fix method return type

This has the advantage that fields are named/labled and there can be potentially more than 2 (data1 & data2) fields on the events.

This removes the need for the (potentialy confusing) overloading data1 with `dc_event_get_data1_str` to add more information to events.
And also allows gradual/partial moving to the jsonrpc api, when needed or wanted.

deltachat-ffi/deltachat.h

@@ -5951,6 +5951,19 @@ char* dc_event_get_data2_str(dc_event_t* event);
  */
 uint32_t dc_event_get_account_id(dc_event_t* event);
 
+/**
+ * Get the json representation of the event as the jsonrpc api would return it.
+ * For documentation on this json object see <https://js.jsonrpc.delta.chat/types/T.Event.html>.
+ * 
+ * The difference to the cffi is that the fields are named,
+ * and can also contain more fields than the cffi api (which only has data1 and data2).
+ *
+ * @memberof dc_event_t
+ * @param event The event object as returned from dc_get_next_event().
+ * @return The json representation of the event as string or NULL.
+ *     Must be freed using dc_str_unref().
+ */
+char* dc_event_get_json(dc_event_t* event);
 
 /**
  * Free memory used by an event object.

deltachat-ffi/src/lib.rs

@@ -816,6 +816,24 @@ pub unsafe extern "C" fn dc_event_get_account_id(event: *mut dc_event_t) -> u32
     (*event).id
 }
 
+#[no_mangle]
+pub unsafe extern "C" fn dc_event_get_json(event: *mut dc_event_t) -> *mut libc::c_char {
+    if event.is_null() {
+        eprintln!("ignoring careless call to dc_event_get_json()");
+        return ptr::null_mut();
+    }
+
+    match serde_json::to_string(&deltachat_jsonrpc::api::types::events::Event::from(
+        (*event).clone(),
+    )) {
+        Ok(string) => string.strdup(),
+        Err(error) => {
+            eprintln!("dc_event_get_json() failed to serialise to json: {error:#}");
+            ptr::null_mut()
+        }
+    }
+}
+
 pub type dc_event_emitter_t = EventEmitter;
 
 #[no_mangle]