Usando una estructura como argumento de función con el módulo python ctypes

Question

Estoy intentando portar una extensión C python que escribí para manejar uniones/enlaces simbólicos/etc en Windows a Python puro usando el módulo ctypes. Desafortunadamente, dado que mi uso anterior de Ctypes es bastante limitado, creo que puedo estar cometiendo un error en algún lugar que está causando que mi código funcione incorrectamente. Aquí es lo que tengo hasta ahora:

from os import path 
from ctypes import * 
from ctypes.wintypes import * 

# Python implementation of: 
# 
# typedef struct { 
#  DWORD ReparseTag; 
#  DWORD ReparseDataLength; 
#  WORD Reserved; 
#  WORD ReparseTargetLength; 
#  WORD ReparseTargetMaximumLength; 
#  WORD Reserved1; 
#  WCHAR ReparseTarget[1]; 
# } REPARSE_MOUNTPOINT_DATA_BUFFER, *PREPARSE_MOUNTPOINT_DATA_BUFFER; 

class ReparsePoint(Structure): 
    _fields_ = [ 
     ("ReparseTag", DWORD), 
     ("ReparseDataLength", DWORD), 
     ("Reserved", WORD), 

     ("ReparseTargetLength", WORD), 
     ("ReparseTargetMaximumLength", WORD), 
     ("Reserved1", WORD), 
     ("ReparseTarget", c_wchar_p), 
    ] 

GENERIC_READ = 0x80000000 
GENERIC_WRITE = 0x40000000 

FILE_SHARE_DELETE = 0x00000004 
FILE_SHARE_READ = 0x00000001 
FILE_SHARE_WRITE = 0x00000002 
FILE_SHARE_READ_WRITE = (FILE_SHARE_READ | FILE_SHARE_WRITE) 

OPEN_EXISTING = 3 

IO_REPARSE_TAG_MOUNT_POINT = 0xA0000003 
REPARSE_MOUNTPOINT_HEADER_SIZE = 8 

FSCTL_SET_REPARSE_POINT = 589988 
FILE_FLAG_OPEN_REPARSE_POINT = 2097152 
FILE_FLAG_BACKUP_SEMANTICS = 33554432 
FILE_FLAG_REPARSE_BACKUP = 35651584 # FILE_FLAG_OPEN_REPARSE_POINT | FILE_FLAG_BACKUP_SEMANTICS 

INVALID_HANDLE_VALUE = -1 
LPOVERLAPPED = c_void_p 
LPSECURITY_ATTRIBUTES = c_void_p 

NULL = 0 
FALSE = BOOL(0) 
TRUE = BOOL(1) 

def CreateFile(filename, access, sharemode, creation, flags): 
    return HANDLE(windll.kernel32.CreateFileW(
     LPWSTR(filename), 
     DWORD(access), 
     DWORD(sharemode), 
     LPSECURITY_ATTRIBUTES(NULL), 
     DWORD(creation), 
     DWORD(flags), 
     HANDLE(NULL) 
    )) 

def CreateDirectory(fpath): 
    return windll.kernel32.CreateDirectoryW(LPWSTR(fpath), LPSECURITY_ATTRIBUTES(NULL)) != FALSE 

def RemoveDirectory(fpath): 
    return windll.kernel32.RemoveDirectoryW(LPWSTR(fpath)) != FALSE 

def translate_path(fpath): 
    fpath = path.abspath(fpath) 
    if fpath[len(fpath)-1] == '\\' and fpath[len(fpath)-2] == ':': 
     fpath = fpath[:len(fpath)-1] 
    return '\\??\\%s' % fpath 

def junction(source, link_name): 
    """ Create a junction at link_name pointing to source directory. """ 
    if not path.isdir(source): 
     raise Exception('Junction source does not exist or is not a directory.') 

    link_name = path.abspath(link_name) 
    if path.exists(link_name): 
     raise Exception('Filepath for new junction already exists.') 

    if not CreateDirectory(link_name): 
     raise Exception('Failed to create new directory for target junction.') 

    source = translate_path(source) 
    hFile = CreateFile(link_name, GENERIC_WRITE, 0, OPEN_EXISTING, FILE_FLAG_REPARSE_BACKUP) 
    if hFile == HANDLE(INVALID_HANDLE_VALUE): 
     raise Exception('Failed to open directory for junction creation.') 

    datalen = len(source) * sizeof(c_wchar) 
    reparseInfo = ReparsePoint(
     IO_REPARSE_TAG_MOUNT_POINT, 
     datalen + 12, 
     0, 
     datalen, 
     datalen + sizeof(c_wchar), 
     0, 
     source 
    ) 
    pReparseInfo = pointer(reparseInfo) 

    print reparseInfo.ReparseTarget 
    returnedLength = DWORD(0) 
    result = BOOL(
     windll.kernel32.DeviceIoControl(
      hFile, 
      DWORD(FSCTL_SET_REPARSE_POINT), 
      pReparseInfo, 
      DWORD(reparseInfo.ReparseDataLength + REPARSE_MOUNTPOINT_HEADER_SIZE), 
      LPVOID(NULL), 
      DWORD(0), 
      byref(returnedLength), 
      LPOVERLAPPED(NULL) 
     ) 
    ) == TRUE 

    #if not result: 
     #RemoveDirectory(link_name) 

    windll.kernel32.CloseHandle(hFile) 
    return result 

print junction('G:\\cpp.workspace\\tools', 'test') 
""" 
Just putting this here for the moment so I know how to call the function. 

BOOL WINAPI DeviceIoControl(
    __in   HANDLE hDevice, 
    __in   DWORD dwIoControlCode, 
    __in_opt  LPVOID lpInBuffer, 
    __in   DWORD nInBufferSize, 
    __out_opt LPVOID lpOutBuffer, 
    __in   DWORD nOutBufferSize, 
    __out_opt LPDWORD lpBytesReturned, 
    __inout_opt LPOVERLAPPED lpOverlapped 
); 
""" 

Actualmente cuando es ejecutado, el código crea una carpeta para la unión de destino. (En este caso, prueba) Incluso parece estar aplicando la etiqueta de análisis para indicarle al sistema que la carpeta es un cruce. Sin embargo, en lugar de apuntar a "G: \ cpp.workspace \ tools" (o más bien, a \ ?? \ G: \ cpp.workspace \ tools), el cruce parece apuntar a: 㢨 \

Ahora, obviamente, este es un problema con reparseInfo.ReparseTarget, pero no he podido averiguar qué hice mal.

Answer 1

Esta es una matriz de WCHAR, no un puntero:

#  WCHAR ReparseTarget[1]; 

El [1] es engañosa, la API espera una cadena terminada en nulo al final de la estructura.