blob: ae4120800ae8fc32068b74895cb357e19deb1a69 [file] [log] [blame]
// Copyright 2014 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.
// Functions to help with verifying various |Mojo...Options| structs from the
// (public, C) API. These are "extensible" structs, which all have |struct_size|
// as their first member. All fields (other than |struct_size|) are optional,
// but any |flags| specified must be known to the system (otherwise, an error of
// |MOJO_RESULT_UNIMPLEMENTED| should be returned).
#include <stddef.h>
#include <stdint.h>
#include <algorithm>
#include "base/logging.h"
#include "base/macros.h"
#include "mojo/core/system_impl_export.h"
#include "mojo/public/c/system/types.h"
namespace mojo {
namespace core {
template <class Options>
class UserOptionsReader {
// Constructor from a |const* Options| (which it checks -- this constructor
// has side effects!).
// Note: We initialize |options_reader_| without checking, since we do a check
// in |GetSizeForReader()|.
explicit UserOptionsReader(const Options* options) {
CHECK(options && IsAligned<MOJO_ALIGNOF(Options)>(options));
options_ = GetSizeForReader(options) == 0 ? nullptr : options;
static_assert(offsetof(Options, struct_size) == 0,
"struct_size not first member of Options");
// TODO(vtl): Enable when MSVC supports this (C++11 extended sizeof):
// static_assert(sizeof(Options::struct_size) == sizeof(uint32_t),
// "Options::struct_size not a uint32_t");
// (Or maybe assert that its type is uint32_t?)
bool is_valid() const { return !!options_; }
const Options& options() const {
return *options_;
// Checks that the given (variable-size) |options| passed to the constructor
// (plausibly) has a member at the given offset with the given size. You
// probably want to use |OPTIONS_STRUCT_HAS_MEMBER()| instead.
bool HasMember(size_t offset, size_t size) const {
// We assume that |offset| and |size| are reasonable, since they should come
// from |offsetof(Options, some_member)| and |sizeof(Options::some_member)|,
// respectively.
return options().struct_size >= offset + size;
static inline size_t GetSizeForReader(const Options* options) {
uint32_t struct_size = *reinterpret_cast<const uint32_t*>(options);
if (struct_size < sizeof(uint32_t))
return 0;
return std::min(static_cast<size_t>(struct_size), sizeof(Options));
template <size_t alignment>
static bool IsAligned(const void* pointer) {
return reinterpret_cast<uintptr_t>(pointer) % alignment == 0;
const Options* options_;
// Macro to invoke |UserOptionsReader<Options>::HasMember()| parametrized by
// member name instead of offset and size.
// (We can't just give |HasMember()| a member pointer template argument instead,
// since there's no good/strictly-correct way to get an offset from that.)
// TODO(vtl): With C++11, use |sizeof(Options::member)| instead of (the
// contortion below). We might also be able to pull out the type |Options| from
// |reader| (using |decltype|) instead of requiring a parameter.
#define OPTIONS_STRUCT_HAS_MEMBER(Options, member, reader) \
reader.HasMember(offsetof(Options, member), sizeof(reader.options().member))
} // namespace core
} // namespace mojo