Fix return value of doio_n() when count is larger than the rest

data in socket.

Signed-off-by: Yifan Yuan <tuji.yyf@alibaba-inc.com>

net/basic_socket.h

@@ -108,22 +108,25 @@ __FORCE_INLINE__ int doio(IOCB iocb, WAIT waitcb) {
 
 template <typename IOCB>
 __FORCE_INLINE__ ssize_t doio_n(void *&buf, size_t &count, IOCB iocb) {
- auto count0 = count;
+ ssize_t n = 0;
  while (count > 0) {
  ssize_t ret = iocb();
- if (ret <= 0) return ret;
+ if (ret < 0) return ret; // error
+ if (ret == 0) break; // EOF
  (char *&)buf += ret;
  count -= ret;
+ n += ret;
  }
- return count0;
+ return n;
 }
 
 template <typename IOCB>
 __FORCE_INLINE__ ssize_t doiov_n(iovector_view &v, IOCB iocb) {
  ssize_t count = 0;
  while (v.iovcnt > 0) {
  ssize_t ret = iocb();
- if (ret <= 0) return ret;
+ if (ret < 0) return ret;
+ if (ret == 0) break;
  count += ret;
 
  uint64_t bytes = ret;