There should be no error response code with return value 0 in recv_line.

util.c

@@ -1104,19 +1104,17 @@ char *recv_line(struct pool *pool)
 
 			memset(s, 0, RBUFSIZE);
 			n = recv(pool->sock, s, RECVSIZE, 0);
-			if (n < 1) {
-				if (errno != EAGAIN && errno != EWOULDBLOCK) {
-					if (n == 0)
-						ret = RECV_CLOSED;
-					else
-						ret = RECV_RECVFAIL;
-					break;
-				}
-			} else {
-				slen = strlen(s);
-				recalloc_sock(pool, slen);
-				strcat(pool->sockbuf, s);
+			if (!n) {
+				ret = RECV_CLOSED;
+				break;
+			}
+			if (n < 0 && errno != EAGAIN && errno != EWOULDBLOCK) {
+				ret = RECV_RECVFAIL;
+				break;
 			}
+			slen = strlen(s);
+			recalloc_sock(pool, slen);
+			strcat(pool->sockbuf, s);
 			cgtime(&now);
 		} while (tdiff(&now, &rstart) < 60 && !strstr(pool->sockbuf, "\n"));
 		mutex_unlock(&pool->stratum_lock);