Implemented MaxConnections, corrected examples, removed MailAddress.

address.go

@@ -5,12 +5,9 @@ import (
 	"strings"
 )
 
-// MailAddress holds an e-mail address
+func parseAddress(src string) (string, error) {
-type MailAddress string
-
-func parseMailAddress(src string) (MailAddress, error) {
 	if src[0] != '<' || src[len(src)-1] != '>' || strings.Count(src, "@") != 1 {
-		return MailAddress(""), fmt.Errorf("Ill-formatted e-mail address: %s", src)
+		return "", fmt.Errorf("Ill-formatted e-mail address: %s", src)
 	}
-	return MailAddress(src[1 : len(src)-1]), nil
+	return src[1 : len(src)-1], nil
 }

example_test.go

@@ -1,32 +1,32 @@
 package smtpd
 
 import (
-	"bitbucket.org/chrj/smtpd"
 	"errors"
-	"net"
 	"net/smtp"
 	"strings"
 )
 
 func ExampleServer() {
 
+	var server *Server
+
 	// No-op server. Accepts and discards
-	server := &smtpd.Server{}
+	server = &Server{}
-	server.serve()
+	server.ListenAndServe()
 
 	// Relay server. Accepts only from single IP address and forwards using the Gmail smtp
-	server := &smtpd.Server{
+	server = &Server{
 
 		Addr: "0.0.0.0:10025",
 
-		HeloChecker: func(peer smtpd.Peer) error {
+		HeloChecker: func(peer Peer) error {
 			if !strings.HasPrefix(peer.Addr.String(), "42.42.42.42:") {
 				return errors.New("Denied")
 			}
 			return nil
 		},
 
-		Handler: func(peer smtpd.Peer, env smtpd.Envelope) error {
+		Handler: func(peer Peer, env Envelope) error {
 			return smtp.SendMail(
 				"smtp.gmail.com:587", 
 				smtp.PlainAuth(
@@ -35,14 +35,14 @@ func ExampleServer() {
 					"password", 
 					"smtp.gmail.com",
 				),
-				env.Sender,
+				string(env.Sender),
-				env.Recipients,
+				[]string(env.Recipients),
 				env.Data,
 			)
 		},
 
 	}
 
-	server.serve()
+	server.ListenAndServe()
 
 }

protocol.go

@@ -148,7 +148,7 @@ func (session *session) handleMAIL(cmd command) {
 		return
 	}
 
-	addr, err := parseMailAddress(cmd.params[1])
+	addr, err := parseAddress(cmd.params[1])
 
 	if err != nil {
 		session.reply(502, "Ill-formatted e-mail address")
@@ -178,7 +178,7 @@ func (session *session) handleRCPT(cmd command) {
 		return
 	}
 
-	addr, err := parseMailAddress(cmd.params[1])
+	addr, err := parseAddress(cmd.params[1])
 
 	if err != nil {
 		session.reply(502, "Ill-formatted e-mail address")

smtpd.go

@@ -19,6 +19,9 @@ type Server struct {
 	ReadTimeout  time.Duration // Socket timeout for read operations (default: 60s)
 	WriteTimeout time.Duration // Socket timeout for write operations (default: 60s)
 
+	MaxMessageSize int // Max message size in bytes (default: 10240000)
+	MaxConnections int // Max concurrent connections, use -1 to disable (default: 100)
+
 	// New e-mails are handed off to this function.
 	// Can be left empty for a NOOP server.
 	// If an error is returned, it will be reported in the SMTP session.
@@ -28,8 +31,8 @@ type Server struct {
 	// Can be left empty for no restrictions.
 	// If an error is returned, it will be reported in the SMTP session.
 	HeloChecker      func(peer Peer) error                   // Called after HELO/EHLO.
-	SenderChecker    func(peer Peer, addr MailAddress) error // Called after MAIL FROM.
+	SenderChecker    func(peer Peer, addr string) error // Called after MAIL FROM.
-	RecipientChecker func(peer Peer, addr MailAddress) error // Called after each RCPT TO.
+	RecipientChecker func(peer Peer, addr string) error // Called after each RCPT TO.
 
 	// Enable PLAIN/LOGIN authentication, only available after STARTTLS.
 	// Can be left empty for no authentication support.
@@ -37,8 +40,6 @@ type Server struct {
 
 	TLSConfig *tls.Config // Enable STARTTLS support
 	ForceTLS  bool        // Force STARTTLS usage
-
-	MaxMessageSize int // Max message size in bytes (default: 10240000)
 }
 
 // Peer represents the client connecting to the server
@@ -51,8 +52,8 @@ type Peer struct {
 
 // Envelope holds a message
 type Envelope struct {
-	Sender     MailAddress
+	Sender     string
-	Recipients []MailAddress
+	Recipients []string
 	Data       []byte
 }
 
@@ -107,6 +108,14 @@ func (srv *Server) Serve(l net.Listener) error {
 
 	defer l.Close()
 
+	var limiter chan struct{}
+
+	if srv.MaxConnections > 0 {
+		limiter = make(chan struct{}, srv.MaxConnections)
+	} else {
+		limiter = nil
+	}
+
 	for {
 
 		conn, e := l.Accept()
@@ -123,7 +132,19 @@ func (srv *Server) Serve(l net.Listener) error {
 			continue
 		}
 
-		go session.serve()
+		if limiter != nil {
+			go func() {
+				select {
+				case limiter <- struct{}{}:
+					session.serve()
+					<-limiter
+				default:
+					session.reject()
+				}
+			}()
+		} else {
+			go session.serve()
+		}
 
 	}
 
@@ -135,6 +156,10 @@ func (srv *Server) configureDefaults() {
 		srv.MaxMessageSize = 10240000
 	}
 
+	if srv.MaxConnections == 0 {
+		srv.MaxConnections = 100
+	}
+
 	if srv.ReadTimeout == 0 {
 		srv.ReadTimeout = time.Second * 60
 	}
@@ -177,6 +202,11 @@ func (session *session) serve() {
 
 }
 
+func (session *session) reject() {
+	session.reply(450, "Too busy. Try again later.")
+	session.close()
+}
+
 func (session *session) reply(code int, message string) {
 
 	fmt.Fprintf(session.writer, "%d %s\r\n", code, message)

smtpd_test.go

@@ -233,7 +233,7 @@ func TestSenderCheck(t *testing.T) {
 	defer ln.Close()
 
 	server := &Server{
-		SenderChecker: func(peer Peer, addr MailAddress) error { return errors.New("Denied") },
+		SenderChecker: func(peer Peer, addr string) error { return errors.New("Denied") },
 	}
 
 	go func() {
@@ -261,7 +261,7 @@ func TestRecipientCheck(t *testing.T) {
 	defer ln.Close()
 
 	server := &Server{
-		RecipientChecker: func(peer Peer, addr MailAddress) error { return errors.New("Denied") },
+		RecipientChecker: func(peer Peer, addr string) error { return errors.New("Denied") },
 	}
 
 	go func() {
@@ -398,3 +398,33 @@ func TestHandler(t *testing.T) {
 	}
 
 }
+
+func TestMaxConnections(t *testing.T) {
+
+	ln, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("Listen failed: %v", err)
+	}
+
+	defer ln.Close()
+
+	server := &Server{
+		MaxConnections: 1,
+	}
+
+	go func() {
+		server.Serve(ln)
+	}()
+
+	c1, err := smtp.Dial(ln.Addr().String())
+	if err != nil {
+		t.Fatalf("Dial failed: %v", err)
+	}
+
+	_, err = smtp.Dial(ln.Addr().String())
+	if err == nil {
+		t.Fatal("Dial succeeded despite MaxConnections = 1")
+	}
+
+	c1.Close()
+}