lib/smtp: realign all structs

The goal is to minimize memory consumed by struct instance.
Changes,

* Client: from 112 to 80 bytes (-32 bytes)
* Command: from 48 to 32 bytes (-8 bytes)
* Domain: from 32 to 24 bytes (-8 bytes)
* LocalStorage: from 72 to 40 bytes (-32 bytes)
* MailTx: from 128 to 112 bytes (-16 bytes)
* receiver: from 152 to 104 bytes (-48 bytes)
* Response: from 32 to 24 bytes (-8 bytes)
* Server: from 144 to 128 bytes (-16 bytes)
* ServerInfo: from 40 to 32 bytes (-8 bytes)

12 files changed, 67 insertions, 57 deletions

diff --git a/lib/smtp/client.go b/lib/smtp/client.go
index 6620fcbd..791c3212 100644
--- a/lib/smtp/client.go
+++ b/lib/smtp/client.go
@@ -28,12 +28,13 @@ type Client struct {
 	// EHLO command.
 	ServerInfo *ServerInfo
 
+	conn       net.Conn
+	raddr      *net.TCPAddr
+	serverName string
+
 	data []byte
 	buf  bytes.Buffer
 
-	serverName string
-	raddr      *net.TCPAddr
-	conn       net.Conn
 	insecure   bool
 	isTLS      bool
 	isStartTLS bool
diff --git a/lib/smtp/client_test.go b/lib/smtp/client_test.go
index 33f49baa..e8df931e 100644
--- a/lib/smtp/client_test.go
+++ b/lib/smtp/client_test.go
@@ -13,10 +13,11 @@ import (
 
 func TestEhlo(t *testing.T) {
 	cases := []struct {
-		desc          string
-		arg           string
 		exp           *Response
 		expServerInfo *ServerInfo
+
+		desc string
+		arg  string
 	}{{
 		desc: "With no argument",
 		exp: &Response{
@@ -55,12 +56,14 @@ func TestEhlo(t *testing.T) {
 
 func TestAuth(t *testing.T) {
 	cases := []struct {
+		exp *Response
+
 		desc     string
-		mech     Mechanism
 		username string
 		password string
 		expErr   string
-		exp      *Response
+
+		mech Mechanism
 	}{{
 		desc:     "With invalid mechanism",
 		username: testAccountFirst.Short(),
@@ -142,9 +145,9 @@ func TestAuth2(t *testing.T) {
 
 func TestExpand(t *testing.T) {
 	cases := []struct {
+		exp   *Response
 		desc  string
 		mlist string
-		exp   *Response
 	}{{
 		desc:  "With mailing-list",
 		mlist: "mailing-list@test",
@@ -168,9 +171,9 @@ func TestExpand(t *testing.T) {
 
 func TestHelp(t *testing.T) {
 	cases := []struct {
+		exp  *Response
 		desc string
 		arg  string
-		exp  *Response
 	}{{
 		desc: "Without any argument",
 		exp: &Response{
@@ -193,9 +196,9 @@ func TestHelp(t *testing.T) {
 
 func TestSendCommand(t *testing.T) {
 	cases := []struct {
+		exp  *Response
 		desc string
 		cmd  []byte
-		exp  *Response
 	}{{
 		desc: "Send HELO",
 		cmd:  []byte("HELO 192.168.10.1\r\n"),
@@ -233,9 +236,10 @@ func TestSendCommand(t *testing.T) {
 
 func TestMailTx(t *testing.T) {
 	cases := []struct {
+		mail *MailTx
+		exp  *Response
+
 		desc   string
-		mail   *MailTx
-		exp    *Response
 		expErr string
 	}{{
 		desc: "With empty mail",
@@ -278,9 +282,10 @@ func TestMailTx(t *testing.T) {
 
 func TestVerify(t *testing.T) {
 	cases := []struct {
+		exp *Response
+
 		desc    string
 		mailbox string
-		exp     *Response
 	}{{
 		desc:    "With mailbox exist",
 		mailbox: testAccountFirst.Short(),
diff --git a/lib/smtp/command.go b/lib/smtp/command.go
index a21363bd..84457d51 100644
--- a/lib/smtp/command.go
+++ b/lib/smtp/command.go
@@ -33,10 +33,10 @@ const (
 // parameters.
 //
 type Command struct {
-	Kind   CommandKind
+	Params map[string]string
 	Arg    string
 	Param  string
-	Params map[string]string
+	Kind   CommandKind
 }
 
 //
diff --git a/lib/smtp/command_test.go b/lib/smtp/command_test.go
index 950bd4cf..2c66cd51 100644
--- a/lib/smtp/command_test.go
+++ b/lib/smtp/command_test.go
@@ -13,10 +13,10 @@ import (
 
 func TestUnpack(t *testing.T) {
 	cases := []struct {
+		expCmd *Command
+		expErr error
 		desc   string
 		b      string
-		expErr error
-		expCmd *Command
 	}{{
 		desc:   "With invalid length",
 		b:      "DAT\r\n",
diff --git a/lib/smtp/domain.go b/lib/smtp/domain.go
index 284e7471..cc5a20c7 100644
--- a/lib/smtp/domain.go
+++ b/lib/smtp/domain.go
@@ -9,9 +9,10 @@ package smtp
 // DKIM feature.
 //
 type Domain struct {
-	Name     string
-	Accounts map[string]*Account
 	dkimOpts *DKIMOptions
+
+	Accounts map[string]*Account
+	Name     string
 }
 
 //
diff --git a/lib/smtp/localstorage.go b/lib/smtp/localstorage.go
index 002e066f..6fb4a7b0 100644
--- a/lib/smtp/localstorage.go
+++ b/lib/smtp/localstorage.go
@@ -23,10 +23,10 @@ const (
 // retrieved in file system inside a directory.
 //
 type LocalStorage struct {
-	dir  string
-	buff bytes.Buffer
 	enc  *gob.Encoder
 	dec  *gob.Decoder
+	dir  string
+	buff bytes.Buffer
 }
 
 //
diff --git a/lib/smtp/localstorage_test.go b/lib/smtp/localstorage_test.go
index b65d6738..5fecfd1d 100644
--- a/lib/smtp/localstorage_test.go
+++ b/lib/smtp/localstorage_test.go
@@ -17,9 +17,9 @@ func TestStore(t *testing.T) {
 	}
 
 	cases := []struct {
-		desc   string
-		mail   *MailTx
 		expErr error
+		mail   *MailTx
+		desc   string
 	}{{
 		desc: "With nil",
 	}, {
diff --git a/lib/smtp/mail_tx.go b/lib/smtp/mail_tx.go
index d4bebb65..d7a40781 100644
--- a/lib/smtp/mail_tx.go
+++ b/lib/smtp/mail_tx.go
@@ -15,6 +15,12 @@ import (
 // MailTx define a mail transaction.
 //
 type MailTx struct {
+	Postpone time.Time
+
+	// Received contains the time when the message arrived on server.
+	// This field is ignored in Client.Send().
+	Received time.Time
+
 	// ID of message.
 	// This field is ignored in Client.Send().
 	ID string
@@ -31,12 +37,7 @@ type MailTx struct {
 	// This field is optional in Client.Send().
 	Data []byte
 
-	Postpone time.Time
-
-	// Received contains the time when the message arrived on server.
-	// This field is ignored in Client.Send().
-	Received time.Time
-	Retry    int
+	Retry int
 }
 
 //
diff --git a/lib/smtp/receiver.go b/lib/smtp/receiver.go
index 044c9f74..eae934a4 100644
--- a/lib/smtp/receiver.go
+++ b/lib/smtp/receiver.go
@@ -31,17 +31,19 @@ const (
 // receiver represent a connection that receive incoming email in server.
 //
 type receiver struct {
-	mode receiverMode
+	conn net.Conn
+	mail *MailTx
 
-	data          []byte
-	buff          bytes.Buffer
-	conn          net.Conn
 	clientDomain  string
 	clientAddress string
 	localAddress  string
 
-	state         CommandKind
-	mail          *MailTx
+	data []byte
+	buff bytes.Buffer
+
+	mode  receiverMode
+	state CommandKind
+
 	authenticated bool
 }
 
diff --git a/lib/smtp/response.go b/lib/smtp/response.go
index 1bff05ee..68f6fb72 100644
--- a/lib/smtp/response.go
+++ b/lib/smtp/response.go
@@ -17,9 +17,9 @@ import (
 // Response represent a generic single or multilines response from server.
 //
 type Response struct {
-	Code    int
 	Message string
 	Body    []string
+	Code    int
 }
 
 //
diff --git a/lib/smtp/server.go b/lib/smtp/server.go
index 5854bf61..89c25b37 100644
--- a/lib/smtp/server.go
+++ b/lib/smtp/server.go
@@ -25,30 +25,10 @@ const (
 // Server defines parameters for running an SMTP server.
 //
 type Server struct {
-	// address to listen for incoming connections.
-	// This field is optional and exist only for the purpose of testing.
-	// If its empty, it will set default to ":25".
-	address string
-
-	// tlsAddress define an address when listening with security layer.
-	// This field is optional and exist only for the purpose of testing.
-	// If its empty, it will set default to ":465".
-	tlsAddress string
-
-	// TLSCert the server certificate for TLS or nil if no certificate.
-	// This field is optional, if its non nil, the server will also listen
-	// on address defined in TLSAddress.
-	TLSCert *tls.Certificate
-
 	// Env contains server environment.
 	Env *Environment
 
 	//
-	// Exts define list of custom extensions that the server will provide.
-	//
-	Exts []Extension
-
-	//
 	// Handler define an interface that will process the bouncing email,
 	// incoming email, EXPN command, and VRFY command.
 	// This field is optional, if not set, it will default to
@@ -73,6 +53,26 @@ type Server struct {
 	// relayQueue hold mail objects that need to be relayed to other MTA.
 	relayQueue chan *MailTx
 
+	// TLSCert the server certificate for TLS or nil if no certificate.
+	// This field is optional, if its non nil, the server will also listen
+	// on address defined in TLSAddress.
+	TLSCert *tls.Certificate
+
+	// address to listen for incoming connections.
+	// This field is optional and exist only for the purpose of testing.
+	// If its empty, it will set default to ":25".
+	address string
+
+	// tlsAddress define an address when listening with security layer.
+	// This field is optional and exist only for the purpose of testing.
+	// If its empty, it will set default to ":465".
+	tlsAddress string
+
+	//
+	// Exts define list of custom extensions that the server will provide.
+	//
+	Exts []Extension
+
 	wg      sync.WaitGroup
 	running bool
 }
diff --git a/lib/smtp/serverinfo.go b/lib/smtp/serverinfo.go
index 3c4dbe30..facaeef2 100644
--- a/lib/smtp/serverinfo.go
+++ b/lib/smtp/serverinfo.go
@@ -13,9 +13,9 @@ import (
 // command.
 //
 type ServerInfo struct {
+	Exts   map[string][]string
 	Domain string
 	Info   string
-	Exts   map[string][]string
 }
 
 //