Wait for join-group to finish using ongoing channel

The ongoing mechanism actually has a channel to wait on instead of
sleeping in a loop.  Let's use it.

src/securejoin/mod.rs

@@ -4,6 +4,7 @@ use std::convert::TryFrom;
 use std::time::{Duration, Instant};
 
 use anyhow::{bail, Context as _, Error, Result};
+use async_std::channel::Receiver;
 use async_std::sync::Mutex;
 use percent_encoding::{utf8_percent_encode, AsciiSet, NON_ALPHANUMERIC};
 
@@ -70,6 +71,20 @@ pub(crate) struct Bob {
     inner: Mutex<Option<BobState>>,
 }
 
+/// Return value for [`Bob::start_protocol`].
+///
+/// This indicates which protocol variant was started and provides the required information
+/// about it.
+enum StartedProtocolVariant {
+    /// The setup-contact protocol, to verify a contact.
+    SetupContact,
+    /// The secure-join protocol, to join a group.
+    SecureJoin {
+        ongoing_receiver: Receiver<()>,
+        group_id: String,
+    },
+}
+
 impl Bob {
     /// Starts the securejoin protocol with the QR `invite`.
     ///
@@ -78,19 +93,32 @@ impl Bob {
     ///
     /// This function takes care of starting the "ongoing" mechanism if required and
     /// handling errors while starting the protocol.
-    async fn start_protocol(&self, context: &Context, invite: QrInvite) -> Result<(), JoinError> {
+    ///
+    /// # Returns
+    ///
+    /// If the started protocol is joining a group the returned struct contains information
+    /// about the group and ongoing process.
+    async fn start_protocol(
+        &self,
+        context: &Context,
+        invite: QrInvite,
+    ) -> Result<StartedProtocolVariant, JoinError> {
         let mut guard = self.inner.lock().await;
         if guard.is_some() {
             return Err(JoinError::AlreadyRunning);
         }
-        let did_alloc_ongoing = match invite {
-            QrInvite::Group { .. } => {
-                if context.alloc_ongoing().await.is_err() {
-                    return Err(JoinError::OngoingRunning);
+        let variant = match invite {
+            QrInvite::Group { ref grpid, .. } => {
+                let receiver = context
+                    .alloc_ongoing()
+                    .await
+                    .map_err(|_| JoinError::OngoingRunning)?;
+                StartedProtocolVariant::SecureJoin {
+                    ongoing_receiver: receiver,
+                    group_id: grpid.clone(),
                 }
-                true
             }
-            _ => false,
+            _ => StartedProtocolVariant::SetupContact,
         };
         match BobState::start_protocol(context, invite).await {
             Ok((state, stage)) => {
@@ -98,10 +126,10 @@ impl Bob {
                     joiner_progress!(context, state.invite().contact_id(), 400);
                 }
                 *guard = Some(state);
-                Ok(())
+                Ok(variant)
             }
             Err(err) => {
-                if did_alloc_ongoing {
+                if let StartedProtocolVariant::SecureJoin { .. } = variant {
                     context.free_ongoing().await;
                 }
                 Err(err)
@@ -233,6 +261,8 @@ pub enum JoinError {
     // Note that this can only occur if we failed to create the chat correctly.
     #[error("No Chat found for group (this is a bug)")]
     MissingChat(#[source] sql::Error),
+    #[error("Ongoing sender dropped (this is a bug)")]
+    OngoingSenderDropped,
 }
 
 /// Take a scanned QR-code and do the setup-contact/join-group/invite handshake.
@@ -262,10 +292,8 @@ async fn securejoin(context: &Context, qr: &str) -> Result<ChatId, JoinError> {
     let qr_scan = check_qr(context, &qr).await;
     let invite = QrInvite::try_from(qr_scan)?;
 
-    context.bob.start_protocol(context, invite.clone()).await?;
-
-    match invite {
-        QrInvite::Contact { .. } => {
+    match context.bob.start_protocol(context, invite.clone()).await? {
+        StartedProtocolVariant::SetupContact => {
             // for a one-to-one-chat, the chat is already known, return the chat-id,
             // the verification runs in background
             let chat_id = chat::create_by_contact_id(context, invite.contact_id())
@@ -273,11 +301,15 @@ async fn securejoin(context: &Context, qr: &str) -> Result<ChatId, JoinError> {
                 .map_err(JoinError::UnknownContact)?;
             Ok(chat_id)
         }
-        QrInvite::Group { ref grpid, .. } => {
-            // for a group-join, wait until the secure-join is done and the group is created
-            while !context.shall_stop_ongoing().await {
-                async_std::task::sleep(Duration::from_millis(50)).await;
-            }
+        StartedProtocolVariant::SecureJoin {
+            ongoing_receiver,
+            group_id,
+        } => {
+            // for a group-join, wait until the protocol is finished and the group is created
+            ongoing_receiver
+                .recv()
+                .await
+                .map_err(|_| JoinError::OngoingSenderDropped)?;
 
             // handle_securejoin_handshake() calls Context::stop_ongoing before the group
             // chat is created (it is created after handle_securejoin_handshake() returns by
@@ -287,7 +319,7 @@ async fn securejoin(context: &Context, qr: &str) -> Result<ChatId, JoinError> {
             let start = Instant::now();
             let chatid = loop {
                 {
-                    match chat::get_chat_id_by_grpid(context, grpid).await {
+                    match chat::get_chat_id_by_grpid(context, &group_id).await {
                         Ok((chatid, _is_protected, _blocked)) => break chatid,
                         Err(err) => {
                             if start.elapsed() > Duration::from_secs(7) {