pickfirst: Interleave IPv6 and IPv4 addresses for happy eyeballs

balancer/pickfirst/pickfirstleaf/pickfirstleaf.go

@@ -29,6 +29,7 @@
 	"encoding/json"
 	"errors"
 	"fmt"
+	"net"
 	"sync"
 
 	"google.golang.org/grpc/balancer"
@@ -61,6 +62,14 @@
 // TODO: change to pick-first when this becomes the default pick_first policy.
 const logPrefix = "[pick-first-leaf-lb %p] "
 
+type ipAddrType int
+
+const (
+	ipTypeUnknown ipAddrType = iota
+	ipv4
+	ipv6
+)
+
 type pickfirstBuilder struct{}
 
 func (pickfirstBuilder) Build(cc balancer.ClientConn, _ balancer.BuildOptions) balancer.Balancer {
@@ -206,9 +215,6 @@
 		// "Flatten the list by concatenating the ordered list of addresses for
 		// each of the endpoints, in order." - A61
 		for _, endpoint := range endpoints {
-			// "In the flattened list, interleave addresses from the two address
-			// families, as per RFC-8305 section 4." - A61
-			// TODO: support the above language.
 			newAddrs = append(newAddrs, endpoint.Addresses...)
 		}
 	} else {
@@ -232,6 +238,10 @@
 	// SubConn multiple times in the same pass. We don't want this.
 	newAddrs = deDupAddresses(newAddrs)
 
+	// Interleave addresses of both families (IPv4 and IPv6) as per RFC-8305
+	// section 4.
+	newAddrs = interleaveAddresses(newAddrs)
+
 	// Since we have a new set of addresses, we are again at first pass.
 	b.firstPass = true
 
@@ -314,6 +324,64 @@
 	return retAddrs
 }
 
+func interleaveAddresses(addrs []resolver.Address) []resolver.Address {
+	// Group the addresses by their type and determine the order in which to
+	// interleave the address families. The order of interleaving the families
+	// is the order in which the first address of a particular type appears in
+	// the address list.
+	familyAddrsMap := map[ipAddrType][]resolver.Address{}
+	interleavingOrder := []ipAddrType{}
+	for _, addr := range addrs {
+		typ := addressType(addr.Addr)
+		if _, found := familyAddrsMap[typ]; !found {
+			interleavingOrder = append(interleavingOrder, typ)
+		}
+		familyAddrsMap[typ] = append(familyAddrsMap[typ], addr)
+	}
+
+	interleavedAddrs := make([]resolver.Address, 0, len(addrs))
+
+	for curTypeIndex := 0; len(interleavedAddrs) < len(addrs); curTypeIndex = (curTypeIndex + 1) % len(interleavingOrder) {
+		// Some IP types may have fewer addresses than others, so we look for
+		// the next type that has a remaining member to add to the interleaved
+		// list.
+		typ := interleavingOrder[curTypeIndex]
+		remainingMembers := familyAddrsMap[typ]
+		if len(remainingMembers) > 0 {
+			interleavedAddrs = append(interleavedAddrs, remainingMembers[0])
+			familyAddrsMap[typ] = remainingMembers[1:]
+		}
+	}
+
+	return interleavedAddrs
+}
+
+func addressType(address string) ipAddrType {
+	// Try parsing addresses without a port specified.
+	ip := net.ParseIP(address)
+	if ip == nil {
+		// Try to parse the IP after removing the port.
+		host, _, err := net.SplitHostPort(address)
+		if err != nil {
+			return ipTypeUnknown
+		}
+		ip = net.ParseIP(host)
+	}
+
+	// If using the passthrough resolver, the hostnames would be unresolved
+	// and therefore not valid IP addresses.
+	if ip == nil {
+		return ipTypeUnknown
+	}
+
+	if ip.To4() != nil {
+		return ipv4
+	} else if ip.To16() != nil {
+		return ipv6
+	}
+	return ipTypeUnknown
+}
+
 // reconcileSubConnsLocked updates the active subchannels based on a new address
 // list from the resolver. It does this by:
 //   - closing subchannels: any existing subchannels associated with addresses

balancer/pickfirst/pickfirstleaf/pickfirstleaf_ext_test.go

@@ -851,6 +851,114 @@ func (s) TestPickFirstLeaf_EmptyAddressList(t *testing.T) {
 	}
 }
 
+func (s) TestPickFirstLeaf_InterleavingIPV4Preffered(t *testing.T) {
+	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
+	defer cancel()
+	cc := testutils.NewBalancerClientConn(t)
+	bal := balancer.Get(pickfirstleaf.Name).Build(cc, balancer.BuildOptions{})
+	defer bal.Close()
+	ccState := balancer.ClientConnState{
+		ResolverState: resolver.State{
+			Endpoints: []resolver.Endpoint{
+				{Addresses: []resolver.Address{{Addr: "1.1.1.1"}}}, // no port
+				{Addresses: []resolver.Address{{Addr: "2.2.2.2:2"}}},
+				{Addresses: []resolver.Address{{Addr: "3.3.3.3:3"}}},
+				{Addresses: []resolver.Address{{Addr: "4.4.4.4:4"}}},
+				{Addresses: []resolver.Address{{Addr: "[0001:0001:0001:0001:0001:0001:0001:0001]:8080"}}}, // ipv6 with port
+				{Addresses: []resolver.Address{{Addr: "0002:0002:0002:0002:0002:0002:0002:0002"}}},
+				{Addresses: []resolver.Address{{Addr: "0003:0003:0003:0003:0003:0003:0003:0003"}}},
+				{Addresses: []resolver.Address{{Addr: "grpc.io:80"}}}, // not an IP.
+			},
+		},
+	}
+	if err := bal.UpdateClientConnState(ccState); err != nil {
+		t.Fatalf("UpdateClientConnState(%v) returned error: %v", ccState, err)
+	}
+
+	wantAddrs := []resolver.Address{
+		{Addr: "1.1.1.1"},
+		{Addr: "[0001:0001:0001:0001:0001:0001:0001:0001]:8080"},
+		{Addr: "grpc.io:80"},
+		{Addr: "2.2.2.2:2"},
+		{Addr: "0002:0002:0002:0002:0002:0002:0002:0002"},
+		{Addr: "3.3.3.3:3"},
+		{Addr: "0003:0003:0003:0003:0003:0003:0003:0003"},
+		{Addr: "4.4.4.4:4"},
+	}
+
+	gotAddrs, err := subConnAddresses(ctx, cc, 8)
+	if err != nil {
+		t.Fatalf("%v", err)
+	}
+	if diff := cmp.Diff(wantAddrs, gotAddrs); diff != "" {
+		t.Errorf("subconn creation order mismatch (-want +got):\n%s", diff)
+	}
+}
+
+func (s) TestPickFirstLeaf_InterleavingIPv6Preffered(t *testing.T) {
+	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
+	defer cancel()
+	cc := testutils.NewBalancerClientConn(t)
+	bal := balancer.Get(pickfirstleaf.Name).Build(cc, balancer.BuildOptions{})
+	defer bal.Close()
+	ccState := balancer.ClientConnState{
+		ResolverState: resolver.State{
+			Endpoints: []resolver.Endpoint{
+				{Addresses: []resolver.Address{{Addr: "[0001:0001:0001:0001:0001:0001:0001:0001]:8080"}}}, // ipv6 with port
+				{Addresses: []resolver.Address{{Addr: "1.1.1.1"}}},                                        // no port
+				{Addresses: []resolver.Address{{Addr: "2.2.2.2:2"}}},
+				{Addresses: []resolver.Address{{Addr: "3.3.3.3:3"}}},
+				{Addresses: []resolver.Address{{Addr: "4.4.4.4:4"}}},
+				{Addresses: []resolver.Address{{Addr: "0002:0002:0002:0002:0002:0002:0002:0002"}}},
+				{Addresses: []resolver.Address{{Addr: "0003:0003:0003:0003:0003:0003:0003:0003"}}},
+				{Addresses: []resolver.Address{{Addr: "grpc.io:80"}}}, // not an IP.
+			},
+		},
+	}
+	if err := bal.UpdateClientConnState(ccState); err != nil {
+		t.Fatalf("UpdateClientConnState(%v) returned error: %v", ccState, err)
+	}
+
+	wantAddrs := []resolver.Address{
+		{Addr: "[0001:0001:0001:0001:0001:0001:0001:0001]:8080"},
+		{Addr: "1.1.1.1"},
+		{Addr: "grpc.io:80"},
+		{Addr: "0002:0002:0002:0002:0002:0002:0002:0002"},
+		{Addr: "2.2.2.2:2"},
+		{Addr: "0003:0003:0003:0003:0003:0003:0003:0003"},
+		{Addr: "3.3.3.3:3"},
+		{Addr: "4.4.4.4:4"},
+	}
+
+	gotAddrs, err := subConnAddresses(ctx, cc, 8)
+	if err != nil {
+		t.Fatalf("%v", err)
+	}
+	if diff := cmp.Diff(wantAddrs, gotAddrs); diff != "" {
+		t.Errorf("subconn creation order mismatch (-want +got):\n%s", diff)
+	}
+}
+func subConnAddresses(ctx context.Context, cc *testutils.BalancerClientConn, subConnCount int) ([]resolver.Address, error) {
+	addresses := []resolver.Address{}
+	for i := 0; i < subConnCount; i++ {
+		select {
+		case <-ctx.Done():
+			return nil, fmt.Errorf("Context timed out waiting for SubConn")
+		case sc := <-cc.NewSubConnCh:
+			if len(sc.Addresses) != 1 {
+				return nil, fmt.Errorf("len(SubConn.Addresses) = %d, want 1", len(sc.Addresses))
+			}
+			addresses = append(addresses, sc.Addresses[0])
+			sc.UpdateState(balancer.SubConnState{ConnectivityState: connectivity.Connecting})
+			sc.UpdateState(balancer.SubConnState{
+				ConnectivityState: connectivity.TransientFailure,
+				ConnectionError:   fmt.Errorf("test error"),
+			})
+		}
+	}
+	return addresses, nil
+}
+
 // stateStoringBalancer stores the state of the subconns being created.
 type stateStoringBalancer struct {
 	balancer.Balancer

internal/testutils/balancer.go

@@ -37,6 +37,7 @@ type TestSubConn struct {
 	ConnectCh     chan struct{}
 	stateListener func(balancer.SubConnState)
 	connectCalled *grpcsync.Event
+	Addresses     []resolver.Address
 }
 
 // NewTestSubConn returns a newly initialized SubConn.  Typically, subconns
@@ -131,6 +132,7 @@ func (tcc *BalancerClientConn) NewSubConn(a []resolver.Address, o balancer.NewSu
 		ConnectCh:     make(chan struct{}, 1),
 		stateListener: o.StateListener,
 		connectCalled: grpcsync.NewEvent(),
+		Addresses:     a,
 	}
 	tcc.subConnIdx++
 	tcc.logger.Logf("testClientConn: NewSubConn(%v, %+v) => %s", a, o, sc)