Add get_module_filename

vlib/os/const.v

@@ -1,5 +1,11 @@
 module os
 
+// Ref - winnt.h
+const (
+	SUCCESS = 0 // ERROR_SUCCESS
+	ERROR_INSUFFICIENT_BUFFER = 130
+)
+
 const (
 	FILE_SHARE_READ   = 1
 	FILE_SHARE_WRITE  = 2

vlib/os/os_win.v

@@ -2,16 +2,38 @@ module os
 
 // Ref - https://docs.microsoft.com/en-us/windows/desktop/winprog/windows-data-types
 // A handle to an object.
-/* 
+type HANDLE voidptr
-type HANDLE voidptr // C.HANDLE
 
+// Ref - https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/get-osfhandle?view=vs-2019
+// get_file_handle retrieves the operating-system file handle that is associated with the specified file descriptor.
 pub fn get_file_handle(path string) HANDLE {
     mode := 'rb'
-    _fh := C.fopen(path.cstr(), mode.cstr())
+    _fd := C.fopen(path.cstr(), mode.cstr())
-    if isnil(_fh) {
+    if _fd == 0 {
-	      return HANDLE(INVALID_HANDLE_VALUE)
+	    return HANDLE(INVALID_HANDLE_VALUE)
     }
-    _handle := C._get_osfhandle(C._fileno(_fh)) // CreateFile? - hah, no -_-
+    _handle := C._get_osfhandle(C._fileno(_fd)) // CreateFile? - hah, no -_-
     return _handle
 }
-*/ 
+
+// Ref - https://docs.microsoft.com/en-us/windows/win32/api/libloaderapi/nf-libloaderapi-getmodulefilenamea
+// get_module_filename retrieves the fully qualified path for the file that contains the specified module. 
+// The module must have been loaded by the current process.
+pub fn get_module_filename(handle HANDLE) ?string {
+    mut sz := int(1024) // Optimized length 
+    mut buf := [byte(0); sz] // Not work for GetModuleFileNameW :(
+    for {
+        status := C.GetModuleFileName(handle, &buf, sz)
+        switch status {
+        case SUCCESS:
+            _filename := tos(buf.data, sz)
+            return _filename
+        case ERROR_INSUFFICIENT_BUFFER:
+            sz += 1024 // increment buffer cluster by 1024
+            buf = [byte(0); sz] // clear buffer
+        default:
+            // Must handled with GetLastError and converted by FormatMessage
+            return error('Cannot get file name from handle.')
+        }
+    }
+}