PowerShell/impl/getusername.cpp

//! @file getusername.cpp
//! @author Andrew Schwartzmeyer <andschwa@microsoft.com>
//! @brief Implements GetUserName Win32 API

#include <errno.h>
#include <langinfo.h>
#include <locale.h>
#include <unistd.h>
#include <string>
#include <unicode/utypes.h>
#include <unicode/ucnv.h>
#include <unicode/ustring.h>
#include <unicode/uchar.h>
#include "getusername.h"

//! @brief GetUserName retrieves the name of the user associated with
//! the current thread.
//!
//! GetUserNameW is the Unicode variation. See [MSDN documentation].
//!
//! @param[out] lpBuffer
//! @parblock
//! A pointer to the buffer to receive the user's
//! logon name. If this buffer is not large enough to contain the
//! entire user name, the function fails.
//!
//! WCHAR_T* is a Unicode [LPTSTR].
//! @endparblock
//!
//! @param[in, out] lpnSize
//! @parblock
//! On input, this variable specifies the size of the lpBuffer buffer,
//! in TCHARs. On output, the variable receives the number of TCHARs
//! copied to the buffer, including the terminating null character.
//!
//! TCHAR is a Unicode 16-bit [WCHAR].
//!
//! If lpBuffer is too small, the function fails and GetLastError
//! returns ERROR_INSUFFICIENT_BUFFER. This parameter receives the
//! required buffer size, including the terminating null character.
//! @endparblock
//!
//! @exception errno Passes these errors via errno to GetLastError:
//! - ERROR_INVALID_PARAMETER: parameter is not valid
//! - ERROR_BAD_ENVIRONMENT: locale is not UTF-8
//! - ERROR_TOO_MANY_OPEN_FILES: already have the maximum allowed number of open files
//! - ERROR_NO_ASSOCIATION: calling process has no controlling terminal
//! - ERROR_INSUFFICIENT_BUFFER: buffer not large enough to hold username string
//! - ERROR_NO_SUCH_USER: there was no corresponding entry in the utmp-file
//! - ERROR_OUTOFMEMORY: insufficient memory to allocate passwd structure
//! - ERROR_NO_ASSOCIATION: standard input didn't refer to a terminal
//! - ERROR_INVALID_FUNCTION: getlogin_r() returned an unrecognized error code
//!
//! @retval 1 If the function succeeds, the return value is a nonzero
//! value, and the variable pointed to by lpnSize contains the number
//! of TCHARs copied to the buffer specified by lpBuffer, including
//! the terminating null character.
//!
//! @retval 0 If the function fails, the return value is zero. To get
//! extended error information, call GetLastError.
//!
//! [MSDN documentation]: https://msdn.microsoft.com/en-us/library/windows/desktop/ms724432(v=vs.85).aspx
//! [WCHAR]: https://msdn.microsoft.com/en-us/library/windows/desktop/aa383751(v=vs.85).aspx#WCHAR
//! [LPTSTR]: https://msdn.microsoft.com/en-us/library/windows/desktop/aa383751(v=vs.85).aspx#LPTSTR
BOOL GetUserNameW(WCHAR_T* lpBuffer, LPDWORD lpnSize)
{
	const std::string utf8 = "UTF-8";

	errno = FALSE;

	// Check parameters
	if (!lpBuffer || !lpnSize) {
		errno = ERROR_INVALID_PARAMETER;
		return 0;
	}

	// Select locale from environment
	setlocale(LC_ALL, "");
	// Check that locale is UTF-8
	if (nl_langinfo(CODESET) != utf8) {
		errno = ERROR_BAD_ENVIRONMENT;
		return FALSE;
	}

	// Get username from system in a thread-safe manner
	std::string username(LOGIN_NAME_MAX, '\0');
	int ret = getlogin_r(&username[0], username.size());
	// Map errno to Win32 Error Codes
	if (ret) {
		switch (errno) {
		case EMFILE:
		case ENFILE:
			errno = ERROR_TOO_MANY_OPEN_FILES;
			break;
		case ENXIO:
			errno = ERROR_NO_ASSOCIATION;
			break;
		case ERANGE:
			errno = ERROR_GEN_FAILURE;
			break;
		case ENOENT:
			errno = ERROR_NO_SUCH_USER;
			break;
		case ENOMEM:
			errno = ERROR_OUTOFMEMORY;
			break;
		case ENOTTY:
			errno = ERROR_NO_ASSOCIATION;
			break;
		default:
			errno = ERROR_INVALID_FUNCTION;
		}
		return FALSE;
	}

	// Convert to char* to WCHAR_T* (UTF-8 to UTF-16 LE w/o BOM)
	std::basic_string<char16_t> username16(LOGIN_NAME_MAX+1, 0);
	icu::UnicodeString username8(username.c_str(), "UTF-8");
	int32_t targetSize = username8.extract(0, username8.length(),
	                                       reinterpret_cast<char*>(&username16[0]),
	                                       (username16.size()-1)*sizeof(char16_t),
	                                       "UTF-16LE");
	// Number of characters including null
	username16.resize(targetSize/sizeof(char16_t)+1);

	// Size in WCHARs including null
	const DWORD size = username16.length();
	if (size > *lpnSize) {
		errno = ERROR_INSUFFICIENT_BUFFER;
		// Set lpnSize if buffer is too small to inform user
		// of necessary size
		*lpnSize = size;
		return 0;
	}

	// Copy bytes from string to buffer
	memcpy(lpBuffer, &username16[0], size*sizeof(char16_t));
	*lpnSize = size;

	return TRUE;
}