uv_recv: Only use first 2 bytes of preamble to determine message type.

Author: Mathieu Borderé

src/uv_encoding.c

@@ -484,18 +484,14 @@ static void decodeTimeoutNow(const uv_buf_t *buf, struct raft_timeout_now *p)
     p->last_log_term = byteGet64(&cursor);
 }
 
-int uvDecodeMessage(const unsigned long type,
+int uvDecodeMessage(uint16_t type,
                     const uv_buf_t *header,
                     struct raft_message *message,
                     size_t *payload_len)
 {
     unsigned i;
     int rv = 0;
 
-    if (type > USHRT_MAX) {
-        return RAFT_INVALID;
-    }
-
     memset(message, 0, sizeof(*message));
 
     message->type = (unsigned short)type;

src/uv_encoding.h

@@ -14,7 +14,7 @@ int uvEncodeMessage(const struct raft_message *message,
                     uv_buf_t **bufs,
                     unsigned *n_bufs);
 
-int uvDecodeMessage(unsigned long type,
+int uvDecodeMessage(uint16_t type,
                     const uv_buf_t *header,
                     struct raft_message *message,
                     size_t *payload_len);

src/uv_recv.c

@@ -253,7 +253,13 @@ static void uvServerReadCb(uv_stream_t *stream,
             type = byteFlip64(s->preamble[0]);
             assert(type > 0);
 
-            rv = uvDecodeMessage((unsigned long)type, &s->header, &s->message,
+	    /* Only use first 2 bytes of the type, cast is safe as raft has far
+	     * less 2^16 - 1 message types.
+	     * TODO: This is preparation to add the version of the message
+	     * in the raft preamble. Once this change has been active for
+	     * sufficiently long time, we can start encoding the version in some
+	     * of the remaining bytes of s->preamble[0]. */
+            rv = uvDecodeMessage((uint16_t)type, &s->header, &s->message,
                                  &s->payload.len);
             if (rv != 0) {
                 Tracef(s->uv->tracer, "decode message: %s",