socket之send与发送缓冲区大小的关系

关于send函数在发送的数据长度大于发送缓冲区大小，或者大于发送缓冲区剩余大小时，socket会怎么反应。参见这篇博客的两种说法/article/8175885.html

自己做了个测试，服务器只起socket在侦听,不recv, 也不send.

//ubuntu10.04 32bit

#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>

int main(void)
{
int fd;
struct sockaddr_in addr;

fd = socket(AF_INET, SOCK_STREAM, 0);
addr.sin_family = AF_INET;
addr.sin_port = htons(103);
addr.sin_addr.s_addr = htonl(INADDR_ANY);
bind(fd, (struct sockaddr *)&addr, sizeof(addr));
listen(fd,5);
}

客户端，将发送缓冲区大小设置成2k,然后一次发送3k的数据。

//ubuntu10.04 32bit

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <arpa/inet.h>
int main()
{
int fd,ret,tmp,sendlen;
struct sockaddr_in addr;
char *buf;
int sendBufLen = 1024*2;
socklen_t optlen = sizeof(int);

buf = (char *)malloc(1024 * 3);
fd = socket(AF_INET, SOCK_STREAM,0 );

setsockopt(fd,SOL_SOCKET, SO_SNDBUF,(const char*)&sendBufLen, sizeof(int));
getsockopt(fd,SOL_SOCKET, SO_SNDBUF,(int *)&tmp, &optlen);
printf("send_tmp=%d,optlen=%d\n",tmp,(int)optlen);    //设置发送缓冲区2048

getsockopt(fd,SOL_SOCKET, SO_RCVBUF,(int *)&tmp, &optlen);
printf("recv_tmp=%d,optlen=%d\n",tmp,(int)optlen);

addr.sin_family = AF_INET;
addr.sin_port = htons(103);
addr.sin_addr.s_addr = inet_addr("222.111.112.204"); //填上自己的IP

ret = connect (fd, (struct sockaddr *)&addr, sizeof(addr));
printf("connect return %d\n",ret);
getchar();
if (ret >= 0)
sendlen = send(fd,buf,1024*3,0);
printf("sendlen=%d\n",sendlen);       //此处返回3072
getchar();

return 0;
}

交互报文



从这里看出当发送长度大于缓冲区大小时，是分次发送，三次加起来 1448 + 1448 + 176 = 3072

在windows下，做同样的测试

// xp vc6.0 32bit

#include <stdio.h>
#include <winsock2.h>
#include <iostream.h>

#pragma  comment (lib,"ws2_32")

void  main()
{

int         len,optval,optlen,iResult;
SOCKADDR_IN clientService;// 地址
SOCKET      ConnectSocket;// socket
WSADATA     wsaData;// 库
unsigned char buf[1024*3];

//初始化socket库， 保存ws2_32.dll已经加载
iResult = WSAStartup(MAKEWORD(2,2), &wsaData);
if (iResult != NO_ERROR)
printf("Error at WSAStartup()\n");

// 创建socket
ConnectSocket = socket(AF_INET, // IPv4
SOCK_STREAM, // 顺序的、可靠的、基于连接的、双向的数据流通信
IPPROTO_TCP  // 使用TCP协议
/*0*/);

if (ConnectSocket == INVALID_SOCKET)
{
printf("Error at socket(): %d\n", WSAGetLastError());
WSACleanup();
return ;
}

optlen = sizeof(optval);
getsockopt(ConnectSocket, SOL_SOCKET, SO_SNDBUF, (char*)&optval, &optlen);
printf("send buf len is %d\n",optval);           //默认发送缓冲区8k
getsockopt(ConnectSocket, SOL_SOCKET, SO_RCVBUF, (char*)&optval, &optlen);
printf("Recv buf len is %d\n",optval);          //默认接收缓冲区8k

optval = 1024 * 2;
setsockopt(ConnectSocket, SOL_SOCKET, SO_SNDBUF, (char*)&optval, optlen);
getsockopt(ConnectSocket, SOL_SOCKET, SO_SNDBUF, (char*)&optval, &optlen);
printf("send buf len change to %d\n",optval);

// 设置服务端的通信协议、IP地址、端口
clientService.sin_family = AF_INET;
clientService.sin_addr.s_addr = inet_addr( "222.111.112.204" );
clientService.sin_port = htons( 103 );

// 连接到服务端
if ( connect(
ConnectSocket, // socket
(SOCKADDR*) &clientService, // 地址
sizeof(clientService) // 地址的大小
) == SOCKET_ERROR)
{
printf( "Failed to connect(%d)\n",WSAGetLastError() );
WSACleanup();
return ;
}

len = send(ConnectSocket, (char*)buf, 1024*3, 0);
printf("send length is %d\n",len);             //这里同样直接返回3072
system("pause");
return;
}

抓取报文



分三次发送1460+1460+152 = 3072

上面都是阻塞的发送，对于socket是非阻塞的话，做同样的测试

//ubuntu10.04 32bit

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <unistd.h>
#include <errno.h>
#include <arpa/inet.h>
int main()
{
int fd,ret,tmp,sendlen,flags,fd_num;
fd_set  rset,wset;
struct timeval tval;
struct sockaddr_in addr;
char *buf;
int sendBufLen = 1024*2;
socklen_t optlen = sizeof(int);

buf = (char *)malloc(1024 * 3);
fd = socket(AF_INET, SOCK_STREAM,0 );

setsockopt(fd,SOL_SOCKET, SO_SNDBUF,(const char*)&sendBufLen, sizeof(int));
getsockopt(fd,SOL_SOCKET, SO_SNDBUF,(int *)&tmp, &optlen);
printf("send_tmp=%d,optlen=%d\n",tmp,(int)optlen);

getsockopt(fd,SOL_SOCKET, SO_RCVBUF,(int *)&tmp, &optlen);
printf("recv_tmp=%d,optlen=%d\n",tmp,(int)optlen);

flags = fcntl(fd,F_GETFL,0);
fcntl(fd,F_SETFL,flags|O_NONBLOCK);

addr.sin_family = AF_INET;
addr.sin_port = htons(103);
addr.sin_addr.s_addr = inet_addr("222.111.112.204");

ret = connect (fd, (struct sockaddr *)&addr, sizeof(addr));

if ((ret < 0) && (errno == EINPROGRESS))
{
FD_ZERO(&rset);
FD_SET(fd,&rset);
wset = rset;
tval.tv_sec = 3;
tval.tv_usec = 0;

if ( -1 == (fd_num = select(fd+1, &rset, &wset, NULL, &tval)))
{
perror("select error");
exit(0);
}
else
{
if ((fd_num == 1) && FD_ISSET(fd, &wset))  //connect only can be write
{
printf("connect OK!\n");
}
else
{
perror("state error");
exit(0);
}
}
}

if (-1 ==(sendlen = send(fd,buf,1024*3,0)))
{
perror("send error");
}
else
{
printf("sendlen=%d\n",sendlen);	  //直接返回3072
}
return 0;
}

和blocking socket表现是一样的，一次send,协议栈分三帧发送。

//xp vc6.0 32bit

#include <stdio.h>
#include <winsock2.h>
#include <iostream.h>

#pragma  comment (lib,"ws2_32")

void  main()
{
int	len,optval,optlen,iResult,fd_num,on=1;
SOCKADDR_IN clientService;// 地址
SOCKET      ConnectSocket;// socket
WSADATA     wsaData;// 库
unsigned char buf[1024*3];//
fd_set		rset,wset;
struct timeval tval;

//初始化socket库， 保存ws2_32.dll已经加载
iResult = WSAStartup(MAKEWORD(2,2), &wsaData);
if (iResult != NO_ERROR)
printf("Error at WSAStartup()\n");

// 创建socket
ConnectSocket = socket(AF_INET, // IPv4
SOCK_STREAM, // 顺序的、可靠的、基于连接的、双向的数据流通信
IPPROTO_TCP  // 使用TCP协议
/*0*/);

if (ConnectSocket == INVALID_SOCKET)
{
printf("Error at socket(): %d\n", WSAGetLastError());
WSACleanup();
return ;
}

if(0 == ioctlsocket(ConnectSocket, FIONBIO, (unsigned long *)&on))
{
printf("socket non-blocking set success!\n");
}

optlen = sizeof(optval);
getsockopt(ConnectSocket, SOL_SOCKET, SO_SNDBUF, (char*)&optval, &optlen);
printf("send buf len is %d\n",optval);
getsockopt(ConnectSocket, SOL_SOCKET, SO_RCVBUF, (char*)&optval, &optlen);
printf("Recv buf len is %d\n",optval);

optval = 1024 * 2;
setsockopt(ConnectSocket, SOL_SOCKET, SO_SNDBUF, (char*)&optval, optlen);
getsockopt(ConnectSocket, SOL_SOCKET, SO_SNDBUF, (char*)&optval, &optlen);
printf("send buf len change to %d\n",optval);

// 设置服务端的通信协议、IP地址、端口
clientService.sin_family = AF_INET;
clientService.sin_addr.s_addr = inet_addr( "222.111.112.204" );
clientService.sin_port = htons( 103 );

// 连接到服务端
if ( connect(
ConnectSocket, // socket
(SOCKADDR*) &clientService, // 地址
sizeof(clientService) // 地址的大小
) == SOCKET_ERROR)
{
if ( WSAEWOULDBLOCK == WSAGetLastError() )
{
FD_ZERO(&rset);
FD_SET(ConnectSocket,&rset);
wset = rset;
tval.tv_sec = 3;
tval.tv_usec = 0;
if (SOCKET_ERROR == (fd_num = select(ConnectSocket+1, &rset, &wset, NULL, &tval)))
{
printf( "select Failed (%d)\n",WSAGetLastError() );
WSACleanup();
return ;
}
else
{
if ((fd_num == 1) && FD_ISSET(ConnectSocket, &wset))  //connect成功后，只能可写，不能可读可写
{
printf("connect OK!\n");
}
else
{
printf( "connect Failed (%d)\n",WSAGetLastError() );
WSACleanup();
return ;
}
}
}
else
{
printf( "Failed to connect(%d)\n",WSAGetLastError() );
WSACleanup();
return ;
}
}

if (SOCKET_ERROR == (len=send(ConnectSocket, (char*)buf, 1024*3, 0)))
{
printf("send error %d\n", WSAGetLastError());
}
else
{
printf("send length is %d\n",len);  //直接返回3072
}

system("pause");
return;
}

可见，当send的数据长度大于socket的缓冲区长度时，不管是windows还是linux,send都会分帧发送。