Mustafa Chelik Mustafa Chelik - 1 year ago 67
C Question

Communicating with PuTTY via pipe

I want to capture PuTTY's STDIN and STDOUT pipes. So I open

putty.exe
via CreateProcess with passing created pipes but I can't read anything from pipes. My code works when I run a bat file.

How can I accomplish this?

Thanks

//This code is from MSDN and I edited it a little
#include <QCoreApplication>
#include <windows.h>
#include <tchar.h>
#include <stdio.h>
#include <strsafe.h>
#pragma comment(lib, "user32.lib")
#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 main(int argc, char *argv[])
{
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.
if ( ! CreatePipe(&g_hChildStd_OUT_Rd, &g_hChildStd_OUT_Wr, &saAttr, 0) )
ErrorExit((PTSTR)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((PTSTR)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((PTSTR)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((PTSTR)TEXT("Stdin SetHandleInformation"));

// Create the child process: putty
CreateChildProcess();

// read from pipe and printf incoming data
ReadFromPipe();
}

// 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.
void ReadFromPipe(void)
{
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;

printf("received hex:\n");
for (int i = 0; i < dwRead; i++)
{
printf("%02X", chBuf[i]);
}
printf("\nactual string: %s\n",chBuf);
}
}

void CreateChildProcess()
// Create a child process that uses the previously created pipes for STDIN and STDOUT.
{
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(L"E:\\putty.exe",
NULL, // 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((PTSTR)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);
}
}

// Format a readable error message, display a message box,
// and exit from the application.
void ErrorExit(PTSTR 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);
}

Answer Source

I found out that PuTTY doesn't have pipe for this purpose and since I didn't want to use plink, I modified PuTTY's source code and embedded pipe in it. Now it works as I want.

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