LWIP之lwip_send函数

最新推荐文章于 2025-06-18 15:51:46 发布

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本文详细解析了lwip网络库中的lwip_send函数实现过程，包括如何使用netconn_write_partly进行TCP数据发送，并介绍了其参数及返回值。此外，还深入探讨了不同标志位的作用及其对发送行为的影响。

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代码如下：

int
lwip_send(int s, const void *data, size_t size, int flags)
{
  struct lwip_sock *sock;
  err_t err;
  u8_t write_flags;
  size_t written;

  LWIP_DEBUGF(SOCKETS_DEBUG, ("lwip_send(%d, data=%p, size=%"SZT_F", flags=0x%x)\n",
                              s, data, size, flags));

  sock = get_socket(s);
  if (!sock) {
    return -1;
  }

  if (sock->conn->type != NETCONN_TCP) {
#if (LWIP_UDP || LWIP_RAW)
    return lwip_sendto(s, data, size, flags, NULL, 0);
#else /* (LWIP_UDP || LWIP_RAW) */
    sock_set_errno(sock, err_to_errno(ERR_ARG));
    return -1;
#endif /* (LWIP_UDP || LWIP_RAW) */
  }

  write_flags = NETCONN_COPY |
    ((flags & MSG_MORE)     ? NETCONN_MORE      : 0) |
    ((flags & MSG_DONTWAIT) ? NETCONN_DONTBLOCK : 0);
  written = 0;
  err = netconn_write_partly(sock->conn, data, size, write_flags, &written);

  LWIP_DEBUGF(SOCKETS_DEBUG, ("lwip_send(%d) err=%d written=%"SZT_F"\n", s, err, written));
  sock_set_errno(sock, err_to_errno(err));
  return (err == ERR_OK ? (int)written : -1);
}

利用了 netconn_write_partly函数:

/**
 * Send data over a TCP netconn.
 *
 * @param conn the TCP netconn over which to send data
 * @param dataptr pointer to the application buffer that contains the data to send
 * @param size size of the application data to send
 * @param apiflags combination of following flags :
 * - NETCONN_COPY: data will be copied into memory belonging to the stack
 * - NETCONN_MORE: for TCP connection, PSH flag will be set on last segment sent
 * - NETCONN_DONTBLOCK: only write the data if all dat can be written at once
 * @param bytes_written pointer to a location that receives the number of written bytes
 * @return ERR_OK if data was sent, any other err_t on error
 */
err_t
netconn_write_partly(struct netconn *conn, const void *dataptr, size_t size,
                     u8_t apiflags, size_t *bytes_written)
{
  struct api_msg msg;
  err_t err;
  u8_t dontblock;

  LWIP_ERROR("netconn_write: invalid conn",  (conn != NULL), return ERR_ARG;);
  LWIP_ERROR("netconn_write: invalid conn->type",  (conn->type == NETCONN_TCP), return ERR_VAL;);
  if (size == 0) {
    return ERR_OK;
  }
  dontblock = netconn_is_nonblocking(conn) || (apiflags & NETCONN_DONTBLOCK);
  if (dontblock && !bytes_written) {
    /* This implies netconn_write() cannot be used for non-blocking send, since
       it has no way to return the number of bytes written. */
    return ERR_VAL;
  }

  /* non-blocking write sends as much  */
  msg.function = do_write;
  msg.msg.conn = conn;
  msg.msg.msg.w.dataptr = dataptr;
  msg.msg.msg.w.apiflags = apiflags;
  msg.msg.msg.w.len = size;
#if LWIP_SO_SNDTIMEO
  if (conn->send_timeout != 0) {
    /* get the time we started, which is later compared to
        sys_now() + conn->send_timeout */
    msg.msg.msg.w.time_started = sys_now();
  } else {
    msg.msg.msg.w.time_started = 0;
  }
#endif /* LWIP_SO_SNDTIMEO */

  /* For locking the core: this _can_ be delayed on low memory/low send buffer,
     but if it is, this is done inside api_msg.c:do_write(), so we can use the
     non-blocking version here. */
  err = TCPIP_APIMSG(&msg);
  if ((err == ERR_OK) && (bytes_written != NULL)) {
    if (dontblock
#if LWIP_SO_SNDTIMEO
        || (conn->send_timeout != 0)
#endif /* LWIP_SO_SNDTIMEO */
       ) {
      /* nonblocking write: maybe the data has been sent partly */
      *bytes_written = msg.msg.msg.w.len;
    } else {
      /* blocking call succeeded: all data has been sent if it */
      *bytes_written = size;
    }
  }

  NETCONN_SET_SAFE_ERR(conn, err);
  return err;
}