Have MDARegions::load() return an error if error in reading region

Remove the TODO about verifying that the previous behavior was correct.
It still returns None if the region is determined not to be there.

Signed-off-by: mulhern <[email protected]>

src/engine/strat_engine/metadata.rs

@@ -380,6 +380,7 @@ mod mda {
         }
 
         /// Construct MDARegions from data on the disk.
+        /// Return an error if there is an error reading either of the regions.
         pub fn load<F>(header_size: Bytes, size: Sectors, f: &mut F) -> EngineResult<MDARegions>
             where F: Read + Seek
         {
@@ -401,18 +402,14 @@ mod mda {
 
             /// Get an MDAHeader for the given index.
             /// If there is a failure reading the first, fall back on the
-            /// second. If there is a failure reading both, return None.
-            /// TODO: Consider whether this is the correct behavior.
-            let mut get_mda = |index: usize| -> Option<MDAHeader> {
-                load_a_region(index)
-                    .or_else(|_| load_a_region(index + 2))
-                    .ok()
-                    .unwrap_or(None)
+            /// second. If there is a failure reading both, return an error.
+            let mut get_mda = |index: usize| -> EngineResult<Option<MDAHeader>> {
+                load_a_region(index).or_else(|_| load_a_region(index + 2))
             };
 
             Ok(MDARegions {
                    region_size: region_size,
-                   mdas: [get_mda(0), get_mda(1)],
+                   mdas: [try!(get_mda(0)), try!(get_mda(1))],
                })
         }
 
@@ -850,17 +847,16 @@ mod tests {
 
     #[test]
     /// Make a buffer just large enough to contain a single static header.
-    /// Verify that the StaticHeader is read and that the BDA's last update
-    /// time is None.
+    /// Verify that the StaticHeader is read and that there is a failure reading
+    /// the BDA.
     fn just_one_static_header() {
         let mut vec = vec![0u8; 2 * SECTOR_SIZE];
         vec[SECTOR_SIZE..2 * SECTOR_SIZE].clone_from_slice(&random_static_header(0, 0)
                                                                 .sigblock_to_buf());
         let mut buf = Cursor::new(vec);
         assert!(StaticHeader::setup(&mut buf).unwrap().is_some());
 
-        let bda = BDA::load(&mut buf).unwrap().unwrap();
-        assert_eq!(bda.last_update_time(), None);
+        assert!(BDA::load(&mut buf).is_err());
     }
 
     #[test]