CODEWITHSUNDEEP
c++windowswinapicreateprocess
OmerR
OmerR

Reputation: 59

CreateProcess with 2 redirected pipes return exitcode 1

I'm new to WIN32 API and could use some help figuring what am I missing in my code. My goal is to run a batch script (or PowerShell script), wait for completion, and then get the stdout / stderr upon completion.

Following this and this article on msdn about creating a process and redirecting stdout and stderr to a handle. I mashed the samples together and came up with the following code:

int execute_commnad(std::string& command,std::string& output,int& timeout_seconds) {
    STARTUPINFO si;
    PROCESS_INFORMATION pi;
    DWORD return_code = NULL;

    ZeroMemory(&pi, sizeof(pi));

    ZeroMemory(&si,sizeof(si));
    si.cb = sizeof(si);
    si.hStdOutput = child_stdout_handle;
    si.hStdError = child_stdout_handle;
    si.dwFlags |= STARTF_USESTDHANDLES;

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

    // Connect Child stdout to parent_stdout_handle
    if (!CreatePipe(&parent_stdout_handle,&child_stdout_handle,&saAttr,0))
    {
        output = "Could not create stdout pipe. Error: " + std::to_string(GetLastError());
        close_handles();
        return -1;
    }

    if (! SetHandleInformation(parent_stdout_handle,HANDLE_FLAG_INHERIT,0))
    {
        output = "Could not set handle information for stdout pipe. Error: " + std::to_string(GetLastError());
        close_handles();
        return -1;
    }

    // Create Process
    if (!CreateProcess(NULL,LPSTR(command.c_str()),NULL,NULL,TRUE,0,NULL,NULL,&si,&pi)) {
        output = "Failed to create process. Error: " + std::to_string(GetLastError());
        close_handles();
        return -1;
    }
    CloseHandle(child_stdout_handle);


    // Wait for process to finish or timeout
    if (timeout_seconds == NULL) {
        WaitForSingleObject(pi.hProcess,INFINITE);
    }
    else {
        WaitForSingleObject(pi.hProcess,DWORD(timeout_seconds * 1000));
    }
    
    if (!GetExitCodeProcess(pi.hProcess,&return_code)) {
        output = "Failed to fetch exit code";
        close_handles();
        return -1;
    }
    
    if (STILL_ACTIVE == return_code) {
        TerminateProcess(sub_process,return_code);
        output = "Command did not finish within defined timeout threshold";
    }
    else if (STATUS_PENDING == return_code) {
        output = "process is pending";
    }
    else {
        DWORD dwRead;
        CHAR chBuf[4096];
        BOOL bSuccess = FALSE;

        for (;;) {
            bSuccess = ReadFile(parent_stdout_handle,chBuf,4096,&dwRead,NULL);
            if (! bSuccess || dwRead == 0) break;
            output = *reinterpret_cast<std::string*>(parent_stdout_handle);
        }
    }
    
    close_handles();
    return 0;    
};


void close_handles(void) {
    CloseHandle(parent_stdout_handle);
    CloseHandle(child_stdout_handle);
    CloseHandle(sub_process);
};

Before executing the function above I create the .bat file using std::ofstream containing "echo hello" and save the FQN of the file into variable named file_name and run the following code:

int rc = 0;
std::string cmd = "cmd.exe /c " + file_name + " " + script_params;
rc = execute_commnad(cmd,this->output,timeout_in_seconds);

When debugging these are the values I get after GetExitCodeProcess:

I have tried replacing cmd.exe with the FQN, but same result, tried running something as simple as cmd.exe /c "echo hello" and still returned return_code 1.

I've been struggling for the last 2 days in finding the reason for it, but to no avail.

Aside for the ineffective code (performance-wise) does anyone has a suggestion to what might be the problem?

Thanks in advance!

Upvotes: 0

Views: 478

Answers (1)

Drake Wu
Drake Wu

Reputation: 7170

Make sure to initialize the child_stdout_handle before passing the handle to CreateProcess.

In addition, you need to print the value of chBuf you read in ReadFile, instead of parent_stdout_handle. Converting file handle to string is meaningless, you could try:

    for (;;) {
        bSuccess = ReadFile(parent_stdout_handle, chBuf, 4096, &dwRead, NULL);
        if (!bSuccess || dwRead == 0) break;
        chBuf[dwRead] = '\0';
        output += chBuf;
    }
    cout << output << endl;

Upvotes: 2

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