[PATCH v6 proxmox-backup 11/18] api: verify fixed index writer size on close

[Robert Obkircher <r.obkircher@proxmox.com>]

Compare it to the value submitted by the client to check that resizing
worked as expected.

Signed-off-by: Robert Obkircher <r.obkircher@proxmox.com>
---
 pbs-datastore/src/fixed_index.rs | 5 +++++
 src/api2/backup/environment.rs   | 8 ++++++++
 2 files changed, 13 insertions(+)

diff --git a/pbs-datastore/src/fixed_index.rs b/pbs-datastore/src/fixed_index.rs
index 350bf2ed..e6d6f3df 100644
--- a/pbs-datastore/src/fixed_index.rs
+++ b/pbs-datastore/src/fixed_index.rs
@@ -424,6 +424,11 @@ impl FixedIndexWriter {
         self.index_length
     }
 
+    /// The current total size of the referenced content.
+    pub fn size(&self) -> u64 {
+        self.size
+    }
+
     fn unmap(&mut self) -> Result<(), Error> {
         let Some(index) = NonNull::new(self.index as *mut std::ffi::c_void) else {
             return Ok(());
diff --git a/src/api2/backup/environment.rs b/src/api2/backup/environment.rs
index 39fe0564..9645f6de 100644
--- a/src/api2/backup/environment.rs
+++ b/src/api2/backup/environment.rs
@@ -633,6 +633,14 @@ impl BackupEnvironment {
             }
         }
 
+        let writer_size = data.index.size();
+        if size != writer_size {
+            bail!(
+                "fixed writer '{}' close failed - unexpected size ({size} != {writer_size})",
+                data.name,
+            );
+        }
+
         let expected_csum = data.index.close()?;
         data.closed = true;
 
-- 
2.47.3