win32: replace readlink(2)

The Windows implementation of readlink(2) has caused problems in
the past.  As, for example, with commit c29dc205d2 (win32: fix
implementation of readlink(2)).

Most uses of readlink(2) in BusyBox are actually calls to the
(considerably more convenient) library function xmalloc_readlink().
Implement a Windows version of that and used it instead of readlink(2).

This improves the handling of symbolic links (and similar reparse
points) in CJK and UTF-8 code pages.

Saves 48-80 bytes.

3 files changed, 17 insertions, 12 deletions

diff --git a/include/mingw.h b/include/mingw.h
index 6e851b43d..1dcc84bde 100644
--- a/include/mingw.h
+++ b/include/mingw.h
@@ -495,7 +495,6 @@ ssize_t mingw_open_read_close(const char *fn, void *buf, size_t size) FAST_FUNC;
 ssize_t mingw_read(int fd, void *buf, size_t count);
 int mingw_close(int fd);
 int pipe(int filedes[2]);
-ssize_t readlink(const char *pathname, char *buf, size_t bufsiz);
 NOIMPL(setgid,gid_t gid UNUSED_PARAM);
 NOIMPL(setegid,gid_t gid UNUSED_PARAM);
 NOIMPL(setsid,void);
diff --git a/libbb/xreadlink.c b/libbb/xreadlink.c
index e6cf90310..fc10a2939 100644
--- a/libbb/xreadlink.c
+++ b/libbb/xreadlink.c
@@ -17,6 +17,7 @@
  * NOTE: This function returns a malloced char* that you will have to free
  * yourself.
  */
+#if !ENABLE_PLATFORM_MINGW32
 char* FAST_FUNC xmalloc_readlink(const char *path)
 {
         enum { GROWBY = 80 }; /* how large we will grow strings by */
@@ -38,6 +39,7 @@ char* FAST_FUNC xmalloc_readlink(const char *path)
 
         return buf;
 }
+#endif
 
 /*
  * This routine is not the same as realpath(), which
diff --git a/win32/mingw.c b/win32/mingw.c
index fec6df73a..8588b1a86 100644
--- a/win32/mingw.c
+++ b/win32/mingw.c
@@ -673,8 +673,7 @@ static int do_lstat(int follow, const char *file_name, struct mingw_stat *buf)
                 buf->st_tag = get_symlink_data(buf->st_attr, file_name, &findbuf);
 
                 if (buf->st_tag) {
-                        ssize_t len;
-                        char content[PATH_MAX];
+                        char *content;
 
                         if (follow) {
                                 /* The file size and times are wrong when Windows follows
@@ -687,8 +686,9 @@ static int do_lstat(int follow, const char *file_name, struct mingw_stat *buf)
 
                         /* Get the contents of a symlink, not its target. */
                         buf->st_mode = S_IFLNK|S_IRWXU|S_IRWXG|S_IRWXO;
-                        len = readlink(file_name, content, PATH_MAX);
-                        buf->st_size = (len < 0 || len == PATH_MAX) ? 0 : len;
+                        content = xmalloc_readlink(file_name);
+                        buf->st_size = content ? strlen(content) : 0;
+                        free(content);
                         buf->st_atim = filetime_to_timespec(&(findbuf.ftLastAccessTime));
                         buf->st_mtim = filetime_to_timespec(&(findbuf.ftLastWriteTime));
                         buf->st_ctim = filetime_to_timespec(&(findbuf.ftCreationTime));
@@ -1642,9 +1642,11 @@ typedef struct {
 } APPEXECLINK_BUFFER;
 
 #define SRPB rptr->SymbolicLinkReparseBuffer
-ssize_t readlink(const char *pathname, char *buf, size_t bufsiz)
+char * FAST_FUNC xmalloc_readlink(const char *pathname)
 {
         HANDLE h;
+        char *buf;
+        int bufsiz;
 
         h = CreateFile(pathname, 0, 0, NULL, OPEN_EXISTING,
                                 FILE_FLAG_OPEN_REPARSE_POINT|FILE_FLAG_BACKUP_SEMANTICS, NULL);
@@ -1688,15 +1690,17 @@ ssize_t readlink(const char *pathname, char *buf, size_t bufsiz)
                 if (name) {
                         name[len] = 0;
                         name = normalize_ntpath(name);
-                        len = wcslen(name);
-                        if (len > bufsiz)
-                                len = bufsiz;
-                        if (WideCharToMultiByte(CP_ACP, 0, name, len, buf, bufsiz, 0, 0))
-                                return len;
+                        bufsiz = WideCharToMultiByte(CP_ACP, 0, name, -1, NULL, 0, 0, 0);
+                        if (bufsiz) {
+                                buf = xmalloc(bufsiz);
+                                if (WideCharToMultiByte(CP_ACP, 0, name, -1, buf, bufsiz, 0, 0))
+                                        return buf;
+                                free(buf);
+                        }
                 }
         }
         errno = err_win_to_posix();
-        return -1;
+        return NULL;
 }
 
 const char *get_busybox_exec_path(void)