can a windows service run a TCP server? - c++

Question

I created 2 programs in c++ using visual studio 2008: a windows service based on this service which i added tcp server code to and a client program using MFC, which has a listbox that displays the ip address and hostname of the computer thats running the service. The user then chooses a server and clicks a connect button. Since there will be many servers running, I used some PHP script on a web host site. The service sends its ip address and host name to the web host, the web host puts the information into a list and the client then accesses this list.
all this works fine with the server code but when i put the server code into the windows service, the client program freezes and doesn't respond when the connect button is clicked. The ip address and host name still appear in the client listbox, i just can't connect to the server i select.
is the windows service stopping the server code from working?
here is the cpp file that contains the server code in the service program:
char* WebPost(char Website[], char Webpage[], char Request[], int RetLen)
{
// Sends an HTTP Post request with POST Data...
SOCKET WebSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
struct hostent *WebHost;
WebHost = gethostbyname(Website);
if (WebHost == NULL)
{
if (WSAGetLastError() == WSANOTINITIALISED)
printf("Error Not Connected!");
else
printf("Error: %d", WSAGetLastError());
Sleep(1000);
exit(0);
}
SOCKADDR_IN SockAddr;
SockAddr.sin_port = htons(80);
SockAddr.sin_family = AF_INET;
SockAddr.sin_addr.s_addr = *((unsigned long*)WebHost->h_addr);
connect(WebSocket, (SOCKADDR*)(&SockAddr), sizeof(SockAddr));
char PostRequest[1024];
sprintf(PostRequest,
"POST %s HTTP/1.1\r\n"
"Host: %s\r\n"
"Content-Length: %hu\r\n"
"Content-Type: application/x-www-form-urlencoded\r\n"
"\r\nD=%s\0",
Webpage, Website,
strlen(Request)+2, Request
);
send(WebSocket, PostRequest, strlen(PostRequest), 0);
// Get return data
char* Data = new char[RetLen];
recv(WebSocket, Data, 4, 0);
for (;;)
{ // Skip HTTP headers
Data[0] = Data[1];
Data[1] = Data[2];
Data[2] = Data[3];
recv(WebSocket, &Data[3], 1, 0);
if (Data[0] == '\r' && Data[1] == '\n'
&& Data[2] == '\r' && Data[3] == '\n')
break;
}
int DataLen = recv(WebSocket, Data, RetLen, 0);
Data[DataLen] = '\0'; // Return the data
shutdown(WebSocket, 2);
closesocket(WebSocket);
return Data;
}
void ServStart()
{
WSADATA wsaData;
if (WSAStartup(MAKEWORD(2,2), &wsaData) != 0)
{
printf("WSAStartup failed with error %ld.\n", WSAGetLastError());
exit(0);
}
if (LOBYTE(wsaData.wVersion) != 2 || HIBYTE(wsaData.wVersion) != 2)
{
printf("The dll do not support the Winsock version %u.%u!\n", LOBYTE(wsaData.wVersion),HIBYTE(wsaData.wVersion));
WSACleanup();
exit(0);
}
//Start listening
ListeningSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
if (ListeningSocket == INVALID_SOCKET)
{
printf("Error at socket, error code: %ld.\n", WSAGetLastError());
WSACleanup();
exit(0);
}
ServerAddr.sin_family = AF_INET;
ServerAddr.sin_port = htons(Port);
ServerAddr.sin_addr.s_addr = htonl(INADDR_ANY);
if (bind(ListeningSocket, (SOCKADDR *)&ServerAddr, sizeof(ServerAddr)) == SOCKET_ERROR)
{
printf("bind failed. Error code: %ld.\n", WSAGetLastError());
closesocket(ListeningSocket);
WSACleanup();
exit(0);
}
if (listen(ListeningSocket, 5) == SOCKET_ERROR)
{
printf("listen: Error listening on socket %ld.\n", WSAGetLastError());
closesocket(ListeningSocket);
WSACleanup();
exit(0);
}
char ac[80];
if (gethostname(ac, sizeof(ac)) == SOCKET_ERROR)
{
printf("Error when getting local host name: ", WSAGetLastError());
exit(0);
}
struct hostent *phe = gethostbyname(ac);
if (phe == 0)
{
printf("Error: ", WSAGetLastError());
exit(0);
}
struct in_addr addr;
memcpy(&addr, phe->h_addr_list[0], sizeof(struct in_addr)); // use the first ip-address
printf("IP used by Server: %s\n", inet_ntoa(addr)); // inet_ntoa(addr) provides the local address.
MyIP = inet_ntoa(addr);
char SendBuf[32];
// * is used as a separator, because it's not allowed in the hostname.
//So it won't interfere with it.
sprintf(SendBuf, "%hhu|%s*%s", cAddIP, MyIP, ac); // Send the server the IP and host name
WebPost(WEBSITE, WEBPAGE, SendBuf, 0);
printf("listening for connections...\n\n");
}
void ShutDown() // Shut down the server (tells the web server I am offline)
{
char SendBuf[32]; // Remove my IP from the list of online servers...
char ac[80];
if (gethostname(ac, sizeof(ac)) == SOCKET_ERROR)
{
printf("Error when getting local host name: ", WSAGetLastError());
exit(0);
}
sprintf(SendBuf, "%hhu|%s*%s", cRemIP, MyIP,ac);
WebPost(WEBSITE, WEBPAGE, SendBuf, 0);
printf("Successful shutdown\n");
Sleep(1000);
WSACleanup();
}
void ServLoop()
{
SOCKADDR_IN SenderInfo;
SOCKET NewConnection;
int ByteReceived, nlen;
char recvbuff[1024];
for (;;)
{
//Main program loop
NewConnection = SOCKET_ERROR;
while(NewConnection == SOCKET_ERROR)
{
NewConnection = accept(ListeningSocket, NULL, NULL); // this is a blocking function
printf("New client got connected, ready to receive and send data...\n\n");
ByteReceived = recv(NewConnection, recvbuff, sizeof(recvbuff), 0);
if (ByteReceived > 0)
{
getsockname(ListeningSocket, (SOCKADDR *)&ServerAddr, (int *)sizeof(ServerAddr));
memset(&SenderInfo, 0, sizeof(SenderInfo));
nlen = sizeof(SenderInfo);
getpeername(NewConnection, (SOCKADDR *)&SenderInfo, &nlen);
}
}
if (shutdown(NewConnection, 2) != 0)
printf("there is something wrong with the shutdown. The error code: %ld\n", WSAGetLastError());
else
printf("shutdown is working...\n");
}
}
// --------------------------------------------
BOOL ConsoleProc(DWORD Msg)
{
switch (Msg)
{
case CTRL_CLOSE_EVENT:
case CTRL_LOGOFF_EVENT:
case CTRL_SHUTDOWN_EVENT:
ShutDown();
return false;
}
return false;
}
// -----------------------------------------------------
CSampleService::CSampleService(PWSTR pszServiceName,
BOOL fCanStop,
BOOL fCanShutdown,
BOOL fCanPauseContinue) :
CServiceBase(pszServiceName, fCanStop, fCanShutdown, fCanPauseContinue),
m_dwTimeout(10 * 1000)
{
// Create a manual-reset event that is not signaled at first to indicate
// the service is stopping.
m_hStoppingEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
if (m_hStoppedEvent == NULL)
{
throw GetLastError();
}
// Create a manual-reset event that is not signaled at first to indicate
// the stopped signal of the service.
m_hStoppedEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
if (m_hStoppedEvent == NULL)
{
throw GetLastError();
}
}
CSampleService::~CSampleService(void)
{
if (m_hStoppedEvent)
{
CloseHandle(m_hStoppedEvent);
m_hStoppedEvent = NULL;
}
if (m_hStoppingEvent)
{
CloseHandle(m_hStoppingEvent);
m_hStoppingEvent = NULL;
}
}
void CSampleService::OnStart(DWORD dwArgc, LPWSTR *lpszArgv)
{
WriteErrorLogEntry(L"CSampleService::Start: function entry");
// Log a service start message to the Application log.
WriteEventLogEntry(L"CppWindowsService in OnStart", EVENTLOG_INFORMATION_TYPE);
// Queue the main service function for execution in a worker thread.
CThreadPool::QueueUserWorkItem(&CSampleService::ServiceWorkerThread, this);
WriteErrorLogEntry(L"CSampleService::Start: function exit");
}
void CSampleService::ServiceWorkerThread(void)
{
WriteErrorLogEntry(L"CSampleService::ServiceWorkerThread: running");
// Periodically check if the service is stopping.
while (WaitForSingleObject(m_hStoppingEvent, m_dwTimeout) == WAIT_TIMEOUT)
{
// Perform main service function here...
// Handle console events
SetConsoleCtrlHandler((PHANDLER_ROUTINE)ConsoleProc, TRUE);
ServStart(); // Main loop is in another thread
ServLoop(); // The never returning server loop
}
// Signal the stopped event.
SetEvent(m_hStoppedEvent);
WriteErrorLogEntry(L"CSampleService::ServiceWorkerThread: done");
}
void CSampleService::OnStop()
{
ShutDown(); //shut down server
SetServiceStatus(SERVICE_STOP_PENDING, ERROR_SUCCESS, 30 * 1000);
WriteErrorLogEntry(L"CSampleService::Stop: function entry");
// Log a service stop message to the Application log.
WriteEventLogEntry(L"CppWindowsService in OnStop", EVENTLOG_INFORMATION_TYPE);
// Indicate that the service is stopping and wait for the finish of the
// main service function (ServiceWorkerThread).
SetEvent(m_hStoppingEvent);
if (WaitForSingleObject(m_hStoppedEvent, INFINITE) != WAIT_OBJECT_0)
{
SetServiceStatus(SERVICE_STOP_PENDING, ERROR_INVALID_DATA, 30 * 1000);
WriteErrorLogEntry(L"OnStop: Service Start", GetLastError());
throw GetLastError();
}
WriteErrorLogEntry(L"CSampleService::Stop: function exit");
}

Answer 1

The answer to your specific question is, yes, a windows service can run a TCP server.
The answer to why yours does not work is not clear. At first glance the service code looks reasonable. It's possible connections to your service are being blocked by your OS firewall (i.e. your console one is in the accept list but your service one is not). You might convert some of your error printf logic into something that prints to a file instead (e.g. fprintf?) so you can take a look at what's going on...

Answer 2

Sure, of course it can. Why would it not be possible?