openpgp: Rework PartialEq for Signature4.

  - Previously, we compared serialized versions of the packet.  This
    has some problems.  First, it is expensive at it requires two heap
    allocations.  Second, it depends on Sequoia being compiled with
    the serialization code.  Third, it allows little control over what
    parts of the signature are compared.

1 files changed, 7 insertions, 17 deletions

diff --git a/openpgp/src/packet/signature/mod.rs b/openpgp/src/packet/signature/mod.rs
index 51667b35..27607125 100644
--- a/openpgp/src/packet/signature/mod.rs
+++ b/openpgp/src/packet/signature/mod.rs
@@ -22,7 +22,6 @@ use packet::UserAttribute;
 use Packet;
 use packet;
 use packet::signature::subpacket::SubpacketArea;
-use serialize::SerializeInto;
 
 use nettle::{dsa, ecc, ecdsa, ed25519, rsa};
 use nettle::rsa::verify_digest_pkcs1;
@@ -339,22 +338,13 @@ impl fmt::Debug for Signature4 {
 
 impl PartialEq for Signature4 {
     fn eq(&self, other: &Signature4) -> bool {
-        // Comparing the relevant fields is error prone in case we add
-        // a field at some point.  Instead, we compare the serialized
-        // versions.  As a small optimization, we compare the MPIs.
-        // Note: two `Signature4s` could be different even if they have
-        // the same MPI if the MPI was not invalidated when changing a
-        // field.
-        if self.mpis != other.mpis {
-            return false;
-        }
-
-        // Do a full check by serializing the fields.
-        if let (Ok(a), Ok(b)) = (self.to_vec(), other.to_vec()) {
-            a == b
-        } else {
-            false
-        }
+        self.fields.version == other.fields.version
+            && self.fields.sigtype == other.fields.sigtype
+            && self.fields.pk_algo == other.fields.pk_algo
+            && self.fields.hash_algo == other.fields.hash_algo
+            && self.fields.hashed_area == other.fields.hashed_area
+            && self.fields.unhashed_area == other.fields.unhashed_area
+            && self.mpis == other.mpis
     }
 }