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%%	options

copyright owner	=	Dirk Krause
copyright year	=	2015-xxxx
license		=	bsd



%%	header

/**	@file	dk4symlink.h	Find symbolic link target.
*/

#ifndef DK4CONF_H_INCLUDED
#include "dk4conf.h"
#endif

#ifndef DK4TYPES_H_INCLUDED
#include "dk4types.h"
#endif

#ifndef DK4ERROR_H_INCLUDED
#include "dk4error.h"
#endif



#ifdef __cplusplus
extern "C" {
#endif

/**	Find target for symbolic link.
	@param	bptr	Destination buffer pointer.
	@param	szb	Size of destination buffer (number of dkChar).
	@param	fn	File name of link.
	@param	erp	Error report, may be NULL.
	@return	1 on success, 0 on error.

	Error codes:
	- DK4_E_INVALID_ARGUMENTS<br>
	  if bptr or fn is NULL or szb is 0,
	- DK4_E_SYSTEM<br>
	  with errno value in iDetails1 if the readlink() function failed
	  on Linux/Unix,
	- DK4_E_BUFFER_TOO_SMALL<br>
	  if the output buffer is too small,
	- DK4_E_NOT_SUPPORTED<br>
	  if no function was found to read a symbolic link target,
	- DK4_E_NOT_FOUND<br>
	  if the CreateFile() or DeviceIoControl() function failed
	  on Windows.
*/
int
dk4symlink_target(dkChar *bptr, size_t szb, const dkChar *fn, dk4_er_t *erp);

#ifdef __cplusplus
}
#endif

%%	module

#include "dk4symlink.h"

#if DK4_ON_WINDOWS
#ifndef WINDOWS_H_INCLUDED
#include <windows.h>
#define	WINDOWS_H_INCLUDED 1
#endif
#if DK4_HAVE_NTIFS_H
#ifndef NTIFS_H_INCLUDED
#include <ntifs.h>
#define	NTIFS_H_INCLUDED 1
#endif
#endif
#endif

#if DK4_HAVE_UNISTD_H
#ifndef UNISTD_H_INCLUDED
#include <unistd.h>
#define	UNISTD_H_INCLUDED 1
#endif
#endif

#if DK4_HAVE_ERRNO_H
#ifndef ERRNO_H_INCLUDED
#include <errno.h>
#define	ERRNO_H_INCLUDED 1
#endif
#endif

#include "dk4mpl.h"
#include "dk4mem.h"
#include "dk4strd.h"



$!trace-include



#if DK4_ON_WINDOWS

#if !DK4_HAVE_NTIFS_H

typedef struct _REPARSE_DATA_BUFFER {
  ULONG  ReparseTag;
  USHORT ReparseDataLength;
  USHORT Reserved;
  union {
    struct {
      USHORT SubstituteNameOffset;
      USHORT SubstituteNameLength;
      USHORT PrintNameOffset;
      USHORT PrintNameLength;
      ULONG  Flags;
      WCHAR  PathBuffer[1];
    } SymbolicLinkReparseBuffer;
    struct {
      USHORT SubstituteNameOffset;
      USHORT SubstituteNameLength;
      USHORT PrintNameOffset;
      USHORT PrintNameLength;
      WCHAR  PathBuffer[1];
    } MountPointReparseBuffer;
    struct {
      UCHAR DataBuffer[1];
    } GenericReparseBuffer;
  };
} REPARSE_DATA_BUFFER, *PREPARSE_DATA_BUFFER;

#endif


#if defined(FSCTL_GET_REPARSE_POINT)
/**	Size of reparse point information for a symlink.
*/
#define	SYMLINK_INFO_SIZE ((8 * (DK4_MAX_PATH))+sizeof(REPARSE_DATA_BUFFER))
/**	The above size aligned to 16 bytes.
*/
#define	SYMLINK_INFO_ALIGNED (16 * (((SYMLINK_INFO_SIZE) / 16) + 1))

#ifdef MAXIMUM_REPARSE_DATA_BUFFER_SIZE
#define	SYMLINK_BUFFER_SIZE	\
(MAXIMUM_REPARSE_DATA_BUFFER_SIZE + SYMLINK_INFO_ALIGNED)
#endif
#endif

/**	Copy path name from reparse point buffer to destination buffer.
	@param	bptr	Destination buffer.
	@param	szb	Destination buffer size (number of wchar_t).
	@param	sptr	Source pointer.
	@param	offs	Offset of path name in source (in bytes).
	@param	length	Length of path name (in bytes).
	@param	erp	Error report, may be NULL.
	@return	1 on success, 0 on error.
*/
static
int
dk4symlink_copy_string(
  wchar_t	*bptr,
  size_t	 szb,
  const wchar_t	*sptr,
  USHORT	 offs,
  USHORT	 length,
  dk4_er_t	*erp
)
{
  int		 back = 0;
  if ((length / sizeof(wchar_t)) < szb) {
    DK4_MEMCPY(bptr,&(sptr[offs / sizeof(wchar_t)]),length);
    bptr[length / sizeof(wchar_t)] = L'\0';
    back = 1;
  } else {
    dk4error_set_simple_error_code(erp, DK4_E_BUFFER_TOO_SMALL);
  }
  return back;
}

#endif

int
dk4symlink_target(dkChar *bptr, size_t szb, const dkChar *fn, dk4_er_t *erp)
{
#if DK4_ON_WINDOWS
#if defined(FSCTL_GET_REPARSE_POINT)
  char		 	 repdabuf[SYMLINK_BUFFER_SIZE];
  REPARSE_DATA_BUFFER	*rdb;
#endif
  HANDLE		 fh;
  DWORD			 dwres;
  BOOL			 result;
#else
  ssize_t		 res;
#endif
  int			 back	= 0;

  $? "+ dk4symlink_target"
  if ((NULL != bptr) && (NULL != fn) && (0 < szb)) {
    *bptr = dkT('\0');
#if DK4_ON_WINDOWS
#if DK4_CHAR_SIZE > 1
#if DK4_HAVE_GETFINALPATHNAMEBYHANDLE
    fh = CreateFileW(
      fn,
      FILE_READ_ATTRIBUTES,
      FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
      NULL,
      OPEN_EXISTING,
      FILE_FLAG_BACKUP_SEMANTICS,
      NULL
    );
    if (INVALID_HANDLE_VALUE != fh) {
      dwres = GetFinalPathNameByHandleW(fh, bptr, (DWORD)szb, 0);
      if (0 < dwres) {
        if (dwres < (DWORD)szb) {
          back = 1;
        }
      }
      CloseHandle(fh);
    }
#else
    $? ". no GetFinalPathNameByHandle"
#endif
    if (0 == back) {
#if defined(FSCTL_GET_REPARSE_POINT)
      /* !!!!! Second attempt with legacy procedure */
      $? ". legacy procedure"
      fh = CreateFileW(
        fn,
	FILE_READ_ATTRIBUTES,
	(FILE_SHARE_READ | FILE_SHARE_WRITE),
	NULL,
	OPEN_EXISTING,
	(
	  FILE_FLAG_BACKUP_SEMANTICS
	  | FILE_FLAG_OPEN_REPARSE_POINT
	  | FILE_ATTRIBUTE_REPARSE_POINT
	),
	NULL
      );
      if (INVALID_HANDLE_VALUE != fh) {
        dwres = 0;		$? ". CreateFileW"
	result = DeviceIoControl(
	  fh,
	  FSCTL_GET_REPARSE_POINT,
	  NULL,
	  (DWORD)0U,
	  (void *)repdabuf,
	  (DWORD)sizeof(repdabuf),
	  &dwres,
	  NULL
	);
	if (result) {		$? ". DeviceIoControl"
	  rdb = (REPARSE_DATA_BUFFER *)repdabuf;
	  if (IO_REPARSE_TAG_MOUNT_POINT == rdb->ReparseTag) {
	    $? ". mount point"
	    back = dk4symlink_copy_string(
	      bptr, szb,
	      &(rdb->MountPointReparseBuffer.PathBuffer[0]),
	      rdb->MountPointReparseBuffer.SubstituteNameOffset,
	      rdb->MountPointReparseBuffer.SubstituteNameLength,
	      erp
	    );
	  } else {
	    if (IO_REPARSE_TAG_SYMLINK == rdb->ReparseTag) {
              $? ". symbolic link"
	      back = dk4symlink_copy_string(
	        bptr, szb,
		&(rdb->SymbolicLinkReparseBuffer.PathBuffer[0]),
		rdb->SymbolicLinkReparseBuffer.SubstituteNameOffset,
		rdb->SymbolicLinkReparseBuffer.SubstituteNameLength,
		erp
	      );
	    } else {
	      /* !!!!! Not mount point, not symlink */
	      $? "! neither mount point nor symbolic link"
	    }
	  }
	} else {		$? "! DeviceIoControl"
	  dk4error_set_simple_error_code(erp, DK4_E_NOT_FOUND);
	}
        CloseHandle(fh);
      } else {			$? "! CreateFile"
        dk4error_set_simple_error_code(erp, DK4_E_NOT_FOUND);
      }
#else
      dk4error_set_simple_error_code(erp, DK4_E_NOT_SUPPORTED);
#endif
    }
#else
#if DK4_HAVE_GETFINALPATHNAMEBYHANDLE
    fh = CreateFileA(
      fn,
      FILE_READ_ATTRIBUTES,
      FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
      NULL,
      OPEN_EXISTING,
      FILE_FLAG_BACKUP_SEMANTICS,
      NULL
    );
    if (INVALID_HANDLE_VALUE != fh) {
      dwres = GetFinalPathNameByHandleA(fh, bptr, (DWORD)szb, 0);
      if (0 < dwres) {
        if (dwres < (DWORD)szb) {
          back = 1;
        }
      }
      CloseHandle(fh);
    }
#else
    /*	Legacy procedure only available for wchar_t.
    */
    dk4error_set_simple_error_code(erp, DK4_E_NOT_SUPPORTED);
#endif
#endif
    if (0 < back) {
      if (dkT('\\') == bptr[0]) {
        if ((dkT('\\') == bptr[1]) || (dkT('?') == bptr[1])) {
          if (dkT('?') == bptr[2]) {
	    if (dkT('\\') == bptr[3]) {
	      if (260 > dk4str_len(&(bptr[4]))) {
	        dk4str_cpy_to_left(bptr, &(bptr[4]));
	      }
	    }
	  }
        }
      }
    }
#else
#if DK4_CHAR_SIZE > 1
    dk4error_set_simple_error_code(erp, DK4_E_NOT_SUPPORTED);
#else
    errno = 0;
    res = readlink(fn, bptr, szb);
    if (0 < res) {
      if (res < szb) {
        bptr[res] = dkT('\0');
        back = 1;
      } else {				$? "! readlink requires larger buffer"
        bptr[0] = dkT('\0');
        dk4error_set_simple_error_code(erp, DK4_E_BUFFER_TOO_SMALL);
      }
    } else {				$? "! readlink <= 0"
      bptr[0] = dkT('\0');
      if (0 > res) {
        dk4error_set_idetails(erp, DK4_E_SYSTEM, errno);
      }
    }
#endif
#endif
    if (0 == back) { *bptr = dkT('\0'); }
  } else {
    dk4error_set_simple_error_code(erp, DK4_E_INVALID_ARGUMENTS);
  } $? "- dk4symlink_target %d", back
  return back;
}