在 C++ 中的套接字上发送和接收数据

Question

我目前正在学习 C++ 并试图了解套接字。我以前用 C# 和 Java 中的高级语言做过套接字，但在 C++ 中遇到过问题。

我已经完成了 https://msdn.microsoft.com/en-us/library/windows/desktop/ms737593(v=vs.85).aspx 中的示例。

除了有一件事我不确定之外，我的代码几乎可以正常工作。当我编写其他套接字应用程序时，通常在收到换行符后才会收到响应。

我想也许 C++ 一次添加 1 个接收到的字符并添加到缓冲区，所以当我关闭套接字时，缓冲区将包含接收到的所有内容，但它似乎是一个十六进制值，但是ascii 转换器中的十六进制似乎打印出乱码而不是套接字数据。

下面是我的代码

const int DEFAULT_BUF_LEN = 525;
    InitialiseLibrary initLibrary("tunnel.conf");
    if (initLibrary.initialise(0))
    {
        cout << "Failed to initialise library" << endl;
    }   

    BitsLibrary bitsLibrary;
    StaticSettings staticSettings(&bitsLibrary, "tunnel.conf");

    //Open a socket connection
    WSAData wsaData;
    int iResult;

    SOCKET listenSocket = INVALID_SOCKET;
    SOCKET clientSocket = INVALID_SOCKET;

    struct addrinfo *result = NULL;
    struct addrinfo hints;

    int iSendResult;
    char recvBuf[DEFAULT_BUF_LEN];
    int recBufLen = DEFAULT_BUF_LEN;

    iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
    if (iResult != 0)
    {
        cout << "WSAStartup Failed with error: " << iResult << endl;
        return EXIT_FAILURE;
    }

    ZeroMemory(&hints, sizeof(hints));
    hints.ai_family = AF_INET;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_protocol = IPPROTO_TCP;
    hints.ai_flags = AI_PASSIVE;

    iResult = getaddrinfo(NULL, "500", &hints, &result);
    if (iResult != 0)
    {
        cout << "getaddrinfo failed with error: " << iResult << endl;
        return EXIT_FAILURE;
    }

    listenSocket = socket(result->ai_family, result->ai_socktype, result->ai_protocol);
    if (listenSocket == INVALID_SOCKET)
    {
        cout << "Socket failed with error: " << WSAGetLastError() << endl;
        freeaddrinfo(result);
        WSACleanup();
        return EXIT_FAILURE;
    }

    iResult = ::bind(listenSocket, result->ai_addr, (int)result->ai_addrlen);
    if (iResult != 0)
    {
        cout << "bind failed with error: " << iResult << endl;
        FreeAddrInfo(result);
        closesocket(listenSocket);
        WSACleanup();
        return EXIT_FAILURE;
    }

    freeaddrinfo(result);
    iResult = listen(listenSocket, SOMAXCONN);
    if (iResult == SOCKET_ERROR)
    {
        cout << "Listen failed with error: " << WSAGetLastError() << endl;
        closesocket(listenSocket);
        WSACleanup();
        return EXIT_SUCCESS;
    }
    sockaddr_in clientAddr;
    socklen_t sin_size = sizeof(struct sockaddr_in);
    clientSocket = accept(listenSocket, (struct sockaddr*)&clientAddr, &sin_size);
    send(clientSocket, "welcome", string("welcome").length(),0);
    if (clientSocket == INVALID_SOCKET)
    {
        cout << "accept failed with error: " << WSAGetLastError() << endl;
        closesocket(listenSocket);
        WSACleanup();
        return EXIT_FAILURE;
    }

    closesocket(listenSocket);

    do {
        iResult = recv(clientSocket, recvBuf, recBufLen, 0);
        if (iResult > 0)
        {
            cout << "Bytes received: " << iResult << endl;
            cout << "Received: " << recvBuf << endl;

            iSendResult = send(clientSocket, recvBuf, iResult, 0);
            if (iSendResult == SOCKET_ERROR)
            {
                cout << "send failed with error: " << WSAGetLastError() << endl;
                closesocket(clientSocket);
                WSACleanup();
                return EXIT_FAILURE;
            }
            cout << "Bytes sent " << iSendResult << endl;
        }
        else if (iResult == 0)
        {
            cout << "Connection closing" << endl;
        }
        else
        {
            cout << "Recv failed with error: " << WSAGetLastError() << endl;
            closesocket(clientSocket);
            WSACleanup();
            return EXIT_FAILURE;
        }
    } while (iResult > 0);

    iResult = shutdown(clientSocket, SD_SEND);
    if (iResult == SOCKET_ERROR)
    {
        cout << "shutdown failed with error: " << WSAGetLastError() << endl;
        closesocket(clientSocket);
        WSACleanup();
        return EXIT_FAILURE;
    }
    closesocket(clientSocket);
    WSACleanup();

    cout << "Message was: " << recvBuf << endl;

    return EXIT_SUCCESS;

如果我没记错的话，如果我在 C# 中执行此操作并通过 telnet 连接到我的套接字，我可以发送 Hello 但在我发送 \r\n 之前应用程序不会执行任何操作或者缓冲区已满。

但是，在我的 C++ 应用程序中，只要我输入 H，我的应用程序就会立即响应并打印出只包含 H 的 recvBuf 加上一堆空白字符（在 cmd 中显示为正方形） ) 我假设它是数组缓冲区的空白部分，并发送回复。

Answer 1

套接字不关心换行符或空值。只有更高级别的流式 API 才能做到这一点。重要的是 recv() 的 return 值。这会准确告诉您接收到的字节数。缓冲区中超出该计数的任何内容均无效。

Answer 2

在流媒体协议中，建立一个确定内容长度的协议是很有用的。

例如，客户端可以发送内容长度，然后发送数据，服务器将首先读取内容长度，然后循环读取套接字并缓冲数据，直到接收到内容长度字节数.

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