do not check for STARTTLS support when talking to a loopback address. v2 PROPOSED

Paul Vixie: 1
 do not check for STARTTLS support when talking to a loopback address.

 1 files changed, 37 insertions(+), 21 deletions(-)

[PATCH v2] do not check for STARTTLS support when talking to a loopback address. Export this patch

---
 commands/compose/send.go | 58 +++++++++++++++++++++++++---------------
 1 file changed, 37 insertions(+), 21 deletions(-)

diff --git a/commands/compose/send.go b/commands/compose/send.go
index 849182d..d6fb32c 100644
--- a/commands/compose/send.go
+++ b/commands/compose/send.go
@@ -5,6 +5,7 @@ import (
 	"crypto/tls"
 	"fmt"
 	"io"
+	"net"
 	"net/url"
 	"os/exec"
 	"strings"
@@ -360,7 +361,7 @@ func newSmtpSender(ctx sendCtx) (io.WriteCloser, error) {
 func connectSmtp(starttls bool, host string) (*smtp.Client, error) {
 	serverName := host
 	if !strings.ContainsRune(host, ':') {
-		host = host + ":587" // Default to submission port
+		host += ":587" // Default to submission port
 	} else {
 		serverName = host[:strings.IndexRune(host, ':')]
 	}
@@ -368,27 +369,42 @@ func connectSmtp(starttls bool, host string) (*smtp.Client, error) {
 	if err != nil {
 		return nil, errors.Wrap(err, "smtp.Dial")
 	}
-	if sup, _ := conn.Extension("STARTTLS"); sup {
-		if !starttls {
-			err := errors.New("STARTTLS is supported by this server, " +
-				"but not set in accounts.conf. " +
-				"Add smtp-starttls=yes")
-			conn.Close()
-			return nil, err
-		}
-		if err = conn.StartTLS(&tls.Config{
-			ServerName: serverName,
-		}); err != nil {
-			conn.Close()
-			return nil, errors.Wrap(err, "StartTLS")
+	// no way to get the chosen ip out of the smtp.conn; repeat DNS request
+	var localhost bool
+	if ips, err := net.LookupIP(serverName); err == nil {
+		for _, ip := range ips {
+			if ip.IsLoopback() {
+				localhost = true
+				break
+			}
 		}
-	} else {
-		if starttls {
-			err := errors.New("STARTTLS requested, but not supported " +
-				"by this SMTP server. Is someone tampering with your " +
-				"connection?")
-			conn.Close()
-			return nil, err
+	}
+	if !localhost {
+		if sup, _ := conn.Extension("STARTTLS"); sup {
+			if !starttls {
+				err := errors.New("STARTTLS is supported " +
+					"by this non-localhost SMTP server, " +
+					"but not requested in accounts.conf. " +
+					"Add smtp-starttls=yes")
+				conn.Close()
+				return nil, err
+			}
+			if err = conn.StartTLS(&tls.Config{
+				ServerName: serverName,
+			}); err != nil {
+				conn.Close()
+				return nil, errors.Wrap(err, "StartTLS")
+			}
+		} else {
+			if starttls {
+				err := errors.New("STARTTLS requested " +
+					"in accounts.conf, but not supported " +
+					"by this non-localhost SMTP server. " +
+					"Is someone tampering with your " +
+					"connection?")
+				conn.Close()
+				return nil, err
+			}
 		}
 	}
 	return conn, nil
-- 
2.32.0