better check for invalid prefect

parquet/src/arrow/async_reader/metadata.rs

@@ -57,6 +57,12 @@ impl<F: MetadataFetch> MetadataLoader<F> {
             return Err(ParquetError::EOF(format!(
                 "file size of {file_size} is less than footer"
             )));
+        } else if let Some(size_hint) = prefetch {
+            if size_hint < 8 {
+                return Err(ParquetError::EOF(format!(
+                    "prefetch size of {size_hint} is less than footer size"
+                )));
+            }
         }
 
         // If a size hint is provided, read more than the minimum size
@@ -71,10 +77,7 @@ impl<F: MetadataFetch> MetadataLoader<F> {
         let suffix_len = suffix.len();
 
         let mut footer = [0; 8];
-        let Some(footer_start) = suffix_len.checked_sub(8) else {
-            return Err(ParquetError::General("Invalid Parquet file. Corrupt footer".to_string()));
-        };
-        footer.copy_from_slice(&suffix[footer_start..]);
+        footer.copy_from_slice(&suffix[suffix_len - 8..suffix_len]);
 
         let length = decode_footer(&footer)?;
 
@@ -276,6 +279,14 @@ mod tests {
         assert_eq!(actual.file_metadata().schema(), expected);
         assert_eq!(fetch_count.load(Ordering::SeqCst), 2);
 
+        // Metadata hint invalid - below 8
+        fetch_count.store(0, Ordering::SeqCst);
+        let err = fetch_parquet_metadata(&mut fetch, len, Some(7))
+            .await
+            .unwrap_err()
+            .to_string();
+        assert_eq!(err, "EOF: prefetch size of 7 is less than footer size");
+
         // Metadata hint too small
         fetch_count.store(0, Ordering::SeqCst);
         let actual = fetch_parquet_metadata(&mut fetch, len, Some(10))