I'm coding a WinAPI GUI program that needs calling ftp and possibly other console programs while getting their console output to act accordingly ie. waiting for ftp to complete execution before reading all its output wouldn't do.
My current approach is calling CreateProcess() to create a cmd.exe process potentially hiding the ugly console window, AttachConsole() to make it my own, GetStdHandle() to get input and output handles, SetConsoleCursorPosition() to the end of the console buffer, and WriteConsole() with commands such as ftp\n or dir\n. Yet this commands are written but not executed. However, I can manually use the same console ( using CreateProcess() with CREATE_NEW_CONSOLE flag ) to type ftp press enter and get it executed.
Previous approaches involved:
Calling ftp directly with CreateProcess() and redirected inputs/outputs.
Couldn't get ftp output until the CreateProcess() process had already ended.
Using system().
Was advised against its usage before getting any output.
My current stripped down code:
// Next two structures might be a bit misleading, they were used for the 1. previous
// approach
PROCESS_INFORMATION piProcInfo;
ZeroMemory( &piProcInfo, sizeof(PROCESS_INFORMATION));
STARTUPINFO siStartInfo;
ZeroMemory( &siStartInfo, sizeof(STARTUPINFO) );
siStartInfo.cb = sizeof(STARTUPINFO);
siStartInfo.hStdError = g_hChildStd_OUT_Wr;
siStartInfo.hStdOutput = g_hChildStd_OUT_Wr;
siStartInfo.hStdInput = g_hChildStd_IN_Rd;
siStartInfo.dwFlags |= STARTF_USESTDHANDLES;
SECURITY_ATTRIBUTES security;
security.nLength = sizeof(SECURITY_ATTRIBUTES);
security.lpSecurityDescriptor = NULL;
security.bInheritHandle = FALSE;
CreateProcess( NULL, "cmd", &security, &security, FALSE, NORMAL_PRIORITY_CLASS |
CREATE_NEW_CONSOLE, NULL, NULL, &siStartInfo, &piProcInfo);
uint32_t pidConsole = piProcInfo.dwProcessId;
while ( ! AttachConsole(pidConsole) ){};
HANDLE myConsoleIn, myConsoleOut;
myConsoleIn = GetStdHandle(STD_INPUT_HANDLE);
myConsoleOut = GetStdHandle(STD_OUTPUT_HANDLE);
Sleep(100);
CONSOLE_SCREEN_BUFFER_INFO myConsoleCursorInformation = {};
GetConsoleScreenBufferInfo(myConsoleOut,&myConsoleCursorInformation);
SetConsoleCursorPosition(myConsoleOut,myConsoleCursorInformation.dwSize);
CHAR myConsoleBuffer[200]="dir\n";
DWORD myConsoleProcessed;
WriteConsole( myConsoleOut, myConsoleBuffer, 4, &myConsoleProcessed, NULL);
How can I get a command written in the console to execute? Is there an alternative to my attempt of ending commands with a trailing \n ie. using WriteConsole() with a dir\n or ftp\n argument.
I thought about sending a keypress to the process in question after typing the desired command. Yet the created console needs not only to manually press the enter key but also having dir, ftp or whatever command to be manually typed.
Please feel free to point out any missing information !
How can I get a command written in the console to execute? Is there an
alternative to my attempt of ending commands with a trailing \n ie.
using WriteConsole() with a dir\n or ftp\n argument.
Try the following code to see if it works:
STARTUPINFO si;
PROCESS_INFORMATION pi;
ZeroMemory(&si, sizeof(si));
si.cb = sizeof(si);
ZeroMemory(&pi, sizeof(pi));
const wchar_t *cmdPath = L"C:\\Windows\\System32\\cmd.exe";
wchar_t *cmdArgs = (wchar_t *)L"C:\\Windows\\System32\\cmd.exe /k dir";
BOOL result = CreateProcess(cmdPath, cmdArgs, NULL, NULL, FALSE, 0, NULL, NULL, &si, &pi);
DWORD errCode = GetLastError();
if (!result)
{
std::cout << "Create Process failed: " << GetLastError() << std::endl;
}
/K Run Command and then return to the CMD prompt.
This is useful for testing, to examine variables
Use /C if you want "Run Command and then terminate".
Update: Complete code for communicating with a child process(cmd.exe) using pipes.
HANDLE g_hChildStd_IN_Rd = NULL;
HANDLE g_hChildStd_IN_Wr = NULL;
HANDLE g_hChildStd_OUT_Rd = NULL;
HANDLE g_hChildStd_OUT_Wr = NULL;
#define BUFSIZE 1024
void ErrorExit(LPCTSTR lpszFunction)
{
LPVOID lpMsgBuf;
LPVOID lpDisplayBuf;
DWORD dw = GetLastError();
FormatMessage(
FORMAT_MESSAGE_ALLOCATE_BUFFER |
FORMAT_MESSAGE_FROM_SYSTEM |
FORMAT_MESSAGE_IGNORE_INSERTS,
NULL,
dw,
MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
(LPTSTR)&lpMsgBuf,
0, NULL);
lpDisplayBuf = (LPVOID)LocalAlloc(LMEM_ZEROINIT,
(lstrlen((LPCTSTR)lpMsgBuf) + lstrlen((LPCTSTR)lpszFunction) + 40) * sizeof(TCHAR));
StringCchPrintf((LPTSTR)lpDisplayBuf,
LocalSize(lpDisplayBuf) / sizeof(TCHAR),
TEXT("%s failed with error %d: %s"),
lpszFunction, dw, lpMsgBuf);
MessageBox(NULL, (LPCTSTR)lpDisplayBuf, TEXT("Error"), MB_OK);
LocalFree(lpMsgBuf);
LocalFree(lpDisplayBuf);
ExitProcess(1);
}
void ReadFromPipe(void)
{
DWORD dwRead, dwWritten;
CHAR chBuf[BUFSIZE];
BOOL bSuccess = FALSE;
HANDLE hParentStdOut = GetStdHandle(STD_OUTPUT_HANDLE);
for (;;)
{
DWORD bytesAvail = 0;
if (!PeekNamedPipe(g_hChildStd_OUT_Rd, NULL, 0, NULL, &bytesAvail, NULL)) {
std::cout << "Failed to call PeekNamedPipe" << std::endl;
}
if (bytesAvail) {
DWORD n;
BOOL success = ReadFile(g_hChildStd_OUT_Rd, chBuf, BUFSIZE, &n, NULL);
if (!success || n == 0) {
}
bSuccess = WriteFile(hParentStdOut, chBuf,n, &dwWritten, NULL);
}
else
{
break;
}
}
}
void WriteToPipe(void)
{
DWORD dwWritten;
BOOL bSuccess = FALSE;
CHAR buf[] = "dir\n";
bSuccess = WriteFile(g_hChildStd_IN_Wr, buf, sizeof(buf)-1, &dwWritten, NULL);
}
int main()
{
STARTUPINFO si;
PROCESS_INFORMATION pi;
SECURITY_ATTRIBUTES saAttr;
printf("\n->Start of parent execution.\n");
// Set the bInheritHandle flag so pipe handles are inherited.
saAttr.nLength = sizeof(SECURITY_ATTRIBUTES);
saAttr.bInheritHandle = TRUE;
saAttr.lpSecurityDescriptor = NULL;
// Create a pipe for the child process's STDOUT.
if (!CreatePipe(&g_hChildStd_OUT_Rd, &g_hChildStd_OUT_Wr, &saAttr, 0))
ErrorExit(TEXT("StdoutRd CreatePipe"));
// Ensure the read handle to the pipe for STDOUT is not inherited.
if (!SetHandleInformation(g_hChildStd_OUT_Rd, HANDLE_FLAG_INHERIT, 0))
ErrorExit(TEXT("Stdout SetHandleInformation"));
// Create a pipe for the child process's STDIN.
if (!CreatePipe(&g_hChildStd_IN_Rd, &g_hChildStd_IN_Wr, &saAttr, 0))
ErrorExit(TEXT("Stdin CreatePipe"));
// Ensure the write handle to the pipe for STDIN is not inherited.
if (!SetHandleInformation(g_hChildStd_IN_Wr, HANDLE_FLAG_INHERIT, 0))
ErrorExit(TEXT("Stdin SetHandleInformation"));
ZeroMemory(&si, sizeof(si));
si.cb = sizeof(si);
ZeroMemory(&pi, sizeof(pi));
si.cb = sizeof(STARTUPINFO);
si.hStdError = g_hChildStd_OUT_Wr;
si.hStdOutput = g_hChildStd_OUT_Wr;
si.hStdInput = g_hChildStd_IN_Rd;
si.dwFlags |= STARTF_USESTDHANDLES;
TCHAR cmdPath[] = TEXT("C:\\Windows\\System32\\cmd.exe");
BOOL result = CreateProcess(cmdPath, NULL, NULL, NULL, TRUE, 0, NULL, NULL, &si, &pi);
DWORD errCode = GetLastError();
if (!result)
{
std::cout << "Create Process failed: " << GetLastError() << std::endl;
}
for (;;)
{
ReadFromPipe();
WriteToPipe();
}
}
I followed all the instructions provided on the MSDN site for Creating a Child Process with Redirected Input and Output but it gives me error:
CreateProcess failed with error 2: The system cannot find the file
specified
the code that i used is :
#include <windows.h>
#include <tchar.h>
#include <stdio.h>
#include <strsafe.h>
#define BUFSIZE 4096
HANDLE g_hChildStd_IN_Rd = NULL;
HANDLE g_hChildStd_IN_Wr = NULL;
HANDLE g_hChildStd_OUT_Rd = NULL;
HANDLE g_hChildStd_OUT_Wr = NULL;
HANDLE g_hInputFile = NULL;
void CreateChildProcess(void);
void WriteToPipe(void);
void ReadFromPipe(void);
void ErrorExit(PTSTR);
int _tmain(int argc, TCHAR *argv[])
{
SECURITY_ATTRIBUTES saAttr;
printf("\n->Start of parent execution.\n");
// Set the bInheritHandle flag so pipe handles are inherited.
saAttr.nLength = sizeof(SECURITY_ATTRIBUTES);
saAttr.bInheritHandle = TRUE;
saAttr.lpSecurityDescriptor = NULL;
// Create a pipe for the child process's STDOUT.
if ( ! CreatePipe(&g_hChildStd_OUT_Rd, &g_hChildStd_OUT_Wr, &saAttr, 0) )
ErrorExit(TEXT("StdoutRd CreatePipe"));
// Ensure the read handle to the pipe for STDOUT is not inherited.
if ( ! SetHandleInformation(g_hChildStd_OUT_Rd, HANDLE_FLAG_INHERIT, 0) )
ErrorExit(TEXT("Stdout SetHandleInformation"));
// Create a pipe for the child process's STDIN.
if (! CreatePipe(&g_hChildStd_IN_Rd, &g_hChildStd_IN_Wr, &saAttr, 0))
ErrorExit(TEXT("Stdin CreatePipe"));
// Ensure the write handle to the pipe for STDIN is not inherited.
if ( ! SetHandleInformation(g_hChildStd_IN_Wr, HANDLE_FLAG_INHERIT, 0) )
ErrorExit(TEXT("Stdin SetHandleInformation"));
// Create the child process.
CreateChildProcess();
// Get a handle to an input file for the parent.
// This example assumes a plain text file and uses string output to verify data flow.
if (argc == 1)
ErrorExit(TEXT("Please specify an input file.\n"));
g_hInputFile = CreateFile(
argv[1],
GENERIC_READ,
0,
NULL,
OPEN_EXISTING,
FILE_ATTRIBUTE_READONLY,
NULL);
if ( g_hInputFile == INVALID_HANDLE_VALUE )
ErrorExit(TEXT("CreateFile"));
// Write to the pipe that is the standard input for a child process.
// Data is written to the pipe's buffers, so it is not necessary to wait
// until the child process is running before writing data.
WriteToPipe();
printf( "\n->Contents of %s written to child STDIN pipe.\n", argv[1]);
// Read from pipe that is the standard output for child process.
printf( "\n->Contents of child process STDOUT:\n\n", argv[1]);
ReadFromPipe();
printf("\n->End of parent execution.\n");
// The remaining open handles are cleaned up when this process terminates.
// To avoid resource leaks in a larger application, close handles explicitly.
return 0;
}
void CreateChildProcess()
// Create a child process that uses the previously created pipes for STDIN and STDOUT.
{
TCHAR szCmdline[]=TEXT("D:\Visual Studio Projects\LEARN\queues\Debug\queues.exe");
PROCESS_INFORMATION piProcInfo;
STARTUPINFO siStartInfo;
BOOL bSuccess = FALSE;
// Set up members of the PROCESS_INFORMATION structure.
ZeroMemory( &piProcInfo, sizeof(PROCESS_INFORMATION) );
// Set up members of the STARTUPINFO structure.
// This structure specifies the STDIN and STDOUT handles for redirection.
ZeroMemory( &siStartInfo, sizeof(STARTUPINFO) );
siStartInfo.cb = sizeof(STARTUPINFO);
siStartInfo.hStdError = g_hChildStd_OUT_Wr;
siStartInfo.hStdOutput = g_hChildStd_OUT_Wr;
siStartInfo.hStdInput = g_hChildStd_IN_Rd;
siStartInfo.dwFlags |= STARTF_USESTDHANDLES;
// Create the child process.
bSuccess = CreateProcess(NULL,
szCmdline, // command line
NULL, // process security attributes
NULL, // primary thread security attributes
TRUE, // handles are inherited
0, // creation flags
NULL, // use parent's environment
NULL, // use parent's current directory
&siStartInfo, // STARTUPINFO pointer
&piProcInfo); // receives PROCESS_INFORMATION
// If an error occurs, exit the application.
if ( ! bSuccess )
ErrorExit(TEXT("CreateProcess"));
else
{
// Close handles to the child process and its primary thread.
// Some applications might keep these handles to monitor the status
// of the child process, for example.
CloseHandle(piProcInfo.hProcess);
CloseHandle(piProcInfo.hThread);
}
}
void WriteToPipe(void)
// Read from a file and write its contents to the pipe for the child's STDIN.
// Stop when there is no more data.
{
DWORD dwRead, dwWritten;
CHAR chBuf[BUFSIZE];
BOOL bSuccess = FALSE;
for (;;)
{
bSuccess = ReadFile(g_hInputFile, chBuf, BUFSIZE, &dwRead, NULL);
if ( ! bSuccess || dwRead == 0 ) break;
bSuccess = WriteFile(g_hChildStd_IN_Wr, chBuf, dwRead, &dwWritten, NULL);
if ( ! bSuccess ) break;
}
// Close the pipe handle so the child process stops reading.
if ( ! CloseHandle(g_hChildStd_IN_Wr) )
ErrorExit(TEXT("StdInWr CloseHandle"));
}
void ReadFromPipe(void)
// Read output from the child process's pipe for STDOUT
// and write to the parent process's pipe for STDOUT.
// Stop when there is no more data.
{
DWORD dwRead, dwWritten;
CHAR chBuf[BUFSIZE];
BOOL bSuccess = FALSE;
HANDLE hParentStdOut = GetStdHandle(STD_OUTPUT_HANDLE);
for (;;)
{
bSuccess = ReadFile( g_hChildStd_OUT_Rd, chBuf, BUFSIZE, &dwRead, NULL);
if( ! bSuccess || dwRead == 0 ) break;
bSuccess = WriteFile(hParentStdOut, chBuf,
dwRead, &dwWritten, NULL);
if (! bSuccess ) break;
}
}
void ErrorExit(PTSTR lpszFunction)
// Format a readable error message, display a message box,
// and exit from the application.
{
LPVOID lpMsgBuf;
LPVOID lpDisplayBuf;
DWORD dw = GetLastError();
FormatMessage(
FORMAT_MESSAGE_ALLOCATE_BUFFER |
FORMAT_MESSAGE_FROM_SYSTEM |
FORMAT_MESSAGE_IGNORE_INSERTS,
NULL,
dw,
MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
(LPTSTR) &lpMsgBuf,
0, NULL );
lpDisplayBuf = (LPVOID)LocalAlloc(LMEM_ZEROINIT,
(lstrlen((LPCTSTR)lpMsgBuf)+lstrlen((LPCTSTR)lpszFunction)+40)*sizeof(TCHAR));
StringCchPrintf((LPTSTR)lpDisplayBuf,
LocalSize(lpDisplayBuf) / sizeof(TCHAR),
TEXT("%s failed with error %d: %s"),
lpszFunction, dw, lpMsgBuf);
MessageBox(NULL, (LPCTSTR)lpDisplayBuf, TEXT("Error"), MB_OK);
LocalFree(lpMsgBuf);
LocalFree(lpDisplayBuf);
ExitProcess(1);
}
lets just say i want to use my own child process which is :
#include <iostream>
#include <queue>
#include <conio.h>
using namespace std;
int main(){
queue<int> myQ;
for(int i=0; i<10; i++)
{
cout<<"Enqueing..."<< i << endl;
myQ.push(i);
}
cout << "My size is "<< myQ.size()<<endl;
cout<<"Last element of the queue is "<<myQ.back()<<endl;
while(!myQ.empty())
{
cout<<"Dequeing ... "<<myQ.front()<<endl;
}
_getch();
return 0;
}
and want to print the values of the queue in the stdout.. but it shows error that i mentioned earlier .. i already copied the queues.exe to the debug folder of the main program.... but still it shows error..
How to read output from cmd.exe using CreateProcess() and CreatePipe()
I have been trying to create a child process executing cmd.exe with a command-line designating /K dir. The purpose is to read the output from the command back into the parent process using pipes.
I've already got CreateProcess() working, however the step involving pipes are causing me trouble. Using pipes, the new console window is not displaying (like it was before), and the parent process is stuck in the call to ReadFile().
Does anyone have an idea of what I'm doing wrong?
#include <Windows.h>
#include <stdio.h>
#include <tchar.h>
#define BUFFSZ 4096
HANDLE g_hChildStd_IN_Rd = NULL;
HANDLE g_hChildStd_IN_Wr = NULL;
HANDLE g_hChildStd_OUT_Rd = NULL;
HANDLE g_hChildStd_OUT_Wr = NULL;
int wmain(int argc, wchar_t* argv[])
{
int result;
wchar_t aCmd[BUFFSZ] = TEXT("/K dir"); // CMD /?
STARTUPINFO si;
PROCESS_INFORMATION pi;
SECURITY_ATTRIBUTES sa;
printf("Starting...\n");
ZeroMemory(&si, sizeof(STARTUPINFO));
ZeroMemory(&pi, sizeof(PROCESS_INFORMATION));
ZeroMemory(&sa, sizeof(SECURITY_ATTRIBUTES));
// Create one-way pipe for child process STDOUT
if (!CreatePipe(&g_hChildStd_OUT_Rd, &g_hChildStd_OUT_Wr, &sa, 0)) {
printf("CreatePipe() error: %ld\n", GetLastError());
}
// Ensure read handle to pipe for STDOUT is not inherited
if (!SetHandleInformation(g_hChildStd_OUT_Rd, HANDLE_FLAG_INHERIT, 0)) {
printf("SetHandleInformation() error: %ld\n", GetLastError());
}
// Create one-way pipe for child process STDIN
if (!CreatePipe(&g_hChildStd_IN_Rd, &g_hChildStd_IN_Wr, &sa, 0)) {
printf("CreatePipe() error: %ld\n", GetLastError());
}
// Ensure write handle to pipe for STDIN is not inherited
if (!SetHandleInformation(g_hChildStd_IN_Rd, HANDLE_FLAG_INHERIT, 0)) {
printf("SetHandleInformation() error: %ld\n", GetLastError());
}
si.cb = sizeof(STARTUPINFO);
si.hStdError = g_hChildStd_OUT_Wr;
si.hStdOutput = g_hChildStd_OUT_Wr;
si.hStdInput = g_hChildStd_IN_Rd;
si.dwFlags |= STARTF_USESTDHANDLES;
sa.nLength = sizeof(SECURITY_ATTRIBUTES);
sa.lpSecurityDescriptor = NULL;
// Pipe handles are inherited
sa.bInheritHandle = true;
// Creates a child process
result = CreateProcess(
TEXT("C:\\Windows\\System32\\cmd.exe"), // Module
aCmd, // Command-line
NULL, // Process security attributes
NULL, // Primary thread security attributes
true, // Handles are inherited
CREATE_NEW_CONSOLE, // Creation flags
NULL, // Environment (use parent)
NULL, // Current directory (use parent)
&si, // STARTUPINFO pointer
&pi // PROCESS_INFORMATION pointer
);
if (result) {
printf("Child process has been created...\n");
}
else {
printf("Child process could not be created\n");
}
bool bStatus;
CHAR aBuf[BUFFSZ + 1];
DWORD dwRead;
DWORD dwWrite;
// GetStdHandle(STD_OUTPUT_HANDLE)
while (true) {
bStatus = ReadFile(g_hChildStd_OUT_Rd, aBuf, sizeof(aBuf), &dwRead, NULL);
if (!bStatus || dwRead == 0) {
break;
}
aBuf[dwRead] = '\0';
printf("%s\n", aBuf);
}
// Wait until child process exits
WaitForSingleObject(pi.hProcess, INFINITE);
// Close process and thread handles
CloseHandle(pi.hProcess);
CloseHandle(pi.hThread);
printf("Stopping...\n");
return 0;
}
The subtle way out of your problem is to make sure you close the ends of the pipe you don't need.
Your parent process has four handles:
two of them are your ends of the pipe
g_hChildStd_IN_Wr
g_hChildStd_OUT_Rd
two of them are the child's end of the pipe
g_hChildStd_IN_Rd
g_hChildStd_OUT_Wr
╔══════════════════╗ ╔══════════════════╗
║ Parent Process ║ ║ Child Process ║
╠══════════════════╣ ╠══════════════════╣
║ ║ ║ ║
║ g_hChildStd_IN_Wr╟───────────────>║g_hChildStd_IN_Rd ║
║ ║ ║ ║
║g_hChildStd_OUT_Rd║<───────────────╢g_hChildStd_OUT_Wr║
║ ║ ║ ║
╚══════════════════╝ ╚══════════════════╝
Your parent process only needs one end of each pipe:
writable end of the child input pipe: g_hChildStd_IN_Wr
readable end of the child output pipe: g_hChildStd_OUT_Rd
Once you've launched your child process: be sure to close those ends of the pipe you no longer need:
CloseHandle(g_hChildStd_IN_Rd)
CloseHandle(g_hChildStd_OUT_Wr)
Leaving:
╔══════════════════╗ ╔══════════════════╗
║ Parent Process ║ ║ Child Process ║
╠══════════════════╣ ╠══════════════════╣
║ ║ ║ ║
║ g_hChildStd_IN_Wr╟───────────────>║ ║
║ ║ ║ ║
║g_hChildStd_OUT_Rd║<───────────────╢ ║
║ ║ ║ ║
╚══════════════════╝ ╚══════════════════╝
Or more fully:
STARTUP_INFO si;
PROCESS_INFO pi;
result = CreateProcess(..., ref si, ref pi);
//Bonus chatter: A common bug among a lot of programmers:
// they don't realize they are required to call CloseHandle
// on the two handles placed in PROCESS_INFO.
// That's why you should call ShellExecute - it closes them for you.
CloseHandle(pi.hProcess);
CloseHandle(pi.hThread);
/*
We've given the console app the writable end of the pipe during CreateProcess; we don't need it anymore.
We do keep the handle for the *readable* end of the pipe; as we still need to read from it.
The other reason to close the writable-end handle now is so that there's only one out-standing reference to the writeable end: held by the child process.
When the child processes closes, it will close the pipe, and
your call to ReadFile will fail with error code:
109 (The pipe has been ended).
That's how we'll know the console app is done. (no need to wait on process handles with buggy infinite waits)
*/
CloseHandle(g_hChildStd_OUT_Wr);
g_hChildStd_OUT_Wr = 0;
CloseHandle(g_hChildStd_IN_Rd);
g_hChildStd_OUT_Wr = 0;
Waiting on the Child Process (aka the deadlock waiting to happen)
The common problem with most solutions is that people try to wait on a process handle.
they create event objects
they try to MsgWait for events to be signaled
they try to MsgWait for child processes to end
That's wrong. That's all wrong.
There are many problems with these ideas; the main one being:
if you try to wait for the child the terminate
the child will never be able to terminate
If the child is trying to send you output through the pipe, and you're INFINITE waiting, you're not emptying your end of the pipe. Eventually the pipe the child is writing to becomes full. When the child tries to write to a pipe that is full, its WriteFile call waits (i.e. Blocks) for the pipe to have some room.
you're blocked waiting on the child
the child attempts to write to the pipe
you're blocked waiting on the child, so you're not reading data out of the pipe
the pipe becomes full
the child blocks waiting on you
both parent and child are blocked waiting on the other
deadlock
As a result the child process will never terminate; you've deadlocked everything.
The Right Approach - let the client do it's thing
The correct solution comes by simply reading from the pipe.
Once the child process terminates,
it will CloseHandle on its end of the pipes.
The next time you try to read from the pipe
you'll be told the pipe has been closed (ERROR_BROKEN_PIPE).
That's how you know the process is done and you have no more stuff to read.
String outputText = "";
//Read will return when the buffer is full, or if the pipe on the other end has been broken
while (ReadFile(stdOutRead, aBuf, Length(aBuf), &bytesRead, null)
outputText = outputText + Copy(aBuf, 1, bytesRead);
//ReadFile will either tell us that the pipe has closed, or give us an error
DWORD le = GetLastError;
//And finally cleanup
CloseHandle(g_hChildStd_IN_Wr);
CloseHandle(g_hChildStd_OUT_Rd);
if (le != ERROR_BROKEN_PIPE) //"The pipe has been ended."
RaiseLastOSError(le);
All without a dangerous MsgWaitForSingleObject - which is error-prone, difficult to use correctly, and causes the very bug you want to avoid.
Complete Example
We all know what we are using this for: run a child process, and capture it's console output.
Here is some sample Delphi code:
function ExecuteAndCaptureOutput(CommandLine: string): string;
var
securityAttributes: TSecurityAttributes;
stdOutRead, stdOutWrite: THandle;
startupInfo: TStartupInfo;
pi: TProcessInformation;
buffer: AnsiString;
bytesRead: DWORD;
bRes: Boolean;
le: DWORD;
begin
{
Execute a child process, and capture it's command line output.
}
Result := '';
securityAttributes.nlength := SizeOf(TSecurityAttributes);
securityAttributes.bInheritHandle := True;
securityAttributes.lpSecurityDescriptor := nil;
if not CreatePipe({var}stdOutRead, {var}stdOutWrite, #securityAttributes, 0) then
RaiseLastOSError;
try
// Set up members of the STARTUPINFO structure.
startupInfo := Default(TStartupInfo);
startupInfo.cb := SizeOf(startupInfo);
// This structure specifies the STDIN and STDOUT handles for redirection.
startupInfo.dwFlags := startupInfo.dwFlags or STARTF_USESTDHANDLES; //The hStdInput, hStdOutput, and hStdError handles will be valid.
startupInfo.hStdInput := GetStdHandle(STD_INPUT_HANDLE); //don't forget to make it valid (zero is not valid)
startupInfo.hStdOutput := stdOutWrite; //give the console app the writable end of the pipe
startupInfo.hStdError := stdOutWrite; //give the console app the writable end of the pipe
// We also want the console window to be hidden
startupInfo.dwFlags := startupInfo.dwFlags or STARTF_USESHOWWINDOW; //The nShowWindow member member will be valid.
startupInfo.wShowWindow := SW_HIDE; //default is that the console window is visible
// Set up members of the PROCESS_INFORMATION structure.
pi := Default(TProcessInformation);
//WARNING: The Unicode version of CreateProcess can modify the contents of CommandLine.
//Therefore CommandLine cannot point to read-only memory.
//We can ensure it's not read-only with the RTL function UniqueString
UniqueString({var}CommandLine);
bRes := CreateProcess(nil, PChar(CommandLine), nil, nil, True, 0, nil, nil, startupInfo, {var}pi);
if not bRes then
RaiseLastOSError;
//CreateProcess demands that we close these two populated handles when we're done with them. We're done with them.
CloseHandle(pi.hProcess);
CloseHandle(pi.hThread);
{
We've given the console app the writable end of the pipe during CreateProcess; we don't need it anymore.
We do keep the handle for the *readable* end of the pipe; as we still need to read from it.
The other reason to close the writable-end handle now is so that there's only one out-standing reference to the writeable end: held by the console app.
When the app closes, it will close the pipe, and ReadFile will return code 109 (The pipe has been ended).
That's how we'll know the console app is done. (no need to wait on process handles)
}
CloseHandle(stdOutWrite);
stdOutWrite := 0;
SetLength(buffer, 4096);
//Read will return when the buffer is full, or if the pipe on the other end has been broken
while ReadFile(stdOutRead, buffer[1], Length(buffer), {var}bytesRead, nil) do
Result := Result + string(Copy(buffer, 1, bytesRead));
//ReadFile will either tell us that the pipe has closed, or give us an error
le := GetLastError;
if le <> ERROR_BROKEN_PIPE then //"The pipe has been ended."
RaiseLastOSError(le);
finally
CloseHandle(stdOutRead);
if stdOutWrite <> 0 then
CloseHandle(stdOutWrite);
end;
end;
Ian Boyd's answer had this gem: Once you've launched your child process: be sure to close those ends of the pipe you no longer need.
I've produced another version of the CreatePipe + CreateProcess solution which, I hope, is more clear:
int main()
{
BOOL ok = TRUE;
HANDLE hStdInPipeRead = NULL;
HANDLE hStdInPipeWrite = NULL;
HANDLE hStdOutPipeRead = NULL;
HANDLE hStdOutPipeWrite = NULL;
// Create two pipes.
SECURITY_ATTRIBUTES sa = { sizeof(SECURITY_ATTRIBUTES), NULL, TRUE };
ok = CreatePipe(&hStdInPipeRead, &hStdInPipeWrite, &sa, 0);
if (ok == FALSE) return -1;
ok = CreatePipe(&hStdOutPipeRead, &hStdOutPipeWrite, &sa, 0);
if (ok == FALSE) return -1;
// Create the process.
STARTUPINFO si = { };
si.cb = sizeof(STARTUPINFO);
si.dwFlags = STARTF_USESTDHANDLES;
si.hStdError = hStdOutPipeWrite;
si.hStdOutput = hStdOutPipeWrite;
si.hStdInput = hStdInPipeRead;
PROCESS_INFORMATION pi = { };
LPCWSTR lpApplicationName = L"C:\\Windows\\System32\\cmd.exe";
LPWSTR lpCommandLine = (LPWSTR)L"C:\\Windows\\System32\\cmd.exe /c dir";
LPSECURITY_ATTRIBUTES lpProcessAttributes = NULL;
LPSECURITY_ATTRIBUTES lpThreadAttribute = NULL;
BOOL bInheritHandles = TRUE;
DWORD dwCreationFlags = 0;
LPVOID lpEnvironment = NULL;
LPCWSTR lpCurrentDirectory = NULL;
ok = CreateProcess(
lpApplicationName,
lpCommandLine,
lpProcessAttributes,
lpThreadAttribute,
bInheritHandles,
dwCreationFlags,
lpEnvironment,
lpCurrentDirectory,
&si,
&pi);
if (ok == FALSE) return -1;
// Close pipes we do not need.
CloseHandle(hStdOutPipeWrite);
CloseHandle(hStdInPipeRead);
// The main loop for reading output from the DIR command.
char buf[1024 + 1] = { };
DWORD dwRead = 0;
DWORD dwAvail = 0;
ok = ReadFile(hStdOutPipeRead, buf, 1024, &dwRead, NULL);
while (ok == TRUE)
{
buf[dwRead] = '\0';
OutputDebugStringA(buf);
puts(buf);
ok = ReadFile(hStdOutPipeRead, buf, 1024, &dwRead, NULL);
}
// Clean up and exit.
CloseHandle(hStdOutPipeRead);
CloseHandle(hStdInPipeWrite);
DWORD dwExitCode = 0;
GetExitCodeProcess(pi.hProcess, &dwExitCode);
return dwExitCode;
}
Some notes:
The pipe for StdIn is not really required:
This is because the DIR command doesn't require user input (but, I left it in the code, since it is a good template for running other commands)
everyting to do with hStdInPipeRead & hStdInPipeWrite can be omitted
setting si.hStdInput can be omitted
Replace hardcoded L"C:\\Windows\\System32\\cmd.exe" with reading the COMSPEC environment variable.
Replace LPWSTR with LPTSTR if we wish to compile for non-UNICODE.
Replace cmd.exe /k DIR with cmd.exe /c DIR since when the DIR command finishes we don't really want the cmd.exe to stick around.
I too have same scenario. in my case from Lib, need to execute internal exe and read output. The following works without any issues.
void executeCMDInNewProcessAndReadOutput(LPSTR lpCommandLine)
{
STARTUPINFO si;
SECURITY_ATTRIBUTES sa;
PROCESS_INFORMATION pi;
HANDLE g_hChildStd_IN_Rd, g_hChildStd_OUT_Wr, g_hChildStd_OUT_Rd, g_hChildStd_IN_Wr; //pipe handles
char buf[1024]; //i/o buffer
sa.nLength = sizeof(SECURITY_ATTRIBUTES);
sa.bInheritHandle = TRUE;
sa.lpSecurityDescriptor = NULL;
if (CreatePipe(&g_hChildStd_IN_Rd, &g_hChildStd_IN_Wr, &sa, 0)) //create stdin pipe
{
if (CreatePipe(&g_hChildStd_OUT_Rd, &g_hChildStd_OUT_Wr, &sa, 0)) //create stdout pipe
{
//set startupinfo for the spawned process
/*The dwFlags member tells CreateProcess how to make the process.
STARTF_USESTDHANDLES: validates the hStd* members.
STARTF_USESHOWWINDOW: validates the wShowWindow member*/
GetStartupInfo(&si);
si.dwFlags = STARTF_USESTDHANDLES | STARTF_USESHOWWINDOW;
si.wShowWindow = SW_HIDE;
//set the new handles for the child process
si.hStdOutput = g_hChildStd_OUT_Wr;
si.hStdError = g_hChildStd_OUT_Wr;
si.hStdInput = g_hChildStd_IN_Rd;
//spawn the child process
if (CreateProcess(NULL, lpCommandLine, NULL, NULL, TRUE, CREATE_NEW_CONSOLE,
NULL, NULL, &si, &pi))
{
unsigned long bread; //bytes read
unsigned long avail; //bytes available
memset(buf, 0, sizeof(buf));
for (;;)
{
PeekNamedPipe(g_hChildStd_OUT_Rd, buf, 1023, &bread, &avail, NULL);
//check to see if there is any data to read from stdout
if (bread != 0)
{
if (ReadFile(g_hChildStd_OUT_Rd, buf, 1023, &bread, NULL))
{
break;
}
}
}
//clean up all handles
CloseHandle(pi.hThread);
CloseHandle(pi.hProcess);
CloseHandle(g_hChildStd_IN_Rd);
CloseHandle(g_hChildStd_OUT_Wr);
CloseHandle(g_hChildStd_OUT_Rd);
CloseHandle(g_hChildStd_IN_Wr);
}
else
{
CloseHandle(g_hChildStd_IN_Rd);
CloseHandle(g_hChildStd_OUT_Wr);
CloseHandle(g_hChildStd_OUT_Rd);
CloseHandle(g_hChildStd_IN_Wr);
}
}
else
{
CloseHandle(g_hChildStd_IN_Rd);
CloseHandle(g_hChildStd_IN_Wr);
}
}
}
Here is an example (taken from a larger program) of a thread that does what you are looking for. It creates pipes for stdout and stderr for the process it creates then goes into a loop reading those pipes until the program finishes.
DWORD WINAPI ThreadProc(LPVOID lpParameter)
{
#define EVENT_NAME "Global\\RunnerEvt"
HANDLE hev;
SECURITY_ATTRIBUTES psa;
InitSAPtr(&psa);
DWORD waitRc;
DWORD bytesRead;
int manual_triggered = 1;
hev = CreateEvent(&psa, FALSE, FALSE, EVENT_NAME);
// Create pipes we'll read
for(;;)
{
if (manual_triggered)
{
waitRc = WAIT_OBJECT_0;
manual_triggered = 0;
}
else
{
waitRc = WaitForSingleObject(hev, 500);
}
if (waitRc == WAIT_OBJECT_0)
{
`logprint`f(LOG_DBG, "Received command to run process\n");
CreateChildOutFile();
stdOutEvt = CreateEvent(&psa, TRUE, FALSE, 0);
stdOutOvl.hEvent = stdOutEvt;
stdErrEvt = CreateEvent(&psa, TRUE, FALSE, 0);
stdErrOvl.hEvent = stdErrEvt;
gStdOutReadHand = CreateNamedPipe(STD_OUT_PIPE_NAME, PIPE_ACCESS_DUPLEX + FILE_FLAG_OVERLAPPED, PIPE_TYPE_BYTE + PIPE_READMODE_BYTE,
PIPE_UNLIMITED_INSTANCES, 4096, 4096, 0, &psa);
if (gStdOutReadHand == INVALID_HANDLE_VALUE)
{
log(LOG_DBG, "Error %d on create STDOUT pipe\n", GetLastError());
}
gStdErrReadHand = CreateNamedPipe(STD_ERR_PIPE_NAME, PIPE_ACCESS_DUPLEX + FILE_FLAG_OVERLAPPED, PIPE_TYPE_BYTE + PIPE_READMODE_BYTE,
PIPE_UNLIMITED_INSTANCES, 4096, 4096, 0, &psa);
if (gStdErrReadHand == INVALID_HANDLE_VALUE)
{
log(LOG_DBG, "Error %d on create STDERR pipe\n", GetLastError());
}
runProcess();
log(LOG_DBG, "After runProcess, new PID is %d/%x\n", piProcInfo.dwProcessId, piProcInfo.dwProcessId);
if (piProcInfo.dwProcessId == 0)
{
log(LOG_DBG, "runProcess failed, closing child STDIN/STDERR\n");
closeChildPipes();
#define FAIL_MSG "Child process failed to start\n"
writeChildOutFile(FAIL_MSG, strlen(FAIL_MSG) );
CloseHandle(hChildOut);
}
else
{
log(LOG_DBG, "Child process created, setting up for redir/restart/termination\n");
issueRead(gStdOutReadHand, &stdOutOvl, stdOutBuff, &stdOutBytesAvail);
//log(LOG_DBG, "After read set on STDOUT\n");
issueRead(gStdErrReadHand, &stdErrOvl, stdErrBuff, &stdErrBytesAvail);
//log(LOG_DBG, "After read set on STDERR\n");
HANDLE harr[4];
for(;;)
{
harr[0] = hev;
harr[1] = piProcInfo.hProcess;
harr[2] = stdOutEvt;
harr[3] = stdErrEvt;
DWORD waitRc2 = WaitForMultipleObjects(4, harr, FALSE, 500);
#if 0
if (waitRc2 == -1)
{
log(LOG_DBG, "Wait error %d\n", GetLastError());
Sleep(500);
}
log(LOG_DBG, "waitRc2 %d\n", waitRc2);
#endif
if ((waitRc2 - WAIT_OBJECT_0) == 0)
{
log(LOG_DBG, "Woke up because another trigger command was received\n");
#define NEW_CMD_MSG "Child process is being terminated because new trigger received\n"
writeChildOutFile(NEW_CMD_MSG, strlen(NEW_CMD_MSG));
terminateChild();
CloseHandle(hChildOut);
manual_triggered = 1;
break;
}
else if ((waitRc2 - WAIT_OBJECT_0) == 1)
{
//log(LOG_DBG, "Woke up because child has terminated\n");
closeChildPipes();
#define NORM_MSG "Normal child process termination\n"
writeChildOutFile(NORM_MSG, strlen(NORM_MSG));
CloseHandle(hChildOut);
break;
}
else if ((waitRc2 - WAIT_OBJECT_0) == 2)
{
//log(LOG_DBG, "Woke up because child has stdout\n");
if (GetOverlappedResult(gStdOutReadHand, &stdOutOvl, &bytesRead, TRUE))
{
writeChildOutFile(stdOutBuff, bytesRead);
ResetEvent(stdOutEvt);
issueRead(gStdOutReadHand, &stdOutOvl, stdOutBuff, &stdOutBytesAvail);
}
}
else if ((waitRc2 - WAIT_OBJECT_0) == 3)
{
//log(LOG_DBG, "Woke up because child has stderr\n");
if (GetOverlappedResult(gStdErrReadHand, &stdErrOvl, &bytesRead, TRUE))
{
writeChildOutFile(stdErrBuff, bytesRead);
ResetEvent(stdErrEvt);
issueRead(gStdErrReadHand, &stdErrOvl, stdErrBuff, &stdErrBytesAvail);
}
}
else
{
if (gShuttingDown)
{
log(LOG_DBG, "Woke with active child and service is terminating\n");
#define SHUTDOWN_MSG "Child process is being terminated because the service is shutting down\n"
writeChildOutFile(SHUTDOWN_MSG, strlen(SHUTDOWN_MSG));
terminateChild();
CloseHandle(hChildOut);
break;
}
}
if (gShuttingDown)
{
break;
}
}
}
}
else if (gShuttingDown)
{
break;
}
CloseHandle(gStdOutReadHand);
CloseHandle(gStdErrReadHand);
}
return 0;
}
void writeChildOutFile(char *msg, int len)
{
DWORD bytesWritten;
WriteFile(hChildOut, msg, len, &bytesWritten, 0);
}
void terminateChild(void)
{
if (piProcInfo.dwProcessId != 0)
{
TerminateProcess(piProcInfo.hProcess, -1);
CloseHandle(piProcInfo.hThread);
CloseHandle(piProcInfo.hProcess);
closeChildPipes();
}
}
void closeChildPipes(void)
{
CloseHandle(g_hChildStd_OUT_Wr);
CloseHandle(g_hChildStd_ERR_Wr);
}
void runProcess(void)
{
SECURITY_ATTRIBUTES saAttr;
// Set the bInheritHandle flag so pipe handles are inherited.
saAttr.nLength = sizeof(SECURITY_ATTRIBUTES);
saAttr.bInheritHandle = TRUE;
saAttr.lpSecurityDescriptor = NULL;
// Create a pipe for the child process's STDOUT.
TCHAR szCmdline[]=TEXT("cmd.exe /C C:\\temp\\RunnerService.bat");
STARTUPINFO siStartInfo;
BOOL bSuccess = FALSE;
// Set up members of the PROCESS_INFORMATION structure.
ZeroMemory( &piProcInfo, sizeof(PROCESS_INFORMATION) );
g_hChildStd_OUT_Wr = CreateFile (STD_OUT_PIPE_NAME,
FILE_WRITE_DATA,
0,
&saAttr,
OPEN_EXISTING,
0,
NULL);
if (g_hChildStd_OUT_Wr == INVALID_HANDLE_VALUE)
{
log(LOG_DBG, "Error creating child proc stdout file %d\n", GetLastError());
}
g_hChildStd_ERR_Wr = CreateFile (STD_ERR_PIPE_NAME,
FILE_WRITE_DATA,
0,
&saAttr,
OPEN_EXISTING,
0,
NULL);
if (g_hChildStd_ERR_Wr == INVALID_HANDLE_VALUE)
{
log(LOG_DBG, "Error creating child proc stderr file %d\n", GetLastError());
}
// Set up members of the STARTUPINFO structure.
// This structure specifies the STDIN and STDOUT handles for redirection.
ZeroMemory( &siStartInfo, sizeof(STARTUPINFO) );
siStartInfo.cb = sizeof(STARTUPINFO);
siStartInfo.hStdOutput = g_hChildStd_OUT_Wr;
siStartInfo.hStdError = g_hChildStd_ERR_Wr;
siStartInfo.dwFlags |= STARTF_USESTDHANDLES;
// Create the child process.
bSuccess = CreateProcess(NULL,
szCmdline, // command line
NULL, // process security attributes
NULL, // primary thread security attributes
TRUE, // handles are inherited
0, // creation flags
NULL, // use parent's environment
NULL, // use parent's current directory
&siStartInfo, // STARTUPINFO pointer
&piProcInfo); // receives PROCESS_INFORMATION
}
void CreateChildOutFile(void)
{
SYSTEMTIME st;
SECURITY_ATTRIBUTES sa;
char fName[_MAX_PATH];
InitSAPtr(&sa);
GetLocalTime(&st);
sprintf(fName, "C:\\TEMP\\runsvcchild_%02d_%02d_%02d_%04d.out", st.wHour, st.wMinute, st.wSecond, st.wMilliseconds);
hChildOut = CreateFile(fName, GENERIC_WRITE, FILE_SHARE_READ, &sa, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, 0);
}
void issueRead(HANDLE hFile, OVERLAPPED *overLapped, char *buf, DWORD *dwRead)
{
//log(LOG_DBG, "Start of issueRead, hfile %08x, ovl is %08x\n", hFile, overLapped);
BOOL brc = ReadFile(hFile, buf, 4096, dwRead, overLapped);
if (!brc)
{
DWORD dwle = GetLastError();
if (dwle != ERROR_IO_PENDING)
{
log(LOG_DBG, "Error %d on ReadFile\n", dwle);
}
}
else
{
// log(LOG_DBG, "Read issued\n");
}
}
I think you did everything right. But cmd.exe prints nothing or very little amount of data after start and your ReadFile blocks. If you move your cycle
while (true) {
bStatus = ReadFile(g_hChildStd_OUT_Rd, aBuf, sizeof(aBuf), &dwRead, NULL);
if (!bStatus || dwRead == 0) {
break;
}
aBuf[dwRead] = '\0';
printf("%s\n", aBuf);
}
into background thread and run other cycle which will read your input and send it to cmd.exe, I think you can see any effect.
Either you can make read buffer smaller (16 bytes e.g.).
I tried Stephen Quan's answer out and got a segfault. Perhaps someone with more experience might know why that is. At any rate, this should be a more correct example of what he was trying to do:
#include <windows.h>
#include <cstddef>
#include <string>
#include <vector>
#include <cwchar>
using std::string;
using std::wstring;
using std::vector;
using std::size_t;
static inline wstring widen(string str) {
size_t wchar_count = str.size() + 1;
vector<wchar_t> buf(wchar_count);
return wstring{ buf.data(), (size_t)MultiByteToWideChar(CP_UTF8, 0, str.c_str(), -1, buf.data(), (int)wchar_count) };
}
static inline string narrow(wstring wstr) {
int nbytes = WideCharToMultiByte(CP_UTF8, 0, wstr.c_str(), (int)wstr.length(), NULL, 0, NULL, NULL);
vector<char> buf(nbytes);
return string{ buf.data(), (size_t)WideCharToMultiByte(CP_UTF8, 0, wstr.c_str(), (int)wstr.length(), buf.data(), nbytes, NULL, NULL) };
}
string evaluate_shell(string command) {
string output;
wstring wstr_command = widen(command);
wchar_t cwstr_command[32768];
wcsncpy(cwstr_command, wstr_command.c_str(), 32768);
BOOL ok = TRUE;
HANDLE hStdInPipeRead = NULL;
HANDLE hStdInPipeWrite = NULL;
HANDLE hStdOutPipeRead = NULL;
HANDLE hStdOutPipeWrite = NULL;
SECURITY_ATTRIBUTES sa = { sizeof(SECURITY_ATTRIBUTES), NULL, TRUE };
ok = CreatePipe(&hStdInPipeRead, &hStdInPipeWrite, &sa, 0);
if (ok == FALSE) return "";
ok = CreatePipe(&hStdOutPipeRead, &hStdOutPipeWrite, &sa, 0);
if (ok == FALSE) return "";
STARTUPINFOW si = { };
si.cb = sizeof(STARTUPINFOW);
si.dwFlags = STARTF_USESTDHANDLES;
si.hStdError = hStdOutPipeWrite;
si.hStdOutput = hStdOutPipeWrite;
si.hStdInput = hStdInPipeRead;
PROCESS_INFORMATION pi = { };
if (CreateProcessW(NULL, cwstr_command, NULL, NULL, TRUE, CREATE_NO_WINDOW, NULL, NULL, &si, &pi)) {
while (WaitForSingleObject(pi.hProcess, 5) == WAIT_TIMEOUT) {
MSG msg;
if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE)) {
TranslateMessage(&msg);
DispatchMessage(&msg);
}
}
CloseHandle(hStdOutPipeWrite);
CloseHandle(hStdInPipeRead);
char buffer[4096] = { };
DWORD dwRead = 0;
ok = ReadFile(hStdOutPipeRead, buffer, 4095, &dwRead, NULL);
while (ok == TRUE) {
buffer[dwRead] = 0;
ok = ReadFile(hStdOutPipeRead, buffer, 4095, &dwRead, NULL);
}
CloseHandle(hStdOutPipeRead);
CloseHandle(hStdInPipeWrite);
CloseHandle(pi.hProcess);
CloseHandle(pi.hThread);
output = narrow(widen(buffer));
while (output.back() == '\r' || output.back() == '\n')
output.pop_back();
}
return output;
}
I found the below comment on Microsoft's documentation site:
Also, CreateProcessWithLogonW rejects STD handles (0/1/2) i.e. what GetStdHandle() returns by default, when using STARTF_USESTDHANDLES. It returns error 6, invalid handles, because 0/1/2 are not "real" handles. The only way we found to redirect the console input/output was to create custom handles (pipes) and use those instead (e.g. even just as dummy handles that you don't use). This is missing functionality from CreateProcessWithLogonW, because CreateProcess (and maybe CreateProcessAsUser, I didn't verify that) accepts STD handles.
This points to creating custom pipes.
I found this StackOverflow answer which points to using things such as "SafeFileHandle". This is apparently C++/CLI which I am not familiar with how to use. I am using Visual C++ and therefore "native" C++?
I am looking for a simple solution of how to fix this issue. I am a newbie in C++ and the CLI thing confused me because I simply don't know how to use it, or make Visual C++ compatible with it.
Given my normal C++ and my question, HOW EXACTLY would I create the custom pipe which will allow me to get the standard output?
Here is my code:
#include "stdafx.h"
void DisplayError(LPWSTR pszAPI)
{
LPVOID lpvMessageBuffer;
FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER |
FORMAT_MESSAGE_FROM_SYSTEM,
NULL, GetLastError(),
MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
(LPWSTR)&lpvMessageBuffer, 0, NULL);
//
//... now display this string
//
wprintf(L"ERROR: API = %s.\n", pszAPI);
wprintf(L" error code = %d.\n", GetLastError());
wprintf(L" message = %s.\n", (LPWSTR)lpvMessageBuffer);
//
// Free the buffer allocated by the system
//
LocalFree(lpvMessageBuffer);
ExitProcess(GetLastError());
}
void _tmain(int argc, WCHAR *argv[])
{
STARTUPINFO si;
ZeroMemory( &si, sizeof(STARTUPINFO) );
si.cb = sizeof(STARTUPINFO);
HANDLE pipe1 = CreateNamedPipe(L"\\\\.\\pipe\\pipe1", PIPE_ACCESS_DUPLEX,
PIPE_WAIT, 1024, 1024, 1024, 60, NULL);
HANDLE pipe2 = CreateNamedPipe(L"\\\\.\\pipe\\pipe2", PIPE_ACCESS_DUPLEX,
PIPE_WAIT, 1024, 1024, 1024, 60, NULL);
si.dwFlags |= STARTF_USESHOWWINDOW;
si.dwFlags = STARTF_USESTDHANDLES;
si.hStdOutput = pipe1;
si.hStdError = pipe2;
DWORD dwSize;
HANDLE hToken;
LPVOID lpvEnv;
PROCESS_INFORMATION pi = {0};
WCHAR szUserProfile[256] = L"";
si.cb = sizeof(STARTUPINFO);
if (argc != 4)
{
wprintf(L"Usage: %s [user#domain] [password] [cmd]", argv[0]);
wprintf(L"\n\n");
return;
}
//
// TO DO: change NULL to '.' to use local account database
//
if (!LogonUser(argv[1], NULL, argv[2], LOGON32_LOGON_INTERACTIVE,
LOGON32_PROVIDER_DEFAULT, &hToken))
DisplayError(L"LogonUser");
if (!CreateEnvironmentBlock(&lpvEnv, hToken, TRUE))
DisplayError(L"CreateEnvironmentBlock");
dwSize = sizeof(szUserProfile)/sizeof(WCHAR);
if (!GetUserProfileDirectory(hToken, szUserProfile, &dwSize))
DisplayError(L"GetUserProfileDirectory");
//
// TO DO: change NULL to '.' to use local account database
//
if (!CreateProcessWithLogonW(argv[1], NULL, argv[2],
LOGON_WITH_PROFILE, NULL, argv[3],
CREATE_UNICODE_ENVIRONMENT, lpvEnv, szUserProfile,
&si, &pi))
DisplayError(L"CreateProcessWithLogonW");
if (!DestroyEnvironmentBlock(lpvEnv))
DisplayError(L"DestroyEnvironmentBlock");
CloseHandle(hToken);
CloseHandle(pi.hProcess);
CloseHandle(pi.hThread);
}
I tried this and I am getting no output on the console window. As I said, I checked the answer on StackOverflow and this whole C++/CLI thing confuses me. If someone knows a simple solution to redirecting the output using a custom pipe using Visual C++, let me know.
And if I did anything wrong above, let me know as well.
EDIT:
After following the suggestions given by Remy's answer. I came up with the following code, which yields an error code 3: The system cannot find the path specified.
#include "stdafx.h"
HANDLE g_hChildStd_IN_Rd = NULL;
HANDLE g_hChildStd_IN_Wr = NULL;
HANDLE g_hChildStd_OUT_Rd = NULL;
HANDLE g_hChildStd_OUT_Wr = NULL;
HANDLE g_hInputFile = NULL;
int BUFSIZE = 1064;
void CreateChildProcess(void);
void WriteToPipe(void);
void ReadFromPipe(void);
void ErrorExit(PTSTR);
void DisplayError(LPWSTR pszAPI)
{
LPVOID lpvMessageBuffer;
FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER |
FORMAT_MESSAGE_FROM_SYSTEM,
NULL, GetLastError(),
MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
(LPWSTR)&lpvMessageBuffer, 0, NULL);
//
//... now display this string
//
wprintf(L"ERROR: API = %s.\n", pszAPI);
wprintf(L" error code = %d.\n", GetLastError());
wprintf(L" message = %s.\n", (LPWSTR)lpvMessageBuffer);
//
// Free the buffer allocated by the system
//
LocalFree(lpvMessageBuffer);
ExitProcess(GetLastError());
}
void _tmain(int argc, WCHAR *argv[])
{
SECURITY_ATTRIBUTES saAttr;
saAttr.nLength = sizeof(SECURITY_ATTRIBUTES);
saAttr.bInheritHandle = TRUE;
saAttr.lpSecurityDescriptor = NULL;
if ( ! CreatePipe(&g_hChildStd_OUT_Rd, &g_hChildStd_OUT_Wr, &saAttr, 0) )
ErrorExit(TEXT("StdoutRd CreatePipe"));
if ( ! SetHandleInformation(g_hChildStd_OUT_Rd, HANDLE_FLAG_INHERIT, 0) )
ErrorExit(TEXT("Stdout SetHandleInformation"));
if (! CreatePipe(&g_hChildStd_IN_Rd, &g_hChildStd_IN_Wr, &saAttr, 0))
ErrorExit(TEXT("Stdin CreatePipe"));
if ( ! SetHandleInformation(g_hChildStd_IN_Wr, HANDLE_FLAG_INHERIT, 0) )
ErrorExit(TEXT("Stdin SetHandleInformation"));
/////////////////////////////Start CreateChildProcess////////
STARTUPINFO si;
ZeroMemory( &si, sizeof(STARTUPINFO) );
si.cb = sizeof(STARTUPINFO);
si.dwFlags |= STARTF_USESHOWWINDOW;
si.dwFlags |= STARTF_USESTDHANDLES;
si.hStdError = g_hChildStd_OUT_Wr;
si.hStdOutput = g_hChildStd_OUT_Wr;
si.hStdInput = g_hChildStd_IN_Rd;
DWORD dwSize;
HANDLE hToken;
LPVOID lpvEnv;
PROCESS_INFORMATION pi = {0};
WCHAR szUserProfile[256] = L"";
si.cb = sizeof(STARTUPINFO);
if (argc != 4)
{
wprintf(L"Usage: %s [user#domain] [password] [cmd]", argv[0]);
wprintf(L"\n\n");
return;
}
//
// TO DO: change NULL to '.' to use local account database
//
if (!LogonUser(argv[1], NULL, argv[2], LOGON32_LOGON_INTERACTIVE,
LOGON32_PROVIDER_DEFAULT, &hToken))
DisplayError(L"LogonUser");
if (!CreateEnvironmentBlock(&lpvEnv, hToken, TRUE))
DisplayError(L"CreateEnvironmentBlock");
dwSize = sizeof(szUserProfile)/sizeof(WCHAR);
if (!GetUserProfileDirectory(hToken, szUserProfile, &dwSize))
DisplayError(L"GetUserProfileDirectory");
//
// TO DO: change NULL to '.' to use local account database
//
if (!CreateProcessWithLogonW(argv[1], NULL, argv[2],
LOGON_WITH_PROFILE, NULL, argv[3],
CREATE_UNICODE_ENVIRONMENT, lpvEnv, szUserProfile,
&si, &pi))
DisplayError(L"CreateProcessWithLogonW");
if (!DestroyEnvironmentBlock(lpvEnv))
DisplayError(L"DestroyEnvironmentBlock");
CloseHandle(hToken);
CloseHandle(pi.hProcess);
CloseHandle(pi.hThread);
/////////////////////////////End CreateChildProcess///////////
if (argc == 1)
ErrorExit(TEXT("Please specify an input file.\n"));
g_hInputFile = CreateFile(
argv[3],
GENERIC_READ,
0,
NULL,
OPEN_EXISTING,
FILE_ATTRIBUTE_READONLY,
NULL);
if ( g_hInputFile == INVALID_HANDLE_VALUE )
ErrorExit(TEXT("CreateFile"));
WriteToPipe();
printf( "\n->Contents of %s written to child STDIN pipe.\n", argv[1]);
printf( "\n->Contents of child process STDOUT:\n\n", argv[1]);
ReadFromPipe();
}
void WriteToPipe(void)
// Read from a file and write its contents to the pipe for the child's STDIN.
// Stop when there is no more data.
{
DWORD dwRead, dwWritten;
CHAR chBuf[4096];
BOOL bSuccess = FALSE;
for (;;)
{
bSuccess = ReadFile(g_hInputFile, chBuf, BUFSIZE, &dwRead, NULL);
if ( ! bSuccess || dwRead == 0 ) break;
bSuccess = WriteFile(g_hChildStd_IN_Wr, chBuf, dwRead, &dwWritten, NULL);
if ( ! bSuccess ) break;
}
// Close the pipe handle so the child process stops reading.
if ( ! CloseHandle(g_hChildStd_IN_Wr) )
ErrorExit(TEXT("StdInWr CloseHandle"));
}
void ReadFromPipe(void)
// Read output from the child process's pipe for STDOUT
// and write to the parent process's pipe for STDOUT.
// Stop when there is no more data.
{
DWORD dwRead, dwWritten;
CHAR chBuf[4096];
BOOL bSuccess = FALSE;
HANDLE hParentStdOut = GetStdHandle(STD_OUTPUT_HANDLE);
for (;;)
{
bSuccess = ReadFile( g_hChildStd_OUT_Rd, chBuf, BUFSIZE, &dwRead, NULL);
if( ! bSuccess || dwRead == 0 ) break;
bSuccess = WriteFile(hParentStdOut, chBuf,
dwRead, &dwWritten, NULL);
if (! bSuccess ) break;
}
}
void ErrorExit(PTSTR lpszFunction)
// Format a readable error message, display a message box,
// and exit from the application.
{
LPVOID lpMsgBuf;
LPVOID lpDisplayBuf;
DWORD dw = GetLastError();
FormatMessage(
FORMAT_MESSAGE_ALLOCATE_BUFFER |
FORMAT_MESSAGE_FROM_SYSTEM |
FORMAT_MESSAGE_IGNORE_INSERTS,
NULL,
dw,
MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
(LPTSTR) &lpMsgBuf,
0, NULL );
lpDisplayBuf = (LPVOID)LocalAlloc(LMEM_ZEROINIT,
(lstrlen((LPCTSTR)lpMsgBuf)+lstrlen((LPCTSTR)lpszFunction)+40)*sizeof(TCHAR));
StringCchPrintf((LPTSTR)lpDisplayBuf,
LocalSize(lpDisplayBuf) / sizeof(TCHAR),
TEXT("%s failed with error %d: %s"),
lpszFunction, dw, lpMsgBuf);
MessageBox(NULL, (LPCTSTR)lpDisplayBuf, TEXT("Error"), MB_OK);
LocalFree(lpMsgBuf);
LocalFree(lpDisplayBuf);
ExitProcess(1);
}
Use anonymous pipes via CreatePipe(), not named pipes via CreateNamedPipe(). See MSDN for an example:
Creating a Child Process with Redirected Input and Output