当绑定客户端TCP套接字到一个特定的本地端口的Winsock，SO_REUSEADDR没有任何影响 [英] When binding a client TCP socket to a specific local port with Winsock, SO_REUSEADDR does not have any effect

问题描述

我绑定的客户的TCP套接字到特定的本地端口。为了处理那里的插座保持在 TIME_WAIT 状态一段时间的情况下，我使用的setsockopt（）与 SO_REUSEADDR 套接字。

I'm binding a client TCP socket to a specific local port. To handle the situation where the socket remains in TIME_WAIT state for some time, I use setsockopt() with SO_REUSEADDR on a socket.

它工作在Linux，但在Windows上，我得到 WSAEADDRINUSE 不起作用连接（）打电话的时候，在previous连接仍然处于 TIME_WAIT 。

It works on Linux, but does not work on Windows, I get WSAEADDRINUSE on connect() call when the previous connection is still in TIME_WAIT.

MSDN是不完全清楚应与客户端套接字发生什么：

MSDN is not exactly clear what should happen with client sockets:

[...]对于需要多个套接​​字绑定到同一端口号的服务器应用程序，可以考虑使用的setsockopt （ SO_REUSEADDR ）。客户端应用程序通常不需要调用bind都连自动选择一个未使用的端口。 [...]

[...] For server applications that need to bind multiple sockets to the same port number, consider using setsockopt (SO_REUSEADDR). Client applications usually need not call bind at all—connect chooses an unused port automatically. [...]

我如何避免这种情况？

推荐答案

当您创建插座插座（），它只有一个类型和一个协议族。最理想的是绑定（）到一个本地地址：端口太

When you create a socket with socket(), it has only a type and a protocol family. The ideal is to bind() it to a local address:port too.

在同一主机的最后一个连接你通常提到的错误发生：端口没有正常关机（FIN / ACK FIN / ACK）。在这些情况下，插座保持在 TIME_WAIT 状态的一段时间（取决于操作系统，但可调节）。

The error you mentioned normally happens when the last connection to the same host:port didn't have a graceful shutdown (FIN/ACK FIN/ACK). In these cases, the socket stays in TIME_WAIT state for a certain period of time (OS dependent, but adjustable).

当您尝试连接（）到同一个主机和相同的端口会发生什么事则是，它使用默认的套接字的名称/地址/端口/等，但此组合已在使用由您的僵尸的插座。为了避免这种情况，您可以更改本地地址：端口用于建立通过调用绑定（）插座创建后，提供了的sockaddr <连接/ code>结构充满了本地地址和的随机的端口。

What happens then is when you try to connect() to the same host and same port, it uses the default socket's name/address/port/etc, but this combination is already in use by your zombie socket. To avoid this, you can change the local address:port used to establish the connection by calling bind() after the socket creation, providing the sockaddr struct filled with your local address and a random port.

int main() {
    int ret, fd;
    struct sockaddr_in sa_dst;
    struct sockaddr_in sa_loc;
    char buffer[1024] = "GET / HTTP/1.1\r\nHost: www.google.com\r\n\r\n";

    fd = socket(AF_INET, SOCK_STREAM, 0);

    // Local
    memset(&sa_loc, 0, sizeof(struct sockaddr_in));
    sa_loc.sin_family = AF_INET;
    sa_loc.sin_port = htons(LOCAL_RANDOM_PORT);
    sa_loc.sin_addr.s_addr = inet_addr(LOCAL_IP_ADDRESS);

    ret = bind(fd, (struct sockaddr *)&sa_loc, sizeof(struct sockaddr));
    assert(ret != -1);

    // Remote
    memset(&sa_dst, 0, sizeof(struct sockaddr_in));
    sa_dst.sin_family = AF_INET;
    sa_dst.sin_port = htons(80);
    sa_dst.sin_addr.s_addr = inet_addr("64.233.163.104"); // google :)

    ret = connect(fd, (struct sockaddr *)&sa_dst, sizeof(struct sockaddr));
    assert(ret != -1);

    send(fd, buffer, strlen(buffer), 0);
    recv(fd, buffer, sizeof(buffer), 0);
    printf("%s\r\n", buffer);
}

更新：由于使用特定的本地端口是一个要求，考虑设置 SO_LINGER 与 l_onoff = 1 和 l_linger = 0 让你的插座将无法在关闭 / 关闭套接字，它会忽略排队的数据和（希望）关闭FD。作为最后的手段，你可以通过更改此注册表项的值调整 TIME_WAIT 延迟（强烈建议不要！）：

UPDATE: As using a specific local port is a requirement, consider setting SO_LINGER with l_onoff=1 and l_linger=0 so your socket won't block upon close/closesocket, it will just ignore queued data and (hopefully) close the fd. As a last resort you can adjusting the TIME_WAIT delay by changing the value of this registry key (highly discouraged!):

HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\TcpTimedWaitDelay

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