wal_service: fix NodeId order/endian issues

Add fixes suggested in code review.

In a previous commit, I changed the NodeId field order and types to try
to preserve the exact serialization that was happening. Unfortunately,
that serialization was incorrect and the original struct was mostly
correct.

Change uuid to be a [u8; 16] as it was intended to be a byte array; that
will clearly indicate to serde serializers that no endian swaps will
ever be needed.

walkeeper/src/wal_service.rs

@@ -80,8 +80,8 @@ fn read_into(r: &mut impl Read, buf: &mut BytesMut) -> io::Result<usize> {
 /// Unique node identifier used by Paxos
 #[derive(Debug, Clone, Copy, Ord, PartialOrd, PartialEq, Eq, Serialize, Deserialize)]
 struct NodeId {
-    uuid: u128,
-    term: [u8; 8],
+    term: u64,
+    uuid: [u8; 16],
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Serialize, Deserialize)]
@@ -227,8 +227,8 @@ impl SafeKeeperInfo {
                 protocol_version: SK_PROTOCOL_VERSION, /* proxy-safekeeper protocol version */
                 pg_version: UNKNOWN_SERVER_VERSION,    /* Postgres server version */
                 node_id: NodeId {
-                    term: [0; 8],
-                    uuid: 0,
+                    term: 0,
+                    uuid: [0; 16],
                 },
                 system_id: 0, /* Postgres system identifier */
                 timeline_id: ZTimelineId::from([0u8; 16]),
@@ -555,8 +555,8 @@ impl Connection {
             self.send()?;
             bail!(
                 "Reject connection attempt with term {} because my term is {}",
-                hex::encode(prop.node_id.term),
-                hex::encode(my_info.server.node_id.term)
+                prop.node_id.term,
+                my_info.server.node_id.term,
             );
         }
         my_info.server.node_id = prop.node_id;