WSAGetOverlappedResult 没有 return 来自套接字的数据

Question

这是我的代码，我想专注于对 WSARecv 和 WSAGetOverlappedResult 的调用：

#define WIN32_LEAN_AND_MEAN

#include <winsock2.h>
#include <mswsock.h> // for ACCEPT_CONTEXT

#include <windows.h>

#include <stdio.h> // for wprintf
#include <assert.h>


static char buf[128];
static WSABUF recvBuf = {.len = 128, .buf = buf };


int WINAPI wWinMain(
        HINSTANCE hInstance __attribute__((unused)),
        HINSTANCE hPrevInstance __attribute__((unused)),
        LPWSTR pCmdLine __attribute__((unused)),
        int nCmdShow __attribute__((unused))
    ) {
    WSADATA wsaData = {0};
    if (WSAStartup(MAKEWORD(2,2), &wsaData) != 0) {
        wprintf(L"WSAStartup failed, quitting...\n");
        abort();
    }

    SOCKET listenSock = socket(
        AF_INET,
        SOCK_STREAM,
        IPPROTO_TCP
    );

    if (listenSock == INVALID_SOCKET) {
        wprintf(L"Invalid socket, quitting...\n");
        goto cleanupWsa;
    }

    struct sockaddr_in sockAddr = {
        .sin_family = AF_INET,
        .sin_port = htons(8080),
        .sin_addr = INADDR_ANY,
    };

    wchar_t pretty[128];
    DWORD len = sizeof pretty / sizeof(*pretty);
    if (0 != WSAAddressToString(
        (LPSOCKADDR) &sockAddr,
        sizeof sockAddr,
        NULL,
        pretty,
        &len)
    ) {
        wprintf(L"Error during AddressToString, "
            L"check needed address string length %ld, quitting...\n"
            , len);
        goto cleanupSocket;
    }

    wprintf(L"Binding to %ls\n", pretty);

    if (bind(listenSock, (LPSOCKADDR) &sockAddr, sizeof sockAddr)
        == SOCKET_ERROR) {
        wprintf(L"Bind error, quitting...\n");
        goto cleanupSocket;
    }


    if (listen(listenSock, SOMAXCONN) != 0) {
        wprintf(L"Listen error, quitting...\n");
        goto cleanupSocket;
    }


    struct sockaddr s;
    int socklen = sizeof s;
    SOCKET acceptSocket = accept(listenSock, &s, &socklen);

    wprintf(L"ACCEPT\n");

    if (SOCKET_ERROR == setsockopt(
        acceptSocket,
        SOL_SOCKET,
        SO_UPDATE_ACCEPT_CONTEXT,
        (char *)&listenSock,
        sizeof listenSock
    )) {
        wprintf(L"setsockopt update_accept_context failure\n");
        goto cleanupBothSockets;
    }
    DWORD flags = WSA_FLAG_OVERLAPPED;

    WSAOVERLAPPED w;
    memset(&w, 0, sizeof w);
    if (WSARecv(
        acceptSocket,
        &recvBuf,
        1,//dwBufferCount 
        NULL,//lpBytesReceived 
        &flags,
        &w,
        NULL
    ) != SOCKET_ERROR) {
        wprintf(L"Recv: expected SOCKET_ERROR\n");
        goto cleanupBothSockets;
    }
    int errnr = WSAGetLastError();
    if (errnr != WSA_IO_PENDING) {
        wprintf(L"RecvErr %d\n", errnr);
        goto cleanupBothSockets;
    }

    wprintf(L"Running GetOverlappedResult\n");
    DWORD bytes_transferred;
    BOOL ret = WSAGetOverlappedResult(acceptSocket, &w, &bytes_transferred, TRUE, &flags);
    if (ret == FALSE) {
        wprintf(L"OverlappedResult: error\n");
    } else {
        wprintf(L"OverlappedResult: finished with no error, bytes transferred %d", bytes_transferred);
    }

cleanupBothSockets:
    closesocket(acceptSocket);
cleanupSocket:
    closesocket(listenSock);
cleanupWsa:
    WSACleanup();
    return 0;
}

当我运行程序时，它会侦听连接。我连接netcat。连接后，它按预期打印 'ACCEPT'。它还会打印 'Running GetOverlappedResult'，但即使我在 netcat 上写了很多乱码，“OverlappedResult:”行都不会出现，直到我在 netcat 上按下 Control-C，连接中断。然后，我点击了成功分支，它说传输了 0 个字节。

这个程序有什么问题？为什么不在 128 字节缓冲区填满后 WSAGetOverlappedResult return？

我仔细检查了我对 WSARecv 和 WSAGetOverlappedResult 的调用。以下是一些详细信息：

我将 WSARecv 的套接字设置为 acceptSocket，因为我想从已建立的具体连接中读取数据。
我将缓冲区计数设置为 1，因为我只有一个缓冲区，而 C 在内存中不区分具有一个元素的数组和只有一个元素的数组。所以我可以使用 recvBuf 作为一个单一大小的数组。
我将 lpNumberOfBytesRecvd 设置为 null，因为如果我提供 lpOverlapped.

Answer 1

您不能将 WSA_FLAG_OVERLAPPED 传递给 WSARecv。套接字本身已经重叠或不重叠。如果您改为传递 0，程序会注意到来自 netcat.

的字节

此外，您不能假设 WSARecv 将始终生成错误 ERROR_IO_PENDING。数据可能会立即可用，在这种情况下，它只会 return 0。因此，您需要将这两种情况都视为成功处理。

如果您使用例如curl，数据可能立即可用，程序会抱怨它没有得到 ERROR_IO_PENDING，当你用 netcat 手动将东西输入套接字时会得到。

WSAGetOverlappedResult 没有 return 来自套接字的数据

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