windows 套接字的有效性
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Validity of a Socket
提问by ckv
I have created a socket using the following lines of code and i get a valid socket and connection is established between the client and server machines. Is there a possibility that the socket becomes invalid due to network disturbances or any other reason.
我使用以下代码行创建了一个套接字，并获得了一个有效的套接字，并在客户端和服务器计算机之间建立了连接。是否有可能由于网络干扰或任何其他原因导致套接字失效。
If so how do we check whether the socket is valid or not.
如果是这样，我们如何检查套接字是否有效。
SOCKET SocServer;
//To Set up the sockaddr structure
ServerSock.sin_family = AF_INET;
ServerSock.sin_addr.s_addr = INADDR_ANY
ServerSock.sin_port = htons(PortNumber);//port number of 5005
// To Create a socket for listening on PortNumber
if(( SocServer = socket( AF_INET, SOCK_STREAM, 0 )) == INVALID_SOCKET )
{
return FALSE;
}
//To bind the socket with wPortNumber
if(bind(SocServer,(sockaddr*)&ServerSock,sizeof(ServerSock))!=0)
{
return FALSE;
}
// To Listen for the connection on wPortNumber
if(listen(SocServer,SOMAXCONN)!=0)
{
return FALSE;
}
I know i can check for INVALID_SOCKET which in other words means the socket is 0. Is there any other way out because my SocServer will have a value say 2500, i want to check if this socket is valid.
我知道我可以检查 INVALID_SOCKET 换句话说，这意味着套接字为 0。有没有其他出路，因为我的 SocServer 的值是 2500，我想检查这个套接字是否有效。
回答by Hasturkun
Pass your socket to any one of the windows socket functions (eg. getsockopt()), if the socket is invalid, it will return SOCKET_ERRORwhile WSAGetLastError()will return WSAENOTSOCK.
将您的套接字传递给任何一个 Windows 套接字函数（例如getsockopt()），如果套接字无效，它将返回SOCKET_ERROR而WSAGetLastError()将返回WSAENOTSOCK。
It is important to note that INVALID_SOCKETdoes not equal 0(the actual value, which you should not use specifically is ((SOCKET)(~0))
需要注意的是INVALID_SOCKET不等于0（实际值，你不应该专门使用的是((SOCKET)(~0))
回答by LukeN
The socket can become "invalid" when either side (expected or unexpected) disconnects, but not out of the blue due to network interferences (unless it disconnects, read above).
当任何一方（预期的或意外的）断开连接时，套接字可能会变得“无效”，但不会因为网络干扰而突然出现（除非它断开连接，请阅读上文）。
You can detect this by checking the return values of send()and recv()for -1 (SOCKET_ERROR)
您可以通过检查返回值检测这种send()和recv()为-1（SOCKET_ERROR）
回答by Amardeep AC9MF
The socket will not go invalid. But after you listen() you must accept() a connection. That connection may be lost at some point. It could be detected by a failure to write to the socket or recv() returning with error. Then you just recycle back to listen().
套接字不会失效。但是在你 listen() 之后你必须 accept() 一个连接。该连接可能会在某个时候丢失。可以通过写入套接字失败或 recv() 返回错误来检测到它。然后你只需回收回听（）。
回答by Mark B
First, assuming that INVALID_SOCKET (which you don't show) is actually defined as 0 this is incorrect. socketreturns -1 on failure like the other system calls (0 is a valid fd that could be returned).
首先，假设 INVALID_SOCKET（您没有显示）实际上定义为 0，这是不正确的。socket与其他系统调用一样失败时返回 -1（0 是可以返回的有效 fd）。
Then once you accept a connection, your send/writeor recv/readcall will return -1. If you're trying to write, errnowill be set to EPIPEto indicate the socket was closed (by your client). There's no way to just ask if a socket is closed.
然后一旦您接受连接，您的send/write或recv/read调用将返回 -1。如果您正在尝试写入，errno将设置EPIPE为指示套接字已关闭（由您的客户端）。没有办法只询问套接字是否关闭。
