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// Copyright 2024 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef REMOTING_HOST_LINUX_GVARIANT_TYPE_H_
#define REMOTING_HOST_LINUX_GVARIANT_TYPE_H_
#include <glib.h>
#include <array>
#include <concepts>
#include <cstddef>
#include <functional>
#include <initializer_list>
#include <numeric>
#include <optional>
#include <ostream>
#include <ranges>
#include <string>
#include <string_view>
#include <tuple>
#include <type_traits>
#include <utility>
#include <vector>
#include "base/check.h"
#include "base/containers/span.h"
#include "base/strings/strcat.h"
namespace remoting::gvariant {
// Holds a type string for a GVariantRef. N is the length of the string (not
// counting the terminating null byte. When a specific N is provided or
// inferred, Type holds the type string inline and can be used at compile time.
// If N == base::dynamic_extent, the type string is instead held in a
// dynamically-allocated extent. Use with class template argument deduction to
// automatically infer N for compile-time constants. E.g.,
//
// static constexpr Type kTypeString = "i";
//
// will infer N to be 1.
template <std::size_t N = base::dynamic_extent>
class Type;
// Common members of all Types.
class TypeBase {
public:
// Access and conversion.
constexpr const char* c_string() const;
constexpr std::string_view string_view() const;
const GVariantType* gvariant_type() const;
explicit constexpr operator const char*() const;
explicit constexpr operator std::string_view() const;
explicit operator const GVariantType*() const;
explicit constexpr operator Type<>() const;
// Comparison
constexpr bool operator==(const TypeBase& other) const;
constexpr bool IsSubtypeOf(const TypeBase& supertype) const;
// Whether there exists a type that is a subtype of both this and other.
constexpr bool HasCommonTypeWith(const TypeBase& other) const;
// Properties
constexpr bool IsValid() const;
constexpr bool IsDefinite() const;
constexpr bool IsBasic() const;
constexpr bool IsStringType() const; // Is "s", "o", or "g".
constexpr bool IsContainer() const;
constexpr bool IsFixedSizeContainer() const;
// Utility
// Unpacks a fixed-size container into a vector of element types:
// "v": {"*"}
// "(iias)": {"i", "i", "as"}
// "{sv}": {"s", "v"}
// If this is not a fixed-size container, returns std::nullopt.
constexpr std::optional<std::vector<Type<>>> Unpack() const;
// Type-level version of the above.
// Returns a tuple of fixed-size Types instead of an optional vector of
// Type<>.
template <Type C>
static consteval /*std::tuple<Type<Ns>...>*/ auto Unpack()
requires(C.IsFixedSizeContainer());
// Finds the common supertype between this and other.
// "s", "s" -> "s"
// "s", "i" -> "?"
// "av", "as" -> "a*"
// "(uu)", "(ui)" -> "(u?)"
// "(uu)", "(uuu)" -> "r"
// "a{sv}", "a{ss}" -> "a{s*}"
constexpr Type<> CommonSuperTypeWith(const TypeBase& other) const;
// Finds the common supertype of a range of Types.
template <typename R>
requires std::ranges::range<R> &&
std::convertible_to<std::ranges::range_value_t<R>, const TypeBase&>
static constexpr Type<> CommonSuperTypeOf(const R& types);
// Type-level version of the above.
template <Type... Types>
static consteval /*Type<N>*/ auto CommonSuperTypeOf();
// Returns the element type of the container. For tuples, this will be the
// narrowest super type common to all elements as determined by
// CommonSuperType(). For boxed values ("v"), this will always return "*".
// If this is not a container, returns std::nullopt.
constexpr std::optional<Type<>> ContainedType() const;
// Type-level version of the above.
template <Type C>
requires(C.IsContainer())
static consteval /*Type<N>*/ auto ContainedType();
private:
// Returns the contained null-terminated string and string length (not
// including the terminating null).
constexpr virtual std::pair<const char*, std::size_t> contents() const = 0;
// Helpers
// Verifies that |string| is a valid type string representing a single,
// complete type.
static constexpr bool Validate(std::string_view string);
static constexpr bool IsBasicType(char code);
// Given a view within a type string, returns the length of the first single
// complete type. E.g. given "a{sv}i)", returns 5 (the length of "a{sv}"). If
// |view| does not begin with a valid complete type, the returned length is
// unspecified, but will be no greater than view.length().
static constexpr size_t TypeLength(std::string_view view);
// Converts a dynamic Type<> to a fixed Type<N>. get_dynamic must provide a
// constexpr operator() that returns the Type<>. It will be called exactly
// once.
template <typename Callable>
static consteval /* Type<N> */ auto ToFixed(Callable get_dynamic);
// Converts a dynamic std::vector<Type<>> to a fixed std::tuple<Type<N>...>.
// get_dynamic_vector must provide a constexpr operator() that returns the
// std::vector<Type<>>. It will be called exactly once.
template <typename Callable>
static consteval /* std::tuple<Type<N>...> */ auto ToFixedTuple(
Callable get_dynamic_vector);
};
// Type instance that stores the type string inline. Can be used in constant
// and template contexts. In general, using class template argument deduction to
// deduce the proper N from the arguments is preferred to specifying N manually.
template <std::size_t N>
class Type final : public TypeBase {
public:
// Provide N as a member to make checking for fixed-sized Types easier.
static constexpr std::size_t fixed_size = N;
// Constructors
// Construct from string literal.
//
// Implicit to allow GVariantRef<"s"> rather than
// GVariantRef<gvariant::Type("s")>.
// NOLINTNEXTLINE(google-explicit-constructor)
constexpr Type(const char (&string_lit)[N + 1])
: Type(base::span(string_lit).template first<N>()) {
CHECK(string_lit[N] == '\0')
<< "This constructor expects a null-terminated string";
}
// Construct from possibly non-null-terminated string of the proper length.
explicit constexpr Type(base::span<const char, N> string) {
base::span(type_string_).template first<N>().copy_from(string);
type_string_[N] = '\0';
}
// Composite type string concatenating the passed pieces. Each piece must
// be explicitly convertible to a fixed-size Type.
template <typename... Pieces>
requires(sizeof...(Pieces) > 1)
// Not actually callable with one argument, and marking it explicit would
// disallow things like GVariantRef<{"a", kSomeType}>
// NOLINTNEXTLINE(google-explicit-constructor)
constexpr Type(Pieces&&... pieces)
requires(N == (... + decltype(gvariant::Type(
std::forward<Pieces>(pieces)))::fixed_size))
{
base::span<char> remaining = type_string_;
// "Loop" through the passed values by invoking a lambda for each argument.
(
[&]<std::size_t M>(const Type<M>& type) {
remaining.take_first(type.string_view().size())
.copy_from(type.string_view());
}(gvariant::Type(std::forward<Pieces>(pieces))),
...);
remaining.front() = '\0';
}
// Copyable
Type(const Type& other) = default;
Type& operator=(const Type& other) = default;
// Logically private, but must be public to allow structural equality
// comparison when Type<N> is used as a template argument.
std::array<char, N + 1> type_string_;
private:
constexpr std::pair<const char*, std::size_t> contents() const override {
return std::pair(type_string_.data(), N);
}
};
// Type that holds the type_string in a dynamic allocation. Like std::string,
// constexpr constructors and methods are provided to allow the type to be used
// to hold temporary values at compile time. Also like std::string, and unlike
// a fixed-size Type, a dynamic-extent Type used at compile time must be
// destroyed by the end of constant evaluation. It may not be stored for later
// use by runtime code.
template <>
class Type<base::dynamic_extent> final : public TypeBase {
public:
// Dynamic extent constructors.
explicit constexpr Type(std::string string)
: type_string_(std::move(string)) {}
explicit constexpr Type(std::string_view string)
: Type(std::string(string)) {}
explicit constexpr Type(const char* string) : Type(std::string(string)) {}
explicit Type(const GVariantType* type);
// Dynamic concatenating constructor. Each piece must be explicitly
// convertible to a std::string_view.
template <typename... Pieces>
requires(sizeof...(Pieces) > 1)
explicit constexpr Type(Pieces&&... pieces)
: type_string_(
// StrCat can't be used at compile time, but is more efficient at
// run time.
std::is_constant_evaluated()
? (std::string() + ... +
std::string(static_cast<std::string_view>(pieces)))
: base::StrCat({static_cast<std::string_view>(pieces)...})) {}
// Copyable and movable
constexpr Type(const Type& other) = default;
constexpr Type& operator=(const Type& other) = default;
constexpr Type(Type&& other) = default;
constexpr Type& operator=(Type&& other) = default;
private:
constexpr std::pair<const char*, std::size_t> contents() const override {
return std::pair(type_string_.data(), type_string_.size());
}
std::string type_string_;
};
// Deduction guides for Type.
// Compile-time string constants create a fixed-size Type.
template <std::size_t M>
Type(const char (&string_lit)[M]) -> Type<M - 1>;
// Concatenations of any mix of compile-time constants and fixed-size Types
// yield a fixed-size Type.
#if 0
template <typename... Pieces>
requires(sizeof...(Pieces) > 1)
Type(Pieces&&... pieces)
->Type<(... + decltype(Type(std::forward<Pieces>(pieces)))::fixed_size)>;
#else
// The above doesn't work in the current version of Clang, but that can be
// worked around by stamping out the first two arguments manually:
template <typename First, typename Second, typename... Rest>
Type(First&& first, Second&& second, Rest&&... rest)
-> Type<((decltype(Type(std::forward<First>(first)))::fixed_size +
decltype(Type(std::forward<Second>(second)))::fixed_size) +
... + decltype(Type(std::forward<Rest>(rest)))::fixed_size)>;
#endif
// Other constructions will produce a dynamic Type.
template <typename... Pieces>
Type(Pieces&&...) -> Type<base::dynamic_extent>;
// Type implementation.
constexpr const char* TypeBase::c_string() const {
return contents().first;
}
constexpr std::string_view TypeBase::string_view() const {
auto [string, length] = this->contents();
return std::string_view(string, length);
}
constexpr TypeBase::operator const char*() const {
return c_string();
}
constexpr TypeBase::operator std::string_view() const {
return string_view();
}
constexpr TypeBase::operator Type<>() const {
return Type<>(string_view());
}
constexpr bool TypeBase::operator==(const TypeBase& other) const {
return string_view() == other.string_view();
}
constexpr bool TypeBase::IsSubtypeOf(const TypeBase& supertype) const {
if (!IsValid() || !supertype.IsValid()) {
return false;
}
std::string_view sub_view = string_view();
std::string_view super_view = supertype.string_view();
while (!sub_view.empty() && !super_view.empty()) {
if (super_view.front() == sub_view.front() ||
(super_view.front() == '?' && IsBasicType(sub_view.front()))) {
sub_view.remove_prefix(1);
super_view.remove_prefix(1);
} else if (sub_view.front() == ')' || sub_view.front() == '}') {
return false;
} else if (super_view.front() == '*' ||
(super_view.front() == 'r' && sub_view.front() == '(')) {
sub_view.remove_prefix(TypeLength(sub_view));
super_view.remove_prefix(1);
} else {
return false;
}
}
return sub_view.empty() && super_view.empty();
}
constexpr bool TypeBase::HasCommonTypeWith(const TypeBase& other) const {
if (!IsValid() || !other.IsValid()) {
return false;
}
// This is like IsSubtypeOf, but symmetrical.
std::string_view view1 = string_view();
std::string_view view2 = other.string_view();
while (!view1.empty() && !view2.empty()) {
if (view1.front() == view2.front() ||
(view1.front() == '?' && IsBasicType(view2.front())) ||
(view2.front() == '?' && IsBasicType(view1.front()))) {
view1.remove_prefix(1);
view2.remove_prefix(1);
} else if (view1.front() == ')' || view1.front() == '}' ||
view2.front() == ')' || view2.front() == '}') {
return false;
} else if (view1.front() == '*' ||
(view1.front() == 'r' && view2.front() == '(')) {
view1.remove_prefix(1);
view2.remove_prefix(TypeLength(view2));
} else if (view2.front() == '*' ||
(view2.front() == 'r' && view1.front() == '(')) {
view1.remove_prefix(TypeLength(view1));
view2.remove_prefix(1);
} else {
return false;
}
}
return view1.empty() && view2.empty();
}
constexpr bool TypeBase::IsValid() const {
return Validate(string_view());
}
constexpr bool TypeBase::IsDefinite() const {
if (!IsValid()) {
return false;
}
for (char c : this->string_view()) {
// These characters indicate, respectively, any type, any basic type, and
// any tuple, and the presence of any of them makes a type indefinite.
if (c == '*' || c == '?' || c == 'r') {
return false;
}
}
return true;
}
constexpr bool TypeBase::IsBasic() const {
if (string_view().size() != 1) {
return false;
}
return IsBasicType(string_view().front());
}
constexpr bool TypeBase::IsStringType() const {
if (string_view().size() != 1) {
return false;
}
switch (string_view().front()) {
case 's':
case 'o':
case 'g':
return true;
default:
return false;
}
}
constexpr bool TypeBase::IsContainer() const {
if (!IsValid()) {
return false;
}
switch (string_view().front()) {
case 'v':
case 'a':
case 'm':
case 'r':
case '(':
case '{':
return true;
default:
return false;
}
}
constexpr bool TypeBase::IsFixedSizeContainer() const {
if (!IsValid()) {
return false;
}
switch (string_view().front()) {
case 'v':
case '(':
case '{':
return true;
default:
return false;
}
}
constexpr std::optional<std::vector<Type<>>> TypeBase::Unpack() const {
if (!IsFixedSizeContainer()) {
return std::nullopt;
}
std::string_view view = string_view();
std::vector<Type<>> result;
if (view == "v") {
result.emplace_back("*");
} else {
view.remove_prefix(1); // Skip opening '(' or '{'
while (view.front() != ')' && view.front() != '}') {
std::size_t type_length = TypeLength(view);
result.emplace_back(view.substr(0, type_length));
view.remove_prefix(type_length);
}
}
return result;
}
// static
template <Type C>
consteval /*std::tuple<Type<Ns>...>*/ auto TypeBase::Unpack()
requires(C.IsFixedSizeContainer())
{
constexpr auto unpack = []() { return C.Unpack().value(); };
return ToFixedTuple(unpack);
}
constexpr Type<> TypeBase::CommonSuperTypeWith(const TypeBase& other) const {
if (!IsValid() || !other.IsValid()) {
return Type<>("*");
} else if (*this == other) {
return Type<>(*this);
} else if (IsBasic() && other.IsBasic()) {
return Type<>("?");
} else if ((string_view().front() == 'r' &&
other.string_view().front() == '(') ||
(string_view().front() == '(' &&
other.string_view().front() == 'r')) {
return Type<>("r");
} else if (string_view().front() == other.string_view().front()) {
// Containers of the same type. (Only way first char can be equal but not
// the rest.)
const char container_char = string_view().front();
if (container_char == 'a' || container_char == 'm') {
return Type<>(std::string_view(&container_char, 1),
ContainedType().value().CommonSuperTypeWith(
other.ContainedType().value()));
}
// Must be tuple or dict entry.
std::vector<Type<>> my_types = Unpack().value();
std::vector<Type<>> other_types = other.Unpack().value();
if (my_types.size() != other_types.size()) {
// Dict entries always have two entries, so they must be tuples.
return Type<>("r");
}
std::string super_types;
// A supertype is no longer than either subtype.
super_types.reserve(string_view().size());
super_types += container_char;
for (std::size_t i = 0; i < my_types.size(); ++i) {
super_types +=
my_types[i].CommonSuperTypeWith(other_types[i]).string_view();
}
super_types += container_char == '(' ? ")" : "}";
return Type<>(super_types);
} else {
return Type<>("*");
}
}
// static
template <typename R>
requires std::ranges::range<R> &&
std::convertible_to<std::ranges::range_value_t<R>, const TypeBase&>
constexpr Type<> TypeBase::CommonSuperTypeOf(const R& types) {
if (std::ranges::size(types) == 0) {
return Type<>("*");
}
return std::accumulate(
std::next(std::ranges::begin(types)), std::ranges::end(types),
Type<>(static_cast<const TypeBase&>(*std::ranges::begin(types))),
[](const TypeBase& type1, const TypeBase& type2) {
return type1.CommonSuperTypeWith(type2);
});
}
// static
template <Type... Types>
consteval /*Type<N>*/ auto TypeBase::CommonSuperTypeOf() {
constexpr auto find_super_type = []() {
return CommonSuperTypeOf(
std::initializer_list<std::reference_wrapper<const TypeBase>>{
std::cref<TypeBase>(Types)...});
};
return ToFixed(find_super_type);
}
constexpr std::optional<Type<>> TypeBase::ContainedType() const {
if (!IsContainer()) {
return std::nullopt;
}
if (*this == Type("v") || *this == Type("r")) {
return Type<>("*");
} else if (string_view().front() == 'a' || string_view().front() == 'm') {
return Type<>(string_view().substr(1));
} else {
// Tuple or dict entry
std::vector<Type<>> inner_types = Unpack().value();
return CommonSuperTypeOf(inner_types);
}
}
// static
template <Type C>
requires(C.IsContainer())
consteval /*Type<N>*/ auto TypeBase::ContainedType() {
constexpr auto get_contained_type = []() {
return C.ContainedType().value();
};
return ToFixed(get_contained_type);
}
// static
constexpr bool TypeBase::Validate(std::string_view string) {
if (string.empty()) {
return false;
}
switch (string.front()) {
case 'b':
case 'y':
case 'n':
case 'q':
case 'i':
case 'u':
case 'x':
case 't':
case 'd':
case 's':
case 'o':
case 'g':
case 'h':
case 'v':
case 'r':
case '?':
case '*':
return string.size() == 1;
case 'a':
case 'm':
return Validate(string.substr(1));
case '{':
return string.back() == '}' && IsBasicType(string[1]) &&
Validate(string.substr(2, string.size() - 3));
case '(': {
if (string.back() != ')') {
return false;
}
std::string_view remaining = string.substr(1, string.size() - 2);
while (remaining.size() != 0) {
std::size_t type_length = TypeLength(remaining);
if (!Validate(remaining.substr(0, type_length))) {
return false;
}
remaining.remove_prefix(type_length);
}
return true;
}
default:
return false;
}
}
// static
constexpr bool TypeBase::IsBasicType(char code) {
switch (code) {
case 'b':
case 'y':
case 'n':
case 'q':
case 'i':
case 'u':
case 'x':
case 't':
case 'd':
case 's':
case 'o':
case 'g':
case 'h':
// Indefinite type representing any basic type.
case '?':
return true;
default:
return false;
}
}
// static
constexpr size_t TypeBase::TypeLength(std::string_view view) {
std::size_t initial_length = view.length();
while (!view.empty() && (view.front() == 'a' || view.front() == 'm')) {
view.remove_prefix(1);
}
std::size_t depth = 0;
do {
if (view.empty()) {
break;
} else if (view.front() == '(' || view.front() == '{') {
++depth;
} else if (view.front() == ')' || view.front() == '}') {
--depth;
}
view.remove_prefix(1);
} while (depth != 0);
return initial_length - view.length();
}
// static
template <typename Callable>
consteval /* Type<N> */ auto TypeBase::ToFixed(Callable get_dynamic) {
#if 0
// This will hopefully be supported in a future version of C++.
// See https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p3032r2.html
constexpr Type<> type = get_dynamic();
return Type(type.c_string(),
std::integral_constant<std::size_t, type.size()>());
#else
// In the current C++ version, a compile-time value with dynamic allocation
// cannot be stored in a constexpr variable, even in a consteval function from
// which it is guaranteed not to leak to runtime. To avoid calling get_dynamic
// twice (once to get the size and once to get the data), it is necessary to
// initially store the result in an almost-sure-to-be-big-enough fixed-size
// array and then shrink it to the proper size.
struct IntermediateResult {
// A const evaluation compiler error will occur if this isn't big enough.
std::array<char, 10000> data;
std::size_t size;
};
constexpr IntermediateResult intermediate_result = [](Type<> type) {
IntermediateResult intermediate_result{};
intermediate_result.size = type.string_view().size();
base::span(intermediate_result.data)
.first(type.string_view().size())
.copy_from(type.string_view());
return intermediate_result;
}(get_dynamic());
return Type(base::span(intermediate_result.data)
.template first<intermediate_result.size>());
#endif
}
// static
template <typename Callable>
consteval /* std::tuple<Type<N>...> */ auto TypeBase::ToFixedTuple(
Callable get_dynamic_vector) {
// Like with ToFixed(), this function copies the result into almost-sure-to-
// be-big-enough fixed-size arrays that are allowed to be stored in a
// constexpr variable to avoid calling get_dynamic_vector() multiple times.
struct IntermediateResult {
// A const evaluation compiler error will occur if this isn't big enough.
std::array<char, 10000> data;
std::array<std::size_t, 10000> sizes;
std::size_t count;
};
constexpr IntermediateResult intermediate_result =
[](std::vector<Type<>> types) {
IntermediateResult intermediate_result{};
intermediate_result.count = types.size();
base::span<char> data_span = intermediate_result.data;
for (std::size_t i = 0; i < types.size(); ++i) {
intermediate_result.sizes[i] = types[i].string_view().size();
data_span.take_first(types[i].string_view().size())
.copy_from(types[i].string_view());
}
return intermediate_result;
}(get_dynamic_vector());
return [&]<std::size_t... Is>(std::index_sequence<Is...>) {
base::span<const char> data_span = intermediate_result.data;
// Uses brace initialization to guarantee in-order evaluation of arguments.
return std::tuple{
Type(data_span.take_first<intermediate_result.sizes[Is]>())...};
}(std::make_index_sequence<intermediate_result.count>());
}
} // namespace remoting::gvariant
#endif // REMOTING_HOST_LINUX_GVARIANT_TYPE_H_
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