mz_os: split file and link attribute getters (#797)

mz_os_get_file_attribs used lstat on POSIX and GetFileAttributesW
on Win32, both of which return the link's own attributes rather
than the target's. Callers that wanted to follow a symlink had no
way to ask for that, so mz_zip_writer_add_file produced followed
entries tagged ISLNK and readers that tried to recreate them as
symlinks.

Flip mz_os_get_file_attribs to stat on POSIX and to a CreateFile +
GetFileInformationByHandle path on Win32 when the entry is a
reparse point. Add mz_os_get_link_attribs preserving the original
lstat / GetFileAttributesW semantics. Update mz_zip_writer_add_file
to pick the right getter for each branch and to skip symlinks
cleanly when neither store_links nor follow_links is set.

Refs #797.

doc/mz_os.md

@@ -39,6 +39,7 @@ These functions provide support for handling common file system operations.
   - [mz\_os\_close\_dir](#mz_os_close_dir)
   - [mz\_os\_is\_dir](#mz_os_is_dir)
   - [mz\_os\_is\_symlink](#mz_os_is_symlink)
+  - [mz\_os\_get\_link\_attribs](#mz_os_get_link_attribs)
   - [mz\_os\_make\_symlink](#mz_os_make_symlink)
   - [mz\_os\_read\_symlink](#mz_os_read_symlink)
   - [mz\_os\_ms\_time](#mz_os_ms_time)
@@ -621,7 +622,7 @@ if (mz_os_get_file_date(src_path, &modified_date, &accessed_date, &creation_date
 
 ### mz_os_get_file_attribs
 
-Gets a file's attributes.
+Gets a file's attributes, following symbolic links.
 
 **Arguments**
 |Type|Name|Description|
@@ -839,6 +840,29 @@ else
     printf("Path %s is not a symbolic link\n", path);
 ```
 
+### mz_os_get_link_attribs
+
+Gets a symbolic link's attributes.
+
+**Arguments**
+|Type|Name|Description|
+|-|-|-|
+|const char *|path|File path|
+|uint32_t *|attributes|Pointer to store file attributes value|
+
+**Return**
+|Type|Description|
+|-|-|
+|int32_t|[MZ_ERROR](mz_error.md) code, MZ_OK if successful|
+
+**Example**
+```
+const char *path = "c:\\test7.txt";
+uint32_t attributes = 0;
+if (mz_os_get_link_attribs(path, &attributes) == MZ_OK)
+    printf("Link %s attributes %08x\n", path, attributes);
+```
+
 ### mz_os_make_symlink
 
 Creates a symbolic link pointing to a target.

mz_os.h

@@ -146,7 +146,7 @@ int32_t mz_os_set_file_date(const char *path, time_t modified_date, time_t acces
 /* Sets a file's modified, access, and creation dates if supported */
 
 int32_t mz_os_get_file_attribs(const char *path, uint32_t *attributes);
-/* Gets a file's attributes */
+/* Gets a file's attributes, following symbolic links */
 
 int32_t mz_os_set_file_attribs(const char *path, uint32_t attributes);
 /* Sets a file's attributes */
@@ -177,6 +177,9 @@ int32_t mz_os_is_dir(const char *path);
 int32_t mz_os_is_symlink(const char *path);
 /* Checks to see if path is a symbolic link */
 
+int32_t mz_os_get_link_attribs(const char *path, uint32_t *attributes);
+/* Gets a symbolic link's attributes */
+
 int32_t mz_os_make_symlink(const char *path, const char *target_path);
 /* Creates a symbolic link pointing to a target */
 

mz_os_posix.c

@@ -255,7 +255,7 @@ int32_t mz_os_get_file_attribs(const char *path, uint32_t *attributes) {
     int32_t err = MZ_OK;
 
     memset(&path_stat, 0, sizeof(path_stat));
-    if (lstat(path, &path_stat) == -1)
+    if (stat(path, &path_stat) == -1)
         err = MZ_INTERNAL_ERROR;
     *attributes = path_stat.st_mode;
     return err;
@@ -333,6 +333,17 @@ int32_t mz_os_is_symlink(const char *path) {
     return MZ_EXIST_ERROR;
 }
 
+int32_t mz_os_get_link_attribs(const char *path, uint32_t *attributes) {
+    struct stat path_stat;
+    int32_t err = MZ_OK;
+
+    memset(&path_stat, 0, sizeof(path_stat));
+    if (lstat(path, &path_stat) == -1)
+        err = MZ_INTERNAL_ERROR;
+    *attributes = path_stat.st_mode;
+    return err;
+}
+
 int32_t mz_os_make_symlink(const char *path, const char *target_path) {
 #if !HAVE_SYMLINK
     return MZ_SUPPORT_ERROR;

mz_os_win32.c

@@ -336,11 +336,39 @@ int32_t mz_os_get_file_attribs(const char *path, uint32_t *attributes) {
 
     if (!path || !attributes)
         return MZ_PARAM_ERROR;
+
     path_wide = mz_os_unicode_string_create(path, MZ_ENCODING_UTF8);
     if (!path_wide)
         return MZ_PARAM_ERROR;
 
     *attributes = GetFileAttributesW(path_wide);
+
+    /* If target is a reparse point, open with default flags to get attributes */
+    if (*attributes != INVALID_FILE_ATTRIBUTES && (*attributes & FILE_ATTRIBUTE_REPARSE_POINT)) {
+        HANDLE handle = INVALID_HANDLE_VALUE;
+        BY_HANDLE_FILE_INFORMATION info;
+
+#if _WIN32_WINNT >= _WIN32_WINNT_WIN8
+        CREATEFILE2_EXTENDED_PARAMETERS extended_params;
+
+        memset(&extended_params, 0, sizeof(extended_params));
+        extended_params.dwSize = sizeof(extended_params);
+        extended_params.dwFileFlags = FILE_FLAG_BACKUP_SEMANTICS;
+
+        handle = CreateFile2(path_wide, 0, FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, OPEN_EXISTING,
+                             &extended_params);
+#else
+        handle = CreateFileW(path_wide, 0, FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, NULL, OPEN_EXISTING,
+                             FILE_FLAG_BACKUP_SEMANTICS, NULL);
+#endif
+
+        if (handle != INVALID_HANDLE_VALUE) {
+            if (GetFileInformationByHandle(handle, &info))
+                *attributes = info.dwFileAttributes;
+            CloseHandle(handle);
+        }
+    }
+
     mz_os_unicode_string_delete(&path_wide);
 
     if (*attributes == INVALID_FILE_ATTRIBUTES)
@@ -512,6 +540,26 @@ int32_t mz_os_is_symlink(const char *path) {
     return MZ_EXIST_ERROR;
 }
 
+int32_t mz_os_get_link_attribs(const char *path, uint32_t *attributes) {
+    wchar_t *path_wide = NULL;
+    int32_t err = MZ_OK;
+
+    if (!path || !attributes)
+        return MZ_PARAM_ERROR;
+
+    path_wide = mz_os_unicode_string_create(path, MZ_ENCODING_UTF8);
+    if (!path_wide)
+        return MZ_PARAM_ERROR;
+
+    *attributes = GetFileAttributesW(path_wide);
+    mz_os_unicode_string_delete(&path_wide);
+
+    if (*attributes == INVALID_FILE_ATTRIBUTES)
+        err = MZ_INTERNAL_ERROR;
+
+    return err;
+}
+
 int32_t mz_os_make_symlink(const char *path, const char *target_path) {
     typedef BOOLEAN(WINAPI * LPCREATESYMBOLICLINKW)(LPCWSTR, LPCWSTR, DWORD);
     MEMORY_BASIC_INFORMATION mbi;

mz_zip_rw.c

@@ -1628,6 +1628,7 @@ int32_t mz_zip_writer_add_file(void *handle, const char *path, const char *filen
     uint32_t src_attrib = 0;
     int32_t err = MZ_OK;
     uint8_t src_sys = 0;
+    uint8_t is_symlink = 0;
     void *stream = NULL;
     char link_path[1024];
     const char *filename = filename_in_zip;
@@ -1643,6 +1644,12 @@ int32_t mz_zip_writer_add_file(void *handle, const char *path, const char *filen
             return err;
     }
 
+    if (mz_os_is_symlink(path) == MZ_OK)
+        is_symlink = 1;
+
+    if (is_symlink && !writer->store_links && !writer->follow_links)
+        return MZ_OK;
+
     memset(&file_info, 0, sizeof(file_info));
 
     /* The path name saved, should not include a leading slash. */
@@ -1665,7 +1672,11 @@ int32_t mz_zip_writer_add_file(void *handle, const char *path, const char *filen
         file_info.aes_version = MZ_AES_VERSION;
 
     mz_os_get_file_date(path, &file_info.modified_date, &file_info.accessed_date, &file_info.creation_date);
-    mz_os_get_file_attribs(path, &src_attrib);
+
+    if (is_symlink && writer->store_links)
+        mz_os_get_link_attribs(path, &src_attrib);
+    else
+        mz_os_get_file_attribs(path, &src_attrib);
 
     src_sys = MZ_HOST_SYSTEM(file_info.version_madeby);
 
@@ -1678,7 +1689,7 @@ int32_t mz_zip_writer_add_file(void *handle, const char *path, const char *filen
         file_info.external_fa = src_attrib;
     }
 
-    if (writer->store_links && mz_os_is_symlink(path) == MZ_OK) {
+    if (is_symlink && writer->store_links) {
         err = mz_os_read_symlink(path, link_path, sizeof(link_path));
         if (err == MZ_OK)
             file_info.linkname = link_path;