Catch attribute overflow errors (#26)

src/as_path_parser.rs

@@ -93,12 +93,16 @@ impl<'buffer> AsPathParser<'buffer> {
             let asn_path = self.parse_as_path();
 
             if asn_attr_position_end != self.next {
-                let leftover_attr_count = asn_attr_position_end - self.next;
-                for _ in 0..leftover_attr_count {
-                    self.advance()?;
+                let leftover_attr_count = asn_attr_position_end.checked_sub(self.next);
+                match leftover_attr_count {
+                    Some(count) => {
+                        for _ in 0..count {
+                            self.advance()?;
+                        }
+                    }
+                    None => println!("{}", Error::AttributeOverflow),
                 }
             }
-
             asn_path
         } else {
             for _ in 0..attribute_length {

src/error.rs

@@ -26,6 +26,7 @@ pub enum Error {
     UnexpectedEndOfBuffer,
     MultipleAsPaths,
     NoAsPathInAttributePath,
+    AttributeOverflow,
 }
 
 impl Display for Error {
@@ -63,6 +64,10 @@ impl Display for Error {
                 f,
                 "Expected one AS_PATH attribute in BGP Attribute Path, found multiple."
             ),
+            AttributeOverflow => write!(
+                f,
+                "Overflow encountered during AS parsing. Ignoring invalid attribute."
+            ),
         }
     }
 }