Why can't I transfer a big file once time?

I write two programs:Server and Client,and they
create socket using SOCK_STREAM,and I set socket:
int nRecvBuf=600*1024;
setsockopt(m_sock,SOL_SOCKET,SO_RCVBUF,(const char*)&nRecvBuf,sizeof(int));
int nSendBuf=600*1024;
setsockopt(m_sock,SOL_SOCKET,SO_SNDBUF,(const char*)&nSendBuf,sizeof(int));
and I transfer a big file about 400k,but I find I can send the file once time,
but I can't recv the file once time,
I want to know how to recv the file once time?

That's crazy. Just call recv() or send() as many times as necessary to send all the data.