os.stat() does not work for NUL and CON #81255

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1. serhiy-storchaka commented on May 28, 2019

   

   serhiy-storchaka

   on May 28, 2019

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   >>> os.stat('nul')
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   OSError: [WinError 1] Incorrect function: 'nul'
   >>> os.stat('con')
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   OSError: [WinError 87] The parameter is incorrect: 'con'

   But os.open() and os.fstat() work.

   >>> os.fstat(os.open('nul', os.O_RDONLY))
   os.stat_result(st_mode=8192, st_ino=0, st_dev=0, st_nlink=0, st_uid=0, st_gid=0, st_size=0, st_atime=0, st_mtime=0, st_ctime=0)
   >>> os.fstat(os.open('con', os.O_RDONLY))
   os.stat_result(st_mode=8192, st_ino=0, st_dev=0, st_nlink=0, st_uid=0, st_gid=0, st_size=0, st_atime=0, st_mtime=0, st_ctime=0)
2. serhiy-storchaka

   added

   3.7 (EOL)end of lifeend of life

   3.8 (EOL)end of lifeend of life

   OS-windows

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on May 28, 2019
3. mangrisano commented on May 28, 2019

   

   mangrisanomannequin

   on May 28, 2019

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   I've tried to reproduce this behavior on my Mac with python3.8 and python 3.7 but I couldn't.

   If 'nul' doesn't exist, it raises a FileNotFound exception as it should do.
   If 'nul' exists, it shows me the right output.
   Same behavior with 'con'.
4. eryksun commented on May 28, 2019

   

   eryksun

   on May 28, 2019

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   Opening "CON" (i.e. r"\\.\CON") fails with ERROR_INVALID_PARAMETER (87) because it has to be opened with either GENERIC_READ or GENERIC_WRITE data access in order to map it to either the console input buffer or active screen buffer. The CreateFileW call in stat() necessarily requests no data access.

   Calling stat on "NUL" (among others such as "CONIN$", "//./C:", and "//./PhysicalDrive0") fails with ERROR_INVALID_FUNCTION (1) -- or possibly ERROR_INVALID_PARAMETER or ERROR_NOT_SUPPORTED (50), depending on the device. stat() calls GetFileInformationByHandle. This requests FileFsVolumeInformation and FileAllInformation, which commonly fail as unsupported or invalid requests for devices other than filesystem devices. Even volume and raw disk devices fail a FileAllInformation request.

   If we have a valid file handle, we can get the file type via GetFileType(hFile), as _Py_fstat_noraise does in Python/fileutils.c. If opening a handle fails with ERROR_INVALID_PARAMETER for a path that resolves to r"\\.\CON" or r"\\?\CON" via GetFullPathNameW, we can simply set st_mode to _S_IFCHR and return.

   For example:

       if (hFile == INVALID_HANDLE_VALUE) {
           DWORD lastError = GetLastError();
           if (lastError == ERROR_INVALID_PARAMETER) {
               WCHAR fullPath[8];
               if (GetFullPathNameW(path, sizeof(fullPath),
                       fullPath, NULL) == 7 && (
                   _wcsicmp(fullPath, L"\\\\.\\CON") == 0 ||
                   _wcsicmp(fullPath, L"\\\\?\\CON") == 0)) {
                   memset(result, 0, sizeof(*result));
                   result->st_mode = _S_IFCHR;
                   return 0;
               }
           }
           /*
               Existing error handling code.
           */
       } else {
           DWORD type = GetFileType(hFile);
           if (type != FILE_TYPE_DISK) {
               CloseHandle(hFile);
               if (type == FILE_TYPE_UNKNOWN && GetLastError() != 0) {
                   return -1;
               }
               memset(result, 0, sizeof(*result));
               if (type == FILE_TYPE_CHAR) { /* e.g. "//./NUL" */
                   result->st_mode = _S_IFCHR;
               } else if (type == FILE_TYPE_PIPE) { /* e.g. "//./PIPE/Spam" */
                   result->st_mode = _S_IFIFO;
               }
               return 0;
           } else if (!GetFileInformationByHandle(hFile, &info)) {
               DWORD lastError = GetLastError();
               CloseHandle(hFile);
               /* e.g. "//./C:" or "//./PhysicalDrive0" */
               if (lastError == ERROR_INVALID_FUNCTION ||
                   lastError == ERROR_INVALID_PARAMETER ||
                   lastError == ERROR_NOT_SUPPORTED) {
                   memset(result, 0, sizeof(*result));
                   result->st_mode = _S_IFREG;
                   return 0;
               }
               return -1;
           }
       }
5. eryksun commented on May 28, 2019

   

   eryksun

   on May 28, 2019

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   GetFullPathNameW(path, sizeof(fullPath),

   That should be sizeof(fullPath) / sizeof(WCHAR), or use Py_ARRAY_LENGTH, or just hard code 8. That's probably not the only mistake. But this is just an example to discuss the details and alternatives.
6. serhiy-storchaka commented on Jun 10, 2019

   

   serhiy-storchaka

   on Jun 10, 2019

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   Do you mind to create a PR Eryk?
7. eryksun

   closed this as completedon Aug 22, 2019
8. serhiy-storchaka commented on Aug 22, 2019

   

   serhiy-storchaka

   on Aug 22, 2019

   MemberAuthor

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   Where it was fixed?
9. eryksun commented on Aug 22, 2019

   

   eryksun

   on Aug 22, 2019

   Contributor

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   Where it was fixed?

   It was addressed in bpo-37834. PR 15231 includes a rewrite of win32_xstat_impl. The file type was needed, so the rewrite could also address the problem of character devices such as CON and NUL.
10. ezio-melotti

    transferred this issue fromon Apr 10, 2022