 @@ func (t *dnsgateway) resolvLocked(domain string, typ iptype, tid, uid string) (i
 					all6s := v6only(ans.ips.secipsFor(tid, uid))
 					ip6s = append(ip6s, all6s...)
 					targets = append(targets, domainsFor(ans.baseans, tid, uid, core.FirstOf(all6s), xalive)...)
-					until = min(until, life)
+					until = minNonZeroDuration(until, life)
 				} else {
 					// TODO: stale targets?
 					staleips = append(staleips, ans.ips.secips(xall)...)

intra/dnsx/alg_cache_test.go

@@ -0,0 +1,62 @@
+package dnsx
+
+import (
+	"net/netip"
+	"testing"
+	"time"
+
+	"github.com/miekg/dns"
+)
+
+func TestResolvLockedUntilUsesRemainingTTL(t *testing.T) {
+	q := new(dns.Msg)
+	q.SetQuestion("example.com.", dns.TypeA)
+	domain := qname(q)
+
+	tid := "tid"
+	uid := "uid"
+	ttl := time.Now().Add(30 * time.Second)
+
+	realip := netip.MustParseAddr("1.1.1.1")
+	algip := netip.MustParseAddr("100.64.0.1")
+
+	xips := NewXips(tid, uid, []netip.Addr{realip}, nil, ttl)
+	if xips == nil {
+		t.Fatalf("expected xips")
+	}
+	xdomains := NewXdomains(tid, uid, []string{domain}, ttl)
+	if xdomains == nil {
+		t.Fatalf("expected xdomains")
+	}
+
+	gw := &dnsgateway{
+		alg: map[string]*algans{
+			domain + key4 + "0": {
+				algip: algip,
+				baseans: &baseans{
+					ips:     xips,
+					domains: xdomains,
+					ttl:     ttl,
+				},
+			},
+		},
+		nat: make(map[netip.Addr]*baseans),
+		ptr: make(map[netip.Addr]*baseans),
+	}
+
+	_, _, _, until, _ := gw.resolvLocked(domain, typreal, tid, uid)
+	if until <= 0 {
+		t.Fatalf("expected positive ttl, got %s", until)
+	}
+
+	ans, err := gw.fromInternalCache(tid, uid, q, typreal)
+	if err != nil {
+		t.Fatalf("expected cache hit, got error %v", err)
+	}
+	if len(ans.Answer) == 0 {
+		t.Fatalf("expected at least one answer")
+	}
+	if got := ans.Answer[0].Header().Ttl; got < 20 {
+		t.Fatalf("expected ttl >= 20s, got %d", got)
+	}
+}