ref(jsonrpc): Getting backup provider QR code now blocks (#4198)

This changes the JSON-RPC APIs to get a QR code from the backup
provider to block.  It means once you have a (blocking) call to
provide_backup() you can call get_backup_qr() or get_backup_qr_svg()
and they will block until the QR code is available.

Calling get_backup_qr() or get_backup_qr_svg() when there is no backup
provider will immediately error.

src/context.rs

@@ -23,7 +23,6 @@ use crate::events::{Event, EventEmitter, EventType, Events};
 use crate::key::{DcKey, SignedPublicKey};
 use crate::login_param::LoginParam;
 use crate::message::{self, MessageState, MsgId};
-use crate::qr::Qr;
 use crate::quota::QuotaInfo;
 use crate::scheduler::SchedulerState;
 use crate::sql::Sql;
@@ -241,14 +240,6 @@ pub struct InnerContext {
 
     /// If debug logging is enabled, this contains all necessary information
     pub(crate) debug_logging: RwLock<Option<DebugLogging>>,
-
-    /// QR code for currently running [`BackupProvider`].
-    ///
-    /// This is only available if a backup export is currently running, it will also be
-    /// holding the ongoing process while running.
-    ///
-    /// [`BackupProvider`]: crate::imex::BackupProvider
-    pub(crate) export_provider: std::sync::Mutex<Option<Qr>>,
 }
 
 #[derive(Debug)]
@@ -393,7 +384,6 @@ impl Context {
             last_full_folder_scan: Mutex::new(None),
             last_error: std::sync::RwLock::new("".to_string()),
             debug_logging: RwLock::new(None),
-            export_provider: std::sync::Mutex::new(None),
         };
 
         let ctx = Context {
@@ -568,17 +558,6 @@ impl Context {
         }
     }
 
-    /// Returns the QR-code of the currently running [`BackupProvider`].
-    ///
-    /// [`BackupProvider`]: crate::imex::BackupProvider
-    pub fn backup_export_qr(&self) -> Option<Qr> {
-        self.export_provider
-            .lock()
-            .expect("poisoned lock")
-            .as_ref()
-            .cloned()
-    }
-
     /*******************************************************************************
      * UI chat/message related API
      ******************************************************************************/

src/imex/transfer.rs

@@ -126,16 +126,14 @@ impl BackupProvider {
         let handle = {
             let context = context.clone();
             tokio::spawn(async move {
-                let res = Self::watch_provider(&context, provider, cancel_token, dbfile).await;
+                let res = Self::watch_provider(&context, provider, cancel_token).await;
                 context.free_ongoing().await;
                 paused_guard.resume().await;
+                drop(dbfile);
                 res
             })
         };
-        let slf = Self { handle, ticket };
-        let qr = slf.qr();
-        *context.export_provider.lock().expect("poisoned lock") = Some(qr);
-        Ok(slf)
+        Ok(Self { handle, ticket })
     }
 
     /// Creates the provider task.
@@ -189,7 +187,6 @@ impl BackupProvider {
         context: &Context,
         mut provider: Provider,
         cancel_token: Receiver<()>,
-        _dbfile: TempPathGuard,
     ) -> Result<()> {
         // _dbfile exists so we can clean up the file once it is no longer needed
         let mut events = provider.subscribe();
@@ -255,11 +252,6 @@ impl BackupProvider {
                 },
             }
         };
-        context
-            .export_provider
-            .lock()
-            .expect("poisoned lock")
-            .take();
         match &res {
             Ok(_) => context.emit_event(SendProgress::Completed.into()),
             Err(err) => {