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

src/mimeparser.rs

@@ -28,6 +28,7 @@ use crate::param::{Param, Params};
 use crate::peerstate::Peerstate;
 use crate::simplify::simplify;
 use crate::stock_str;
+use crate::sync::SyncItems;
 
 /// A parsed MIME message.
 ///
@@ -61,6 +62,7 @@ pub struct MimeMessage {
     pub is_system_message: SystemMessage,
     pub location_kml: Option<location::Kml>,
     pub message_kml: Option<location::Kml>,
+    pub(crate) sync_items: Option<SyncItems>,
     pub(crate) user_avatar: Option<AvatarAction>,
     pub(crate) group_avatar: Option<AvatarAction>,
     pub(crate) mdn_reports: Vec<Report>,
@@ -124,6 +126,10 @@ pub enum SystemMessage {
     // Chat protection state changed
     ChatProtectionEnabled = 11,
     ChatProtectionDisabled = 12,
+
+    /// Self-sent-message that contains only json used for multi-device-sync;
+    /// if possible, we attach that to other messages as for locations.
+    MultiDeviceSync = 20,
 }
 
 impl Default for SystemMessage {
@@ -279,6 +285,7 @@ impl MimeMessage {
             is_system_message: SystemMessage::Unknown,
             location_kml: None,
             message_kml: None,
+            sync_items: None,
             user_avatar: None,
             group_avatar: None,
             failure_report: None,
@@ -813,6 +820,12 @@ impl MimeMessage {
                                 }
                             }
                         }
+                        Some("multi-device-sync") => {
+                            if let Some(second) = mail.subparts.get(1) {
+                                self.add_single_part_if_known(context, second, is_related)
+                                    .await?;
+                            }
+                        }
                         Some(_) => {
                             if let Some(first) = mail.subparts.get(0) {
                                 any_part_added = self
@@ -999,7 +1012,20 @@ impl MimeMessage {
                 }
                 return;
             }
+        } else if filename == "multi-device-sync.json" {
+            let serialized = String::from_utf8_lossy(decoded_data)
+                .parse()
+                .unwrap_or_default();
+            self.sync_items = context
+                .parse_sync_items(serialized)
+                .await
+                .map_err(|err| {
+                    warn!(context, "failed to parse sync data: {}", err);
+                })
+                .ok();
+            return;
         }
+
         /* we have a regular file attachment,
         write decoded data to new blob object */