LWIP使用RAW接收UDP整帧数据

很多lwip的教程里都有udp的回环程序例子，就是每收到一包数据立刻回环发出去。如下：

void?udp_echo_XXX_receive_callback(void?*arg,?struct?udp_pcb *upcb,?struct?pbuf *p,?const?ip_addr_t?*addr,?u16_t?port){??/* Connect to the remote client */??udp_connect(upcb, addr, UDP_CLIENT_PORT);??/* Tell the client that we have accepted it */??udp_send(upcb, p);??/* free the UDP connection, so we can accept new clients */??udp_disconnect(upcb);??/* Free the p buffer */??pbuf_free(p);}

这段代码中p是一段udp数据。UDP协议一帧（带帧头）最长可以发送64KB的数据，在实际使用中如果想接收一整帧在处理，可以使用类似如下的程序：

struct?udp_par_struct{? u8 receive_state; ? ? ? ? ? ? ??//接收状态? u32 from_addr; ? ? ? ? ? ? ? ? ?//IP地址——来源? u16 from_port; ? ? ? ? ? ? ? ? ?//端口——来源??uint32_t?udp_re_num; ? ? ? ? ? ?//接收数据长度??uint32_t?udp_tx_num; ? ? ? ? ? ?//发送数据长度??uint8_t?udp_send_date[2000];??uint8_t?udp_receive_date[2000];};?
void?udp_recv_demo_callback(void?*arg,?struct?udp_pcb *upcb,?struct?pbuf *p,?const?ip_addr_t?*addr,?u16_t?port){??int?receive_count =?0;??unsigned?char?*receive_data;??struct?pbuf* P_next;??struct?udp_par_struct?*udp_par_struct_date = (struct?udp_par_struct*)arg;? ????memcpy(udp_par_struct_date->udp_receive_date,p->payload,p->len);?//先复制第一个内存块的包? P_next = p->next;? receive_count = receive_count + p->len;? receive_data = &udp_par_struct_date->udp_receive_date[0] + p->len;??while(P_next)? {? ? ??if((receive_count + P_next->len) ?>?sizeof(udp_par_struct_date->udp_receive_date))?break;? ? ??memcpy(receive_data,P_next->payload,P_next->len);? ? ? receive_data = receive_data + P_next->len;? ? ? receive_count = receive_count + P_next->len;? ? ? P_next = P_next->next;? }??pbuf_free(p);? udp_par_struct_date->udp_re_num = receive_count;? udp_par_struct_date->receive_state = UDP_RECEIVED;? udp_par_struct_date->from_addr = addr->addr;? udp_par_struct_date->from_port = port;??
??xxx_print("receive IP = %d.%d.%d.%d ?",udp_par_struct_date->from_addr&0xFF,? ?(udp_par_struct_date->from_addr>>8)&0xFF,(udp_par_struct_date->from_addr>>16)&0xFF,(udp_par_struct_date->from_addr>>24)&0xFF);??xxx_print("receive port = %d ?",udp_par_struct_date->from_port);??xxx_print("receive num = %d ?",udp_par_struct_date->udp_re_num);??for(int?i =?0;i<receive_count;i++)? {? ??xxx_print("0x%x ", udp_par_struct_date->udp_receive_date[i]);? }??xxx_print("nr");}

以上代码中使用结构体udp_par_struct（例子最大接收2000字节，可自己调整）存储UDP的数据和状态，通过判断p->next是否为空指针来判断这整帧是否接收完毕。接收完整帧后通过结构体中的receive_state 置标志位。同时可存储其他参数。

这样可接收一整帧之后再进行协议处理。