subject_name: rm unused err return for IP subj. cmp.

Previously the ip address module's `presented_id_matches_reference_id`
function returned `Result<bool, Error>`, similar to the DNS subject name
function of the same name.

In the case of the IP address implementation there is no codepath that
returns an error. The lengths of the inputs are checked ahead of time,
and the DER reads are infallible for the byte-for-byte compare. All of
our unit tests also expect a true/false return, not an error.

With the above in mind this commit changes the
`presented_id_matches_reference_id` return type to `bool` and updates
the call-sites and unit tests accordingly.

src/subject_name/ip_address.rs

@@ -203,12 +203,12 @@ impl<'a> From<IpAddrRef<'a>> for &'a [u8] {
 pub(super) fn presented_id_matches_reference_id(
     presented_id: untrusted::Input,
     reference_id: untrusted::Input,
-) -> Result<bool, Error> {
+) -> bool {
     match (presented_id.len(), reference_id.len()) {
         (4, 4) => (),
         (16, 16) => (),
         _ => {
-            return Ok(false);
+            return false;
         }
     };
 
@@ -218,11 +218,11 @@ pub(super) fn presented_id_matches_reference_id(
         let presented_ip_address_byte = presented_ip_address.read_byte().unwrap();
         let reference_ip_address_byte = reference_ip_address.read_byte().unwrap();
         if presented_ip_address_byte != reference_ip_address_byte {
-            return Ok(false);
+            return false;
         }
     }
 
-    Ok(true)
+    true
 }
 
 // https://tools.ietf.org/html/rfc5280#section-4.2.1.10 says:
@@ -1138,61 +1138,40 @@ mod tests {
 
     #[test]
     fn test_presented_id_matches_reference_id() {
-        assert_eq!(
-            presented_id_matches_reference_id(
-                untrusted::Input::from(&[]),
-                untrusted::Input::from(&[])
-            ),
-            Ok(false),
-        );
-
-        assert_eq!(
-            presented_id_matches_reference_id(
-                untrusted::Input::from(&[0x01]),
-                untrusted::Input::from(&[])
-            ),
-            Ok(false),
-        );
-
-        assert_eq!(
-            presented_id_matches_reference_id(
-                untrusted::Input::from(&[]),
-                untrusted::Input::from(&[0x01])
-            ),
-            Ok(false),
-        );
-
-        assert_eq!(
-            presented_id_matches_reference_id(
-                untrusted::Input::from(&[1, 2, 3, 4]),
-                untrusted::Input::from(&[1, 2, 3, 4])
-            ),
-            Ok(true),
-        );
-
-        assert_eq!(
-            presented_id_matches_reference_id(
-                untrusted::Input::from(&[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16]),
-                untrusted::Input::from(&[1, 2, 3, 4])
-            ),
-            Ok(false),
-        );
-
-        assert_eq!(
-            presented_id_matches_reference_id(
-                untrusted::Input::from(&[1, 2, 3, 4]),
-                untrusted::Input::from(&[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16])
-            ),
-            Ok(false),
-        );
-
-        assert_eq!(
-            presented_id_matches_reference_id(
-                untrusted::Input::from(&[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16]),
-                untrusted::Input::from(&[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16])
-            ),
-            Ok(true),
-        );
+        assert!(!presented_id_matches_reference_id(
+            untrusted::Input::from(&[]),
+            untrusted::Input::from(&[]),
+        ));
+
+        assert!(!presented_id_matches_reference_id(
+            untrusted::Input::from(&[0x01]),
+            untrusted::Input::from(&[])
+        ));
+
+        assert!(!presented_id_matches_reference_id(
+            untrusted::Input::from(&[]),
+            untrusted::Input::from(&[0x01])
+        ));
+
+        assert!(presented_id_matches_reference_id(
+            untrusted::Input::from(&[1, 2, 3, 4]),
+            untrusted::Input::from(&[1, 2, 3, 4])
+        ));
+
+        assert!(!presented_id_matches_reference_id(
+            untrusted::Input::from(&[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16]),
+            untrusted::Input::from(&[1, 2, 3, 4])
+        ));
+
+        assert!(!presented_id_matches_reference_id(
+            untrusted::Input::from(&[1, 2, 3, 4]),
+            untrusted::Input::from(&[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16])
+        ));
+
+        assert!(presented_id_matches_reference_id(
+            untrusted::Input::from(&[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16]),
+            untrusted::Input::from(&[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16])
+        ));
     }
 
     #[test]

src/subject_name/verify.rs

@@ -75,11 +75,8 @@ pub(crate) fn verify_cert_subject_name(
         &mut |name| {
             if let GeneralName::IpAddress(presented_id) = name {
                 match ip_address::presented_id_matches_reference_id(presented_id, ip_address) {
-                    Ok(true) => return NameIteration::Stop(Ok(())),
-                    Ok(false) => (),
-                    Err(_) => {
-                        return NameIteration::Stop(Err(Error::BadDer));
-                    }
+                    true => return NameIteration::Stop(Ok(())),
+                    false => (),
                 }
             }
             NameIteration::KeepGoing