Question

So I keep bouncing between named and anonymous pipes and here is my issue. I tried named pipes and they just didn’t seem to work properly for what I wanted, so I’m back to anonymous pipes. However, the anonymous pipe needs to read input from a pipe (to a program that I did not create) and continuously read it as more information is available to the pipe. Here is the relevant code which I currently have:

void Arc_Redirect::createProcesses()
{
    TCHAR programName[]=TEXT("program.exe");
    PROCESS_INFORMATION pi; 
    STARTUPINFO si;

    SECURITY_ATTRIBUTES sa;
    sa.nLength = sizeof(SECURITY_ATTRIBUTES);
    sa.bInheritHandle = TRUE;
    sa.lpSecurityDescriptor = NULL;

    if(!CreatePipe(&outStd[0].hOutRead,&outStd[0].hOutWrite,&sa,0) || !CreatePipe(&outStd[0].hInRead,&outStd[0].hInWrite,&sa,0))
        throw "Error: Could not CreatePipe();!";

    if(!SetHandleInformation(outStd[0].hOutRead,HANDLE_FLAG_INHERIT,0) || !SetHandleInformation(outStd[0].hInWrite,HANDLE_FLAG_INHERIT,0))
        throw "Error: Could not SetHandleInformation();";


    // Set stuff up
    ZeroMemory(&pi, sizeof(PROCESS_INFORMATION));
    ZeroMemory(&si, sizeof(STARTUPINFO));
    si.cb = sizeof(STARTUPINFO); 
    si.hStdError = outStd[0].hOutWrite;
    si.hStdOutput = outStd[0].hOutWrite;
    si.hStdInput = outStd[0].hInRead;
    si.dwFlags = STARTF_USESHOWWINDOW|STARTF_USESTDHANDLES;

    outStd[0].o1.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);

    if(!CreateProcess(programName,NULL,NULL,NULL,TRUE,0,NULL,NULL,&si,&pi))
        throw "Error: Could not start Program!";

    // Cleanup the useless handles
    if(!CloseHandle(pi.hThread) || !CloseHandle(pi.hProcess))
        throw "Error: Could not CloseHandle();";
}

And here is how I am reading the pipe:

void Arc_Redirect::readPipe()
{
    CHAR chBuf[BUFSIZE];
    DWORD dwRead;

    ReadFile(outStd[0].hOutRead,chBuf,sizeof(chBuf),&dwRead,&outStd[0].o1);
    chBuf[dwRead] = '\0';
    SetDlgItemText(global,IDO_WORLDOUT,chBuf);
    ResetEvent(outStd[0].o1.hEvent);

}

BUFSIZE is defined at 0x1000 and outStd is defined as PIPE_HANDLES (struct below)

typedef struct
{
    HANDLE hOutRead;
    HANDLE hOutWrite;
    HANDLE hInRead;
    HANDLE hInWrite;
    OVERLAPPED o1;
    TCHAR chReq[BUFSIZE];
    TCHAR chReply[BUFSIZE];
    DWORD dwRead;
    DWORD dwWritten;
    DWORD dwState;
    DWORD cbRet;
    BOOL pendingIO;
} PIPE_HANDLES, *LPSTDPIPE;

Now, I can properly call readPipe(); once and it does exactly what I want. However, if I try to call it again, it fails. Any ideas on how I can fix this issue? Like I said, I need to keep the connection open and read incrementally. For sake of argument, say I need to read every 5 secs; the program I am reading from will have different output every 5 secs that needs to be read. Any help?

Regards,
Dennis M.

Answer 1

It is impossible to guess why it fails if you don’t find out why. ReadFile returns FALSE when it fails. You should then call GetLastError() to get a diagnostic.

Never ignore Windows API return values. At the very least assert them.