windows - ConnectEx要求套接字为 "initially bound"，但是要做什么呢？

ConnectEx函数需要一个“未连接的，先前绑定(bind)的套接字”。实际上，如果我在示例中省略了bind步骤(请参见下文)，则ConnectEx会失败，而WSAEINVAL失败。

这是我目前的理解:在调用ConnectEx，bind到INADDR_ANY和端口0的套接字之前(除非已绑定(bind)):

struct sockaddr_in addr;
ZeroMemory(&addr, sizeof(addr));
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = INADDR_ANY;
addr.sin_port = 0;
rc = bind(sock, (SOCKADDR*) &addr, sizeof(addr));
if (rc != 0) { ... bind failed; call WSAGetLastError to see why ... }

或对于IPv6套接字:

struct sockaddr_in6 addr;
ZeroMemory(&addr, sizeof(addr));
addr.sin6_family = AF_INET6;
addr.sin6_addr = in6addr_any;
addr.sin6_port = 0;
rc = bind(sock, (SOCKADDR*) &addr, sizeof(addr));
if (rc != 0) { ... bind failed; call WSAGetLastError to see why ... }

这使操作系统可以为我们的套接字分配一个本地地址(与我们要连接的远程地址相对)。 connect自动执行此步骤，但ConnectEx不会自动执行此步骤。

我的问题是:

我的评估正确吗？

有没有办法执行与地址族无关的自动绑定(bind)，还是我必须手动处理AF_INET，AF_INET6，AF_BTH(蓝牙)等中的每一个？

有效的ConnectEx示例(也在Gist:https://gist.github.com/4158972上):

#include <stdio.h>
#include <WinSock2.h>
#include <MSWSock.h>
#include <WS2tcpip.h>

#pragma comment(lib, "Ws2_32.lib")

struct mswsock_s {
    LPFN_CONNECTEX ConnectEx;
} mswsock;

static BOOL load_mswsock(void)
{
    SOCKET sock;
    DWORD dwBytes;
    int rc;

    /* Dummy socket needed for WSAIoctl */
    sock = socket(AF_INET, SOCK_STREAM, 0);
    if (sock == INVALID_SOCKET)
        return FALSE;

    {
        GUID guid = WSAID_CONNECTEX;
        rc = WSAIoctl(sock, SIO_GET_EXTENSION_FUNCTION_POINTER,
                      &guid, sizeof(guid),
                      &mswsock.ConnectEx, sizeof(mswsock.ConnectEx),
                      &dwBytes, NULL, NULL);
        if (rc != 0)
            return FALSE;
    }

    rc = closesocket(sock);
    if (rc != 0)
        return FALSE;

    return TRUE;
}

int main(int argc, char *argv[])
{
    int rc;
    BOOL ok;
    WSADATA wsaData;
    SOCKET sock;

    rc = WSAStartup(MAKEWORD(2,2), &wsaData);
    if (rc != 0) {
        printf("WSAStartup failed: %d\n", rc);
        return 1;
    }
    if (LOBYTE(wsaData.wVersion) != 2 || HIBYTE(wsaData.wVersion) != 2) {
        printf("Your computer is from the wrong millenium.\n");
        WSACleanup();
        return 1;
    }

    if (!load_mswsock()) {
        printf("Error loading mswsock functions: %d\n", WSAGetLastError());
        return 1;
    }

    sock = socket(AF_INET, SOCK_STREAM, 0);
    if (sock == INVALID_SOCKET) {
        printf("socket: %d\n", WSAGetLastError());
        return 1;
    }

    /* ConnectEx requires the socket to be initially bound. */
    {
        struct sockaddr_in addr;
        ZeroMemory(&addr, sizeof(addr));
        addr.sin_family = AF_INET;
        addr.sin_addr.s_addr = INADDR_ANY;
        addr.sin_port = 0;
        rc = bind(sock, (SOCKADDR*) &addr, sizeof(addr));
        if (rc != 0) {
            printf("bind failed: %d\n", WSAGetLastError());
            return 1;
        }
    }

    /* Issue ConnectEx and wait for the operation to complete. */
    {
        OVERLAPPED ol;
        ZeroMemory(&ol, sizeof(ol));

        sockaddr_in addr;
        ZeroMemory(&addr, sizeof(addr));
        addr.sin_family = AF_INET;
        addr.sin_addr.s_addr = inet_addr("173.194.37.36"); // google.com
        addr.sin_port = htons(80);

        ok = mswsock.ConnectEx(sock, (SOCKADDR*) &addr, sizeof(addr), NULL, 0, NULL, &ol);
        if (ok) {
            printf("ConnectEx succeeded immediately\n");
        } else if (WSAGetLastError() == ERROR_IO_PENDING) {
            printf("ConnectEx pending\n");

            DWORD numBytes;
            ok = GetOverlappedResult((HANDLE) sock, &ol, &numBytes, TRUE);
            if (ok)
                printf("ConnectEx succeeded\n");
            else
                printf("ConnectEx failed: %d\n", WSAGetLastError());
        } else {
            printf("ConnectEx failed: %d\n", WSAGetLastError());
            return 1;
        }
    }

    /* Make the socket more well-behaved. */
    rc = setsockopt(sock, SOL_SOCKET, SO_UPDATE_CONNECT_CONTEXT, NULL, 0);
    if (rc != 0) {
        printf("SO_UPDATE_CONNECT_CONTEXT failed: %d\n", WSAGetLastError());
        return 1;
    }

    /* This will fail if SO_UPDATE_CONNECT_CONTEXT was not performed. */
    rc = shutdown(sock, SD_BOTH);
    if (rc != 0) {
        printf("shutdown failed: %d\n", WSAGetLastError());
        return 1;
    }

    printf("Done\n");
    return 0;
}

最佳答案

正确的。



是的。



我相信INADDR_ANY在所有地址族中都是一堆零，因此您可以尝试使用memset()并完全省略对addr.sin_addr.s_addr的赋值。这是否是犹太洁食，可移植，在政治上是正确的等等，这是我将不再讨论的另一个问题。

考虑到保存系统调用是其存在的动机，并且考虑到大多数程序根本不会绑定(bind)出站套接字，Microsoft似乎并没有在内部设法让ConnectEx()调用bind()很好奇。