mingw: fix getcwd when the parent directory cannot be queried

`GetLongPathName()` function may fail when it is unable to query
the parent directory of a path component to determine the long name
for that component. It happens, because it uses `FindFirstFile()`
function for each next short part of path. The `FindFirstFile()`
requires `List Directory` and `Synchronize` desired access for a calling
process.

In case of lacking such permission for some part of path,
the `GetLongPathName()` returns 0 as result and `GetLastError()`
returns ERROR_ACCESS_DENIED.

`GetFinalPathNameByHandle()` function can help in such cases, because
it requires `Read Attributes` and `Synchronize` desired access to the
target path only.

The `GetFinalPathNameByHandle()` function was introduced on
`Windows Server 2008/Windows Vista`. So we need to load it dynamically.

`CreateFile()` parameters:
    `lpFileName` = path to the current directory
    `dwDesiredAccess` = 0 (it means `Read Attributes` and `Synchronize`)
    `dwShareMode` = FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE
                    (it prevents `Sharing Violation`)
    `lpSecurityAttributes` = NULL (default security attributes)
    `dwCreationDisposition` = OPEN_EXISTING
                              (required to obtain a directory handle)
    `dwFlagsAndAttributes` = FILE_FLAG_BACKUP_SEMANTICS
                             (required to obtain a directory handle)
    `hTemplateFile` = NULL (when opening an existing file or directory,
                            `CreateFile` ignores this parameter)

The string that is returned by `GetFinalPathNameByHandle()` function
uses the \\?\ syntax. To skip the prefix and convert backslashes
to slashes, the `normalize_ntpath()` mingw function will be used.

Note: `GetFinalPathNameByHandle()` function returns a final path.
It is the path that is returned when a path is fully resolved.
For example, for a symbolic link named "C:\tmp\mydir" that points to
"D:\yourdir", the final path would be "D:\yourdir".

Signed-off-by: Anton Serbulov <aserbulov@plesk.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/compat/mingw.c b/compat/mingw.c
index 2c3e27ce9e11e368ea60039cc9783a6d18acffb3..19addfa5d5925bb65b92962ab38025071167df41 100644 (file)
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -202,6 +202,31 @@ static int ask_yes_no_if_possible(const char *format, ...)
        }
 }
 
+/* Normalizes NT paths as returned by some low-level APIs. */
+static wchar_t *normalize_ntpath(wchar_t *wbuf)
+{
+       int i;
+       /* fix absolute path prefixes */
+       if (wbuf[0] == '\\') {
+               /* strip NT namespace prefixes */
+               if (!wcsncmp(wbuf, L"\\??\\", 4) ||
+                   !wcsncmp(wbuf, L"\\\\?\\", 4))
+                       wbuf += 4;
+               else if (!wcsnicmp(wbuf, L"\\DosDevices\\", 12))
+                       wbuf += 12;
+               /* replace remaining '...UNC\' with '\\' */
+               if (!wcsnicmp(wbuf, L"UNC\\", 4)) {
+                       wbuf += 2;
+                       *wbuf = '\\';
+               }
+       }
+       /* convert backslashes to slashes */
+       for (i = 0; wbuf[i]; i++)
+               if (wbuf[i] == '\\')
+                       wbuf[i] = '/';
+       return wbuf;
+}
+
 int mingw_unlink(const char *pathname)
 {
        int ret, tries = 0;
@@ -925,6 +950,20 @@ char *mingw_getcwd(char *pointer, int len)
                return NULL;
        }
        ret = GetLongPathNameW(cwd, wpointer, ARRAY_SIZE(wpointer));
+       if (!ret && GetLastError() == ERROR_ACCESS_DENIED) {
+               HANDLE hnd = CreateFileW(cwd, 0,
+                       FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, NULL,
+                       OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL);
+               if (hnd == INVALID_HANDLE_VALUE)
+                       return NULL;
+               ret = GetFinalPathNameByHandleW(hnd, wpointer, ARRAY_SIZE(wpointer), 0);
+               CloseHandle(hnd);
+               if (!ret || ret >= ARRAY_SIZE(wpointer))
+                       return NULL;
+               if (xwcstoutf(pointer, normalize_ntpath(wpointer), len) < 0)
+                       return NULL;
+               return pointer;
+       }
        if (!ret || ret >= ARRAY_SIZE(wpointer))
                return NULL;
        if (xwcstoutf(pointer, wpointer, len) < 0)