send: move code to lib for reuse

Move the code which handles the preparation of a sender into which the
message can be written into lib to allow for reuse. Also hide the
sending backend a bit more from the `:send` command code by introducing
a NewSender function which determines which backend should be used and
invokes the appropriate sender factory function.

Rename send() to sendHelper() to avoid collision.

Signed-off-by: Karel Balej <balejk@matfyz.cz>
Acked-by: Robin Jarry <robin@jarry.cc>

1 files changed, 136 insertions, 0 deletions

diff --git a/lib/send/smtp.go b/lib/send/smtp.go
new file mode 100644
index 00000000..2cc53d25
--- /dev/null
+++ b/lib/send/smtp.go
@@ -0,0 +1,136 @@
+package send
+
+import (
+	"crypto/tls"
+	"fmt"
+	"io"
+	"net/url"
+	"strings"
+
+	"github.com/emersion/go-message/mail"
+	"github.com/emersion/go-smtp"
+	"github.com/pkg/errors"
+)
+
+func connectSmtp(starttls bool, host string, domain string) (*smtp.Client, error) {
+	serverName := host
+	if !strings.ContainsRune(host, ':') {
+		host += ":587" // Default to submission port
+	} else {
+		serverName = host[:strings.IndexRune(host, ':')]
+	}
+	conn, err := smtp.Dial(host)
+	if err != nil {
+		return nil, errors.Wrap(err, "smtp.Dial")
+	}
+	if domain != "" {
+		err := conn.Hello(domain)
+		if err != nil {
+			return nil, errors.Wrap(err, "Hello")
+		}
+	}
+	if starttls {
+		if sup, _ := conn.Extension("STARTTLS"); !sup {
+			err := errors.New("STARTTLS requested, but not supported " +
+				"by this SMTP server. Is someone tampering with your " +
+				"connection?")
+			conn.Close()
+			return nil, err
+		}
+		if err = conn.StartTLS(&tls.Config{
+			ServerName: serverName,
+		}); err != nil {
+			conn.Close()
+			return nil, errors.Wrap(err, "StartTLS")
+		}
+	}
+
+	return conn, nil
+}
+
+func connectSmtps(host string) (*smtp.Client, error) {
+	serverName := host
+	if !strings.ContainsRune(host, ':') {
+		host += ":465" // Default to smtps port
+	} else {
+		serverName = host[:strings.IndexRune(host, ':')]
+	}
+	conn, err := smtp.DialTLS(host, &tls.Config{
+		ServerName: serverName,
+	})
+	if err != nil {
+		return nil, errors.Wrap(err, "smtp.DialTLS")
+	}
+	return conn, nil
+}
+
+type smtpSender struct {
+	conn *smtp.Client
+	w    io.WriteCloser
+}
+
+func (s *smtpSender) Write(p []byte) (int, error) {
+	return s.w.Write(p)
+}
+
+func (s *smtpSender) Close() error {
+	we := s.w.Close()
+	ce := s.conn.Close()
+	if we != nil {
+		return we
+	}
+	return ce
+}
+
+func newSmtpSender(
+	protocol string, auth string, uri *url.URL, domain string,
+	from *mail.Address, rcpts []*mail.Address,
+) (io.WriteCloser, error) {
+	var err error
+	var conn *smtp.Client
+	switch protocol {
+	case "smtp":
+		conn, err = connectSmtp(true, uri.Host, domain)
+	case "smtp+insecure":
+		conn, err = connectSmtp(false, uri.Host, domain)
+	case "smtps":
+		conn, err = connectSmtps(uri.Host)
+	default:
+		return nil, fmt.Errorf("not a smtp protocol %s", protocol)
+	}
+
+	if err != nil {
+		return nil, errors.Wrap(err, "Connection failed")
+	}
+
+	saslclient, err := newSaslClient(auth, uri)
+	if err != nil {
+		conn.Close()
+		return nil, err
+	}
+	if saslclient != nil {
+		if err := conn.Auth(saslclient); err != nil {
+			conn.Close()
+			return nil, errors.Wrap(err, "conn.Auth")
+		}
+	}
+	s := &smtpSender{
+		conn: conn,
+	}
+	if err := s.conn.Mail(from.Address, nil); err != nil {
+		conn.Close()
+		return nil, errors.Wrap(err, "conn.Mail")
+	}
+	for _, rcpt := range rcpts {
+		if err := s.conn.Rcpt(rcpt.Address); err != nil {
+			conn.Close()
+			return nil, errors.Wrap(err, "conn.Rcpt")
+		}
+	}
+	s.w, err = s.conn.Data()
+	if err != nil {
+		conn.Close()
+		return nil, errors.Wrap(err, "conn.Data")
+	}
+	return s.w, nil
+}