add dc_skip_device_msg() and belonging tests

deltachat-ffi/deltachat.h

@@ -1135,6 +1135,44 @@ uint32_t        dc_add_device_msg            (dc_context_t* context, dc_msg_t* m
 uint32_t        dc_add_device_msg_once       (dc_context_t* context, const char* label, dc_msg_t* msg);
 
 
+/**
+ * Skip a device-message permanently.
+ * Subsequent calls to dc_add_device_msg_once() with the same label
+ * won't add the device-message then.
+ * This might be handy if you want to add
+ * eg. different messages for first-install and updates.
+ *
+ * @memberof dc_context_t
+ * @param context The context as created by dc_context_new().
+ * @param label A unique name for the message to skip.
+ *     The label is typically not displayed to the user and
+ *     must be created from the characters `A-Z`, `a-z`, `0-9`, `_` or `-`.
+ *     If a message with that label already exist,
+ *     nothing happens.
+ * @return None.
+ *
+ * Example:
+ * ~~~
+ * dc_msg_t* welcome_msg = dc_msg_new(DC_MSG_TEXT);
+ * dc_msg_set_text(welcome_msg, "great that you give this app a try!");
+ *
+ * dc_msg_t* changelog_msg = dc_msg_new(DC_MSG_TEXT);
+ * dc_msg_set_text(changelog_msg, "we have added 3 new emojis :)");
+ *
+ * if (dc_add_device_msg_once(context, "welcome", welcome_msg)) {
+ *     // do not add the changelog on a new installations -
+ *     // not now and not when this code is executed again
+ *     dc_skip_device_msg(context, "update-123");
+ * } else {
+ *     // welcome message was not added now, this is an oder installation,
+ *     // add a changelog
+ *     dc_add_device_msg_once(context, "update-123", changelog_msg);
+ * }
+ * ~~~
+ */
+void            dc_skip_device_msg           (dc_context_t* context, const char* label);
+
+
 /**
  * Get draft for a chat, if any.
  * See dc_set_draft() for more details about drafts.

deltachat-ffi/src/lib.rs

@@ -849,6 +849,24 @@ pub unsafe extern "C" fn dc_add_device_msg_once(
         .unwrap_or(0)
 }
 
+#[no_mangle]
+pub unsafe extern "C" fn dc_skip_device_msg(
+    context: *mut dc_context_t,
+    label: *const libc::c_char,
+) {
+    if context.is_null() || label.is_null() {
+        eprintln!("ignoring careless call to dc_skip_device_msg()");
+        return;
+    }
+    let ffi_context = &mut *context;
+    ffi_context
+        .with_inner(|ctx| {
+            chat::skip_device_msg(ctx, &to_string_lossy(label))
+                .unwrap_or_log_default(ctx, "Failed to skip device message")
+        })
+        .unwrap_or(())
+}
+
 #[no_mangle]
 pub unsafe extern "C" fn dc_get_draft(context: *mut dc_context_t, chat_id: u32) -> *mut dc_msg_t {
     if context.is_null() {

src/chat.rs

@@ -1974,6 +1974,7 @@ fn add_device_msg_maybe_labelled(
 
     // if the device message is labeled and was ever added, do nothing
     if let Some(label) = label {
+        ensure!(!label.is_empty(), "cannot add empty label");
         if let Ok(()) = context.sql.query_row(
             "SELECT label FROM devmsglabels WHERE label=?",
             params![label],
@@ -2009,10 +2010,7 @@ fn add_device_msg_maybe_labelled(
     let msg_id = MsgId::new(row_id);
 
     if let Some(label) = label {
-        context.sql.execute(
-            "INSERT INTO devmsglabels (label, msg_id) VALUES (?, ?);",
-            params![label, msg_id],
-        )?;
+        skip_device_msg(context, label)?;
     }
 
     if !msg_id.is_unset() {
@@ -2022,6 +2020,25 @@ fn add_device_msg_maybe_labelled(
     Ok(msg_id)
 }
 
+pub fn skip_device_msg(context: &Context, label: &str) -> Result<(), Error> {
+    ensure!(!label.is_empty(), "cannot skip empty label");
+    if let Ok(()) = context.sql.query_row(
+        "SELECT label FROM devmsglabels WHERE label=?",
+        params![label],
+        |_| Ok(()),
+    ) {
+        info!(context, "device-message {} already added", label);
+        return Ok(());
+    }
+
+    context.sql.execute(
+        "INSERT INTO devmsglabels (label) VALUES (?);",
+        params![label],
+    )?;
+
+    Ok(())
+}
+
 pub fn add_info_msg(context: &Context, chat_id: u32, text: impl AsRef<str>) {
     let rfc724_mid = dc_create_outgoing_rfc724_mid(None, "@device");
 
@@ -2214,6 +2231,26 @@ mod tests {
         assert!(msg2_id.as_ref().unwrap().is_unset());
     }
 
+    #[test]
+    fn test_skip_device_msg() {
+        let t = test_context(Some(Box::new(logging_cb)));
+        let res = skip_device_msg(&t.ctx, "");
+        assert!(res.is_err());
+        let res = skip_device_msg(&t.ctx, "some-label");
+        assert!(res.is_ok());
+
+        let mut msg = Message::new(Viewtype::Text);
+        msg.text = Some("message text".to_string());
+
+        let msg_id = add_device_msg_once(&t.ctx, "some-label", &mut msg);
+        assert!(msg_id.is_ok());
+        assert!(msg_id.as_ref().unwrap().is_unset());
+
+        let msg_id = add_device_msg_once(&t.ctx, "unused-label", &mut msg);
+        assert!(msg_id.is_ok());
+        assert!(!msg_id.as_ref().unwrap().is_unset());
+    }
+
     fn chatlist_len(ctx: &Context, listflags: usize) -> usize {
         Chatlist::try_load(ctx, listflags, None, None)
             .unwrap()

src/sql.rs

@@ -815,7 +815,7 @@ fn open(
             // records in the devmsglabels are kept when the message is deleted.
             // so, msg_id may or may not exist.
             sql.execute(
-                "CREATE TABLE devmsglabels (id INTEGER PRIMARY KEY AUTOINCREMENT, label TEXT, msg_id INTEGER);",
+                "CREATE TABLE devmsglabels (id INTEGER PRIMARY KEY AUTOINCREMENT, label TEXT, msg_id INTEGER DEFAULT 0);",
                 NO_PARAMS,
             )?;
             sql.execute(