Add try_read_u32 function to read 4 u8s to a u32

src/decoder.rs

@@ -18,14 +18,20 @@ pub fn try_read_magic<I: Iterator<Item=u8>>(bytes: &mut I) -> Result<(), DecodeE
 }
 
 fn try_read_u32<I: Iterator<Item=u8>>(bytes: &mut I) -> Result<u32, DecodeError> {
-    let mut res: u32 = 0;
-    let i = bytes.take(4)
-        .enumerate()
-        .reduce(|acc, (idx, val)| {
-            (0, 0)
-        });
+    let mut repacker = || {
+        if let Some(next_byte) = bytes.next() {
+            return Result::<u32, DecodeError>::Ok(next_byte as u32);
+        } else {
+            return Err(DecodeError::EarlyIteratorExhaustion);
+        }
+    };
 
-    Ok(res)
+    Ok(
+        (repacker()? << 24)
+      + (repacker()? << 16)
+      + (repacker()? << 8)
+      + (repacker()?)
+    )
 }
 
 mod codec_utils {
@@ -603,4 +609,21 @@ mod test {
             iters += 1;
         }
     }
+
+    #[test]
+    fn test_try_read_u32() {
+        let input = [10u8, 200u8, 255u8, 1u8, 254u8, 123u8, 45u8];
+        let expected =  180_944_641;
+        assert_eq!(
+            try_read_u32(&mut input.into_iter()).expect("Couldn't read u32 from byte array"),
+            expected
+        );
+
+        let too_short = [0u8];
+        let expected = Result::<u32, DecodeError>::Err(DecodeError::EarlyIteratorExhaustion);
+        assert_eq!(
+            try_read_u32(&mut too_short.into_iter()),
+            expected
+        );
+    }
 }

src/error.rs

@@ -1,5 +1,5 @@
 
-#[derive(Debug)]
+#[derive(Debug, PartialEq)]
 pub enum DecodeError {
     Magic,
     Channels,