add multi-device sync (#2669)

* add basic multi-device-sync functions

* generate json

* add context.parse_sync_items()

* add context.execute_sync_items()

* piggyback sync-commands message, add body for human-readable part

* avoid double json renderings

* mimeparser parses incoming .json sync-files

* do not piggyback sync-files

* execute sync items

* return status of send_sync_msg()

* send sync messages as multipart/report

* add a per-item-timestamp and also allow adding other per-item-fields in the future

* if the self-chat does not exist, create it blocked/hidden

* create tokens closer to real qr-code needs

* respect bcc_self setting, add test for that

* sync qr code tokens after promoting groups

* send sync-messages only if an experimental switch is set

* trigger send_sync_msg() after sending messages and after creating/redraw/revive qr-code

* add DC_STR_* constants to deltachat.h

* adapt to refactored qr module as of #2729

* tweak test

* use SendSyncMsgs config name instead of SendExperimentalSyncMsgs - we can remove or rename the config nevertheless, but have the option to keep it without renaming

* tweak docs

* remove currently unused effective timestamp calculation

* clarify when send_sync_msg() is called

* make sure, sync-messages are encrypted and are sent by SELF

* tweak docs, fix typos

examples/repl/cmdline.rs

@@ -386,6 +386,7 @@ pub async fn cmdline(context: Context, line: &str, chat_id: &mut ChatId) -> Resu
                  sendsticker <file> [<text>]\n\
                  sendfile <file> [<text>]\n\
                  sendhtml <file for html-part> [<text for plain-part>]\n\
+                 sendsyncmsg\n\
                  videochat\n\
                  draft [<text>]\n\
                  devicemsg <text>\n\
@@ -895,6 +896,10 @@ pub async fn cmdline(context: Context, line: &str, chat_id: &mut ChatId) -> Resu
             }));
             chat::send_msg(&context, sel_chat.as_ref().unwrap().get_id(), &mut msg).await?;
         }
+        "sendsyncmsg" => match context.send_sync_msg().await? {
+            Some(msg_id) => println!("sync message sent as {}.", msg_id),
+            None => println!("sync message not needed."),
+        },
         "videochat" => {
             ensure!(sel_chat.is_some(), "No chat selected.");
             chat::send_videochat_invitation(&context, sel_chat.as_ref().unwrap().get_id()).await?;

examples/repl/main.rs

@@ -167,7 +167,7 @@ const DB_COMMANDS: [&str; 10] = [
     "housekeeping",
 ];
 
-const CHAT_COMMANDS: [&str; 34] = [
+const CHAT_COMMANDS: [&str; 35] = [
     "listchats",
     "listarchived",
     "chat",
@@ -188,6 +188,7 @@ const CHAT_COMMANDS: [&str; 34] = [
     "sendimage",
     "sendfile",
     "sendhtml",
+    "sendsyncmsg",
     "videochat",
     "draft",
     "listmedia",