fix parse eval on SW_ARG2 calculate r->rlen error (#654)

Update src/proto/nc_redis.c
Co-authored-by: NTyson Andre <tyson.andre@uwaterloo.ca>

src/proto/nc_redis.c

@@ -1633,7 +1633,19 @@ redis_parse_req(struct msg *r)
 
             m = p + r->rlen;
             if (m >= b->last) {
-                r->rlen -= (uint32_t)(b->last - p);
+                /* 
+                 * For EVAL/EVALHASH, the r->token has been assigned a value.  When
+                 * m >= b->last happens will need to repair mbuf.  
+                 * 
+                 * At the end of redis_parse_req, r->token will be used to choose
+                 * the start (p) for the next call to redis_parse_req and clear
+                 * r->token when repairing this and adding more data.
+                 * 
+                 * So, only when r->token == NULL we need to calculate r->rlen again.
+                 */
+                if (r->token == NULL) {
+                    r->rlen -= (uint32_t)(b->last - p);
+                }
                 m = b->last - 1;
                 p = m;
                 break;