feat: Group and broadcast channel descriptions (#7829)

fix https://github.com/chatmail/core/issues/7766

Implementation notes:

- Descriptions are only sent with member additions, when the description
is changed, and when promoting a previously-unpromoted group, in order
not to waste bandwith.
- Descriptions are not loaded everytime a chat object is loaded, because
they are only needed for the profile. Instead, they are in their own
table, and can be loaded with their own JsonRPC call.

---------

Co-authored-by: iequidoo <117991069+iequidoo@users.noreply.github.com>

src/receive_imf.rs

@@ -8,7 +8,8 @@ use std::sync::LazyLock;
 use anyhow::{Context as _, Result, ensure};
 use data_encoding::BASE32_NOPAD;
 use deltachat_contact_tools::{
-    ContactAddress, addr_cmp, addr_normalize, may_be_valid_addr, sanitize_single_line,
+    ContactAddress, addr_cmp, addr_normalize, may_be_valid_addr, sanitize_bidi_characters,
+    sanitize_single_line,
 };
 use iroh_gossip::proto::TopicId;
 use mailparse::SingleInfo;
@@ -3101,7 +3102,7 @@ async fn apply_group_changes(
     }
 
     if is_from_in_chat {
-        apply_chat_name_and_avatar_changes(
+        apply_chat_name_avatar_and_description_changes(
             context,
             mime_parser,
             from_id,
@@ -3280,7 +3281,7 @@ async fn apply_group_changes(
 ///
 /// - `send_event_chat_modified` is set to `true` if ChatModified event should be sent
 /// - `better_msg` is filled with an info message about name change, if necessary
-async fn apply_chat_name_and_avatar_changes(
+async fn apply_chat_name_avatar_and_description_changes(
     context: &Context,
     mime_parser: &MimeMessage,
     from_id: ContactId,
@@ -3339,6 +3340,51 @@ async fn apply_chat_name_and_avatar_changes(
         }
     }
 
+    // ========== Apply chat description changes ==========
+
+    if let Some(new_description) = mime_parser
+        .get_header(HeaderDef::ChatGroupDescription)
+        .map(|d| d.trim())
+    {
+        let new_description = sanitize_bidi_characters(new_description.trim());
+        let old_description = chat::get_chat_description(context, chat.id).await?;
+
+        let old_timestamp = chat
+            .param
+            .get_i64(Param::GroupDescriptionTimestamp)
+            .unwrap_or(0);
+        let timestamp_in_header = mime_parser
+            .get_header(HeaderDef::ChatGroupDescriptionTimestamp)
+            .and_then(|s| s.parse::<i64>().ok());
+
+        let new_timestamp = timestamp_in_header.unwrap_or(mime_parser.timestamp_sent);
+        // To provide consistency, compare descriptions if timestamps are equal.
+        if (old_timestamp, &old_description) < (new_timestamp, &new_description)
+            && chat
+                .id
+                .update_timestamp(context, Param::GroupDescriptionTimestamp, new_timestamp)
+                .await?
+            && new_description != old_description
+        {
+            info!(context, "Updating description for chat {}.", chat.id);
+            context
+                .sql
+                .execute(
+                    "INSERT OR REPLACE INTO chats_descriptions(chat_id, description) VALUES(?, ?)",
+                    (chat.id, &new_description),
+                )
+                .await?;
+            *send_event_chat_modified = true;
+        }
+        if mime_parser
+            .get_header(HeaderDef::ChatGroupDescriptionChanged)
+            .is_some()
+        {
+            better_msg
+                .get_or_insert(stock_str::msg_chat_description_changed(context, from_id).await);
+        }
+    }
+
     // ========== Apply chat avatar changes ==========
 
     if let (Some(value), None) = (mime_parser.get_header(HeaderDef::ChatContent), &better_msg)
@@ -3667,7 +3713,7 @@ async fn apply_out_broadcast_changes(
     let mut better_msg = None;
 
     if from_id == ContactId::SELF {
-        apply_chat_name_and_avatar_changes(
+        apply_chat_name_avatar_and_description_changes(
             context,
             mime_parser,
             from_id,
@@ -3757,7 +3803,7 @@ async fn apply_in_broadcast_changes(
     let mut send_event_chat_modified = false;
     let mut better_msg = None;
 
-    apply_chat_name_and_avatar_changes(
+    apply_chat_name_avatar_and_description_changes(
         context,
         mime_parser,
         from_id,