src/backup/data_blob.rs: add create_zero_chunk() helper

src/backup/data_blob.rs

@@ -426,3 +426,20 @@ impl <'a, 'b> DataChunkBuilder<'a, 'b> {
         Ok((chunk, self.digest))
     }
 }
+
+/// Create a chunk filled with zeroes
+pub fn create_zero_chunk(
+    crypt_config: Option<&CryptConfig>,
+    chunk_size: usize,
+    compress: bool,
+) -> Result<(DataBlob, [u8; 32]), Error> {
+
+    let mut zero_bytes = Vec::with_capacity(chunk_size);
+    zero_bytes.resize(chunk_size, 0u8);
+    let mut chunk_builder = DataChunkBuilder::new(&zero_bytes).compress(compress);
+    if let Some(ref crypt_config) = crypt_config {
+        chunk_builder = chunk_builder.crypt_config(crypt_config);
+    }
+
+    chunk_builder.build()
+}