LWIP UDP socket编程 可以指定本地端口号及发送长度不能太长问题分析

LWIP UDP socket编程 可以指定本地端口号及发送长度不能太长问题分析

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<span class="link_postdate">2016-03-01 17:02</span>
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发送方：

/*
* File: main.c
* Author: tianshuai
*
* Created on 2011年11月29日, 下午10:34
*
* 主要实现：发送20个文本消息，然后再发送一个终止消息
*/

#include <stdio.h>
#include <stdlib.h>

#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

int port=6789;
int main(int argc, char** argv) {
int socket_descriptor; //套接口描述字
int iter=0;
char buf[80];
struct sockaddr_in address;//处理网络通信的地址

bzero(&address,sizeof(address));
address.sin_family=AF_INET;
address.sin_addr.s_addr=inet_addr(”127.0.0.1”);//这里不一样
address.sin_port=htons(port);

//创建一个 UDP socket

socket_descriptor=socket(AF_INET,SOCK_DGRAM,0);//IPV4 SOCK_DGRAM 数据报套接字（UDP协议）

for(iter=0;iter<=20;iter++)
{
/*
* sprintf(s, ”%8d%8d”, 123, 4567); //产生：” 123 4567”
* 将格式化后到 字符串存放到s当中
*/
sprintf(buf,”data packet with ID %d\n”,iter);

/*int PASCAL FAR sendto( SOCKET s, const char FAR* buf, int len, int flags,const struct sockaddr FAR* to, int tolen);　　
* s：一个标识套接口的描述字。　
* buf：包含待发送数据的缓冲区。　　
* len：buf缓冲区中数据的长度。　
* flags：调用方式标志位。　　
* to：（可选）指针，指向目的套接口的地址。　
* tolen：to所指地址的长度。
　　 */
sendto(socket_descriptor,buf,sizeof(buf),0,(struct sockaddr *)&address,sizeof(address));
}

sprintf(buf,”stop\n”);
sendto(socket_descriptor,buf,sizeof(buf),0,(struct sockaddr *)&address,sizeof(address));//发送stop 命令
close(socket_descriptor);
printf(”Messages Sent,terminating\n”);

exit(0);

return (EXIT_SUCCESS);
}



接收方：

/*
* File: main.c
* Author: tianshuai
*
* Created on 2011年11月29日, 下午10:34
*/

#include <stdio.h>
#include <stdlib.h>

#include <string.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

int port=6789;

int main(int argc, char** argv) {

int sin_len;
char message[256];

int socket_descriptor;
struct sockaddr_in sin;
printf(”Waiting for data form sender \n”);

bzero(&sin,sizeof(sin));
sin.sin_family=AF_INET;
sin.sin_addr.s_addr=htonl(INADDR_ANY);
sin.sin_port=htons(port);
sin_len=sizeof(sin);

socket_descriptor=socket(AF_INET,SOCK_DGRAM,0);
bind(socket_descriptor,(struct sockaddr *)&sin,sizeof(sin));

while(1)
{
recvfrom(socket_descriptor,message,sizeof(message),0,(struct sockaddr *)&sin,&sin_len);
printf(”Response from server:%s\n”,message);
if(strncmp(message,“stop”,4) == 0)//接受到的消息为 “stop”
{

printf(”Sender has told me to end the connection\n”);
break;
&nb
bbc1
sp; }
}

close(socket_descriptor);
exit(0);

return (EXIT_SUCCESS);
}

以上是网上找的。

以下是自己的UDP客户端

int iUDPClientSock = -1;

struct sockaddr_in ServerAddress;

struct sockaddr_in ClientAddress;

/* 设置目的IP地址和端口号 */

ServerAddress.sin_family = AF_INET;

ServerAddress.sin_port = htons(TCP_SERVER_PORT);

u32InetAddr = inet_addr(TCP_SERVER_IP);

ServerAddress.sin_addr.s_addr = u32InetAddr;

memset(&ServerAddress.sin_zero,0,sizeof(ServerAddress.sin_zero));

ClientAddress.sin_family = AF_INET;

ClientAddress.sin_port = htons(2000); //绑定本地的2000端口，可有可无

u32InetAddr = inet_addr(“192.168.0.10”);

ClientAddress.sin_addr.s_addr = u32InetAddr;

memset(&ClientAddress.sin_zero,0,sizeof(ClientAddress.sin_zero));

if ((bind( iUDPClientSock, (struct sockaddr *) &ClientAddress, sizeof(ClientAddress))) < 0) //绑定本地的2000端口，可有可无

{

PlatErrorPrint(0x0000000, “SendTask udp bind err!”);

}

iSendLen = sendto(iUDPClientSock,g_pu8SendDataPos,TCP_SEND_LEN//要发送数据的长度,0,(const struct sockaddr *)&ServerAddress//远方服务器的地址和端口,sizeof(ServerAddress));

if((close(iTCPClientSock)) < 0)//关闭连接

问题调试：

刚开始发送的UDP数据长度TCP_SEND_LEN为15K,现象很奇怪，主站始终接收不到数据，WireShark也监测不到，LWIP的底层接口有时报等待发送完成信号量超时。

后来把发送长度改为1472就可以了。

分析原因：LWIP的配置项中IP层的分片功能没有打开，导致当UDP发送数据太大时，让MAC层发送的数据数大于MTU的1500，会出问题。

而TCP不会出现这个问题，是由于TCP本身有分片功能，不在IP层分片，所以TCP可以发送大于1500的数据。










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