我正在创建一个客户端程序，该程序与通过 LAN 连接到我的 PC 的设备进行通信。
我的程序和设备之间的典型通信如下：
Program -> Device 1616000D 08 02 00 00 00 21 11 A1 00 01 22 08 00 // Sender sends data (a specific command to the device) to Receiver
Program <- Device 16160002 80 00 // Receiver sends ACK to sender
Program <- Device 16160005 08 20 00 00 00 // Receiver sends command response to sender
Program -> Device 16160002 80 00 // Sender sends ACK to receiver
第一个字节序列的最后一个十六进制数字表示后面的数据大小（D = 13 字节）。
我的发送例程如下所示：
bool TcpConnection::SendCommand(const Command& rCommand, const std::vector<BYTE>& rvecCommandOptions)
{
std::vector<BYTE> vecCommandData;
m_commandBuilder.BuildCommand(rCommand, rvecCommandOptions, vecCommandData);
if (vecCommandData.empty())
return false;
PerIoData *pPerIoData = new PerIoData;
if (!pPerIoData)
return false;
SecureZeroMemory(&(pPerIoData->m_overlapped), sizeof(WSAOVERLAPPED));
pPerIoData->m_socket = m_socket.Get();
pPerIoData->m_overlapped.hEvent = WSACreateEvent();
pPerIoData->m_vecBuffer.assign(vecCommandData.begin(), vecCommandData.end());
pPerIoData->m_wsaBuf.buf = (CHAR*)(&(pPerIoData->m_vecBuffer[0]));
pPerIoData->m_wsaBuf.len = pPerIoData->m_vecBuffer.size();
pPerIoData->m_dwFlags = 0;
pPerIoData->m_dwNumberOfBytesSent = 0;
pPerIoData->m_dwNumberOfBytesToSend = pPerIoData->m_wsaBuf.len;
pPerIoData->m_operationType = OP_TYPE_SEND;
if (!m_socket.Send(pPerIoData))
return false;
return true;
}
我的工作线程例程看起来像：
DWORD WINAPI TcpConnection::WorkerThread(LPVOID lpParameter)
{
HANDLE hCompletionPort = (HANDLE)lpParameter;
DWORD dwNumberOfBytesTransferred;
ULONG ulCompletionKey;
PerIoData *pPerIoData;
DWORD dwNumberOfBytesReceived;
DWORD dwNumberOfBytesSent;
DWORD dwFlags;
while (GetQueuedCompletionStatus(hCompletionPort, &dwNumberOfBytesTransferred, &ulCompletionKey, (LPOVERLAPPED*)&pPerIoData, INFINITE))
{
if (!pPerIoData)
continue;
if ((dwNumberOfBytesTransferred == 0) && ((pPerIoData->m_operationType == OP_TYPE_SEND) || (pPerIoData->m_operationType == OP_TYPE_RECEIVE)))
{
closesocket(pPerIoData->m_socket);
delete pPerIoData;
continue;
}
if (pPerIoData->m_operationType == OP_TYPE_SEND)
{
pPerIoData->m_dwNumberOfBytesSent += dwNumberOfBytesTransferred;
if (pPerIoData->m_dwNumberOfBytesSent < pPerIoData->m_dwNumberOfBytesToSend)
{
pPerIoData->m_wsaBuf.buf = (CHAR*)(&(pPerIoData->m_vecBuffer[pPerIoData->m_dwNumberOfBytesSent]));
pPerIoData->m_wsaBuf.len = (pPerIoData->m_dwNumberOfBytesToSend - pPerIoData->m_dwNumberOfBytesSent);
if (WSASend(pPerIoData->m_socket, &(pPerIoData->m_wsaBuf), 1, &dwNumberOfBytesTransferred, 0, &(pPerIoData->m_overlapped), NULL) == 0)
continue;
if (WSAGetLastError() == WSA_IO_PENDING)
continue;
}
else if (pPerIoData->m_dwNumberOfBytesSent == pPerIoData->m_dwNumberOfBytesToSend)
{
delete pPerIoData;
}
// Q1. Do I create a new instance of PerIoData here before calling WSARecv() or reuse pPerIoData?
// QA. If I did do "PerIoData pPerIoData = new PerIoData" here, how do I handle if this momory allocation request has failed? Should I simply "continue" or "return -1"?
// QB. Or is this a wrong place to do this memory allocation to achive the typical communication between my program and the device?
SecureZeroMemory(&(pPerIoData->m_overlapped), sizeof(WSAOVERLAPPED));
pPerIoData->m_overlapped.hEvent = WSACreateEvent();
pPerIoData->m_wsaBuf.buf = (CHAR*)(&(pPerIoData->m_vecBuffer[0]));
pPerIoData->m_wsaBuf.len = pPerIoData->m_vecBuffer.size();
pPerIoData->m_operationType = OP_TYPE_RECEIVE;
if (WSARecv(pPerIoData->m_socket, &(pPerIoData->m_wsaBuf), 1, &dwNumberOfBytesReceived, &(pPerIoData->m_dwFlags), &(pPerIoData->m_overlapped), NULL) == 0)
continue;
if (WSAGetLastError() == WSA_IO_PENDING)
continue;
}
else if (pPerIoData->m_operationType == OP_TYPE_RECEIVE)
{
if ((pPerIoData->m_vecBuffer[0] == 0x16) && (pPerIoData->m_vecBuffer[1] == 0x16))
{
// Q2. Do I need to do SecureZeroMemory(&(pPerIoData->m_overlapped), sizeof(WSAOVERLAPPED)); here?
// Q3. Or do I new PerIoData?
pPerIoData->m_wsaBuf.buf = (CHAR*)(&(pPerIoData->m_vecBuffer[0]));
pPerIoData->m_wsaBuf.len = pPerIoData->m_vecBuffer.size();
pPerIoData->m_operationType = OP_TYPE_RECEIVE;
// QC. At this point two syn bytes (0x16) are received. I now need to receive two more bytes of data (000D = 13 bytes) to find out the size of the actual command response data.
// If I clear my m_vecBuffer here and try to resize its size to two, I get this debug assertion: "vector iterators incompatible" at runtime. Do you know how I can fix this problem?
if (WSARecv(pPerIoData->m_socket, &(pPerIoData->m_wsaBuf), 1, &dwNumberOfBytesReceived, &(pPerIoData->m_dwFlags), &(pPerIoData->m_overlapped), NULL) == 0)
continue;
if (WSAGetLastError() == WSA_IO_PENDING)
continue;
}
// QD. I'm not sure how to structure this if clause for when m_operationType is OP_TYPE_RECEIVE. I mean how do I distinguish one receive operation for getting two syn bytes from another for getting data size?
// One way I can think of doing is to create more receive operation types such as OP_TYPE_RECEIVE_DATA_SIZE or OP_TYPE_RECEIVE_DATA? So you can have something like below.
// Is this how you would do it?
}
//else if (pPerIoData->m_operationType == OP_TYPE_RECEIVE_DATA_SIZE)
//{
// Call WSARecv() again to get command response data
//}
}
return 0;
}
请在上面的代码中查看我的问题。
非常感谢