learn SMTP STARTTLS

1 files changed, 47 insertions, 0 deletions

diff --git a/tls-getcerts.go b/tls-getcerts.go
index d598d27..d386b90 100644
--- a/tls-getcerts.go
+++ b/tls-getcerts.go
@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"io"
 	"net"
+	"net/textproto"
 	"net/url"
 	"os"
 	"strings"
@@ -62,6 +63,47 @@ func xmppStartTLS(connRaw net.Conn, host string) error {
 	return nil
 }
 
+// smtpCmd is a convenience function that sends a command, and reads
+// (but discards) the response
+func smtpCmd(tp *textproto.Conn, expectCode int, format string, args ...interface{}) error {
+	id, err := tp.Cmd(format, args...)
+	if err != nil {
+		return err
+	}
+	tp.StartResponse(id)
+	defer tp.EndResponse(id)
+	_, _, err = tp.ReadResponse(expectCode)
+	return err
+}
+
+func smtpStartTLS(connRaw net.Conn, host string) error {
+	tp := textproto.NewConn(connRaw)
+
+	// let the server introduce itself
+	_, _, err := tp.ReadResponse(220)
+	if err != nil {
+		return err
+	}
+	// introduce ourself
+	localhost, err := os.Hostname()
+	if err != nil {
+		localhost = "localhost"
+	}
+	err = smtpCmd(tp, 250, "EHLO %s", localhost)
+	if err != nil {
+		err := smtpCmd(tp, 250, "HELO %s", localhost)
+		if err != nil {
+			return err
+		}
+	}
+	// starttls
+	err = smtpCmd(tp, 220, "STARTTLS")
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
 func getcert(socket string) (*x509.Certificate, error) {
 	u, err := url.Parse(socket)
 	if err != nil {
@@ -85,6 +127,11 @@ func getcert(socket string) (*x509.Certificate, error) {
 		if err != nil {
 			return nil, err
 		}
+	case "/smtp":
+		err = smtpStartTLS(connRaw, host)
+		if err != nil {
+			return nil, err
+		}
 	default:
 		return nil, fmt.Errorf("Unknown negotiation path: %q", u.Path)
 	}