[FFmpeg-devel] [PATCH 1/2] avutil/wchar_filename, file_open: Support long file names on Windows

[softworkz <ffmpegagent@gmail.com>]

From: softworkz <softworkz@hotmail.com>

Signed-off-by: softworkz <softworkz@hotmail.com>
---
 libavutil/file_open.c      |   2 +-
 libavutil/wchar_filename.h | 123 +++++++++++++++++++++++++++++++++++++
 2 files changed, 124 insertions(+), 1 deletion(-)

diff --git a/libavutil/file_open.c b/libavutil/file_open.c
index cc302f2f76..57c5e78d51 100644
--- a/libavutil/file_open.c
+++ b/libavutil/file_open.c
@@ -45,7 +45,7 @@ static int win32_open(const char *filename_utf8, int oflag, int pmode)
     wchar_t *filename_w;
 
     /* convert UTF-8 to wide chars */
-    if (utf8towchar(filename_utf8, &filename_w))
+    if (get_extended_win32_path(filename_utf8, &filename_w))
         return -1;
     if (!filename_w)
         goto fallback;
diff --git a/libavutil/wchar_filename.h b/libavutil/wchar_filename.h
index 90f082452c..94b4087de0 100644
--- a/libavutil/wchar_filename.h
+++ b/libavutil/wchar_filename.h
@@ -40,6 +40,129 @@ static inline int utf8towchar(const char *filename_utf8, wchar_t **filename_w)
     MultiByteToWideChar(CP_UTF8, 0, filename_utf8, -1, *filename_w, num_chars);
     return 0;
 }
+
+static inline int path_is_extended(const wchar_t *path)
+{
+    // see .NET6: PathInternal.IsExtended()
+    size_t len = wcslen(path);
+    if (len >= 4  && path[0] == L'\\' && (path[1] == L'\\' || path[1] == L'?') && path[2] == L'?' && path[3] == L'\\')
+        return 1;
+
+    return 0;
+}
+
+static inline int get_full_path_name(wchar_t **ppath_w)
+{
+    int num_chars;
+    wchar_t *temp_w;
+
+    // see .NET6: PathHelper.GetFullPathName()
+    num_chars = GetFullPathNameW(*ppath_w, 0, NULL, NULL);
+    if (num_chars <= 0) {
+        errno = EINVAL;
+        return -1;
+    }
+
+    temp_w = (wchar_t *)av_calloc(num_chars, sizeof(wchar_t));
+    if (!temp_w) {
+        errno = ENOMEM;
+        return -1;
+    }
+
+    num_chars = GetFullPathNameW(*ppath_w, num_chars, temp_w, NULL);
+    if (num_chars <= 0) {
+        errno = EINVAL;
+        return -1;
+    }
+
+    av_freep(ppath_w);
+    *ppath_w = temp_w;
+
+    return 0;
+}
+
+static inline int path_normalize(wchar_t **ppath_w)
+{
+    int ret;
+
+    // see .NET6: PathHelper.Normalize()
+    if ((ret = get_full_path_name(ppath_w)) < 0)
+        return ret;
+
+    /* What .NET does at this point is to call PathHelper.TryExpandShortFileName()
+       in case the path contains a '~' character.
+       We don't need to do this as we don't need to normalize the file name
+       for presentation, and the extended path prefix works with 8.3 path
+       components as well */
+    return 0;
+}
+
+static inline int add_extended_prefix(wchar_t **ppath_w)
+{
+    const wchar_t *unc_prefix           = L"\\\\?\\UNC\\";
+    const wchar_t *extended_path_prefix = L"\\\\?\\";
+    const wchar_t *path_w               = *ppath_w;
+    const size_t len                    = wcslen(path_w);
+    wchar_t *temp_w;
+
+    if (len < 2)
+        return 0;
+
+    // see .NET6: PathInternal.EnsureExtendedPrefix()
+    if (path_w[0] == L'\\' && path_w[1] == L'\\') {
+        temp_w = (wchar_t *)av_calloc(len + 6 + 1, sizeof(wchar_t));
+        if (!temp_w) {
+            errno = ENOMEM;
+            return -1;
+        }
+        wcscpy(temp_w, unc_prefix);
+        wcscat(temp_w, path_w + 2);
+    } else {
+        temp_w = (wchar_t *)av_calloc(len + 4 + 1, sizeof(wchar_t));
+        if (!temp_w) {
+            errno = ENOMEM;
+            return -1;
+        }
+        wcscpy(temp_w, extended_path_prefix);
+        wcscat(temp_w, path_w);
+    }
+
+    av_freep(ppath_w);
+    *ppath_w = temp_w;
+
+    return 0;
+}
+
+static inline int get_extended_win32_path(const char *path, wchar_t **ppath_w)
+{
+    int ret;
+    size_t len;
+
+    // see .NET6: Path.GetFullPath() and Path.GetFullPathInternal()
+    if ((ret = utf8towchar(path, ppath_w)) < 0)
+        return ret;
+
+    if (path_is_extended(*ppath_w)) {
+        /* \\?\ paths are considered normalized by definition. Windows doesn't normalize \\?\
+           paths and neither should we. Even if we wanted to, GetFullPathName does not work
+           properly with device paths. If one wants to pass a \\?\ path through normalization
+           one can chop off the prefix, pass it to GetFullPath and add it again. */
+        return 0;
+    }
+
+    if ((ret = path_normalize(ppath_w)) < 0)
+        return ret;
+
+    // see .NET6: PathInternal.EnsureExtendedPrefixIfNeeded()
+    len = wcslen(*ppath_w);
+    if (len >= 260 || (*ppath_w)[len - 1] == L' ' || (*ppath_w)[len - 1] == L'.') {
+        if ((ret = add_extended_prefix(ppath_w)) < 0)
+            return ret;
+    }
+
+    return 0;
+}
+
 #endif
 
 #endif /* AVUTIL_WCHAR_FILENAME_H */
-- 
ffmpeg-codebot

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