Support "near" parameter in prepared query service block

command/agent/dns.go

@@ -598,6 +598,15 @@ func (d *DNSServer) preparedQueryLookup(network, datacenter, query string, req,
 			Token:      d.agent.config.ACLToken,
 			AllowStale: d.config.AllowStale,
 		},
+
+		// Always pass the local agent through. In the DNS interface, there
+		// is no provision for passing additional query parameters, so we
+		// send the local agent's data through to allow distance sorting
+		// relative to ourself on the server side.
+		Agent: structs.QuerySource{
+			Datacenter: d.agent.config.Datacenter,
+			Node:       d.agent.config.NodeName,
+		},
 	}
 
 	// TODO (slackpad) - What's a safe limit we can set here? It seems like

command/agent/dns_test.go

@@ -3166,3 +3166,37 @@ func TestDNS_InvalidQueries(t *testing.T) {
 		}
 	}
 }
+
+func TestDNS_PreparedQuery_AgentSource(t *testing.T) {
+	dir, srv := makeDNSServer(t)
+	defer os.RemoveAll(dir)
+	defer srv.agent.Shutdown()
+
+	testutil.WaitForLeader(t, srv.agent.RPC, "dc1")
+
+	m := MockPreparedQuery{}
+	if err := srv.agent.InjectEndpoint("PreparedQuery", &m); err != nil {
+		t.Fatalf("err: %v", err)
+	}
+
+	m.executeFn = func(args *structs.PreparedQueryExecuteRequest, reply *structs.PreparedQueryExecuteResponse) error {
+		// Check that the agent inserted its self-name and datacenter to
+		// the RPC request body.
+		if args.Agent.Datacenter != srv.agent.config.Datacenter ||
+			args.Agent.Node != srv.agent.config.NodeName {
+			t.Fatalf("bad: %#v", args.Agent)
+		}
+		return nil
+	}
+
+	{
+		m := new(dns.Msg)
+		m.SetQuestion("foo.query.consul.", dns.TypeSRV)
+
+		c := new(dns.Client)
+		addr, _ := srv.agent.config.ClientListener("", srv.agent.config.Ports.DNS)
+		if _, _, err := c.Exchange(m, addr.String()); err != nil {
+			t.Fatalf("err: %v", err)
+		}
+	}
+}

command/agent/prepared_query_endpoint.go

@@ -96,6 +96,10 @@ func parseLimit(req *http.Request, limit *int) error {
 func (s *HTTPServer) preparedQueryExecute(id string, resp http.ResponseWriter, req *http.Request) (interface{}, error) {
 	args := structs.PreparedQueryExecuteRequest{
 		QueryIDOrName: id,
+		Agent: structs.QuerySource{
+			Node:       s.agent.config.NodeName,
+			Datacenter: s.agent.config.Datacenter,
+		},
 	}
 	s.parseSource(req, &args.Source)
 	if done := s.parse(resp, req, &args.Datacenter, &args.QueryOptions); done {
@@ -131,6 +135,10 @@ func (s *HTTPServer) preparedQueryExecute(id string, resp http.ResponseWriter, r
 func (s *HTTPServer) preparedQueryExplain(id string, resp http.ResponseWriter, req *http.Request) (interface{}, error) {
 	args := structs.PreparedQueryExecuteRequest{
 		QueryIDOrName: id,
+		Agent: structs.QuerySource{
+			Node:       s.agent.config.NodeName,
+			Datacenter: s.agent.config.Datacenter,
+		},
 	}
 	s.parseSource(req, &args.Source)
 	if done := s.parse(resp, req, &args.Datacenter, &args.QueryOptions); done {

command/agent/prepared_query_endpoint_test.go

@@ -286,6 +286,10 @@ func TestPreparedQuery_Execute(t *testing.T) {
 					Datacenter: "dc1",
 					Node:       "my-node",
 				},
+				Agent: structs.QuerySource{
+					Datacenter: srv.agent.config.Datacenter,
+					Node:       srv.agent.config.NodeName,
+				},
 				QueryOptions: structs.QueryOptions{
 					Token:             "my-token",
 					RequireConsistent: true,
@@ -323,6 +327,38 @@ func TestPreparedQuery_Execute(t *testing.T) {
 		}
 	})
 
+	// Ensure the proper params are set when no special args are passed
+	httpTest(t, func(srv *HTTPServer) {
+		m := MockPreparedQuery{}
+		if err := srv.agent.InjectEndpoint("PreparedQuery", &m); err != nil {
+			t.Fatalf("err: %v", err)
+		}
+
+		m.executeFn = func(args *structs.PreparedQueryExecuteRequest, reply *structs.PreparedQueryExecuteResponse) error {
+			if args.Source.Node != "" {
+				t.Fatalf("expect node to be empty, got %q", args.Source.Node)
+			}
+			expect := structs.QuerySource{
+				Datacenter: srv.agent.config.Datacenter,
+				Node:       srv.agent.config.NodeName,
+			}
+			if !reflect.DeepEqual(args.Agent, expect) {
+				t.Fatalf("expect: %#v\nactual: %#v", expect, args.Agent)
+			}
+			return nil
+		}
+
+		req, err := http.NewRequest("GET", "/v1/query/my-id/execute", nil)
+		if err != nil {
+			t.Fatalf("err: %v", err)
+		}
+
+		resp := httptest.NewRecorder()
+		if _, err := srv.PreparedQuerySpecific(resp, req); err != nil {
+			t.Fatalf("err: %v", err)
+		}
+	})
+
 	httpTest(t, func(srv *HTTPServer) {
 		body := bytes.NewBuffer(nil)
 		req, err := http.NewRequest("GET", "/v1/query/not-there/execute", body)
@@ -357,6 +393,10 @@ func TestPreparedQuery_Explain(t *testing.T) {
 					Datacenter: "dc1",
 					Node:       "my-node",
 				},
+				Agent: structs.QuerySource{
+					Datacenter: srv.agent.config.Datacenter,
+					Node:       srv.agent.config.NodeName,
+				},
 				QueryOptions: structs.QueryOptions{
 					Token:             "my-token",
 					RequireConsistent: true,

consul/prepared_query/walk_test.go

@@ -20,6 +20,7 @@ func TestWalk_ServiceQuery(t *testing.T) {
 		Failover: structs.QueryDatacenterOptions{
 			Datacenters: []string{"dc1", "dc2"},
 		},
+		Near: "_agent",
 		Tags: []string{"tag1", "tag2", "tag3"},
 	}
 	if err := walk(service, fn); err != nil {
@@ -30,6 +31,7 @@ func TestWalk_ServiceQuery(t *testing.T) {
 		".Service:the-service",
 		".Failover.Datacenters[0]:dc1",
 		".Failover.Datacenters[1]:dc2",
+		".Near:_agent",
 		".Tags[0]:tag1",
 		".Tags[1]:tag2",
 		".Tags[2]:tag3",

consul/prepared_query_endpoint.go

@@ -368,7 +368,25 @@ func (p *PreparedQuery) Execute(args *structs.PreparedQueryExecuteRequest,
 	// Shuffle the results in case coordinates are not available if they
 	// requested an RTT sort.
 	reply.Nodes.Shuffle()
-	if err := p.srv.sortNodesByDistanceFrom(args.Source, reply.Nodes); err != nil {
+
+	// Build the query source. This can be provided by the client, or by
+	// the prepared query. Client-specified takes priority.
+	qs := args.Source
+	if qs.Datacenter == "" {
+		qs.Datacenter = args.Agent.Datacenter
+	}
+	if query.Service.Near != "" && qs.Node == "" {
+		qs.Node = query.Service.Near
+	}
+
+	// Respect the magic "_agent" flag.
+	if qs.Node == "_agent" {
+		qs.Node = args.Agent.Node
+	}
+
+	// Perform the distance sort
+	err = p.srv.sortNodesByDistanceFrom(qs, reply.Nodes)
+	if err != nil {
 		return err
 	}
 

consul/prepared_query_endpoint_test.go

@@ -1607,6 +1607,197 @@ func TestPreparedQuery_Execute(t *testing.T) {
 		t.Fatalf("unique shuffle ratio too low: %d/100", len(uniques))
 	}
 
+	// Set the query to return results nearest to node3. This is the only
+	// node with coordinates, and it carries the service we are asking for,
+	// so node3 should always show up first.
+	query.Op = structs.PreparedQueryUpdate
+	query.Query.Service.Near = "node3"
+	if err := msgpackrpc.CallWithCodec(codec1, "PreparedQuery.Apply", &query, &query.Query.ID); err != nil {
+		t.Fatalf("err: %v", err)
+	}
+
+	// Now run the query and make sure the sort looks right.
+	{
+		req := structs.PreparedQueryExecuteRequest{
+			Agent: structs.QuerySource{
+				Datacenter: "dc1",
+				Node:       "node3",
+			},
+			Datacenter:    "dc1",
+			QueryIDOrName: query.Query.ID,
+			QueryOptions:  structs.QueryOptions{Token: execToken},
+		}
+
+		var reply structs.PreparedQueryExecuteResponse
+
+		for i := 0; i < 10; i++ {
+			if err := msgpackrpc.CallWithCodec(codec1, "PreparedQuery.Execute", &req, &reply); err != nil {
+				t.Fatalf("err: %v", err)
+			}
+			if n := len(reply.Nodes); n != 10 {
+				t.Fatalf("expect 10 nodes, got: %d", n)
+			}
+			if node := reply.Nodes[0].Node.Node; node != "node3" {
+				t.Fatalf("expect node3 first, got: %q", node)
+			}
+		}
+	}
+
+	// Query again, but this time set a client-supplied query source. This
+	// proves that we allow overriding the baked-in value with ?near.
+	{
+		// Set up the query with a non-existent node. This will cause the
+		// nodes to be shuffled if the passed node is respected, proving
+		// that we allow the override to happen.
+		req := structs.PreparedQueryExecuteRequest{
+			Source: structs.QuerySource{
+				Datacenter: "dc1",
+				Node:       "foo",
+			},
+			Agent: structs.QuerySource{
+				Datacenter: "dc1",
+				Node:       "node3",
+			},
+			Datacenter:    "dc1",
+			QueryIDOrName: query.Query.ID,
+			QueryOptions:  structs.QueryOptions{Token: execToken},
+		}
+
+		var reply structs.PreparedQueryExecuteResponse
+
+		shuffled := false
+		for i := 0; i < 10; i++ {
+			if err := msgpackrpc.CallWithCodec(codec1, "PreparedQuery.Execute", &req, &reply); err != nil {
+				t.Fatalf("err: %v", err)
+			}
+			if n := len(reply.Nodes); n != 10 {
+				t.Fatalf("expect 10 nodes, got: %d", n)
+			}
+			if node := reply.Nodes[0].Node.Node; node != "node3" {
+				shuffled = true
+				break
+			}
+		}
+
+		if !shuffled {
+			t.Fatalf("expect nodes to be shuffled")
+		}
+	}
+
+	// Bake the magic "_agent" flag into the query.
+	query.Query.Service.Near = "_agent"
+	if err := msgpackrpc.CallWithCodec(codec1, "PreparedQuery.Apply", &query, &query.Query.ID); err != nil {
+		t.Fatalf("err: %v", err)
+	}
+
+	// Check that we sort the local agent first when the magic flag is set.
+	{
+		req := structs.PreparedQueryExecuteRequest{
+			Agent: structs.QuerySource{
+				Datacenter: "dc1",
+				Node:       "node3",
+			},
+			Datacenter:    "dc1",
+			QueryIDOrName: query.Query.ID,
+			QueryOptions:  structs.QueryOptions{Token: execToken},
+		}
+
+		var reply structs.PreparedQueryExecuteResponse
+
+		for i := 0; i < 10; i++ {
+			if err := msgpackrpc.CallWithCodec(codec1, "PreparedQuery.Execute", &req, &reply); err != nil {
+				t.Fatalf("err: %v", err)
+			}
+			if n := len(reply.Nodes); n != 10 {
+				t.Fatalf("expect 10 nodes, got: %d", n)
+			}
+			if node := reply.Nodes[0].Node.Node; node != "node3" {
+				t.Fatalf("expect node3 first, got: %q", node)
+			}
+		}
+	}
+
+	// Check that the query isn't just sorting "node3" first because we
+	// provided it in the Agent query source. Proves that we use the
+	// Agent source when the magic "_agent" flag is passed.
+	{
+		req := structs.PreparedQueryExecuteRequest{
+			Agent: structs.QuerySource{
+				Datacenter: "dc1",
+				Node:       "foo",
+			},
+			Datacenter:    "dc1",
+			QueryIDOrName: query.Query.ID,
+			QueryOptions:  structs.QueryOptions{Token: execToken},
+		}
+
+		var reply structs.PreparedQueryExecuteResponse
+
+		// Expect the set to be shuffled since we have no coordinates
+		// on the "foo" node.
+		shuffled := false
+		for i := 0; i < 10; i++ {
+			if err := msgpackrpc.CallWithCodec(codec1, "PreparedQuery.Execute", &req, &reply); err != nil {
+				t.Fatalf("err: %v", err)
+			}
+			if n := len(reply.Nodes); n != 10 {
+				t.Fatalf("expect 10 nodes, got: %d", n)
+			}
+			if node := reply.Nodes[0].Node.Node; node != "node3" {
+				shuffled = true
+				break
+			}
+		}
+
+		if !shuffled {
+			t.Fatal("expect nodes to be shuffled")
+		}
+	}
+
+	// Shuffles if the response comes from a non-local DC. Proves that the
+	// agent query source does not interfere with the order.
+	{
+		req := structs.PreparedQueryExecuteRequest{
+			Source: structs.QuerySource{
+				Datacenter: "dc2",
+				Node:       "node3",
+			},
+			Agent: structs.QuerySource{
+				Datacenter: "dc1",
+				Node:       "node3",
+			},
+			Datacenter:    "dc1",
+			QueryIDOrName: query.Query.ID,
+			QueryOptions:  structs.QueryOptions{Token: execToken},
+		}
+
+		var reply structs.PreparedQueryExecuteResponse
+
+		shuffled := false
+		for i := 0; i < 10; i++ {
+			if err := msgpackrpc.CallWithCodec(codec1, "PreparedQuery.Execute", &req, &reply); err != nil {
+				t.Fatalf("err: %v", err)
+			}
+			if n := len(reply.Nodes); n != 10 {
+				t.Fatalf("expect 10 nodes, got: %d", n)
+			}
+			if reply.Nodes[0].Node.Node != "node3" {
+				shuffled = true
+				break
+			}
+		}
+
+		if !shuffled {
+			t.Fatal("expect node shuffle for remote results")
+		}
+	}
+
+	// Un-bake the near parameter.
+	query.Query.Service.Near = ""
+	if err := msgpackrpc.CallWithCodec(codec1, "PreparedQuery.Apply", &query, &query.Query.ID); err != nil {
+		t.Fatalf("err: %v", err)
+	}
+
 	// Update the health of a node to mark it critical.
 	setHealth := func(node string, health string) {
 		req := structs.RegisterRequest{
@@ -1683,7 +1874,6 @@ func TestPreparedQuery_Execute(t *testing.T) {
 	}
 
 	// Make the query more picky so it excludes warning nodes.
-	query.Op = structs.PreparedQueryUpdate
 	query.Query.Service.OnlyPassing = true
 	if err := msgpackrpc.CallWithCodec(codec1, "PreparedQuery.Apply", &query, &query.Query.ID); err != nil {
 		t.Fatalf("err: %v", err)