Rust: Add validation to decode

mojo/public/rust/tests/util/mod.rs

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 //! This module contains useful functions and macros for testing.
 
 pub mod mojom_validation;
 
 use std::ffi::{CStr, CString};
 use std::os::raw::c_char;
@@ skipping 50 matching lines @@
     let mut num_handles: usize = 0;
     let mut data: *mut u8 = ptr::null_mut();
     let mut data_len: usize = 0;
     let error = unsafe {
         ParseValidationTest(input_c.as_ptr(),
                             &mut num_handles as *mut usize,
                             &mut data as *mut *mut u8,
                             &mut data_len as *mut usize)
     };
     if error == ptr::null_mut() {
-        if data == ptr::null_mut() {
+        if data == ptr::null_mut() || data_len == 0 {
             // We assume we were just given an empty file
             Ok((Vec::new(), 0))
         } else {
             // Make a copy of the buffer
             let buffer;
             unsafe {
                 buffer = slice::from_raw_parts(data, data_len).to_vec();
                 free(data);
             }
             Ok((buffer, num_handles))
         }
     } else {
         let err_str;
         unsafe {
             // Copy the error string
             err_str = CStr::from_ptr(error)
                            .to_str()
                            .expect("Could not convert error message to UTF-8!")
                            .to_owned();
             free(error as *mut u8);
         }
         Err(err_str)
     }
 }