Redirecting Input/Output of New Process

From:

=?Utf-8?B?TWF0dA==?= <Matt@discussions.microsoft.com>

Newsgroups:

microsoft.public.vc.language

Date:

Wed, 12 Mar 2008 19:17:00 -0700

Message-ID:

<A5781D74-23D3-4C1F-8260-48E26F7AD2BD@microsoft.com>

I've done some searching around for the past few days and I'm trying to be
able to spawn a process, send some information to its standard input, and
read from its standard output.

I think I'm really close, and I understand that I need to create pipes and
then pass them to the startup info structure given to CreateProcess(), but
something isn't quite right.

I can't tell if sending information to stdin (from my program to the client
process) is working, but it doesn't block, which is partially a good sign.

What I CAN tell is that recieving information from stdout (from the client
program to my program) isn't doing anything. When I do ReadFile(), even for
one byte, on the stdout stream, it blocks indefinitely. The program SHOULD
have at least output its header, so something doesn't seem quite right here.

This is my code for redirecting the outputs:

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

    HANDLE outStream, inStream, childOutStream, childInStream;
    HANDLE self = GetCurrentProcess();

    PROCESS_INFORMATION *pi = new PROCESS_INFORMATION;

    // Create our input/output pipes
    try
    {
        // create stdout
        HANDLE tmp;
        if (!CreatePipe(&tmp, &childOutStream, &saAttr, 0))
            throw (unsigned int)1;
        if (!DuplicateHandle(self, tmp, self, &outStream, 0, FALSE,
DUPLICATE_SAME_ACCESS))
            throw (unsigned int)1;

        // Close the original version
        CloseHandle(tmp);

        // create stdin
        if (!CreatePipe(&childInStream, &tmp, &saAttr, 0))
            throw (unsigned int) 1;
        if (!DuplicateHandle(self, tmp, self, &inStream, 0, FALSE,
DUPLICATE_SAME_ACCESS))
            throw (unsigned int) 1;

        // Close the original
        CloseHandle(tmp);
    }
    catch(...)
    {
        CloseHandle(inStream);
        CloseHandle(outStream);
        CloseHandle(childOutStream);
        CloseHandle(childInStream);
        throw;
    }


    // Build the startup info
    STARTUPINFOA siInfo;
    ZeroMemory(&siInfo, sizeof(siInfo)); // cheap trick since most
of it is zero...
    siInfo.cb = sizeof(siInfo);
    siInfo.dwFlags = STARTF_USESTDHANDLES | // use our new stdin/stdout
                     STARTF_USESHOWWINDOW; // Do not create a new
console window (hide it)
    siInfo.hStdInput = inStream;
    siInfo.hStdOutput = outStream;
    siInfo.hStdError = GetStdHandle(STD_ERROR_HANDLE);

    char* str = new char[strlen(exe)+2+5+1];
    sprintf(str, "\"%s\" -int", exe);


    // Execute!
    if (!CreateProcessA(NULL, str, NULL, NULL, TRUE, 0, NULL, NULL, &siInfo,
pi))
    {
        delete[] str;
        CloseHandle(inStream);
        CloseHandle(outStream);
        CloseHandle(childOutStream);
        CloseHandle(childInStream);
        throw (unsigned int)-1;
    }

Everything seems to go as planned, but when I execute...
char buf[1];
if (!ReadFile(outStream, buf, 1, &nBytes, NULL))
            throw GetLastError();

It just sits there forever.

I'm sure this is just something extremely trivial I'm missing. Any ideas?

Thanks,
-- Matt