From b1af486e109e0f76df55090c4f256cce84cf9f5f Mon Sep 17 00:00:00 2001
From: link2xt <link2xt@testrun.org>
Date: Tue, 7 Sep 2021 21:13:05 +0000
Subject: [PATCH] Log all decisions when applying ephemeral timer to chats

This should make it easier to debug problems related to timer
rollbacks and reported failure to disable the timer in some chats.
---
 src/dc_receive_imf.rs | 72 ++++++++++++++++++++++++++++++++-----------
 1 file changed, 54 insertions(+), 18 deletions(-)

diff --git a/src/dc_receive_imf.rs b/src/dc_receive_imf.rs
index f134fdcb1..862b549bd 100644
--- a/src/dc_receive_imf.rs
+++ b/src/dc_receive_imf.rs
@@ -856,37 +856,73 @@ async fn add_parts(
 
     // Apply ephemeral timer changes to the chat.
     //
-    // Only non-hidden timers are applied now. Timers from hidden
+    // Only non-hidden timers are applied. Timers from hidden
     // messages such as read receipts can be useful to detect
     // ephemeral timer support, but timer changes without visible
     // received messages may be confusing to the user.
     if !*hidden
         && !location_kml_is
         && !is_mdn
-        && (is_dc_message != MessengerMessage::Yes
-            || parent.is_none()
-            || parent.unwrap().ephemeral_timer != ephemeral_timer)
         && chat_id.get_ephemeral_timer(context).await? != ephemeral_timer
-        && chat_id
-            .update_timestamp(context, Param::EphemeralSettingsTimestamp, *sent_timestamp)
-            .await?
     {
-        if let Err(err) = chat_id
-            .inner_set_ephemeral_timer(context, ephemeral_timer)
-            .await
+        info!(
+            context,
+            "received new ephemeral timer value {:?} for chat {}, checking if it should be applied",
+            ephemeral_timer,
+            chat_id
+        );
+        if is_dc_message == MessengerMessage::Yes
+            && mime_parser
+                .parts
+                .get(0)
+                .and_then(|part| part.param.get(Param::Quote))
+                .is_none()
+            && parent.map(|p| p.ephemeral_timer) == Some(ephemeral_timer)
         {
+            // The message is a Delta Chat message without a quote, so it must be a reply to the
+            // last message in the chat as seen by the sender. The timer is the same in both the
+            // received message and its parent, so we know that the sender has not seen any change
+            // of the timer between these messages. As our timer value is different, it means the
+            // sender has not received some timer update that we have seen or sent ourselves, so we
+            // ignore incoming timer to prevent a rollback.
             warn!(
                 context,
-                "failed to modify timer for chat {}: {}", chat_id, err
+                "ignoring ephemeral timer change to {:?} for chat {} to avoid rollback",
+                ephemeral_timer,
+                chat_id
             );
-        } else if mime_parser.is_system_message != SystemMessage::EphemeralTimerChanged {
-            chat::add_info_msg(
+        } else if chat_id
+            .update_timestamp(context, Param::EphemeralSettingsTimestamp, *sent_timestamp)
+            .await?
+        {
+            if let Err(err) = chat_id
+                .inner_set_ephemeral_timer(context, ephemeral_timer)
+                .await
+            {
+                warn!(
+                    context,
+                    "failed to modify timer for chat {}: {}", chat_id, err
+                );
+            } else {
+                info!(
+                    context,
+                    "updated ephemeral timer to {:?} for chat {}", ephemeral_timer, chat_id
+                );
+                if mime_parser.is_system_message != SystemMessage::EphemeralTimerChanged {
+                    chat::add_info_msg(
+                        context,
+                        chat_id,
+                        stock_ephemeral_timer_changed(context, ephemeral_timer, from_id).await,
+                        sort_timestamp,
+                    )
+                    .await;
+                }
+            }
+        } else {
+            warn!(
                 context,
-                chat_id,
-                stock_ephemeral_timer_changed(context, ephemeral_timer, from_id).await,
-                sort_timestamp,
-            )
-            .await;
+                "ignoring ephemeral timer change to {:?} because it's outdated", ephemeral_timer
+            );
         }
     }