fix sync download failing when temp dir on different mount

https://forums.ankiweb.net/t/problems-with-2-1-41-on-arch-linux/8103

rslib/src/backend/http_sync_server.rs

@@ -189,7 +189,7 @@ impl Backend {
     fn download(&self) -> Result<Vec<u8>> {
         let server = Box::new(self.col_into_server()?);
         let mut rt = Runtime::new().unwrap();
-        let file = rt.block_on(server.full_download())?;
+        let file = rt.block_on(server.full_download(None))?;
         let path = file.into_temp_path().keep()?;
         Ok(path.to_str().expect("path was not in utf8").into())
     }

rslib/src/sync/http_client.rs

@@ -142,11 +142,19 @@ impl SyncServer for HTTPSyncClient {
         Ok(())
     }
 
-    /// Download collection into a temporary file, returning it.
-    /// Caller should persist the file in the correct path after checking it.
-    /// Progress func must be set first.
-    async fn full_download(mut self: Box<Self>) -> Result<NamedTempFile> {
-        let mut temp_file = NamedTempFile::new()?;
+    /// Download collection into a temporary file, returning it. Caller should
+    /// persist the file in the correct path after checking it. Progress func
+    /// must be set first. The caller should pass the collection's folder in as
+    /// the temp folder if it wishes to atomically .persist() it.
+    async fn full_download(
+        mut self: Box<Self>,
+        col_folder: Option<&Path>,
+    ) -> Result<NamedTempFile> {
+        let mut temp_file = if let Some(folder) = col_folder {
+            NamedTempFile::new_in(folder)
+        } else {
+            NamedTempFile::new()
+        }?;
         let (size, mut stream) = self.download_inner().await?;
         let mut progress = FullSyncProgress {
             transferred_bytes: 0,
@@ -410,7 +418,7 @@ mod test {
         syncer.set_full_sync_progress_fn(Some(Box::new(|progress, _throttle| {
             println!("progress: {:?}", progress);
         })));
-        let out_path = syncer.full_download().await?;
+        let out_path = syncer.full_download(None).await?;
 
         let mut syncer = Box::new(HTTPSyncClient::new(None, 0));
         syncer.set_full_sync_progress_fn(Some(Box::new(|progress, _throttle| {

rslib/src/sync/mod.rs

@@ -672,8 +672,11 @@ impl Collection {
 
     pub(crate) async fn full_download_inner(self, server: Box<dyn SyncServer>) -> Result<()> {
         let col_path = self.col_path.clone();
+        let col_folder = col_path
+            .parent()
+            .ok_or_else(|| AnkiError::invalid_input("couldn't get col_folder"))?;
         self.close(false)?;
-        let out_file = server.full_download().await?;
+        let out_file = server.full_download(Some(col_folder)).await?;
         // check file ok
         let db = open_and_check_sqlite_file(out_file.path())?;
         db.execute_batch("update col set ls=mod")?;

rslib/src/sync/server.rs

@@ -36,7 +36,10 @@ pub trait SyncServer {
     /// If `can_consume` is true, the local server will move or remove the file, instead
     /// creating a copy. The remote server ignores this argument.
     async fn full_upload(self: Box<Self>, col_path: &Path, can_consume: bool) -> Result<()>;
-    async fn full_download(self: Box<Self>) -> Result<NamedTempFile>;
+    /// If the calling code intends to .persist() the named temp file to
+    /// atomically update the collection, it should pass in the collection's
+    /// folder, as .persist() can't work across filesystems.
+    async fn full_download(self: Box<Self>, temp_folder: Option<&Path>) -> Result<NamedTempFile>;
 }
 
 pub struct LocalServer {
@@ -199,7 +202,12 @@ impl SyncServer for LocalServer {
         fs::rename(col_path, &target_col_path).map_err(Into::into)
     }
 
-    async fn full_download(mut self: Box<Self>) -> Result<NamedTempFile> {
+    /// The provided folder is ignored, as in the server case the local data
+    /// will be sent over the network, instead of written into a local file.
+    async fn full_download(
+        mut self: Box<Self>,
+        _col_folder: Option<&Path>,
+    ) -> Result<NamedTempFile> {
         // bump usn/mod & close
         self.col.transact(None, |col| col.storage.increment_usn())?;
         let col_path = self.col.col_path.clone();