net/smtp: close conn in SendMail; add Client.Close method

R=rsc, dave, bradfitz
CC=golang-dev
https://golang.org/cl/10082044

src/pkg/net/smtp/smtp.go

@@ -41,12 +41,13 @@ type Client struct {
 }
 
 // Dial returns a new Client connected to an SMTP server at addr.
+// The addr must include a port number.
 func Dial(addr string) (*Client, error) {
 	conn, err := net.Dial("tcp", addr)
 	if err != nil {
 		return nil, err
 	}
-	host := addr[:strings.Index(addr, ":")]
+	host, _, _ := net.SplitHostPort(addr)
 	return NewClient(conn, host)
 }
 
@@ -63,6 +64,11 @@ func NewClient(conn net.Conn, host string) (*Client, error) {
 	return c, nil
 }
 
+// Close closes the connection.
+func (c *Client) Close() error {
+	return c.Text.Close()
+}
+
 // hello runs a hello exchange if needed.
 func (c *Client) hello() error {
 	if !c.didHello {
@@ -264,7 +270,8 @@ func SendMail(addr string, a Auth, from string, to []string, msg []byte) error {
 	if err != nil {
 		return err
 	}
-	if err := c.hello(); err != nil {
+	defer c.Close()
+	if err = c.hello(); err != nil {
 		return err
 	}
 	if ok, _ := c.Extension("STARTTLS"); ok {

src/pkg/net/smtp/smtp_test.go

@@ -238,6 +238,7 @@ func TestNewClient(t *testing.T) {
 	if err != nil {
 		t.Fatalf("NewClient: %v\n(after %v)", err, out())
 	}
+	defer c.Close()
 	if ok, args := c.Extension("aUtH"); !ok || args != "LOGIN PLAIN" {
 		t.Fatalf("Expected AUTH supported")
 	}
@@ -278,6 +279,7 @@ func TestNewClient2(t *testing.T) {
 	if err != nil {
 		t.Fatalf("NewClient: %v", err)
 	}
+	defer c.Close()
 	if ok, _ := c.Extension("DSN"); ok {
 		t.Fatalf("Shouldn't support DSN")
 	}
@@ -323,6 +325,7 @@ func TestHello(t *testing.T) {
 		if err != nil {
 			t.Fatalf("NewClient: %v", err)
 		}
+		defer c.Close()
 		c.localName = "customhost"
 		err = nil