My socket program is a server-client structure.

Something strange, there have a low probability that when the TCP socket just construct(client connect and server accept).

and I use select than read the socket, it will return -1 and errno is 104(Connection reset by peer).

But I do not send anything neither server nor client, in a normal way it should block at select function(my select function did not set time-out limit), but the read function return -1.

Why it happen? Or how can I do can get more detail to debug this problem?

Thank you all.

Platform: ubuntu 13.04 64bits, gcc compiler

minimal version of my code:

server:

for(;;)
    {
        rset= allset;
        select(maxfd+1, &rset, NULL, NULL, NULL);

        //read socket
        if( FD_ISSET(fconn[i].fd, &rset) )
        {
            len=read(fconn[i].fd, &tcp_buf.b[4], PACKET_LENGTH);

            //the connection will close
            if( len<0 )
            {
                printf("%s, fconn %s read length:%d, errno:%d(%s), close connection\n", crtTime(), fconn[i].ip, len, errno, strerror(errno) );
                close( fconn[i].fd );
                FD_CLR( fconn[i].fd, &allset );
            }
        }

        //construct new connection
        if( FD_ISSET(forwardSockfd, &rset) )
        {
            clilen= sizeof(cliaddr);
            connfd= accept( forwardSockfd, (struct sockaddr*)&cliaddr, &clilen );
            inet_ntop( AF_INET, &cliaddr.sin_addr, ip, sizeof(ip) );
            client_port= (int)cliaddr.sin_port;

            //set send buffer size
            int sendBuf= SOCKET_BUF_LENGTH;
            setsockopt(connfd, SOL_SOCKET, SO_SNDBUF, &sendBuf, sizeof(sendBuf));

            FD_SET( connfd, &allset );
        }
    }

client (my read function):

int readline(int fd, void* ptr, int len)
{
    int    rtn= len;
    void*  bp= ptr;
    int    rc;
    fd_set fdset;

    FD_ZERO(&fdset);
    FD_SET(fd, &fdset);
    while( len>0 )
    {
        select(fd+1, &fdset, NULL, NULL, NULL);
        rc=read(fd, bp, len);


        if(rc>0)
        {
            bp+= rc;
            len-= rc;
        }

        else
        {
            return rc;
        }
    }

    return rtn;
}