Add xds support to grid

cfg.go

@@ -27,6 +27,9 @@ type ClientCfg struct {
 	ConnectionsPerPeer int
 	// Logger optionally used for logging, default is to not log.
 	Logger Logger
+
+	// XDSCreds specifies whether the server should use xDS APIs to receive security configuration
+	XDSCreds bool
 }
 
 // setClientCfgDefaults for those fields that have their zero value.
@@ -57,6 +60,8 @@ type ServerCfg struct {
 	Logger Logger
 	// Annotations optionally used annotating a grid server with metadata
 	Annotations []string
+	// XDSCreds specifies whether the server should use xDS APIs to receive security configuration
+	XDSCreds bool
 }
 
 // setServerCfgDefaults for those fields that have their zero value.

client.go

@@ -17,6 +17,9 @@ import (
 	"github.com/lytics/retry"
 	etcdv3 "go.etcd.io/etcd/client/v3"
 	"google.golang.org/grpc"
+	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/credentials/insecure"
+	xdscreds "google.golang.org/grpc/credentials/xds"
 	healthpb "google.golang.org/grpc/health/grpc_health_v1"
 )
 
@@ -25,9 +28,9 @@ import (
 // the type itself.
 //
 // For example:
-//     Register(MyMsg{})    // Correct
-//     Register(&MyMsg{})   // Incorrect
 //
+//	Register(MyMsg{})    // Correct
+//	Register(&MyMsg{})   // Incorrect
 func Register(v interface{}) error {
 	return codec.Register(v)
 }
@@ -104,13 +107,21 @@ type Client struct {
 	addresses       map[string]string
 	clientsAndConns map[string]*clientAndConnPool
 	// Test hook.
-	cs *clientStats
+	cs    *clientStats
+	creds credentials.TransportCredentials
 }
 
 // NewClient using the given etcd client and configuration.
 func NewClient(etcd *etcdv3.Client, cfg ClientCfg) (*Client, error) {
 	setClientCfgDefaults(&cfg)
 
+	creds := insecure.NewCredentials()
+	if cfg.XDSCreds {
+		var err error
+		if creds, err = xdscreds.NewClientCredentials(xdscreds.ClientOptions{FallbackCreds: insecure.NewCredentials()}); err != nil {
+			return nil, fmt.Errorf("failed to create client-side xDS credentials: %w", err)
+		}
+	}
 	r, err := registry.New(etcd)
 	if err != nil {
 		return nil, err
@@ -123,6 +134,7 @@ func NewClient(etcd *etcdv3.Client, cfg ClientCfg) (*Client, error) {
 	}
 
 	return &Client{
+		creds:           creds,
 		cfg:             cfg,
 		registry:        r,
 		addresses:       make(map[string]string),
@@ -277,7 +289,7 @@ func (c *Client) getCCLocked(ctx context.Context, nsReceiver string) (*clientAnd
 			c.cs.Inc(numGRPCDial)
 
 			// Dial the destination.
-			conn, err := grpc.Dial(address, grpc.WithInsecure(), grpc.WithBackoffMaxDelay(20*time.Second))
+			conn, err := grpc.Dial(address, grpc.WithTransportCredentials(c.creds), grpc.WithBackoffMaxDelay(20*time.Second))
 			if err != nil {
 				return nil, noID, err
 			}

go.mod

@@ -7,18 +7,25 @@ require (
 	github.com/stretchr/testify v1.8.2
 	go.etcd.io/etcd/client/v3 v3.5.7
 	go.etcd.io/etcd/server/v3 v3.5.7
-	google.golang.org/grpc v1.54.0
+	google.golang.org/grpc v1.55.0
 	google.golang.org/protobuf v1.30.0
 )
 
 require (
+	cloud.google.com/go/compute v1.19.0 // indirect
+	cloud.google.com/go/compute/metadata v0.2.3 // indirect
 	github.com/beorn7/perks v1.0.1 // indirect
 	github.com/cenkalti/backoff/v4 v4.2.0 // indirect
+	github.com/census-instrumentation/opencensus-proto v0.4.1 // indirect
 	github.com/cespare/xxhash/v2 v2.2.0 // indirect
+	github.com/cncf/udpa/go v0.0.0-20220112060539-c52dc94e7fbe // indirect
+	github.com/cncf/xds/go v0.0.0-20230310173818-32f1caf87195 // indirect
 	github.com/coreos/go-semver v0.3.1 // indirect
 	github.com/coreos/go-systemd/v22 v22.5.0 // indirect
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/dustin/go-humanize v1.0.1 // indirect
+	github.com/envoyproxy/go-control-plane v0.11.0 // indirect
+	github.com/envoyproxy/protoc-gen-validate v0.10.0 // indirect
 	github.com/go-logr/logr v1.2.3 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
 	github.com/gogo/protobuf v1.3.2 // indirect
@@ -65,9 +72,11 @@ require (
 	go.uber.org/zap v1.24.0 // indirect
 	golang.org/x/crypto v0.7.0 // indirect
 	golang.org/x/net v0.8.0 // indirect
+	golang.org/x/oauth2 v0.6.0 // indirect
 	golang.org/x/sys v0.6.0 // indirect
 	golang.org/x/text v0.8.0 // indirect
 	golang.org/x/time v0.3.0 // indirect
+	google.golang.org/appengine v1.6.7 // indirect
 	google.golang.org/genproto v0.0.0-20230327215041-6ac7f18bb9d5 // indirect
 	gopkg.in/natefinch/lumberjack.v2 v2.2.1 // indirect
 	gopkg.in/yaml.v2 v2.4.0 // indirect

go.sum

@@ -21,7 +21,9 @@ cloud.google.com/go/bigquery v1.5.0/go.mod h1:snEHRnqQbz117VIFhE8bmtwIDY80NLUZUM
 cloud.google.com/go/bigquery v1.7.0/go.mod h1://okPTzCYNXSlb24MZs83e2Do+h+VXtc4gLoIoXIAPc=
 cloud.google.com/go/bigquery v1.8.0/go.mod h1:J5hqkt3O0uAFnINi6JXValWIb1v0goeZM77hZzJN/fQ=
 cloud.google.com/go/compute v1.19.0 h1:+9zda3WGgW1ZSTlVppLCYFIr48Pa35q1uG2N1itbCEQ=
+cloud.google.com/go/compute v1.19.0/go.mod h1:rikpw2y+UMidAe9tISo04EHNOIf42RLYF/q8Bs93scU=
 cloud.google.com/go/compute/metadata v0.2.3 h1:mg4jlk7mCAj6xXp9UJ4fjI9VUI5rubuGBW5aJ7UnBMY=
+cloud.google.com/go/compute/metadata v0.2.3/go.mod h1:VAV5nSsACxMJvgaAuX6Pk2AawlZn8kiOGuCv6gTkwuA=
 cloud.google.com/go/datastore v1.0.0/go.mod h1:LXYbyblFSglQ5pkeyhO+Qmw7ukd3C+pD7TKLgZqpHYE=
 cloud.google.com/go/datastore v1.1.0/go.mod h1:umbIZjpQpHh4hmRpGhH4tLFup+FVzqBi1b3c64qFpCk=
 cloud.google.com/go/pubsub v1.0.1/go.mod h1:R0Gpsv3s54REJCy4fxDixWD93lHJMoZTyQ2kNxGRt3I=
@@ -45,6 +47,8 @@ github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6r
 github.com/cenkalti/backoff/v4 v4.2.0 h1:HN5dHm3WBOgndBH6E8V0q2jIYIR3s9yglV8k/+MN3u4=
 github.com/cenkalti/backoff/v4 v4.2.0/go.mod h1:Y3VNntkOUPxTVeUxJ/G5vcM//AlwfmyYozVcomhLiZE=
 github.com/census-instrumentation/opencensus-proto v0.2.1/go.mod h1:f6KPmirojxKA12rnyqOA5BBL4O983OfeGPqjHWSTneU=
+github.com/census-instrumentation/opencensus-proto v0.4.1 h1:iKLQ0xPNFxR/2hzXZMrBo8f1j86j5WHzznCCQxV/b8g=
+github.com/census-instrumentation/opencensus-proto v0.4.1/go.mod h1:4T9NM4+4Vw91VeyqjLS6ao50K5bOcLKN6Q42XnYaRYw=
 github.com/certifi/gocertifi v0.0.0-20200922220541-2c3bb06c6054 h1:uH66TXeswKn5PW5zdZ39xEwfS9an067BirqA+P4QaLI=
 github.com/cespare/xxhash v1.1.0/go.mod h1:XrSqR1VqqWfGrhpAt58auRo0WTKS1nRRg3ghfAqPWnc=
 github.com/cespare/xxhash/v2 v2.1.1/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
@@ -57,10 +61,14 @@ github.com/client9/misspell v0.3.4/go.mod h1:qj6jICC3Q7zFZvVWo7KLAzC3yx5G7kyvSDk
 github.com/cncf/udpa/go v0.0.0-20191209042840-269d4d468f6f/go.mod h1:M8M6+tZqaGXZJjfX53e64911xZQV5JYwmTeXPW+k8Sc=
 github.com/cncf/udpa/go v0.0.0-20201120205902-5459f2c99403/go.mod h1:WmhPx2Nbnhtbo57+VJT5O0JRkEi1Wbu0z5j0R8u5Hbk=
 github.com/cncf/udpa/go v0.0.0-20210930031921-04548b0d99d4/go.mod h1:6pvJx4me5XPnfI9Z40ddWsdw2W/uZgQLFXToKeRcDiI=
+github.com/cncf/udpa/go v0.0.0-20220112060539-c52dc94e7fbe h1:QQ3GSy+MqSHxm/d8nCtnAiZdYFd45cYZPs8vOOIYKfk=
+github.com/cncf/udpa/go v0.0.0-20220112060539-c52dc94e7fbe/go.mod h1:6pvJx4me5XPnfI9Z40ddWsdw2W/uZgQLFXToKeRcDiI=
 github.com/cncf/xds/go v0.0.0-20210312221358-fbca930ec8ed/go.mod h1:eXthEFrGJvWHgFFCl3hGmgk+/aYT6PnTQLykKQRLhEs=
 github.com/cncf/xds/go v0.0.0-20210805033703-aa0b78936158/go.mod h1:eXthEFrGJvWHgFFCl3hGmgk+/aYT6PnTQLykKQRLhEs=
 github.com/cncf/xds/go v0.0.0-20210922020428-25de7278fc84/go.mod h1:eXthEFrGJvWHgFFCl3hGmgk+/aYT6PnTQLykKQRLhEs=
 github.com/cncf/xds/go v0.0.0-20211011173535-cb28da3451f1/go.mod h1:eXthEFrGJvWHgFFCl3hGmgk+/aYT6PnTQLykKQRLhEs=
+github.com/cncf/xds/go v0.0.0-20230310173818-32f1caf87195 h1:58f1tJ1ra+zFINPlwLWvQsR9CzAKt2e+EWV2yX9oXQ4=
+github.com/cncf/xds/go v0.0.0-20230310173818-32f1caf87195/go.mod h1:eXthEFrGJvWHgFFCl3hGmgk+/aYT6PnTQLykKQRLhEs=
 github.com/cockroachdb/datadriven v0.0.0-20200714090401-bf6692d28da5 h1:xD/lrqdvwsc+O2bjSSi3YqY73Ke3LAiSCx49aCesA0E=
 github.com/cockroachdb/errors v1.2.4 h1:Lap807SXTH5tri2TivECb/4abUkMZC9zRoLarvcKDqs=
 github.com/cockroachdb/logtags v0.0.0-20190617123548-eb05cc24525f h1:o/kfcElHqOiXqcou5a3rIlMc7oJbMQkeLk0VQJ7zgqY=
@@ -79,7 +87,11 @@ github.com/envoyproxy/go-control-plane v0.9.4/go.mod h1:6rpuAdCZL397s3pYoYcLgu1m
 github.com/envoyproxy/go-control-plane v0.9.9-0.20201210154907-fd9021fe5dad/go.mod h1:cXg6YxExXjJnVBQHBLXeUAgxn2UodCpnH306RInaBQk=
 github.com/envoyproxy/go-control-plane v0.9.9-0.20210512163311-63b5d3c536b0/go.mod h1:hliV/p42l8fGbc6Y9bQ70uLwIvmJyVE5k4iMKlh8wCQ=
 github.com/envoyproxy/go-control-plane v0.9.10-0.20210907150352-cf90f659a021/go.mod h1:AFq3mo9L8Lqqiid3OhADV3RfLJnjiw63cSpi+fDTRC0=
+github.com/envoyproxy/go-control-plane v0.11.0 h1:jtLewhRR2vMRNnq2ZZUoCjUlgut+Y0+sDDWPOfwOi1o=
+github.com/envoyproxy/go-control-plane v0.11.0/go.mod h1:VnHyVMpzcLvCFt9yUz1UnCwHLhwx1WguiVDV7pTG/tI=
 github.com/envoyproxy/protoc-gen-validate v0.1.0/go.mod h1:iSmxcyjqTsJpI2R4NaDN7+kN2VEUnK/pcBlmesArF7c=
+github.com/envoyproxy/protoc-gen-validate v0.10.0 h1:oIfnZFdC0YhpNNEX+SuIqko4cqqVZeN9IGTrhZje83Y=
+github.com/envoyproxy/protoc-gen-validate v0.10.0/go.mod h1:DRjgyB0I43LtJapqN6NiRwroiAU2PaFuvk/vjgh61ss=
 github.com/getsentry/raven-go v0.2.0 h1:no+xWJRb5ZI7eE8TWgIq1jLulQiIoLG0IfYxv5JYMGs=
 github.com/ghodss/yaml v1.0.0/go.mod h1:4dBDuWmgqj2HViK6kFavaiC9ZROes6MMH2rRYeMEF04=
 github.com/go-gl/glfw v0.0.0-20190409004039-e6da0acd62b1/go.mod h1:vR7hzQXu2zJy9AVAgeJqvqgH9Q5CA+iKCZ2gyEVpxRU=
@@ -99,8 +111,8 @@ github.com/gogo/protobuf v1.3.2/go.mod h1:P1XiOD3dCwIKUDQYPy72D8LYyHL2YPYrpS2s69
 github.com/golang-jwt/jwt/v4 v4.5.0 h1:7cYmW1XlMY7h7ii7UhUyChSgS5wUJEnm9uZVTGqOWzg=
 github.com/golang-jwt/jwt/v4 v4.5.0/go.mod h1:m21LjoU+eqJr34lmDMbreY2eSTRJ1cv77w39/MY0Ch0=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b/go.mod h1:SBH7ygxi8pfUlaOkMMuAQtPIUF8ecWP5IEl/CR7VP2Q=
-github.com/golang/glog v1.0.0 h1:nfP3RFugxnNRyKgeWd4oI1nYvXpxrx8ck8ZrcizshdQ=
 github.com/golang/glog v1.0.0/go.mod h1:EWib/APOK0SL3dFbYqvxE3UYd8E6s1ouQ7iEp/0LWV4=
+github.com/golang/glog v1.1.0 h1:/d3pCKDPWNnvIWe0vVUpNP32qc8U3PDVxySP/y360qE=
 github.com/golang/groupcache v0.0.0-20190702054246-869f871628b6/go.mod h1:cIg4eruTrX1D+g88fzRXU5OdNfaM+9IcxsU14FzY7Hc=
 github.com/golang/groupcache v0.0.0-20191227052852-215e87163ea7/go.mod h1:cIg4eruTrX1D+g88fzRXU5OdNfaM+9IcxsU14FzY7Hc=
 github.com/golang/groupcache v0.0.0-20200121045136-8c9f03a8e57e/go.mod h1:cIg4eruTrX1D+g88fzRXU5OdNfaM+9IcxsU14FzY7Hc=
@@ -368,7 +380,8 @@ golang.org/x/oauth2 v0.0.0-20190604053449-0f29369cfe45/go.mod h1:gOpvHmFTYa4Iltr
 golang.org/x/oauth2 v0.0.0-20191202225959-858c2ad4c8b6/go.mod h1:gOpvHmFTYa4IltrdGE7lF6nIHvwfUNPOp7c8zoXwtLw=
 golang.org/x/oauth2 v0.0.0-20200107190931-bf48bf16ab8d/go.mod h1:gOpvHmFTYa4IltrdGE7lF6nIHvwfUNPOp7c8zoXwtLw=
 golang.org/x/oauth2 v0.0.0-20211104180415-d3ed0bb246c8/go.mod h1:KelEdhl1UZF7XfJ4dDtk6s++YSgaE7mD/BuKKDLBl4A=
-golang.org/x/oauth2 v0.5.0 h1:HuArIo48skDwlrvM3sEdHXElYslAMsf3KwRkkW4MC4s=
+golang.org/x/oauth2 v0.6.0 h1:Lh8GPgSKBfWSwFvtuWOfeI3aAAnbXTSutYxJiOJFgIw=
+golang.org/x/oauth2 v0.6.0/go.mod h1:ycmewcwgD4Rpr3eZJLSB4Kyyljb3qDh40vJ8STE5HKw=
 golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20181108010431-42b317875d0f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20181221193216-37e7f081c4d4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
@@ -499,6 +512,7 @@ google.golang.org/appengine v1.6.1/go.mod h1:i06prIuMbXzDqacNJfV5OdTW448YApPu5ww
 google.golang.org/appengine v1.6.5/go.mod h1:8WjMMxjGQR8xUklV/ARdw2HLXBOI7O7uCIDZVag1xfc=
 google.golang.org/appengine v1.6.6/go.mod h1:8WjMMxjGQR8xUklV/ARdw2HLXBOI7O7uCIDZVag1xfc=
 google.golang.org/appengine v1.6.7 h1:FZR1q0exgwxzPzp/aF+VccGrSfxfPpkBqjIIEq3ru6c=
+google.golang.org/appengine v1.6.7/go.mod h1:8WjMMxjGQR8xUklV/ARdw2HLXBOI7O7uCIDZVag1xfc=
 google.golang.org/genproto v0.0.0-20180817151627-c66870c02cf8/go.mod h1:JiN7NxoALGmiZfu7CAH4rXhgtRTLTxftemlI0sWmxmc=
 google.golang.org/genproto v0.0.0-20190307195333-5fe7a883aa19/go.mod h1:VzzqZJRnGkLBvHegQrXjBqPurQTc5/KpmUdxsrq26oE=
 google.golang.org/genproto v0.0.0-20190418145605-e7d98fc518a7/go.mod h1:VzzqZJRnGkLBvHegQrXjBqPurQTc5/KpmUdxsrq26oE=
@@ -549,8 +563,8 @@ google.golang.org/grpc v1.33.1/go.mod h1:fr5YgcSWrqhRRxogOsw7RzIpsmvOZ6IcH4kBYTp
 google.golang.org/grpc v1.36.0/go.mod h1:qjiiYl8FncCW8feJPdyg3v6XW24KsRHe+dy9BAGRRjU=
 google.golang.org/grpc v1.40.0/go.mod h1:ogyxbiOoUXAkP+4+xa6PZSE9DZgIHtSpzjDTB9KAK34=
 google.golang.org/grpc v1.42.0/go.mod h1:k+4IHHFw41K8+bbowsex27ge2rCb65oeWqe4jJ590SU=
-google.golang.org/grpc v1.54.0 h1:EhTqbhiYeixwWQtAEZAxmV9MGqcjEU2mFx52xCzNyag=
-google.golang.org/grpc v1.54.0/go.mod h1:PUSEXI6iWghWaB6lXM4knEgpJNu2qUcKfDtNci3EC2g=
+google.golang.org/grpc v1.55.0 h1:3Oj82/tFSCeUrRTg/5E/7d/W5A1tj6Ky1ABAuZuv5ag=
+google.golang.org/grpc v1.55.0/go.mod h1:iYEXKGkEBhg1PjZQvoYEVPTDkHo1/bjTnfwTeGONTY8=
 google.golang.org/protobuf v0.0.0-20200109180630-ec00e32a8dfd/go.mod h1:DFci5gLYBciE7Vtevhsrf46CRTquxDuWsQurQQe4oz8=
 google.golang.org/protobuf v0.0.0-20200221191635-4d8936d0db64/go.mod h1:kwYJMbMJ01Woi6D6+Kah6886xMZcty6N08ah7+eCXa0=
 google.golang.org/protobuf v0.0.0-20200228230310-ab0ca4ff8a60/go.mod h1:cfTl7dwQJ+fmap5saPgwCLgHXTUD7jkjRqWcaiX5VyM=

server.go

@@ -15,8 +15,12 @@ import (
 	"github.com/lytics/retry"
 	etcdv3 "go.etcd.io/etcd/client/v3"
 	"google.golang.org/grpc"
+	"google.golang.org/grpc/credentials"
+	"google.golang.org/grpc/credentials/insecure"
+	xdscreds "google.golang.org/grpc/credentials/xds"
 	"google.golang.org/grpc/health"
 	healthpb "google.golang.org/grpc/health/grpc_health_v1"
+	"google.golang.org/grpc/xds"
 )
 
 var (
@@ -42,13 +46,14 @@ type Server struct {
 	cancel    func()
 	cfg       ServerCfg
 	etcd      *etcdv3.Client
-	grpc      *grpc.Server
+	grpc      *xds.GRPCServer
 	health    *health.Server
 	stop      sync.Once
 	fatalErr  chan error
 	actors    *makeActorRegistry
 	registry  *registry.Registry
 	mailboxes *mailboxRegistry
+	creds     credentials.TransportCredentials
 }
 
 // NewServer for the grid. The namespace must contain only characters
@@ -63,6 +68,13 @@ func NewServer(etcd *etcdv3.Client, cfg ServerCfg) (*Server, error) {
 		return nil, ErrNilEtcd
 	}
 
+	creds := insecure.NewCredentials()
+	if cfg.XDSCreds {
+		var err error
+		if creds, err = xdscreds.NewServerCredentials(xdscreds.ServerOptions{FallbackCreds: insecure.NewCredentials()}); err != nil {
+			return nil, fmt.Errorf("failed to create server-side xDS credentials: %w", err)
+		}
+	}
 	// Create a registry client, through which other
 	// entities like peers, actors, and mailboxes
 	// will be discovered.
@@ -78,15 +90,17 @@ func NewServer(etcd *etcdv3.Client, cfg ServerCfg) (*Server, error) {
 		r.Logger = cfg.Logger
 	}
 
+	grpcServer := xds.NewGRPCServer(grpc.Creds(creds))
 	server := &Server{
 		cfg:       cfg,
 		etcd:      etcd,
-		grpc:      grpc.NewServer(),
+		grpc:      grpcServer,
 		health:    health.NewServer(),
 		actors:    newMakeActorRegistry(),
 		fatalErr:  make(chan error, 1),
 		registry:  r,
 		mailboxes: newMailboxRegistry(),
+		creds:     creds,
 	}
 
 	// Create a context that each actor this leader creates
@@ -108,21 +122,21 @@ func NewServer(etcd *etcdv3.Client, cfg ServerCfg) (*Server, error) {
 //
 // Example Usage:
 //
-//     mailbox, err := server.NewMailbox("incoming", 10)
-//     ...
-//     defer mailbox.Close()
+//	mailbox, err := server.NewMailbox("incoming", 10)
+//	...
+//	defer mailbox.Close()
 //
-//     for {
-//         select {
-//         case req := <-mailbox.C:
-//             // Do something with request, and then respond
-//             // or ack. A response or ack is required.
-//             switch m := req.Msg().(type) {
-//             case HiMsg:
-//                 req.Respond(&HelloMsg{})
-//             }
-//         }
-//     }
+//	for {
+//	    select {
+//	    case req := <-mailbox.C:
+//	        // Do something with request, and then respond
+//	        // or ack. A response or ack is required.
+//	        switch m := req.Msg().(type) {
+//	        case HiMsg:
+//	            req.Respond(&HelloMsg{})
+//	        }
+//	    }
+//	}
 //
 // If the mailbox has already been created, in the calling process or
 // any other process, an error is returned, since only one mailbox