JSON-RPC: retrieve events via long polling

This way is more compatible to JSON-RPC libraries
that do not support receiving notifications from the server
and allows describing event types in the OpenRPC specification.

Event thread converting events to notifications in the FFI
is removed, so it is now possible to construct a dc_jsonrpc_instance_t
while still retrieving events via dc_event_emitter_t.

deltachat-jsonrpc/src/api/mod.rs

@@ -49,6 +49,7 @@ use types::message::MessageObject;
 use types::provider_info::ProviderInfo;
 use types::webxdc::WebxdcMessageInfo;
 
+use self::events::Event;
 use self::types::message::MessageLoadResult;
 use self::types::{
     chat::{BasicChat, JSONRPCChatVisibility, MuteDuration},
@@ -165,6 +166,16 @@ impl CommandApi {
         get_info()
     }
 
+    /// Get the next event.
+    async fn get_next_event(&self) -> Result<Event> {
+        let event_emitter = self.accounts.read().await.get_event_emitter();
+        event_emitter
+            .recv()
+            .await
+            .map(|event| event.into())
+            .context("event channel is closed")
+    }
+
     // ---------------------------------------------
     // Account Management
     // ---------------------------------------------