compose: allow sending format=flowed messages

Allow composing and sending messages with:

  Content-Type: text/plain; Format=Flowed

This requires additional configuration in the text editor to actually
produce the required trailing spaces at the end of lines that are part
of the same paragraph. For example, with vim:

  "~/.vim/ftplugin/mail.vim

  setlocal textwidth=72
  setlocal formatoptions=1jnwtcql
  setlocal comments+=nb:>

Link: https://www.rfc-editor.org/rfc/rfc3676.html
Signed-off-by: Robin Jarry <robin@jarry.cc>
Tested-by: Moritz Poldrack <moritz@poldrack.dev>

1 files changed, 13 insertions, 8 deletions

diff --git a/widgets/compose.go b/widgets/compose.go
index 3ae41989..5795ccba 100644
--- a/widgets/compose.go
+++ b/widgets/compose.go
@@ -825,20 +825,20 @@ func (c *Composer) ShouldWarnAttachment() (bool, error) {
 }
 
 func writeMsgImpl(c *Composer, header *mail.Header, writer io.Writer) error {
+	mimeParams := map[string]string{"Charset": "UTF-8"}
+	if config.Compose.FormatFlowed {
+		mimeParams["Format"] = "Flowed"
+	}
 	if len(c.attachments) == 0 && len(c.textParts) == 0 {
 		// no attachments
-		return writeInlineBody(header, c.email, writer)
+		return writeInlineBody(header, c.email, writer, mimeParams)
 	} else {
 		// with attachments
 		w, err := mail.CreateWriter(writer, *header)
 		if err != nil {
 			return errors.Wrap(err, "CreateWriter")
 		}
-		newPart, err := lib.NewPart(
-			"text/plain",
-			map[string]string{"Charset": "UTF-8"},
-			c.email,
-		)
+		newPart, err := lib.NewPart("text/plain", mimeParams, c.email)
 		if err != nil {
 			return err
 		}
@@ -856,8 +856,13 @@ func writeMsgImpl(c *Composer, header *mail.Header, writer io.Writer) error {
 	return nil
 }
 
-func writeInlineBody(header *mail.Header, body io.Reader, writer io.Writer) error {
-	header.SetContentType("text/plain", map[string]string{"charset": "UTF-8"})
+func writeInlineBody(
+	header *mail.Header,
+	body io.Reader,
+	writer io.Writer,
+	mimeParams map[string]string,
+) error {
+	header.SetContentType("text/plain", mimeParams)
 	w, err := mail.CreateSingleInlineWriter(writer, *header)
 	if err != nil {
 		return errors.Wrap(err, "CreateSingleInlineWriter")