peering: replicate all SpiffeID values necessary for the importing side to do SAN validation (#13612)

When traversing an exported peered service, the discovery chain
evaluation at the other side may re-route the request to a variety of
endpoints. Furthermore we intend to terminate mTLS at the mesh gateway
for arriving peered traffic that is http-like (L7), so the caller needs
to know the mesh gateway's SpiffeID in that case as well.

The following new SpiffeID values will be shipped back in the peerstream
replication:

- tcp: all possible SpiffeIDs resulting from the service-resolver
        component of the exported discovery chain

- http-like: the SpiffeID of the mesh gateway

agent/consul/state/config_entry.go

@@ -506,20 +506,13 @@ var serviceGraphKinds = []string{
 
 // discoveryChainTargets will return a list of services listed as a target for the input's discovery chain
 func (s *Store) discoveryChainTargetsTxn(tx ReadTxn, ws memdb.WatchSet, dc, service string, entMeta *acl.EnterpriseMeta) (uint64, []structs.ServiceName, error) {
-	source := structs.NewServiceName(service, entMeta)
-	req := discoverychain.CompileRequest{
-		ServiceName:          source.Name,
-		EvaluateInNamespace:  source.NamespaceOrDefault(),
-		EvaluateInPartition:  source.PartitionOrDefault(),
-		EvaluateInDatacenter: dc,
-	}
-	idx, chain, _, err := s.serviceDiscoveryChainTxn(tx, ws, source.Name, entMeta, req)
+	idx, targets, err := s.discoveryChainOriginalTargetsTxn(tx, ws, dc, service, entMeta)
 	if err != nil {
-		return 0, nil, fmt.Errorf("failed to fetch discovery chain for %q: %v", source.String(), err)
+		return 0, nil, err
 	}
 
 	var resp []structs.ServiceName
-	for _, t := range chain.Targets {
+	for _, t := range targets {
 		em := acl.NewEnterpriseMetaWithPartition(entMeta.PartitionOrDefault(), t.Namespace)
 		target := structs.NewServiceName(t.Service, &em)
 
@@ -531,6 +524,22 @@ func (s *Store) discoveryChainTargetsTxn(tx ReadTxn, ws memdb.WatchSet, dc, serv
 	return idx, resp, nil
 }
 
+func (s *Store) discoveryChainOriginalTargetsTxn(tx ReadTxn, ws memdb.WatchSet, dc, service string, entMeta *acl.EnterpriseMeta) (uint64, []*structs.DiscoveryTarget, error) {
+	source := structs.NewServiceName(service, entMeta)
+	req := discoverychain.CompileRequest{
+		ServiceName:          source.Name,
+		EvaluateInNamespace:  source.NamespaceOrDefault(),
+		EvaluateInPartition:  source.PartitionOrDefault(),
+		EvaluateInDatacenter: dc,
+	}
+	idx, chain, _, err := s.serviceDiscoveryChainTxn(tx, ws, source.Name, entMeta, req)
+	if err != nil {
+		return 0, nil, fmt.Errorf("failed to fetch discovery chain for %q: %v", source.String(), err)
+	}
+
+	return idx, maps.SliceOfValues(chain.Targets), nil
+}
+
 // discoveryChainSourcesTxn will return a list of services whose discovery chains have the given service as a target
 func (s *Store) discoveryChainSourcesTxn(tx ReadTxn, ws memdb.WatchSet, dc string, destination structs.ServiceName) (uint64, []structs.ServiceName, error) {
 	seenLink := map[structs.ServiceName]bool{destination: true}

agent/consul/state/peering.go

@@ -3,6 +3,7 @@ package state
 import (
 	"errors"
 	"fmt"
+	"sort"
 	"strings"
 
 	"github.com/golang/protobuf/proto"
@@ -309,7 +310,7 @@ func (s *Store) PeeringTerminateByID(idx uint64, id string) error {
 // gateway's config entry, which we wouldn't want to replicate. How would
 // client peers know to route through terminating gateways when they're not
 // dialing through a remote mesh gateway?
-func (s *Store) ExportedServicesForPeer(ws memdb.WatchSet, peerID string) (uint64, *structs.ExportedServiceList, error) {
+func (s *Store) ExportedServicesForPeer(ws memdb.WatchSet, peerID string, dc string) (uint64, *structs.ExportedServiceList, error) {
 	tx := s.db.ReadTxn()
 	defer tx.Abort()
 
@@ -321,7 +322,7 @@ func (s *Store) ExportedServicesForPeer(ws memdb.WatchSet, peerID string) (uint6
 		return 0, &structs.ExportedServiceList{}, nil
 	}
 
-	return s.exportedServicesForPeerTxn(ws, tx, peering)
+	return s.exportedServicesForPeerTxn(ws, tx, peering, dc)
 }
 
 func (s *Store) ExportedServicesForAllPeersByName(ws memdb.WatchSet, entMeta acl.EnterpriseMeta) (uint64, map[string]structs.ServiceList, error) {
@@ -335,7 +336,7 @@ func (s *Store) ExportedServicesForAllPeersByName(ws memdb.WatchSet, entMeta acl
 
 	out := make(map[string]structs.ServiceList)
 	for _, peering := range peerings {
-		idx, list, err := s.exportedServicesForPeerTxn(ws, tx, peering)
+		idx, list, err := s.exportedServicesForPeerTxn(ws, tx, peering, "")
 		if err != nil {
 			return 0, nil, fmt.Errorf("failed to list exported services for peer %q: %w", peering.ID, err)
 		}
@@ -351,7 +352,11 @@ func (s *Store) ExportedServicesForAllPeersByName(ws memdb.WatchSet, entMeta acl
 	return maxIdx, out, nil
 }
 
-func (s *Store) exportedServicesForPeerTxn(ws memdb.WatchSet, tx ReadTxn, peering *pbpeering.Peering) (uint64, *structs.ExportedServiceList, error) {
+// exportedServicesForPeerTxn will find all services that are exported to a
+// specific peering, and optionally include information about discovery chain
+// reachable targets for these exported services if the "dc" parameter is
+// specified.
+func (s *Store) exportedServicesForPeerTxn(ws memdb.WatchSet, tx ReadTxn, peering *pbpeering.Peering, dc string) (uint64, *structs.ExportedServiceList, error) {
 	maxIdx := peering.ModifyIndex
 
 	entMeta := structs.NodeEnterpriseMetaInPartition(peering.Partition)
@@ -437,42 +442,63 @@ func (s *Store) exportedServicesForPeerTxn(ws memdb.WatchSet, tx ReadTxn, peerin
 	normal := maps.SliceOfKeys(normalSet)
 	disco := maps.SliceOfKeys(discoSet)
 
-	structs.ServiceList(normal).Sort()
-	structs.ServiceList(disco).Sort()
-
-	serviceProtocols := make(map[structs.ServiceName]string)
-	populateProtocol := func(svc structs.ServiceName) error {
-		if _, ok := serviceProtocols[svc]; ok {
+	chainInfo := make(map[structs.ServiceName]structs.ExportedDiscoveryChainInfo)
+	populateChainInfo := func(svc structs.ServiceName) error {
+		if _, ok := chainInfo[svc]; ok {
 			return nil // already processed
 		}
 
+		var info structs.ExportedDiscoveryChainInfo
+
 		idx, protocol, err := protocolForService(tx, ws, svc)
 		if err != nil {
-			return fmt.Errorf("failed to get protocol for service: %w", err)
+			return fmt.Errorf("failed to get protocol for service %q: %w", svc, err)
 		}
 
 		if idx > maxIdx {
 			maxIdx = idx
 		}
+		info.Protocol = protocol
+
+		if dc != "" && !structs.IsProtocolHTTPLike(protocol) {
+			// We only need to populate the targets for replication purposes for L4 protocols, which
+			// do not ultimately get intercepted by the mesh gateways.
+			idx, targets, err := s.discoveryChainOriginalTargetsTxn(tx, ws, dc, svc.Name, &svc.EnterpriseMeta)
+			if err != nil {
+				return fmt.Errorf("failed to get discovery chain targets for service %q: %w", svc, err)
+			}
+
+			if idx > maxIdx {
+				maxIdx = idx
+			}
+
+			sort.Slice(targets, func(i, j int) bool {
+				return targets[i].ID < targets[j].ID
+			})
+
+			info.TCPTargets = targets
+		}
 
-		serviceProtocols[svc] = protocol
+		chainInfo[svc] = info
 		return nil
 	}
+
 	for _, svc := range normal {
-		if err := populateProtocol(svc); err != nil {
+		if err := populateChainInfo(svc); err != nil {
 			return 0, nil, err
 		}
 	}
 	for _, svc := range disco {
-		if err := populateProtocol(svc); err != nil {
+		if err := populateChainInfo(svc); err != nil {
 			return 0, nil, err
 		}
 	}
 
+	structs.ServiceList(normal).Sort()
+
 	list := &structs.ExportedServiceList{
-		Services:        normal,
-		DiscoChains:     disco,
-		ConnectProtocol: serviceProtocols,
+		Services:    normal,
+		DiscoChains: chainInfo,
 	}
 
 	return maxIdx, list, nil
@@ -521,25 +547,44 @@ func peeringsForServiceTxn(tx ReadTxn, ws memdb.WatchSet, serviceName string, en
 	return maxIdx, peerings, nil
 }
 
-// TrustBundleListByService returns the trust bundles for all peers that the given service is exported to.
-func (s *Store) TrustBundleListByService(ws memdb.WatchSet, service string, entMeta acl.EnterpriseMeta) (uint64, []*pbpeering.PeeringTrustBundle, error) {
+// TrustBundleListByService returns the trust bundles for all peers that the
+// given service is exported to, via a discovery chain target.
+func (s *Store) TrustBundleListByService(ws memdb.WatchSet, service, dc string, entMeta acl.EnterpriseMeta) (uint64, []*pbpeering.PeeringTrustBundle, error) {
 	tx := s.db.ReadTxn()
 	defer tx.Abort()
 
-	maxIdx, peers, err := peeringsForServiceTxn(tx, ws, service, entMeta)
+	realSvc := structs.NewServiceName(service, &entMeta)
+
+	maxIdx, chainNames, err := s.discoveryChainSourcesTxn(tx, ws, dc, realSvc)
 	if err != nil {
-		return 0, nil, fmt.Errorf("failed to get peers for service %s: %v", service, err)
+		return 0, nil, fmt.Errorf("failed to list all discovery chains referring to %q: %w", realSvc, err)
 	}
 
+	peerNames := make(map[string]struct{})
+	for _, chainSvc := range chainNames {
+		idx, peers, err := peeringsForServiceTxn(tx, ws, chainSvc.Name, chainSvc.EnterpriseMeta)
+		if err != nil {
+			return 0, nil, fmt.Errorf("failed to get peers for service %s: %v", chainSvc, err)
+		}
+		if idx > maxIdx {
+			maxIdx = idx
+		}
+		for _, peer := range peers {
+			peerNames[peer.Name] = struct{}{}
+		}
+	}
+	peerNamesSlice := maps.SliceOfKeys(peerNames)
+	sort.Strings(peerNamesSlice)
+
 	var resp []*pbpeering.PeeringTrustBundle
-	for _, peer := range peers {
+	for _, peerName := range peerNamesSlice {
 		pq := Query{
-			Value:          strings.ToLower(peer.Name),
+			Value:          strings.ToLower(peerName),
 			EnterpriseMeta: *structs.NodeEnterpriseMetaInPartition(entMeta.PartitionOrDefault()),
 		}
 		idx, trustBundle, err := peeringTrustBundleReadTxn(tx, ws, pq)
 		if err != nil {
-			return 0, nil, fmt.Errorf("failed to read trust bundle for peer %s: %v", peer.Name, err)
+			return 0, nil, fmt.Errorf("failed to read trust bundle for peer %s: %v", peerName, err)
 		}
 		if idx > maxIdx {
 			maxIdx = idx
@@ -548,6 +593,7 @@ func (s *Store) TrustBundleListByService(ws memdb.WatchSet, service string, entM
 			resp = append(resp, trustBundle)
 		}
 	}
+
 	return maxIdx, resp, nil
 }
 

agent/consul/state/peering_test.go

@@ -8,6 +8,7 @@ import (
 	"github.com/stretchr/testify/require"
 
 	"github.com/hashicorp/consul/acl"
+	"github.com/hashicorp/consul/agent/connect"
 	"github.com/hashicorp/consul/agent/structs"
 	"github.com/hashicorp/consul/proto/pbpeering"
 	"github.com/hashicorp/consul/proto/prototest"
@@ -674,6 +675,13 @@ func TestStateStore_ExportedServicesForPeer(t *testing.T) {
 
 	var lastIdx uint64
 
+	ca := &structs.CAConfiguration{
+		Provider:  "consul",
+		ClusterID: connect.TestClusterID,
+	}
+	lastIdx++
+	require.NoError(t, s.CASetConfig(lastIdx, ca))
+
 	lastIdx++
 	require.NoError(t, s.PeeringWrite(lastIdx, &pbpeering.Peering{
 		ID:   testUUID(),
@@ -705,10 +713,18 @@ func TestStateStore_ExportedServicesForPeer(t *testing.T) {
 		require.NoError(t, s.EnsureConfigEntry(lastIdx, entry))
 	}
 
+	newTarget := func(service, serviceSubset, datacenter string) *structs.DiscoveryTarget {
+		t := structs.NewDiscoveryTarget(service, serviceSubset, "default", "default", datacenter)
+		t.SNI = connect.TargetSNI(t, connect.TestTrustDomain)
+		t.Name = t.SNI
+		t.ConnectTimeout = 5 * time.Second // default
+		return t
+	}
+
 	testutil.RunStep(t, "no exported services", func(t *testing.T) {
 		expect := &structs.ExportedServiceList{}
 
-		idx, got, err := s.ExportedServicesForPeer(ws, id)
+		idx, got, err := s.ExportedServicesForPeer(ws, id, "dc1")
 		require.NoError(t, err)
 		require.Equal(t, lastIdx, idx)
 		require.Equal(t, expect, got)
@@ -754,13 +770,23 @@ func TestStateStore_ExportedServicesForPeer(t *testing.T) {
 					EnterpriseMeta: *defaultEntMeta,
 				},
 			},
-			ConnectProtocol: map[structs.ServiceName]string{
-				newSN("mysql"): "tcp",
-				newSN("redis"): "tcp",
+			DiscoChains: map[structs.ServiceName]structs.ExportedDiscoveryChainInfo{
+				newSN("mysql"): {
+					Protocol: "tcp",
+					TCPTargets: []*structs.DiscoveryTarget{
+						newTarget("mysql", "", "dc1"),
+					},
+				},
+				newSN("redis"): {
+					Protocol: "tcp",
+					TCPTargets: []*structs.DiscoveryTarget{
+						newTarget("redis", "", "dc1"),
+					},
+				},
 			},
 		}
 
-		idx, got, err := s.ExportedServicesForPeer(ws, id)
+		idx, got, err := s.ExportedServicesForPeer(ws, id, "dc1")
 		require.NoError(t, err)
 		require.Equal(t, lastIdx, idx)
 		require.Equal(t, expect, got)
@@ -800,11 +826,16 @@ func TestStateStore_ExportedServicesForPeer(t *testing.T) {
 					EnterpriseMeta: *defaultEntMeta,
 				},
 			},
-			ConnectProtocol: map[structs.ServiceName]string{
-				newSN("billing"): "tcp",
+			DiscoChains: map[structs.ServiceName]structs.ExportedDiscoveryChainInfo{
+				newSN("billing"): {
+					Protocol: "tcp",
+					TCPTargets: []*structs.DiscoveryTarget{
+						newTarget("billing", "", "dc1"),
+					},
+				},
 			},
 		}
-		idx, got, err := s.ExportedServicesForPeer(ws, id)
+		idx, got, err := s.ExportedServicesForPeer(ws, id, "dc1")
 		require.NoError(t, err)
 		require.Equal(t, lastIdx, idx)
 		require.Equal(t, expect, got)
@@ -869,29 +900,25 @@ func TestStateStore_ExportedServicesForPeer(t *testing.T) {
 				},
 				// NOTE: no payments-proxy here
 			},
-			DiscoChains: []structs.ServiceName{
-				{
-					Name:           "resolver",
-					EnterpriseMeta: *defaultEntMeta,
+			DiscoChains: map[structs.ServiceName]structs.ExportedDiscoveryChainInfo{
+				newSN("billing"): {
+					Protocol: "http",
 				},
-				{
-					Name:           "router",
-					EnterpriseMeta: *defaultEntMeta,
+				newSN("payments"): {
+					Protocol: "http",
 				},
-				{
-					Name:           "splitter",
-					EnterpriseMeta: *defaultEntMeta,
+				newSN("resolver"): {
+					Protocol: "http",
+				},
+				newSN("router"): {
+					Protocol: "http",
+				},
+				newSN("splitter"): {
+					Protocol: "http",
 				},
-			},
-			ConnectProtocol: map[structs.ServiceName]string{
-				newSN("billing"):  "http",
-				newSN("payments"): "http",
-				newSN("resolver"): "http",
-				newSN("router"):   "http",
-				newSN("splitter"): "http",
 			},
 		}
-		idx, got, err := s.ExportedServicesForPeer(ws, id)
+		idx, got, err := s.ExportedServicesForPeer(ws, id, "dc1")
 		require.NoError(t, err)
 		require.Equal(t, lastIdx, idx)
 		require.Equal(t, expect, got)
@@ -915,23 +942,19 @@ func TestStateStore_ExportedServicesForPeer(t *testing.T) {
 				},
 				// NOTE: no payments-proxy here
 			},
-			DiscoChains: []structs.ServiceName{
-				{
-					Name:           "resolver",
-					EnterpriseMeta: *defaultEntMeta,
+			DiscoChains: map[structs.ServiceName]structs.ExportedDiscoveryChainInfo{
+				newSN("payments"): {
+					Protocol: "http",
 				},
-				{
-					Name:           "router",
-					EnterpriseMeta: *defaultEntMeta,
+				newSN("resolver"): {
+					Protocol: "http",
+				},
+				newSN("router"): {
+					Protocol: "http",
 				},
-			},
-			ConnectProtocol: map[structs.ServiceName]string{
-				newSN("payments"): "http",
-				newSN("resolver"): "http",
-				newSN("router"):   "http",
 			},
 		}
-		idx, got, err := s.ExportedServicesForPeer(ws, id)
+		idx, got, err := s.ExportedServicesForPeer(ws, id, "dc1")
 		require.NoError(t, err)
 		require.Equal(t, lastIdx, idx)
 		require.Equal(t, expect, got)
@@ -941,7 +964,7 @@ func TestStateStore_ExportedServicesForPeer(t *testing.T) {
 		expect := &structs.ExportedServiceList{}
 
 		require.NoError(t, s.DeleteConfigEntry(lastIdx, structs.ExportedServices, "default", defaultEntMeta))
-		idx, got, err := s.ExportedServicesForPeer(ws, id)
+		idx, got, err := s.ExportedServicesForPeer(ws, id, "dc1")
 		require.NoError(t, err)
 		require.Equal(t, lastIdx, idx)
 		require.Equal(t, expect, got)
@@ -1218,15 +1241,22 @@ func TestStore_TrustBundleListByService(t *testing.T) {
 	entMeta := *acl.DefaultEnterpriseMeta()
 
 	var lastIdx uint64
-	ws := memdb.NewWatchSet()
+
+	ca := &structs.CAConfiguration{
+		Provider:  "consul",
+		ClusterID: connect.TestClusterID,
+	}
+	lastIdx++
+	require.NoError(t, store.CASetConfig(lastIdx, ca))
 
 	var (
 		peerID1 = testUUID()
 		peerID2 = testUUID()
 	)
 
+	ws := memdb.NewWatchSet()
 	testutil.RunStep(t, "no results on initial setup", func(t *testing.T) {
-		idx, resp, err := store.TrustBundleListByService(ws, "foo", entMeta)
+		idx, resp, err := store.TrustBundleListByService(ws, "foo", "dc1", entMeta)
 		require.NoError(t, err)
 		require.Equal(t, lastIdx, idx)
 		require.Len(t, resp, 0)
@@ -1248,7 +1278,7 @@ func TestStore_TrustBundleListByService(t *testing.T) {
 
 		require.False(t, watchFired(ws))
 
-		idx, resp, err := store.TrustBundleListByService(ws, "foo", entMeta)
+		idx, resp, err := store.TrustBundleListByService(ws, "foo", "dc1", entMeta)
 		require.NoError(t, err)
 		require.Len(t, resp, 0)
 		require.Equal(t, lastIdx-2, idx)
@@ -1264,10 +1294,10 @@ func TestStore_TrustBundleListByService(t *testing.T) {
 		// The peering is only watched after the service is exported via config entry.
 		require.False(t, watchFired(ws))
 
-		idx, resp, err := store.TrustBundleListByService(ws, "foo", entMeta)
+		idx, resp, err := store.TrustBundleListByService(ws, "foo", "dc1", entMeta)
 		require.NoError(t, err)
-		require.Equal(t, uint64(0), idx)
 		require.Len(t, resp, 0)
+		require.Equal(t, lastIdx-3, idx)
 	})
 
 	testutil.RunStep(t, "exporting the service does not yield trust bundles", func(t *testing.T) {
@@ -1290,7 +1320,7 @@ func TestStore_TrustBundleListByService(t *testing.T) {
 		require.True(t, watchFired(ws))
 		ws = memdb.NewWatchSet()
 
-		idx, resp, err := store.TrustBundleListByService(ws, "foo", entMeta)
+		idx, resp, err := store.TrustBundleListByService(ws, "foo", "dc1", entMeta)
 		require.NoError(t, err)
 		require.Equal(t, lastIdx, idx)
 		require.Len(t, resp, 0)
@@ -1307,7 +1337,7 @@ func TestStore_TrustBundleListByService(t *testing.T) {
 		require.True(t, watchFired(ws))
 		ws = memdb.NewWatchSet()
 
-		idx, resp, err := store.TrustBundleListByService(ws, "foo", entMeta)
+		idx, resp, err := store.TrustBundleListByService(ws, "foo", "dc1", entMeta)
 		require.NoError(t, err)
 		require.Equal(t, lastIdx, idx)
 		require.Len(t, resp, 1)
@@ -1321,7 +1351,7 @@ func TestStore_TrustBundleListByService(t *testing.T) {
 		require.True(t, watchFired(ws))
 		ws = memdb.NewWatchSet()
 
-		idx, resp, err := store.TrustBundleListByService(ws, "foo", entMeta)
+		idx, resp, err := store.TrustBundleListByService(ws, "foo", "dc1", entMeta)
 		require.NoError(t, err)
 		require.Equal(t, lastIdx, idx)
 		require.Len(t, resp, 0)
@@ -1346,7 +1376,7 @@ func TestStore_TrustBundleListByService(t *testing.T) {
 		require.True(t, watchFired(ws))
 		ws = memdb.NewWatchSet()
 
-		idx, resp, err := store.TrustBundleListByService(ws, "foo", entMeta)
+		idx, resp, err := store.TrustBundleListByService(ws, "foo", "dc1", entMeta)
 		require.NoError(t, err)
 		require.Equal(t, lastIdx, idx)
 		require.Len(t, resp, 1)
@@ -1371,7 +1401,7 @@ func TestStore_TrustBundleListByService(t *testing.T) {
 		require.False(t, watchFired(ws))
 		ws = memdb.NewWatchSet()
 
-		idx, resp, err := store.TrustBundleListByService(ws, "foo", entMeta)
+		idx, resp, err := store.TrustBundleListByService(ws, "foo", "dc1", entMeta)
 		require.NoError(t, err)
 		require.Equal(t, lastIdx-2, idx)
 		require.Len(t, resp, 1)
@@ -1400,7 +1430,7 @@ func TestStore_TrustBundleListByService(t *testing.T) {
 		require.True(t, watchFired(ws))
 		ws = memdb.NewWatchSet()
 
-		idx, resp, err := store.TrustBundleListByService(ws, "foo", entMeta)
+		idx, resp, err := store.TrustBundleListByService(ws, "foo", "dc1", entMeta)
 		require.NoError(t, err)
 		require.Equal(t, lastIdx, idx)
 		require.Len(t, resp, 2)
@@ -1419,7 +1449,7 @@ func TestStore_TrustBundleListByService(t *testing.T) {
 		require.True(t, watchFired(ws))
 		ws = memdb.NewWatchSet()
 
-		idx, resp, err := store.TrustBundleListByService(ws, "foo", entMeta)
+		idx, resp, err := store.TrustBundleListByService(ws, "foo", "dc1", entMeta)
 		require.NoError(t, err)
 		require.Equal(t, lastIdx, idx)
 		require.Len(t, resp, 1)
@@ -1432,7 +1462,7 @@ func TestStore_TrustBundleListByService(t *testing.T) {
 
 		require.False(t, watchFired(ws))
 
-		idx, resp, err := store.TrustBundleListByService(ws, "foo", entMeta)
+		idx, resp, err := store.TrustBundleListByService(ws, "foo", "dc1", entMeta)
 		require.NoError(t, err)
 		require.Equal(t, lastIdx-1, idx)
 		require.Len(t, resp, 1)

agent/rpc/peering/service.go

@@ -130,12 +130,12 @@ type Store interface {
 	PeeringList(ws memdb.WatchSet, entMeta acl.EnterpriseMeta) (uint64, []*pbpeering.Peering, error)
 	PeeringTrustBundleRead(ws memdb.WatchSet, q state.Query) (uint64, *pbpeering.PeeringTrustBundle, error)
 	PeeringTrustBundleList(ws memdb.WatchSet, entMeta acl.EnterpriseMeta) (uint64, []*pbpeering.PeeringTrustBundle, error)
-	ExportedServicesForPeer(ws memdb.WatchSet, peerID string) (uint64, *structs.ExportedServiceList, error)
+	ExportedServicesForPeer(ws memdb.WatchSet, peerID, dc string) (uint64, *structs.ExportedServiceList, error)
 	ServiceDump(ws memdb.WatchSet, kind structs.ServiceKind, useKind bool, entMeta *acl.EnterpriseMeta, peerName string) (uint64, structs.CheckServiceNodes, error)
 	CheckServiceNodes(ws memdb.WatchSet, serviceName string, entMeta *acl.EnterpriseMeta, peerName string) (uint64, structs.CheckServiceNodes, error)
 	NodeServices(ws memdb.WatchSet, nodeNameOrID string, entMeta *acl.EnterpriseMeta, peerName string) (uint64, *structs.NodeServices, error)
 	CAConfig(ws memdb.WatchSet) (uint64, *structs.CAConfiguration, error)
-	TrustBundleListByService(ws memdb.WatchSet, service string, entMeta acl.EnterpriseMeta) (uint64, []*pbpeering.PeeringTrustBundle, error)
+	TrustBundleListByService(ws memdb.WatchSet, service, dc string, entMeta acl.EnterpriseMeta) (uint64, []*pbpeering.PeeringTrustBundle, error)
 	AbandonCh() <-chan struct{}
 }
 
@@ -533,7 +533,7 @@ func (s *Service) TrustBundleListByService(ctx context.Context, req *pbpeering.T
 
 	switch {
 	case req.ServiceName != "":
-		idx, bundles, err = s.Backend.Store().TrustBundleListByService(nil, req.ServiceName, entMeta)
+		idx, bundles, err = s.Backend.Store().TrustBundleListByService(nil, req.ServiceName, s.config.Datacenter, entMeta)
 	case req.Kind == string(structs.ServiceKindMeshGateway):
 		idx, bundles, err = s.Backend.Store().PeeringTrustBundleList(nil, entMeta)
 	case req.Kind != "":

agent/rpc/peering/service_test.go

@@ -490,8 +490,8 @@ func TestPeeringService_TrustBundleListByService(t *testing.T) {
 	resp, err := client.TrustBundleListByService(context.Background(), &req)
 	require.NoError(t, err)
 	require.Len(t, resp.Bundles, 2)
-	require.Equal(t, []string{"foo-root-1"}, resp.Bundles[0].RootPEMs)
-	require.Equal(t, []string{"bar-root-1"}, resp.Bundles[1].RootPEMs)
+	require.Equal(t, []string{"bar-root-1"}, resp.Bundles[0].RootPEMs)
+	require.Equal(t, []string{"foo-root-1"}, resp.Bundles[1].RootPEMs)
 }
 
 func Test_StreamHandler_UpsertServices(t *testing.T) {
@@ -912,7 +912,10 @@ func newTestServer(t *testing.T, cb func(conf *consul.Config)) testingServer {
 	testrpc.WaitForLeader(t, server.RPC, conf.Datacenter)
 
 	backend := consul.NewPeeringBackend(server, deps.GRPCConnPool)
-	handler := &peering.Service{Backend: backend}
+	handler := peering.NewService(testutil.Logger(t), peering.Config{
+		Datacenter:     "dc1",
+		ConnectEnabled: true,
+	}, backend)
 
 	grpcServer := gogrpc.NewServer()
 	pbpeering.RegisterPeeringServiceServer(grpcServer, handler)

agent/rpc/peering/stream_test.go

@@ -655,6 +655,18 @@ func TestStreamResources_Server_ServiceUpdates(t *testing.T) {
 	lastIdx++
 	require.NoError(t, store.EnsureService(lastIdx, "foo", mysql.Service))
 
+	mongoSvcDefaults := &structs.ServiceConfigEntry{
+		Kind:     structs.ServiceDefaults,
+		Name:     "mongo",
+		Protocol: "grpc",
+	}
+	require.NoError(t, mongoSvcDefaults.Normalize())
+	require.NoError(t, mongoSvcDefaults.Validate())
+	lastIdx++
+	require.NoError(t, store.EnsureConfigEntry(lastIdx, mongoSvcDefaults))
+
+	// NOTE: for this test we'll just live in a fantasy realm where we assume
+	// that mongo understands gRPC
 	var (
 		mongoSN      = structs.NewServiceName("mongo", nil).String()
 		mongoProxySN = structs.NewServiceName("mongo-sidecar-proxy", nil).String()
@@ -681,6 +693,8 @@ func TestStreamResources_Server_ServiceUpdates(t *testing.T) {
 				},
 			},
 		}
+		require.NoError(t, entry.Normalize())
+		require.NoError(t, entry.Validate())
 		lastIdx++
 		require.NoError(t, store.EnsureConfigEntry(lastIdx, entry))
 
@@ -744,8 +758,13 @@ func TestStreamResources_Server_ServiceUpdates(t *testing.T) {
 				require.NoError(t, ptypes.UnmarshalAny(msg.GetResponse().Resource, &nodes))
 				require.Len(t, nodes.Nodes, 1)
 
-				svid := "spiffe://11111111-2222-3333-4444-555555555555.consul/ns/default/dc/dc1/svc/mongo"
-				require.Equal(t, []string{svid}, nodes.Nodes[0].Service.Connect.PeerMeta.SpiffeID)
+				pm := nodes.Nodes[0].Service.Connect.PeerMeta
+				require.Equal(t, "grpc", pm.Protocol)
+				spiffeIDs := []string{
+					"spiffe://11111111-2222-3333-4444-555555555555.consul/ns/default/dc/dc1/svc/mongo",
+					"spiffe://11111111-2222-3333-4444-555555555555.consul/gateway/mesh/dc/dc1",
+				}
+				require.Equal(t, spiffeIDs, pm.SpiffeID)
 			},
 			func(t *testing.T, msg *pbpeering.ReplicationMessage) {
 				require.Equal(t, pbpeering.TypeURLService, msg.GetResponse().ResourceURL)
@@ -756,8 +775,12 @@ func TestStreamResources_Server_ServiceUpdates(t *testing.T) {
 				require.NoError(t, ptypes.UnmarshalAny(msg.GetResponse().Resource, &nodes))
 				require.Len(t, nodes.Nodes, 1)
 
-				svid := "spiffe://11111111-2222-3333-4444-555555555555.consul/ns/default/dc/dc1/svc/mysql"
-				require.Equal(t, []string{svid}, nodes.Nodes[0].Service.Connect.PeerMeta.SpiffeID)
+				pm := nodes.Nodes[0].Service.Connect.PeerMeta
+				require.Equal(t, "tcp", pm.Protocol)
+				spiffeIDs := []string{
+					"spiffe://11111111-2222-3333-4444-555555555555.consul/ns/default/dc/dc1/svc/mysql",
+				}
+				require.Equal(t, spiffeIDs, pm.SpiffeID)
 			},
 		)
 	})
@@ -800,6 +823,8 @@ func TestStreamResources_Server_ServiceUpdates(t *testing.T) {
 				},
 			},
 		}
+		require.NoError(t, entry.Normalize())
+		require.NoError(t, entry.Validate())
 		lastIdx++
 		err := store.EnsureConfigEntry(lastIdx, entry)
 		require.NoError(t, err)

agent/rpc/peering/subscription_blocking.go

@@ -23,7 +23,7 @@ func (m *subscriptionManager) notifyExportedServicesForPeerID(ctx context.Contex
 	// match the list of services exported to the peer.
 	m.syncViaBlockingQuery(ctx, "exported-services", func(ctx context.Context, store Store, ws memdb.WatchSet) (interface{}, error) {
 		// Get exported services for peer id
-		_, list, err := store.ExportedServicesForPeer(ws, peerID)
+		_, list, err := store.ExportedServicesForPeer(ws, peerID, m.config.Datacenter)
 		if err != nil {
 			return nil, fmt.Errorf("failed to watch exported services for peer %q: %w", peerID, err)
 		}

agent/rpc/peering/subscription_manager.go

@@ -238,8 +238,8 @@ func (m *subscriptionManager) handleEvent(ctx context.Context, state *subscripti
 
 		if state.exportList != nil {
 			// Trigger public events for all synthetic discovery chain replies.
-			for chainName, protocol := range state.connectServices {
-				m.emitEventForDiscoveryChain(ctx, state, pending, chainName, protocol)
+			for chainName, info := range state.connectServices {
+				m.emitEventForDiscoveryChain(ctx, state, pending, chainName, info)
 			}
 		}
 
@@ -456,17 +456,17 @@ func (m *subscriptionManager) syncDiscoveryChains(
 	ctx context.Context,
 	state *subscriptionState,
 	pending *pendingPayload,
-	chainsByName map[structs.ServiceName]string, // TODO(peering):rename variable
+	chainsByName map[structs.ServiceName]structs.ExportedDiscoveryChainInfo,
 ) {
 	// if it was newly added, then try to emit an UPDATE event
-	for chainName, protocol := range chainsByName {
-		if oldProtocol, ok := state.connectServices[chainName]; ok && protocol == oldProtocol {
+	for chainName, info := range chainsByName {
+		if oldInfo, ok := state.connectServices[chainName]; ok && info.Equal(oldInfo) {
 			continue
 		}
 
-		state.connectServices[chainName] = protocol
+		state.connectServices[chainName] = info
 
-		m.emitEventForDiscoveryChain(ctx, state, pending, chainName, protocol)
+		m.emitEventForDiscoveryChain(ctx, state, pending, chainName, info)
 	}
 
 	// if it was dropped, try to emit an DELETE event
@@ -498,7 +498,7 @@ func (m *subscriptionManager) emitEventForDiscoveryChain(
 	state *subscriptionState,
 	pending *pendingPayload,
 	chainName structs.ServiceName,
-	protocol string,
+	info structs.ExportedDiscoveryChainInfo,
 ) {
 	if _, ok := state.connectServices[chainName]; !ok {
 		return // not found
@@ -519,7 +519,7 @@ func (m *subscriptionManager) emitEventForDiscoveryChain(
 			m.config.Datacenter,
 			m.trustDomain,
 			chainName,
-			protocol,
+			info,
 			state.meshGateway,
 		),
 	)
@@ -532,7 +532,7 @@ func createDiscoChainHealth(
 	peerName string,
 	datacenter, trustDomain string,
 	sn structs.ServiceName,
-	protocol string,
+	info structs.ExportedDiscoveryChainInfo,
 	pb *pbservice.IndexedCheckServiceNodes,
 ) *pbservice.IndexedCheckServiceNodes {
 	fakeProxyName := sn.Name + syntheticProxyNameSuffix
@@ -546,6 +546,7 @@ func createDiscoChainHealth(
 			Datacenter: datacenter,
 			Service:    sn.Name,
 		}
+		mainSpiffeIDString := spiffeID.URI().String()
 
 		sni := connect.PeeredServiceSNI(
 			sn.Name,
@@ -559,9 +560,35 @@ func createDiscoChainHealth(
 		//
 		// TODO(peering): should this be replicated by service and not by instance?
 		peerMeta = &pbservice.PeeringServiceMeta{
-			SNI:      []string{sni},
-			SpiffeID: []string{spiffeID.URI().String()},
-			Protocol: protocol,
+			SNI: []string{sni},
+			SpiffeID: []string{
+				mainSpiffeIDString,
+			},
+			Protocol: info.Protocol,
+		}
+
+		if structs.IsProtocolHTTPLike(info.Protocol) {
+			gwSpiffeID := connect.SpiffeIDMeshGateway{
+				Host:       trustDomain,
+				Partition:  sn.PartitionOrDefault(),
+				Datacenter: datacenter,
+			}
+
+			peerMeta.SpiffeID = append(peerMeta.SpiffeID, gwSpiffeID.URI().String())
+		} else {
+			for _, target := range info.TCPTargets {
+				targetSpiffeID := connect.SpiffeIDService{
+					Host:       trustDomain,
+					Partition:  target.Partition,
+					Namespace:  target.Namespace,
+					Datacenter: target.Datacenter,
+					Service:    target.Service,
+				}
+				targetSpiffeIDString := targetSpiffeID.URI().String()
+				if targetSpiffeIDString != mainSpiffeIDString {
+					peerMeta.SpiffeID = append(peerMeta.SpiffeID, targetSpiffeIDString)
+				}
+			}
 		}
 	}
 

agent/rpc/peering/subscription_manager_test.go

@@ -281,6 +281,156 @@ func TestSubscriptionManager_RegisterDeregister(t *testing.T) {
 		)
 	})
 
+	testutil.RunStep(t, "peer meta changes when L4 disco chain changes", func(t *testing.T) {
+		backend.ensureConfigEntry(t, &structs.ServiceResolverConfigEntry{
+			Kind: structs.ServiceResolver,
+			Name: "mysql",
+			Failover: map[string]structs.ServiceResolverFailover{
+				"*": {
+					Service:     "failover",
+					Datacenters: []string{"dc2", "dc3"},
+				},
+			},
+		})
+
+		// ensure we get updated peer meta
+
+		expectEvents(t, subCh,
+			func(t *testing.T, got cache.UpdateEvent) {
+				require.Equal(t, mysqlProxyCorrID, got.CorrelationID)
+				res := got.Result.(*pbservice.IndexedCheckServiceNodes)
+				require.Equal(t, uint64(0), res.Index)
+
+				require.Len(t, res.Nodes, 1)
+				prototest.AssertDeepEqual(t, &pbservice.CheckServiceNode{
+					Node: pbNode("mgw", "10.1.1.1", partition),
+					Service: &pbservice.NodeService{
+						Kind:    "connect-proxy",
+						ID:      "mysql-sidecar-proxy-instance-0",
+						Service: "mysql-sidecar-proxy",
+						Port:    8443,
+						Weights: &pbservice.Weights{
+							Passing: 1,
+							Warning: 1,
+						},
+						EnterpriseMeta: pbcommon.DefaultEnterpriseMeta,
+						Proxy: &pbservice.ConnectProxyConfig{
+							DestinationServiceID:   "mysql-instance-0",
+							DestinationServiceName: "mysql",
+						},
+						Connect: &pbservice.ServiceConnect{
+							PeerMeta: &pbservice.PeeringServiceMeta{
+								SNI: []string{
+									"mysql.default.default.my-peering.external.11111111-2222-3333-4444-555555555555.consul",
+								},
+								SpiffeID: []string{
+									"spiffe://11111111-2222-3333-4444-555555555555.consul/ns/default/dc/dc1/svc/mysql",
+									"spiffe://11111111-2222-3333-4444-555555555555.consul/ns/default/dc/dc2/svc/failover",
+									"spiffe://11111111-2222-3333-4444-555555555555.consul/ns/default/dc/dc3/svc/failover",
+								},
+								Protocol: "tcp",
+							},
+						},
+					},
+				}, res.Nodes[0])
+			},
+		)
+
+		// reset so the next subtest is valid
+		backend.deleteConfigEntry(t, structs.ServiceResolver, "mysql")
+
+		// ensure we get peer meta is restored
+
+		expectEvents(t, subCh,
+			func(t *testing.T, got cache.UpdateEvent) {
+				require.Equal(t, mysqlProxyCorrID, got.CorrelationID)
+				res := got.Result.(*pbservice.IndexedCheckServiceNodes)
+				require.Equal(t, uint64(0), res.Index)
+
+				require.Len(t, res.Nodes, 1)
+				prototest.AssertDeepEqual(t, &pbservice.CheckServiceNode{
+					Node: pbNode("mgw", "10.1.1.1", partition),
+					Service: &pbservice.NodeService{
+						Kind:    "connect-proxy",
+						ID:      "mysql-sidecar-proxy-instance-0",
+						Service: "mysql-sidecar-proxy",
+						Port:    8443,
+						Weights: &pbservice.Weights{
+							Passing: 1,
+							Warning: 1,
+						},
+						EnterpriseMeta: pbcommon.DefaultEnterpriseMeta,
+						Proxy: &pbservice.ConnectProxyConfig{
+							DestinationServiceID:   "mysql-instance-0",
+							DestinationServiceName: "mysql",
+						},
+						Connect: &pbservice.ServiceConnect{
+							PeerMeta: &pbservice.PeeringServiceMeta{
+								SNI: []string{
+									"mysql.default.default.my-peering.external.11111111-2222-3333-4444-555555555555.consul",
+								},
+								SpiffeID: []string{
+									"spiffe://11111111-2222-3333-4444-555555555555.consul/ns/default/dc/dc1/svc/mysql",
+								},
+								Protocol: "tcp",
+							},
+						},
+					},
+				}, res.Nodes[0])
+			},
+		)
+	})
+
+	testutil.RunStep(t, "peer meta changes when protocol switches from L4 to L7", func(t *testing.T) {
+		// NOTE: for this test we'll just live in a fantasy realm where we assume
+		// that mysql understands gRPC
+		backend.ensureConfigEntry(t, &structs.ServiceConfigEntry{
+			Kind:     structs.ServiceDefaults,
+			Name:     "mysql",
+			Protocol: "grpc",
+		})
+
+		expectEvents(t, subCh,
+			func(t *testing.T, got cache.UpdateEvent) {
+				require.Equal(t, mysqlProxyCorrID, got.CorrelationID)
+				res := got.Result.(*pbservice.IndexedCheckServiceNodes)
+				require.Equal(t, uint64(0), res.Index)
+
+				require.Len(t, res.Nodes, 1)
+				prototest.AssertDeepEqual(t, &pbservice.CheckServiceNode{
+					Node: pbNode("mgw", "10.1.1.1", partition),
+					Service: &pbservice.NodeService{
+						Kind:    "connect-proxy",
+						ID:      "mysql-sidecar-proxy-instance-0",
+						Service: "mysql-sidecar-proxy",
+						Port:    8443,
+						Weights: &pbservice.Weights{
+							Passing: 1,
+							Warning: 1,
+						},
+						EnterpriseMeta: pbcommon.DefaultEnterpriseMeta,
+						Proxy: &pbservice.ConnectProxyConfig{
+							DestinationServiceID:   "mysql-instance-0",
+							DestinationServiceName: "mysql",
+						},
+						Connect: &pbservice.ServiceConnect{
+							PeerMeta: &pbservice.PeeringServiceMeta{
+								SNI: []string{
+									"mysql.default.default.my-peering.external.11111111-2222-3333-4444-555555555555.consul",
+								},
+								SpiffeID: []string{
+									"spiffe://11111111-2222-3333-4444-555555555555.consul/ns/default/dc/dc1/svc/mysql",
+									"spiffe://11111111-2222-3333-4444-555555555555.consul/gateway/mesh/dc/dc1",
+								},
+								Protocol: "grpc",
+							},
+						},
+					},
+				}, res.Nodes[0])
+			},
+		)
+	})
+
 	testutil.RunStep(t, "deregister the last instance and the output is empty", func(t *testing.T) {
 		backend.deleteService(t, "bar", mysql2.Service.ID)
 
@@ -514,6 +664,11 @@ func newTestSubscriptionBackend(t *testing.T) *testSubscriptionBackend {
 		store:          store,
 	}
 
+	backend.ensureCAConfig(t, &structs.CAConfiguration{
+		Provider:  "consul",
+		ClusterID: connect.TestClusterID,
+	})
+
 	// Create some placeholder data to ensure raft index > 0
 	//
 	// TODO(peering): is there some extremely subtle max-index table reading bug in play?
@@ -545,6 +700,12 @@ func (b *testSubscriptionBackend) ensureConfigEntry(t *testing.T, entry structs.
 	return b.lastIdx
 }
 
+func (b *testSubscriptionBackend) deleteConfigEntry(t *testing.T, kind, name string) uint64 {
+	b.lastIdx++
+	require.NoError(t, b.store.DeleteConfigEntry(b.lastIdx, kind, name, nil))
+	return b.lastIdx
+}
+
 func (b *testSubscriptionBackend) ensureNode(t *testing.T, node *structs.Node) uint64 {
 	b.lastIdx++
 	require.NoError(t, b.store.EnsureNode(b.lastIdx, node))

agent/rpc/peering/subscription_state.go

@@ -26,7 +26,7 @@ type subscriptionState struct {
 	exportList *structs.ExportedServiceList
 
 	watchedServices map[structs.ServiceName]context.CancelFunc
-	connectServices map[structs.ServiceName]string // value:protocol
+	connectServices map[structs.ServiceName]structs.ExportedDiscoveryChainInfo
 
 	// eventVersions is a duplicate event suppression system keyed by the "id"
 	// not the "correlationID"
@@ -48,7 +48,7 @@ func newSubscriptionState(peerName, partition string) *subscriptionState {
 		peerName:        peerName,
 		partition:       partition,
 		watchedServices: make(map[structs.ServiceName]context.CancelFunc),
-		connectServices: make(map[structs.ServiceName]string),
+		connectServices: make(map[structs.ServiceName]structs.ExportedDiscoveryChainInfo),
 		eventVersions:   make(map[string]string),
 	}
 }

agent/structs/discovery_chain.go

@@ -6,7 +6,6 @@ import (
 	"time"
 
 	"github.com/hashicorp/consul/acl"
-
 	"github.com/hashicorp/consul/lib"
 )
 
@@ -290,3 +289,7 @@ func (t *DiscoveryTarget) String() string {
 func (t *DiscoveryTarget) ServiceID() ServiceID {
 	return NewServiceID(t.Service, t.GetEnterpriseMetadata())
 }
+
+func (t *DiscoveryTarget) ServiceName() ServiceName {
+	return NewServiceName(t.Service, t.GetEnterpriseMetadata())
+}

agent/structs/peering.go

@@ -19,26 +19,54 @@ type ExportedServiceList struct {
 	// service discovery and service mesh.
 	Services []ServiceName
 
-	// DiscoChains is a list of exported service that ONLY apply to service mesh.
-	DiscoChains []ServiceName
+	// DiscoChains is a map of service names to their exported discovery chains
+	// for service mesh purposes as defined in the exported-services
+	// configuration entry.
+	DiscoChains map[ServiceName]ExportedDiscoveryChainInfo
+}
+
+// NOTE: this is not serialized via msgpack so it can be changed without concern.
+type ExportedDiscoveryChainInfo struct {
+	// Protocol is the overall protocol associated with this discovery chain.
+	Protocol string
+
+	// TCPTargets is the list of discovery chain targets that are reachable by
+	// this discovery chain.
+	//
+	// NOTE: this is only populated if Protocol=tcp.
+	TCPTargets []*DiscoveryTarget
+}
+
+func (i ExportedDiscoveryChainInfo) Equal(o ExportedDiscoveryChainInfo) bool {
+	switch {
+	case i.Protocol != o.Protocol:
+		return false
+	case len(i.TCPTargets) != len(o.TCPTargets):
+		return false
+	}
+
+	for j := 0; j < len(i.TCPTargets); j++ {
+		if i.TCPTargets[j].ID != o.TCPTargets[j].ID {
+			return false
+		}
+	}
 
-	// TODO(peering): reduce duplication here in the response
-	ConnectProtocol map[ServiceName]string
+	return true
 }
 
 // ListAllDiscoveryChains returns all discovery chains (union of Services and
 // DiscoChains).
-func (list *ExportedServiceList) ListAllDiscoveryChains() map[ServiceName]string {
-	chainsByName := make(map[ServiceName]string)
+func (list *ExportedServiceList) ListAllDiscoveryChains() map[ServiceName]ExportedDiscoveryChainInfo {
+	chainsByName := make(map[ServiceName]ExportedDiscoveryChainInfo)
 	if list == nil {
 		return chainsByName
 	}
 
 	for _, svc := range list.Services {
-		chainsByName[svc] = list.ConnectProtocol[svc]
+		chainsByName[svc] = list.DiscoChains[svc]
 	}
-	for _, chainName := range list.DiscoChains {
-		chainsByName[chainName] = list.ConnectProtocol[chainName]
+	for chainName, info := range list.DiscoChains {
+		chainsByName[chainName] = info
 	}
 	return chainsByName
 }

lib/maps/maps.go

@@ -10,3 +10,14 @@ func SliceOfKeys[K comparable, V any](m map[K]V) []K {
 	}
 	return res
 }
+
+func SliceOfValues[K comparable, V any](m map[K]V) []V {
+	if len(m) == 0 {
+		return nil
+	}
+	res := make([]V, 0, len(m))
+	for _, v := range m {
+		res = append(res, v)
+	}
+	return res
+}

lib/maps/maps_test.go

@@ -39,3 +39,37 @@ func TestSliceOfKeys(t *testing.T) {
 		require.ElementsMatch(t, []id{{Name: "foo"}, {Name: "bar"}}, SliceOfKeys(m))
 	})
 }
+
+func TestSliceOfValues(t *testing.T) {
+	t.Run("string to int", func(t *testing.T) {
+		m := make(map[string]int)
+		require.Equal(t, []int(nil), SliceOfValues(m))
+		m["foo"] = 5
+		m["bar"] = 6
+		require.ElementsMatch(t, []int{5, 6}, SliceOfValues(m))
+	})
+
+	type blah struct {
+		V string
+	}
+
+	t.Run("int to struct", func(t *testing.T) {
+		m := make(map[int]blah)
+		require.Equal(t, []blah(nil), SliceOfValues(m))
+		m[5] = blah{V: "foo"}
+		m[6] = blah{V: "bar"}
+		require.ElementsMatch(t, []blah{{V: "foo"}, {V: "bar"}}, SliceOfValues(m))
+	})
+
+	type id struct {
+		Name string
+	}
+
+	t.Run("struct to struct pointer", func(t *testing.T) {
+		m := make(map[id]*blah)
+		require.Equal(t, []*blah(nil), SliceOfValues(m))
+		m[id{Name: "foo"}] = &blah{V: "oof"}
+		m[id{Name: "bar"}] = &blah{V: "rab"}
+		require.ElementsMatch(t, []*blah{{V: "oof"}, {V: "rab"}}, SliceOfValues(m))
+	})
+}