Adding upstream version 3.6.2.

Signed-off-by: Daniel Baumann <daniel@debian.org>

sender_explicit_tls.go

@@ -0,0 +1,64 @@
+package mailyak
+
+import (
+	"crypto/tls"
+	"net"
+)
+
+// senderExplicitTLS connects to a SMTP server over a TLS connection, performs a
+// handshake and validation according to the provided tls.Config before sending
+// the email.
+type senderExplicitTLS struct {
+	hostAndPort string
+	hostname    string
+
+	// tlsConfig is always non-nil
+	tlsConfig *tls.Config
+}
+
+// Connect to the SMTP host configured in m, and send the email.
+func (s *senderExplicitTLS) Send(m sendableMail) error {
+	conn, err := tls.Dial("tcp", s.hostAndPort, s.tlsConfig)
+	if err != nil {
+		return err
+	}
+	defer func() { _ = conn.Close() }()
+
+	// Perform the SMTP protocol conversation, using the provided TLS ServerName
+	// as the SMTP server name.
+	return smtpExchange(m, conn, s.hostname, false)
+}
+
+// newSenderWithExplicitTLS constructs a new senderExplicitTLS.
+//
+// If tlsConfig is nil, a sensible default with maximum compatability is
+// generated.
+func newSenderWithExplicitTLS(hostAndPort string, tlsConfig *tls.Config) (*senderExplicitTLS, error) {
+	// Split the hostname from the addr.
+	//
+	// This hostname is used during TLS negotiation and during SMTP
+	// authentication.
+	hostName, _, err := net.SplitHostPort(hostAndPort)
+	if err != nil {
+		return nil, err
+	}
+
+	if tlsConfig != nil {
+		// Clone the user-provided TLS config to prevent it being
+		// mutated by the caller.
+		tlsConfig = tlsConfig.Clone()
+	} else {
+		// If there is no TLS config provided, initialise a default.
+		//nolint:gosec // Maximum compatability but please use TLS >= 1.2
+		tlsConfig = &tls.Config{
+			ServerName: hostName,
+		}
+	}
+
+	return &senderExplicitTLS{
+		hostAndPort: hostAndPort,
+		hostname:    hostName,
+
+		tlsConfig: tlsConfig,
+	}, nil
+}