【原创】通过 ioctl + FIONREAD 判定数据可读

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14:00:38 epoll_ctl(26, EPOLL_CTL_MOD, 31, {EPOLLIN, {u32=31, u64=31}}) = 0
14:00:38 epoll_wait(26, {{EPOLLIN, {u32=31, u64=31}}}, 32, 9698) = 1
14:00:38 clock_gettime(CLOCK_MONOTONIC, {152386, 122371397}) = 0
14:00:38 gettimeofday({1445666438, 713982}, NULL) = 0
14:00:38 ioctl(31, FIONREAD, [16])      = 0
14:00:38 readv(31, [{"\0224Vx\0\0\0\3\0\0\0\0\0\0\0\0", 16}], 1) = 16

14:00:38 epoll_ctl(26, EPOLL_CTL_ADD, 31, {EPOLLIN, {u32=31, u64=31}}) = 0
14:00:38 epoll_wait(26, {{EPOLLIN, {u32=31, u64=31}}}, 32, 10000) = 1
14:00:43 clock_gettime(CLOCK_MONOTONIC, {152390, 497764210}) = 0
14:00:43 gettimeofday({1445666443, 89440}, NULL) = 0

发现此时 socket 中可读数据为 0 
14:00:43 ioctl(31, FIONREAD, [0])       = 0

这里会看到一些乱七八糟的数据（应该是由于 readv 用于保存读取结果的 buffer 没有清空的缘故）
14:00:43 readv(31, [{"[pid]:25002     [UpuWrapper]: [UpuClientMsgCallBack] ClientSeesion:0x94f50f8 recive upu result msg:3, result type:0, nResultCount:0 \n\0\2\0@\0\320W\371\10\2\0@\0\320W@\0\320Wdows\",\"status\":\"callidle\",\"nuaddr\":\"172.16.185.135\",\"mtaddr\":\"172.16.72.105\",\"userdomain\":\"0q0y1aphxubof8ycru6fsgsk\",\"devid\":\"10103000000002000000000000000002\",\"data\":\"\"}]\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\10\2\0\0\231\7\2\0\0\0\0\0/localtime\0\0\10\2\0\0\201\7\2\0\0\0\0\0domain\00005\0\0\0 \2\0\0$\0\0\0008\f\320W\0\0\0\0\10\0\0\0\1\0\0\0\300\10\320W\0\0\0\0@\2\0\0,\0\0\0\340\10\320W\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0h\2\0\0,\0\0\0\350\f\320W\0\0\0\0\n\0\0\0h\v\320W\1\0\0\0D\f\320W4\v\320W\n\0\0\0\220\2\0\0004\0\0\0\270\t\320W4\v\320W\344\n\320W\344\n\320W|\n\320W4\n\320WT\t\320WT\t\320W\374\10\320W\374\10\320W\0\0\0\0\201\0\0\0@\0\320W@\0\320W\20\0\0\0,\0\0\0\260\f\320W4\n\320W\204\f\320W\250\n\320W\2\0\0\0prototype\0001\0\0\0\0\0I\0\0\0\200\0\320W\200\0\320W0000002000000000000000002\"\0ff\"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0@\3\0\0004\0\0\0\0\0\0\0c52a-deb2-499c-add5-db70f1f62bff\0\0\0\0\0\0\0\0\31\6\2\0@\0\320Wx\6\320W\20\0\0\0004\0\0\0\10\t\320Wc52a-deb2-499c-add5-db70f1f62bff\0\0\0\0\0\0\0\0\331\5\2\0x\6\320W8\t\320W\0\0\0\0\0\0\0\0\0\0\0\0moid\0\0\0\0)\0\0\0H\v\320Wx\6\320W\20\0\0\0\34\0\0\0\200\10\320W110000423\0\0\0H\0\0\0$\0\0\0(\v\320W4\v\320W"..., 4096}], 1) = 0

• ioctl 能够判定 socket 缓冲区中可读数据的数量，两种情况下 ioctl 调用都返回 0 ，即成功。
• readv 在两种情况都进行了数据读取，TCP 链路正常情况下，readv 返回读取的数据字节数；TCP 链路异常情况下，readv 返回 0 。

// here some Code:

char recBuffer[BUFFERLENGTH] = {0};
int bytesAv = 0;
int bytesRead = 0;
int flags = 0;
if ( ioctl (m_Socket,FIONREAD,&bytesAv) < 0 )
{
    // Error
}
if ( bytesAv < 1 )
{
    // No Data Available
}
bytesRead = recv(m_Socket,recBuffer,BUFFERLENGTH,flags);

if ( ioctl (m_Socket,FIONREAD,&bytesAv) < 0 )
{ // Error 
}

// BYTES MIGHT BE RECEIVED BY HARDWARE/OS HERE!

if ( bytesAv < 1 ) // AND HERE!
{
    // No Data Available
    // BUT BYTES MIGHT BE RECEIVED BY HARDWARE/OS HERE!
}

// AND MORE BYTES MIGHT BE RECEIVED BY HARDWARE/OS HERE!

bytesRead = recv(m_Socket,recBuffer,BUFFERLENGTH,flags);
// AND NOW bytesRead IS NOT EQUAL TO 0!

【原创】通过 ioctl + FIONREAD 判定数据可读

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原文地址：http://my.oschina.net/moooofly/blog/522725