db::read -- io::Cursor instead of take

src/db.rs

@@ -191,28 +191,25 @@ where
             return Err("index out of range".into());
         }
 
+        let next_pos: usize = (index + 1) * LEN_SIZE;
+        let next_end: usize = next_pos + LEN_SIZE;
+
         // read item data pos
         let data_pos = if 0 == index {
             self.first_pos
         } else {
             let tab_pos: usize = index * LEN_SIZE;
-            let pos_curr_data: [u8; LEN_SIZE] = self.mmap[tab_pos..(tab_pos + LEN_SIZE)]
-                .try_into()
-                .str_err()?;
+            let pos_curr_data: [u8; LEN_SIZE] =
+                self.mmap[tab_pos..next_pos].try_into().str_err()?;
             LSize::from_le_bytes(pos_curr_data)
         } as usize;
 
         // read next item pos
-        let next_pos: usize = (index + 1) * LEN_SIZE;
-        let pos_next_data: [u8; LEN_SIZE] = self.mmap[next_pos..(next_pos + LEN_SIZE)]
-            .try_into()
-            .str_err()?;
+        let pos_next_data: [u8; LEN_SIZE] = self.mmap[next_pos..next_end].try_into().str_err()?;
         let data_pos_next = LSize::from_le_bytes(pos_next_data) as usize;
-        // calc item data length
-        let data_len = data_pos_next - data_pos;
 
         // read & unpack item data
-        let reader = self.mmap[data_pos..data_pos_next].take(data_len as u64);
+        let reader = io::Cursor::new(self.mmap[data_pos..data_pos_next].as_ref());
         let data = zstd::decode_all(reader).str_err()?;
 
         // decode item