feat: Make one-to-one chats read-only the first seconds of a SecureJoin (#5512)

This protects Bob (the joiner) of sending unexpected-unencrypted messages during an otherwise nicely
running SecureJoin.

If things get stuck, however, we do not want to block communication -- the chat is just
opportunistic as usual, but that needs to be communicated:
1. If Bob's chat with Alice is `Unprotected` and a SecureJoin is started, then add info-message
   "Establishing guaranteed end-to-end encryption, please wait..." and let `Chat::can_send()` return
   `false`.
2. Once the info-message "Messages are guaranteed to be e2ee from now on" is added, let
   `Chat::can_send()` return `true`.
3. If after SECUREJOIN_WAIT_TIMEOUT seconds `2.` did not happen, add another info-message "Could not
   yet establish guaranteed end-to-end encryption but you may already send a message" and also let
   `Chat::can_send()` return `true`.

Both `2.` and `3.` require the event `ChatModified` being sent out so that UI pick up the change wrt
`Chat::can_send()` (this is the same way how groups become updated wrt `can_send()` changes).

SECUREJOIN_WAIT_TIMEOUT should be 10-20 seconds so that we are reasonably sure that the app remains
active and receiving also on mobile devices. If the app is killed during this time then we may need
to do step 3 for any pending Bob-join chats (right now, Bob can only join one chat at a time).

src/chat.rs

@@ -12,6 +12,7 @@ use deltachat_contact_tools::{strip_rtlo_characters, ContactAddress};
 use deltachat_derive::{FromSql, ToSql};
 use serde::{Deserialize, Serialize};
 use strum_macros::EnumIter;
+use tokio::task;
 
 use crate::aheader::EncryptPreference;
 use crate::blob::BlobObject;
@@ -38,6 +39,7 @@ use crate::mimeparser::SystemMessage;
 use crate::param::{Param, Params};
 use crate::peerstate::Peerstate;
 use crate::receive_imf::ReceivedMsg;
+use crate::securejoin::BobState;
 use crate::smtp::send_msg_to_smtp;
 use crate::sql;
 use crate::stock_str;
@@ -126,6 +128,10 @@ pub(crate) enum CantSendReason {
 
     /// Not a member of the chat.
     NotAMember,
+
+    /// Temporary state for 1:1 chats while SecureJoin is in progress, after a timeout sending
+    /// messages (incl. unencrypted if we don't yet know the contact's pubkey) is allowed.
+    SecurejoinWait,
 }
 
 impl fmt::Display for CantSendReason {
@@ -145,6 +151,7 @@ impl fmt::Display for CantSendReason {
                 write!(f, "mailing list does not have a know post address")
             }
             Self::NotAMember => write!(f, "not a member of the chat"),
+            Self::SecurejoinWait => write!(f, "awaiting SecureJoin for 1:1 chat"),
         }
     }
 }
@@ -610,7 +617,10 @@ impl ChatId {
         let sort_to_bottom = true;
         let ts = self
             .calc_sort_timestamp(context, timestamp_sent, sort_to_bottom, false)
-            .await?;
+            .await?
+            // Always sort protection messages below `SystemMessage::SecurejoinWait{,Timeout}` ones
+            // in case of race conditions.
+            .saturating_add(1);
         self.set_protection_for_timestamp_sort(context, protect, ts, contact_id)
             .await
     }
@@ -1407,6 +1417,18 @@ impl ChatId {
 
         Ok(sort_timestamp)
     }
+
+    /// Spawns a task checking after a timeout whether the SecureJoin has finished for the 1:1 chat
+    /// and otherwise notifying the user accordingly.
+    pub(crate) fn spawn_securejoin_wait(self, context: &Context, timeout: u64) {
+        let context = context.clone();
+        task::spawn(async move {
+            tokio::time::sleep(Duration::from_secs(timeout)).await;
+            let chat = Chat::load_from_db(&context, self).await?;
+            chat.check_securejoin_wait(&context, 0).await?;
+            Result::<()>::Ok(())
+        });
+    }
 }
 
 impl std::fmt::Display for ChatId {
@@ -1586,6 +1608,12 @@ impl Chat {
             Some(ReadOnlyMailingList)
         } else if !self.is_self_in_chat(context).await? {
             Some(NotAMember)
+        } else if self
+            .check_securejoin_wait(context, constants::SECUREJOIN_WAIT_TIMEOUT)
+            .await?
+            > 0
+        {
+            Some(SecurejoinWait)
         } else {
             None
         };
@@ -1599,6 +1627,69 @@ impl Chat {
         Ok(self.why_cant_send(context).await?.is_none())
     }
 
+    /// Returns the remaining timeout for the 1:1 chat in-progress SecureJoin.
+    ///
+    /// If the timeout has expired, notifies the user that sending messages is possible. See also
+    /// [`CantSendReason::SecurejoinWait`].
+    pub(crate) async fn check_securejoin_wait(
+        &self,
+        context: &Context,
+        timeout: u64,
+    ) -> Result<u64> {
+        if self.typ != Chattype::Single || self.protected != ProtectionStatus::Unprotected {
+            return Ok(0);
+        }
+        let (mut param0, mut param1) = (Params::new(), Params::new());
+        param0.set_cmd(SystemMessage::SecurejoinWait);
+        param1.set_cmd(SystemMessage::SecurejoinWaitTimeout);
+        let (param0, param1) = (param0.to_string(), param1.to_string());
+        let Some((param, ts_sort, ts_start)) = context
+            .sql
+            .query_row_optional(
+                "SELECT param, timestamp, timestamp_sent FROM msgs WHERE id=\
+                 (SELECT MAX(id) FROM msgs WHERE chat_id=? AND param IN (?, ?))",
+                (self.id, &param0, &param1),
+                |row| {
+                    let param: String = row.get(0)?;
+                    let ts_sort: i64 = row.get(1)?;
+                    let ts_start: i64 = row.get(2)?;
+                    Ok((param, ts_sort, ts_start))
+                },
+            )
+            .await?
+        else {
+            return Ok(0);
+        };
+        if param == param1 {
+            return Ok(0);
+        }
+        let now = time();
+        // Don't await SecureJoin if the clock was set back.
+        if ts_start <= now {
+            let timeout = ts_start
+                .saturating_add(timeout.try_into()?)
+                .saturating_sub(now);
+            if timeout > 0 {
+                return Ok(timeout as u64);
+            }
+        }
+        add_info_msg_with_cmd(
+            context,
+            self.id,
+            &stock_str::securejoin_wait_timeout(context).await,
+            SystemMessage::SecurejoinWaitTimeout,
+            // Use the sort timestamp of the "please wait" message, this way the added message is
+            // never sorted below the protection message if the SecureJoin finishes in parallel.
+            ts_sort,
+            Some(now),
+            None,
+            None,
+        )
+        .await?;
+        context.emit_event(EventType::ChatModified(self.id));
+        Ok(0)
+    }
+
     /// Checks if the user is part of a chat
     /// and has basically the permissions to edit the chat therefore.
     /// The function does not check if the chat type allows editing of concrete elements.
@@ -2334,6 +2425,26 @@ pub(crate) async fn update_special_chat_names(context: &Context) -> Result<()> {
     Ok(())
 }
 
+/// Checks if there is a 1:1 chat in-progress SecureJoin for Bob and, if necessary, schedules a task
+/// unblocking the chat and notifying the user accordingly.
+pub(crate) async fn resume_securejoin_wait(context: &Context) -> Result<()> {
+    let Some(bobstate) = BobState::from_db(&context.sql).await? else {
+        return Ok(());
+    };
+    if !bobstate.in_progress() {
+        return Ok(());
+    }
+    let chat_id = bobstate.alice_chat();
+    let chat = Chat::load_from_db(context, chat_id).await?;
+    let timeout = chat
+        .check_securejoin_wait(context, constants::SECUREJOIN_WAIT_TIMEOUT)
+        .await?;
+    if timeout > 0 {
+        chat_id.spawn_securejoin_wait(context, timeout);
+    }
+    Ok(())
+}
+
 /// Handle a [`ChatId`] and its [`Blocked`] status at once.
 ///
 /// This struct is an optimisation to read a [`ChatId`] and its [`Blocked`] status at once
@@ -2587,7 +2698,9 @@ async fn prepare_msg_common(
     if let Some(reason) = chat.why_cant_send(context).await? {
         if matches!(
             reason,
-            CantSendReason::ProtectionBroken | CantSendReason::ContactRequest
+            CantSendReason::ProtectionBroken
+                | CantSendReason::ContactRequest
+                | CantSendReason::SecurejoinWait
         ) && msg.param.get_cmd() == SystemMessage::SecurejoinMessage
         {
             // Send out the message, the securejoin message is supposed to repair the verification.