feat(compression): implement transparent LZ4 chunk compression with V1 backwards compatibility

src/vfs.rs

@@ -86,6 +86,7 @@ pub struct SanctumFile {
     meta: SanctumMetaData,
     // (chunk_index, decrypted_payload, is_dirty)
     cached_chunk: Option<(u32, Vec<u8>, bool)>,
+    format_version: u32,
 }
 
 impl Debug for SanctumFile {
@@ -94,6 +95,7 @@ impl Debug for SanctumFile {
             .field("node_id", &self.node_id)
             .field("file_size", &self.file_size)
             .field("cursor", &self.cursor)
+            .field("format_version", &self.format_version)
             .finish()
     }
 }
@@ -103,6 +105,7 @@ impl SanctumFile {
         node: NodeRecord,
         db: Database,
         dek: Arc<Zeroizing<[u8; 32]>>,
+        format_version: u32,
     ) -> Self {
         let meta = SanctumMetaData {
             is_dir: node.is_dir,
@@ -119,14 +122,16 @@ impl SanctumFile {
             dek,
             meta,
             cached_chunk: None,
+            format_version,
         }
     }
 
+
     /// Schreibt den aktuell im RAM gehaltenen Chunk verschlüsselt in die SQLite-Datenbank zurück.
     fn flush_cached_chunk(&mut self) -> Result<(), FsError> {
         if let Some((idx, ref data, true)) = self.cached_chunk {
             let (ciphertext, nonce, tag) =
-                encrypt_chunk(&self.dek, self.node_id, idx, data).map_err(|e| {
+                encrypt_chunk(&self.dek, self.node_id, idx, data, self.format_version).map_err(|e| {
                     error!("Verschlüsselungsfehler beim Chunk-Flush: {e}");
                     FsError::GeneralFailure
                 })?;
@@ -166,6 +171,7 @@ impl SanctumFile {
                     &record.ciphertext,
                     &record.nonce,
                     &record.tag,
+                    self.format_version,
                 )
                 .map_err(|e| {
                     error!("AEAD-Entschlüsselungsfehler bei Chunk #{chunk_index}: {e}");
@@ -339,13 +345,15 @@ impl DavFile for SanctumFile {
 pub struct SanctumFs {
     db: Database,
     dek: Arc<Zeroizing<[u8; 32]>>,
+    format_version: u32,
 }
 
 impl SanctumFs {
-    pub fn new(db: Database, dek: Zeroizing<[u8; 32]>) -> Self {
+    pub fn new(db: Database, dek: Zeroizing<[u8; 32]>, format_version: u32) -> Self {
         Self {
             db,
             dek: Arc::new(dek),
+            format_version,
         }
     }
 
@@ -432,7 +440,7 @@ impl DavFileSystem for SanctumFs {
                 }
             };
 
-            let file = SanctumFile::new(node, self.db.clone(), self.dek.clone());
+            let file = SanctumFile::new(node, self.db.clone(), self.dek.clone(), self.format_version);
             Ok(Box::new(file) as Box<dyn DavFile>)
         })
     }
@@ -678,11 +686,12 @@ impl DavFileSystem for SanctumFs {
                         &record.ciphertext,
                         &record.nonce,
                         &record.tag,
+                        self.format_version,
                     )
                     .map_err(|_| FsError::GeneralFailure)?;
 
                     let (new_ct, new_nonce, new_tag) =
-                        encrypt_chunk(&self.dek, dest_node.id, idx, &plaintext)
+                        encrypt_chunk(&self.dek, dest_node.id, idx, &plaintext, self.format_version)
                             .map_err(|_| FsError::GeneralFailure)?;
 
                     self.db