[PATCH proxmox-backup] fix #7305: client: restore: filter out last snapshot if not finished

[Christian Ebner <c.ebner@proxmox.com>]

When invoking the client CLI for restore via:
```
proxmox-backup-client restore <snapshot> <archive> <target>
```
but <archive> providing a backup group only, the client falls back to
restore the last snapshot of that group for convenience.

The snapshot listing used to identify the last snapshot returns
however all snapshots, including unfinished ones, a restore on an
unfinished one will therefore fail.

Fix this by filtering the snapshot to be restored by checking the
presence of the manifest file and are therefore considered finished.
If the file is not present, skip the snapshot and try for the next
one, if any. Also adapt the helper function name to reflect this
change.

Ideally this would happen on the server side, guarded by some flag,
but that will not work with older server versions.

Fixes: https://bugzilla.proxmox.com/show_bug.cgi?id=7305
Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
---
changes since version 1:
- Skip any considered snapshot without manifest
- Refactor based on Fabian's suggestions

 proxmox-backup-client/src/main.rs | 29 ++++++++++++++++++++++++++---
 1 file changed, 26 insertions(+), 3 deletions(-)

diff --git a/proxmox-backup-client/src/main.rs b/proxmox-backup-client/src/main.rs
index 999e50205..10a864a0f 100644
--- a/proxmox-backup-client/src/main.rs
+++ b/proxmox-backup-client/src/main.rs
@@ -160,7 +160,7 @@ async fn api_datastore_list_snapshots(
     Ok(result["data"].take())
 }
 
-pub async fn api_datastore_latest_snapshot(
+pub async fn api_datastore_latest_finished_snapshot(
     client: &HttpClient,
     store: &str,
     ns: &BackupNamespace,
@@ -175,7 +175,30 @@ pub async fn api_datastore_latest_snapshot(
 
     list.sort_unstable_by(|a, b| b.backup.time.cmp(&a.backup.time));
 
-    Ok((group, list[0].backup.time).into())
+    let last_finished_time = list
+        .iter()
+        .find_map(|snapshot_item| {
+            // only once a snapshots contains the manifest it is considered finished
+            snapshot_item
+                .files
+                .iter()
+                .find_map(|content| {
+                    if content.filename == MANIFEST_BLOB_NAME.as_ref() {
+                        Some(snapshot_item.backup.time)
+                    } else {
+                        None
+                    }
+                })
+                .or_else(|| {
+                    log::info!("skipped not finished snapshot {}", snapshot_item.backup);
+                    None
+                })
+        })
+        .ok_or_else(|| {
+            format_err!("backup group {group} does not contain any finished snapshots.")
+        })?;
+
+    Ok((group, last_finished_time).into())
 }
 
 pub async fn dir_or_last_from_group(
@@ -187,7 +210,7 @@ pub async fn dir_or_last_from_group(
     match path.parse::<BackupPart>()? {
         BackupPart::Dir(dir) => Ok(dir),
         BackupPart::Group(group) => {
-            api_datastore_latest_snapshot(client, repo.store(), ns, group).await
+            api_datastore_latest_finished_snapshot(client, repo.store(), ns, group).await
         }
     }
 }
-- 
2.47.3