LwIP之netbuf

 netbuf是应用程序和协议栈内核交互的一种数据结构

netbuf并不复杂，下面是实现代码

/* 创建netbuf */
struct netbuf *netbuf_new(void)
{
  struct netbuf *buf;

  /* 为netbuf申请内存空间 */
  buf = (struct netbuf *)memp_malloc(MEMP_NETBUF);
  if(buf != NULL) 
  {
	/* 清空参数 */
    buf->p = NULL;
    buf->ptr = NULL;
    ip_addr_set_any(&buf->addr);
    buf->port = 0;
		
    return buf;
  } 
  else 
  {
    return NULL;
  }
}

/* 删除netbuf */
void netbuf_delete(struct netbuf *buf)
{
  if(buf != NULL) 
  {
	/* 先释放pbuf */
    if(buf->p != NULL) 
	{
      pbuf_free(buf->p);
      buf->p = buf->ptr = NULL;
    }
		
	/* 再释放netbuf */
    memp_free(MEMP_NETBUF, buf);
  }
}

/* 为netbuf申请数据(pbuf)空间 */
void *netbuf_alloc(struct netbuf *buf, u16_t size)
{
  /* 为netbuf申请数据(pbuf)空间 */
  if(buf->p != NULL) 
  {
    pbuf_free(buf->p);
  }
  buf->p = pbuf_alloc(PBUF_TRANSPORT, size, PBUF_RAM);
  if(buf->p == NULL) 
  {
	return NULL;
  }

  /* ptr指针初始化指向第一个pbuf */
  buf->ptr = buf->p;
	
  /* 返回数据有效数据指针 */
  return buf->p->payload;
}

/* 释放netbuf的数据(pbuf)空间 */
void netbuf_free(struct netbuf *buf)
{
  if(buf->p != NULL) 
  {
    pbuf_free(buf->p);
  }
	
  buf->p = buf->ptr = NULL;
}

/* 为netbuf申请PBUF_REF型pbuf内存，指向已存在RAM */
err_t netbuf_ref(struct netbuf *buf, const void *dataptr, u16_t size)
{
  if(buf->p != NULL) 
  {
    pbuf_free(buf->p);
  }
	
  buf->p = pbuf_alloc(PBUF_TRANSPORT, 0, PBUF_REF);
  if(buf->p == NULL) 
  {
    buf->ptr = NULL;
    return ERR_MEM;
  }
  buf->p->payload = (void *)dataptr;
  buf->p->len = buf->p->tot_len = size;
  buf->ptr = buf->p;

  return ERR_OK;
}

/* 将两个netbuf拼接起来 */
void netbuf_chain(struct netbuf *head, struct netbuf *tail)
{
  pbuf_cat(head->p, tail->p);
  head->ptr = head->p;
  memp_free(MEMP_NETBUF, tail);
}

/* 获取netbuf有效数据指针和数据长度 */
err_t netbuf_data(struct netbuf *buf, void **dataptr, u16_t *len)
{
  if(buf->ptr == NULL) 
  {
    return ERR_BUF;
  }
  *dataptr = buf->ptr->payload;
  *len = buf->ptr->len;

  return ERR_OK;
}

/* 向后偏移netbuf的pbuf偏移指针 */
s8_t netbuf_next(struct netbuf *buf)
{
  if(buf->ptr->next == NULL) 
  {
    return -1;
  }
	
  buf->ptr = buf->ptr->next;
  if(buf->ptr->next == NULL) 
  {
    return 1;
  }

  return 0;
}

/* netbuf的pbuf偏移指针指向第一个pbuf */
void netbuf_first(struct netbuf *buf)
{
  buf->ptr = buf->p;
}