datastore: move blob loading into BackupDir impl and adapt call sites

data blobs can only appear in a BackupDir (snapshot) in the backup
hierachy, so makes more sense that it lives in there.

As it wasn't widely used anyway it's easy to move the single
non-package call site over to the new one directly and drop the
implementation from Datastore completely.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

pbs-datastore/src/backup_info.rs

@@ -11,7 +11,7 @@ use pbs_api_types::{BackupType, GroupFilter, BACKUP_DATE_REGEX, BACKUP_FILE_REGE
 use pbs_config::{open_backup_lockfile, BackupLockGuard};
 
 use crate::manifest::{MANIFEST_BLOB_NAME, MANIFEST_LOCK_NAME};
-use crate::DataStore;
+use crate::{DataStore, DataBlob};
 
 /// BackupGroup is a directory containing a list of BackupDir
 #[derive(Clone)]
@@ -345,6 +345,18 @@ impl BackupDir {
         proxmox_time::epoch_to_rfc3339_utc(backup_time)
     }
 
+    /// load a `DataBlob` from this snapshot's backup dir.
+    pub fn load_blob(&self, filename: &str) -> Result<DataBlob, Error> {
+        let mut path = self.full_path();
+        path.push(filename);
+
+        proxmox_lang::try_block!({
+            let mut file = std::fs::File::open(&path)?;
+            DataBlob::load_from_reader(&mut file)
+        })
+        .map_err(|err| format_err!("unable to load blob '{:?}' - {}", path, err))
+    }
+
     /// Returns the filename to lock a manifest
     ///
     /// Also creates the basedir. The lockfile is located in