Question

我正在尝试通过套接字发送大量数据，有时当我调用send（在Windows上）时，它不会按预期发送我请求的所有数据。所以，我写了一个应该解决了我的问题的小功能 - 但它导致数据没有被正确发送并导致图像被破坏的问题。我正在创建一个简单的聊天室，您可以在其中相互发送图像（屏幕截图）。

为什么我的功能不起作用？

我怎样才能让它发挥作用？

void _internal_SendFile_alignment_512(SOCKET sock, BYTE *data, DWORD datasize)
{       
    Sock::Packet packet;
    packet.DataSize = datasize;
    packet.PacketType = PACKET_FILETRANSFER_INITIATE;
    DWORD until = datasize / 512;

    send(sock, (const char*)&packet, sizeof(packet), 0);

    unsigned int pos = 0;

    while( pos != datasize )
    {
        pos += send(sock, (char *)(data + pos), datasize - pos, 0);
    }

}

我的接收方是：

public override void OnReceiveData(TcpLib.ConnectionState state)
{
    if (state.fileTransfer == true && state.waitingFor > 0)
    {
        byte[] buffer = new byte[state.AvailableData];
        int readBytes = state.Read(buffer, 0, state.AvailableData);
        state.waitingFor -= readBytes;
        state.bw.Write(buffer);
        state.bw.Flush();

        if (state.waitingFor == 0)
        {
            state.bw.Close();
            state.hFile.Close();
            state.fileTransfer = false;
            IPEndPoint ip = state.RemoteEndPoint as IPEndPoint;
            Program.MainForm.log("Ended file transfer with " + ip);
        }
    }
    else if( state.AvailableData > 7)
    {          
        byte[] buffer = new byte[8];
        int readBytes = state.Read(buffer, 0, 8);
        if (readBytes == 8)
        {
            Packet packet = ByteArrayToStructure<Packet>(buffer);
            if (packet.PacketType == PACKET_FILETRANSFER_INITIATE)
            {
                IPEndPoint ip = state.RemoteEndPoint as IPEndPoint;
                String filename = getUniqueFileName("" + ip.Address);
                if (filename == null)
                {
                    Program.MainForm.log("Error getting filename for " + ip);

                    state.EndConnection();
                    return;
                }

                byte[] data = new byte[state.AvailableData];
                readBytes = state.Read(data, 0, state.AvailableData);

                state.waitingFor = packet.DataSize - readBytes;
                state.hFile = new FileStream(filename, FileMode.Append);
                state.bw = new BinaryWriter(state.hFile);
                state.bw.Write(data);
                state.bw.Flush();
                state.fileTransfer = true;
                Program.MainForm.log("Initiated file transfer with " + ip);
            }
        }
    }
}

它接收所有数据，当我调试我的代码并看到send()没有返回总数据大小（即它必须被多次调用）并且图像得到黄线或紫线它 - 我怀疑发送数据有问题。

Answer 1

我误解了问题和解决方案的意图。感谢@Remy Lebeau澄清这一点。在此基础上，您可以编写http://beej.us/guide/bgnet/output/print/bgnet_USLetter.pdf

第7.3节中给出的sendall()函数

int sendall(int s, char *buf, int *len)
{
    int total = 0; // how many bytes we've sent
    int bytesleft = *len; // how many we have left to send
    int n = 0;
    while(total < *len) {
       n = send(s, buf+total, bytesleft, 0);
       if (n == -1) { 
           /* print/log error details */
           break;
       }
       total += n;
       bytesleft -= n;
    }
    *len = total; // return number actually sent here
    return n==-1?-1:0; // return -1 on failure, 0 on success
}

Answer 2

您需要检查send（）的返回值。特别是，您不能简单地假设它是发送的字节数，还有一个错误的情况。试试这个：

while(datasize != 0)
{
    n = send(...);
    if(n == SOCKET_ERROR)
        throw exception("send() failed with errorcode #" + to_string(WSAGetLastEror()));
    // adjust pointer and remaining number of bytes
    datasize -= n;
    data += n;
}

顺便说一句：

制作BYTE const* data，你不会修改它指向的内容。
你的代码的其余部分似乎太复杂了，特别是你没有通过与像512这样的幻数对齐来解决问题。

如何通过套接字发送所有数据？

2 个答案: