[PATCH proxmox-backup 1/2] client: allow skipping signature check on previous manifest fetching

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

Extends the BackupWriter implementation by a method which allows to
download the previous manifest from a PBS instance, but skipping the
signature check even if the backup writer has a crypt_config set.

This will be used to silence misleading logs during encrypting push
sync jobs, by performing the signature check on the call site
instead.

Signed-off-by: Christian Ebner <c.ebner@proxmox.com>
---
 pbs-client/src/backup_writer.rs | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/pbs-client/src/backup_writer.rs b/pbs-client/src/backup_writer.rs
index 49aff3fdd..ea990dbde 100644
--- a/pbs-client/src/backup_writer.rs
+++ b/pbs-client/src/backup_writer.rs
@@ -735,8 +735,25 @@ impl BackupWriter {
         })
     }
 
-    /// Download backup manifest (index.json) of last backup
+    /// Download backup manifest (index.json) of last backup, checking the signature
+    /// using the backup writer's crypt config.
     pub async fn download_previous_manifest(&self) -> Result<BackupManifest, Error> {
+        let manifest = self
+            .download_previous_manifest_without_signature_check()
+            .await?;
+
+        if let Some(crypt_config) = &self.crypt_config {
+            manifest.check_signature(crypt_config)?;
+        }
+
+        Ok(manifest)
+    }
+
+    /// Download backup manifest (index.json) of last backup, but skips the signature
+    /// check by not providing the crypt config when parsing the manifest from the data blob.
+    pub async fn download_previous_manifest_without_signature_check(
+        &self,
+    ) -> Result<BackupManifest, Error> {
         let mut raw_data = Vec::with_capacity(64 * 1024);
 
         let param = json!({ "archive-name": MANIFEST_BLOB_NAME.to_string() });
@@ -748,8 +765,7 @@ impl BackupWriter {
         // no expected digest available
         let data = blob.decode(self.crypt_config.as_ref().map(Arc::as_ref), None)?;
 
-        let manifest =
-            BackupManifest::from_data(&data[..], self.crypt_config.as_ref().map(Arc::as_ref))?;
+        let manifest = BackupManifest::from_data(&data[..], None)?;
 
         Ok(manifest)
     }
-- 
2.47.3