diff --git a/fs/internal/ffi/fs_native.mbt b/fs/internal/ffi/fs_native.mbt
index 914764b..55cd2c3 100644
--- a/fs/internal/ffi/fs_native.mbt
+++ b/fs/internal/ffi/fs_native.mbt
@@ -14,14 +14,14 @@
 
 ///|
 pub fn read_file_to_string(path : String) -> String {
-  let path_bytes = mbt_string_to_utf8_bytes(path)
+  let path_bytes = mbt_string_to_utf8_bytes(path, true)
   let res = read_file_to_bytes_ffi(path_bytes)
   utf8_bytes_to_mbt_string(res)
 }
 
 ///|
 pub fn read_file_to_bytes(path : String) -> Bytes {
-  let path_bytes = mbt_string_to_utf8_bytes(path)
+  let path_bytes = mbt_string_to_utf8_bytes(path, true)
   read_file_to_bytes_ffi(path_bytes)
 }
 
@@ -30,15 +30,15 @@ extern "C" fn read_file_to_bytes_ffi(path : Bytes) -> Bytes = "read_file_to_byte
 
 ///|
 pub fn write_string_to_file(path : String, content : String) -> Unit {
-  let path_bytes = mbt_string_to_utf8_bytes(path)
-  let content_bytes = mbt_string_to_utf8_bytes(content)
+  let path_bytes = mbt_string_to_utf8_bytes(path, true)
+  let content_bytes = mbt_string_to_utf8_bytes(content, false)
   write_bytes_to_file_ffi(path_bytes, content_bytes)
 }
 
 ///|
 pub fn write_bytes_to_file(path : String, content : Bytes) -> Unit {
-  let path = mbt_string_to_utf8_bytes(path)
-  write_bytes_to_file_ffi(path, content)
+  let path_bytes = mbt_string_to_utf8_bytes(path, true)
+  write_bytes_to_file_ffi(path_bytes, content)
 }
 
 ///|
@@ -46,7 +46,7 @@ extern "C" fn write_bytes_to_file_ffi(path : Bytes, content : Bytes) = "write_by
 
 ///|
 pub fn path_exists(path : String) -> Bool {
-  path_exists_ffi(mbt_string_to_utf8_bytes(path)) == 0
+  path_exists_ffi(mbt_string_to_utf8_bytes(path, true)) == 0
 }
 
 ///|
@@ -54,7 +54,7 @@ extern "C" fn path_exists_ffi(path : Bytes) -> Int = "path_exists"
 
 ///|
 pub fn read_dir(path : String) -> Array[String] {
-  let path_bytes = mbt_string_to_utf8_bytes(path)
+  let path_bytes = mbt_string_to_utf8_bytes(path, true)
   let res = read_dir_ffi(path_bytes).map(utf8_bytes_to_mbt_string)
   Array::from_fixed_array(res)
 }
@@ -64,7 +64,7 @@ extern "C" fn read_dir_ffi(path : Bytes) -> FixedArray[Bytes] = "read_dir"
 
 ///|
 pub fn create_dir(path : String) -> Unit {
-  let path_bytes = mbt_string_to_utf8_bytes(path)
+  let path_bytes = mbt_string_to_utf8_bytes(path, true)
   create_dir_ffi(path_bytes)
 }
 
@@ -73,7 +73,7 @@ extern "C" fn create_dir_ffi(path : Bytes) = "create_dir"
 
 ///|
 pub fn is_dir(path : String) -> Bool {
-  let path_bytes = mbt_string_to_utf8_bytes(path)
+  let path_bytes = mbt_string_to_utf8_bytes(path, true)
   is_dir_ffi(path_bytes) == 0
 }
 
@@ -82,7 +82,7 @@ extern "C" fn is_dir_ffi(path : Bytes) -> Int = "is_dir"
 
 ///|
 pub fn is_file(path : String) -> Bool {
-  let path_bytes = mbt_string_to_utf8_bytes(path)
+  let path_bytes = mbt_string_to_utf8_bytes(path, true)
   is_file_ffi(path_bytes) == 0
 }
 
@@ -91,7 +91,7 @@ extern "C" fn is_file_ffi(path : Bytes) -> Int = "is_file"
 
 ///|
 pub fn remove_dir(path : String) -> Unit {
-  remove_dir_ffi(mbt_string_to_utf8_bytes(path))
+  remove_dir_ffi(mbt_string_to_utf8_bytes(path, true))
 }
 
 ///|
@@ -99,7 +99,7 @@ extern "C" fn remove_dir_ffi(path : Bytes) = "remove_dir"
 
 ///|
 pub fn remove_file(path : String) -> Unit {
-  let path_bytes = mbt_string_to_utf8_bytes(path)
+  let path_bytes = mbt_string_to_utf8_bytes(path, true)
   remove_file_ffi(path_bytes)
 }
 
@@ -107,7 +107,7 @@ pub fn remove_file(path : String) -> Unit {
 extern "C" fn remove_file_ffi(path : Bytes) = "remove_file"
 
 ///|
-fn mbt_string_to_utf8_bytes(str : String) -> Bytes {
+fn mbt_string_to_utf8_bytes(str : String, is_filename : Bool) -> Bytes {
   let res : Array[Byte] = []
   let len = str.length()
   let mut i = 0
@@ -138,7 +138,9 @@ fn mbt_string_to_utf8_bytes(str : String) -> Bytes {
     }
     i = i + 1
   }
-  res.push((0).to_byte())
+  if is_filename {
+    res.push((0).to_byte())
+  }
   Bytes::from_array(res)
 }
 
diff --git a/fs/internal/ffi/native_stub.c b/fs/internal/ffi/native_stub.c
index 04b83e7..8afd2c0 100644
--- a/fs/internal/ffi/native_stub.c
+++ b/fs/internal/ffi/native_stub.c
@@ -49,34 +49,22 @@ struct moonbit_bytes* read_file_to_bytes(struct moonbit_bytes *filename) {
         return NULL;
     }
 
+    struct moonbit_bytes* bytes = moonbit_make_bytes(size, 0);
 
-    // allocate memory to store the file content
-    char *buffer = (char *)malloc((size_t)size);
-    if (buffer == NULL) {
-        perror("malloc");
-        fclose((FILE *)(filename->data));
-        return NULL;
-    }
-
-    // read the file content into the buffer
-    size_t bytes_read = fread(buffer, 1, (size_t)size, file);
+    // read the file content into the bytes->data
+    size_t bytes_read = fread(bytes->data, 1, (size_t)size, file);
     if (bytes_read != (size_t)size) {
         perror("fread");
-        free(buffer);
-        fclose((FILE *)(filename->data));
+        fclose(file);
         return NULL;
     }
 
     // close the file
     if (fclose(file) != 0) {
         perror("fclose");
-        free(buffer);
         return NULL;
     }
 
-    struct moonbit_bytes* bytes = moonbit_make_bytes(size, 0);
-    memcpy(bytes->data, buffer, size);
-
     return bytes;
 }
 
@@ -235,7 +223,8 @@ void remove_file(struct moonbit_bytes* path) {
 
 void write_bytes_to_file(struct moonbit_bytes* path, struct moonbit_bytes* content) {
     FILE *file = fopen((const char *)(path->data), "wb");
-    size_t content_size = strlen((const char *)(content->data));
+    size_t content_size = content->header.arr.len;
     fwrite(content->data, 1, content_size, file);
+    fflush(file);
     fclose(file);
 }