Add format_flowed option for composing e-mail

When format_flowed=true, generated text/plain attachments include the
format=flowed MIME parameter.

format_flowed is set to true by default.

meli.conf.5

@@ -227,6 +227,10 @@ command to launch editor. Can have arguments. Draft filename is given as the las
 (optional) embed editor within meli
 .\" default value
 .Pq Em false
+.It Cm format_flowed Ar boolean
+(optional) set format=flowed [RFC367] in text/plain attachments.
+.\" default value
+.Pq Em true
 .El
 .Sh SHORTCUTS
 Shortcuts can take the following values:

ui/src/components/mail/compose.rs

@@ -1202,6 +1202,7 @@ pub fn send_draft(
     use std::process::{Command, Stdio};
     let mut failure = true;
     let settings = &context.settings;
+    let format_flowed = settings.composing.format_flowed;
     let parts = split_command!(settings.composing.mailer_cmd);
     let (cmd, args) = (parts[0], &parts[1..]);
     let mut msmtp = Command::new(cmd)
@@ -1213,8 +1214,18 @@ pub fn send_draft(
     {
         let stdin = msmtp.stdin.as_mut().expect("failed to open stdin");
         if sign_mail.is_true() {
+            let mut content_type = ContentType::default();
+            if format_flowed {
+                if let ContentType::Text {
+                    ref mut parameters, ..
+                } = content_type
+                {
+                    parameters.push((b"format".to_vec(), b"flowed".to_vec()));
+                }
+            }
+
             let mut body: AttachmentBuilder = Attachment::new(
-                Default::default(),
+                content_type,
                 Default::default(),
                 std::mem::replace(&mut draft.body, String::new()).into_bytes(),
             )

ui/src/conf/composing.rs

@@ -18,7 +18,7 @@
  * You should have received a copy of the GNU General Public License
  * along with meli. If not, see <http://www.gnu.org/licenses/>.
  */
-use super::default_vals::{false_val, none};
+use super::default_vals::{false_val, none, true_val};
 
 /// Settings for writing and sending new e-mail
 #[derive(Debug, Serialize, Deserialize, Clone)]
@@ -32,6 +32,10 @@ pub struct ComposingSettings {
     /// Embed editor (for terminal interfaces) instead of forking and waiting.
     #[serde(default = "false_val")]
     pub embed: bool,
+    /// Set "format=flowed" in plain text attachments.
+    /// Default: true
+    #[serde(default = "true_val")]
+    pub format_flowed: bool,
 }
 
 impl Default for ComposingSettings {
@@ -40,6 +44,7 @@ impl Default for ComposingSettings {
             mailer_cmd: String::new(),
             editor_cmd: None,
             embed: false,
+            format_flowed: true,
         }
     }
 }