Add dc_msg_set_subject() C FFI (#4057)

CHANGELOG.md

@@ -17,6 +17,7 @@
 
 - Remove `MimeMessage::from_bytes()` public interface. #4033
 - BREAKING Types: jsonrpc: `get_messages` now returns a map with `MessageLoadResult` instead of failing completely if one of the requested messages could not be loaded. #4038
+- Add dc_msg_set_subject() C-FFI #4057
 
 
 ## 1.108.0

deltachat-ffi/deltachat.h

@@ -4327,6 +4327,18 @@ void            dc_msg_set_text               (dc_msg_t* msg, const char* text);
 void            dc_msg_set_html               (dc_msg_t* msg, const char* html);
 
 
+/**
+ * Sets the email's subject. If it's empty, a default subject
+ * will be used (e.g. `Message from Alice` or `Re: <last subject>`).
+ * This does not alter any information in the database.
+ *
+ * @memberof dc_msg_t
+ * @param msg The message object.
+ * @param subject The new subject.
+ */
+void            dc_msg_set_subject            (dc_msg_t* msg, const char* subject);
+
+
 /**
  * Set different sender name for a message.
  * This overrides the name set by the dc_set_config()-option `displayname`.

deltachat-ffi/src/lib.rs

@@ -3598,6 +3598,16 @@ pub unsafe extern "C" fn dc_msg_set_html(msg: *mut dc_msg_t, html: *const libc::
     ffi_msg.message.set_html(to_opt_string_lossy(html))
 }
 
+#[no_mangle]
+pub unsafe extern "C" fn dc_msg_set_subject(msg: *mut dc_msg_t, subject: *const libc::c_char) {
+    if msg.is_null() {
+        eprintln!("ignoring careless call to dc_msg_get_subject()");
+        return;
+    }
+    let ffi_msg = &mut *msg;
+    ffi_msg.message.set_subject(to_string_lossy(subject));
+}
+
 #[no_mangle]
 pub unsafe extern "C" fn dc_msg_set_override_sender_name(
     msg: *mut dc_msg_t,

src/message.rs

@@ -797,6 +797,12 @@ impl Message {
         self.text = text;
     }
 
+    /// Sets the email's subject. If it's empty, a default subject
+    /// will be used (e.g. `Message from Alice` or `Re: <last subject>`).
+    pub fn set_subject(&mut self, subject: String) {
+        self.subject = subject;
+    }
+
     /// Sets the file associated with a message.
     ///
     /// This function does not use the file or check if it exists,

src/mimefactory.rs

@@ -1612,6 +1612,22 @@ mod tests {
         assert_eq!(maybe_encode_words("äöü"), "=?utf-8?b?w6TDtsO8?=");
     }
 
+    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+    async fn test_manually_set_subject() -> Result<()> {
+        let t = TestContext::new_alice().await;
+        let chat = t.create_chat_with_contact("bob", "bob@example.org").await;
+
+        let mut msg = Message::new(Viewtype::Text);
+        msg.set_subject("Subjeeeeect".to_string());
+
+        let sent_msg = t.send_msg(chat.id, &mut msg).await;
+        let payload = sent_msg.payload();
+
+        assert_eq!(payload.match_indices("Subject: Subjeeeeect").count(), 1);
+
+        Ok(())
+    }
+
     #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
     async fn test_subject_from_mua() {
         // 1.: Receive a mail from an MUA