nghttpx: Respect backend-address-family on dynamic DNS lookup

src/shrpx_dns_tracker.cc

@@ -36,7 +36,8 @@ void gccb(struct ev_loop *loop, ev_timer *w, int revents) {
 }
 } // namespace
 
-DNSTracker::DNSTracker(struct ev_loop *loop) : loop_(loop) {
+DNSTracker::DNSTracker(struct ev_loop *loop, int family)
+    : loop_(loop), family_(family) {
   ev_timer_init(&gc_timer_, gccb, 0., 12_h);
   gc_timer_.data = this;
 }
@@ -111,7 +112,7 @@ DNSResolverStatus DNSTracker::resolve(Address *result, DNSQuery *dnsq) {
       LOG(INFO) << "DNS entry not found for " << dnsq->host;
     }
 
-    auto resolv = std::make_unique<DualDNSResolver>(loop_);
+    auto resolv = std::make_unique<DualDNSResolver>(loop_, family_);
     auto host_copy =
         ImmutableString{std::begin(dnsq->host), std::end(dnsq->host)};
     auto host = StringRef{host_copy};
@@ -180,7 +181,7 @@ DNSResolverStatus DNSTracker::resolve(Address *result, DNSQuery *dnsq) {
                 << ", but it has been expired";
     }
 
-    auto resolv = std::make_unique<DualDNSResolver>(loop_);
+    auto resolv = std::make_unique<DualDNSResolver>(loop_, family_);
     auto host = StringRef{ent.host};
 
     rv = resolv->resolve(host);

src/shrpx_dns_tracker.h

@@ -75,7 +75,7 @@ struct ResolverEntry {
 
 class DNSTracker {
 public:
-  DNSTracker(struct ev_loop *loop);
+  DNSTracker(struct ev_loop *loop, int family);
   ~DNSTracker();
 
   // Lookups host name described in |dnsq|.  If name lookup finishes
@@ -111,6 +111,8 @@ private:
   // increase memory consumption, interval could be very long.
   ev_timer gc_timer_;
   struct ev_loop *loop_;
+  // IP version preference.
+  int family_;
 };
 
 } // namespace shrpx

src/shrpx_dual_dns_resolver.cc

@@ -26,8 +26,8 @@
 
 namespace shrpx {
 
-DualDNSResolver::DualDNSResolver(struct ev_loop *loop)
-    : resolv4_(loop), resolv6_(loop) {
+DualDNSResolver::DualDNSResolver(struct ev_loop *loop, int family)
+    : family_(family), resolv4_(loop), resolv6_(loop) {
   auto cb = [this](DNSResolverStatus, const Address *) {
     Address result;
 
@@ -44,14 +44,22 @@ DualDNSResolver::DualDNSResolver(struct ev_loop *loop)
     cb(status, &result);
   };
 
+  if (family_ == AF_UNSPEC || family_ == AF_INET) {
     resolv4_.set_complete_cb(cb);
+  }
+  if (family_ == AF_UNSPEC || family_ == AF_INET6) {
     resolv6_.set_complete_cb(cb);
   }
+}
 
 int DualDNSResolver::resolve(const StringRef &host) {
-  int rv4, rv6;
+  int rv4 = 0, rv6 = 0;
+  if (family_ == AF_UNSPEC || family_ == AF_INET) {
     rv4 = resolv4_.resolve(host, AF_INET);
+  }
+  if (family_ == AF_UNSPEC || family_ == AF_INET6) {
     rv6 = resolv6_.resolve(host, AF_INET6);
+  }
 
   if (rv4 != 0 && rv6 != 0) {
     return -1;

src/shrpx_dual_dns_resolver.h

@@ -42,7 +42,11 @@ namespace shrpx {
 // how CompleteCb is called have the same semantics with DNSResolver.
 class DualDNSResolver {
 public:
-  DualDNSResolver(struct ev_loop *loop);
+  // |family| controls IP version preference.  If |family| ==
+  // AF_UNSPEC, bot A and AAAA lookups are performed.  If |family| ==
+  // AF_INET, only A lookup is performed.  If |family| == AF_INET6,
+  // only AAAA lookup is performed.
+  DualDNSResolver(struct ev_loop *loop, int family);
 
   // Resolves |host|.  |host| must be NULL-terminated string.
   int resolve(const StringRef &host);
@@ -51,6 +55,8 @@ public:
   DNSResolverStatus get_status(Address *result) const;
 
 private:
+  // IP version preference.
+  int family_;
   // For A record
   DNSResolver resolv4_;
   // For AAAA record

src/shrpx_worker.cc

@@ -161,7 +161,7 @@ Worker::Worker(struct ev_loop *loop, SSL_CTX *sv_ssl_ctx, SSL_CTX *cl_ssl_ctx,
 #endif // ENABLE_HTTP3 && HAVE_LIBBPF
       randgen_(util::make_mt19937()),
       worker_stat_{},
-      dns_tracker_(loop),
+      dns_tracker_(loop, get_config()->conn.downstream->family),
 #ifdef ENABLE_HTTP3
       quic_upstream_addrs_{get_config()->conn.quic_listener.addrs},
 #endif // ENABLE_HTTP3