Fairphone ODM | 25c12f5 | 2023-12-15 17:24:06 +0800 | [diff] [blame] | 1 | /* |
| 2 | * Copyright (C) 2017 The Android Open Source Project |
| 3 | * |
| 4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 5 | * you may not use this file except in compliance with the License. |
| 6 | * You may obtain a copy of the License at |
| 7 | * |
| 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | * |
| 10 | * Unless required by applicable law or agreed to in writing, software |
| 11 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 13 | * See the License for the specific language governing permissions and |
| 14 | * limitations under the License. |
| 15 | */ |
| 16 | |
| 17 | // Result<T, E> is the type that is used to pass a success value of type T or an error code of type |
| 18 | // E, optionally together with an error message. T and E can be any type. If E is omitted it |
| 19 | // defaults to int, which is useful when errno(3) is used as the error code. |
| 20 | // |
| 21 | // Passing a success value or an error value: |
| 22 | // |
| 23 | // Result<std::string> readFile() { |
| 24 | // std::string content; |
| 25 | // if (base::ReadFileToString("path", &content)) { |
| 26 | // return content; // ok case |
| 27 | // } else { |
| 28 | // return ErrnoError() << "failed to read"; // error case |
| 29 | // } |
| 30 | // } |
| 31 | // |
| 32 | // Checking the result and then unwrapping the value or propagating the error: |
| 33 | // |
| 34 | // Result<bool> hasAWord() { |
| 35 | // auto content = readFile(); |
| 36 | // if (!content.ok()) { |
| 37 | // return Error() << "failed to process: " << content.error(); |
| 38 | // } |
| 39 | // return (*content.find("happy") != std::string::npos); |
| 40 | // } |
| 41 | // |
| 42 | // Using custom error code type: |
| 43 | // |
| 44 | // enum class MyError { A, B }; // assume that this is the error code you already have |
| 45 | // |
| 46 | // // To use the error code with Result, define a wrapper class that provides the following |
| 47 | // operations and use the wrapper class as the second type parameter (E) when instantiating |
| 48 | // Result<T, E> |
| 49 | // |
| 50 | // 1. default constructor |
| 51 | // 2. copy constructor / and move constructor if copying is expensive |
| 52 | // 3. conversion operator to the error code type |
| 53 | // 4. value() function that return the error code value |
| 54 | // 5. print() function that gives a string representation of the error ode value |
| 55 | // |
| 56 | // struct MyErrorWrapper { |
| 57 | // MyError val_; |
| 58 | // MyErrorWrapper() : val_(/* reasonable default value */) {} |
| 59 | // MyErrorWrapper(MyError&& e) : val_(std:forward<MyError>(e)) {} |
| 60 | // operator const MyError&() const { return val_; } |
| 61 | // MyError value() const { return val_; } |
| 62 | // std::string print() const { |
| 63 | // switch(val_) { |
| 64 | // MyError::A: return "A"; |
| 65 | // MyError::B: return "B"; |
| 66 | // } |
| 67 | // } |
| 68 | // }; |
| 69 | // |
| 70 | // #define NewMyError(e) Error<MyErrorWrapper>(MyError::e) |
| 71 | // |
| 72 | // Result<T, MyError> val = NewMyError(A) << "some message"; |
| 73 | // |
| 74 | // Formatting the error message using fmtlib: |
| 75 | // |
| 76 | // Errorf("{} errors", num); // equivalent to Error() << num << " errors"; |
| 77 | // ErrnoErrorf("{} errors", num); // equivalent to ErrnoError() << num << " errors"; |
| 78 | // |
| 79 | // Returning success or failure, but not the value: |
| 80 | // |
| 81 | // Result<void> doSomething() { |
| 82 | // if (success) return {}; |
| 83 | // else return Error() << "error occurred"; |
| 84 | // } |
| 85 | // |
| 86 | // Extracting error code: |
| 87 | // |
| 88 | // Result<T> val = Error(3) << "some error occurred"; |
| 89 | // assert(3 == val.error().code()); |
| 90 | // |
| 91 | |
| 92 | #pragma once |
| 93 | |
| 94 | #include <assert.h> |
| 95 | #include <errno.h> |
| 96 | |
| 97 | #include <sstream> |
| 98 | #include <string> |
| 99 | #include <type_traits> |
| 100 | |
| 101 | #include "android-base/errors.h" |
| 102 | #include "android-base/expected.h" |
| 103 | #include "android-base/format.h" |
| 104 | |
| 105 | namespace android { |
| 106 | namespace base { |
| 107 | |
| 108 | // Errno is a wrapper class for errno(3). Use this type instead of `int` when instantiating |
| 109 | // `Result<T, E>` and `Error<E>` template classes. This is required to distinguish errno from other |
| 110 | // integer-based error code types like `status_t`. |
| 111 | struct Errno { |
| 112 | Errno() : val_(0) {} |
| 113 | Errno(int e) : val_(e) {} |
| 114 | int value() const { return val_; } |
| 115 | operator int() const { return value(); } |
| 116 | std::string print() const { return strerror(value()); } |
| 117 | |
| 118 | int val_; |
| 119 | |
| 120 | // TODO(b/209929099): remove this conversion operator. This currently is needed to not break |
| 121 | // existing places where error().code() is used to construct enum values. |
| 122 | template <typename E, typename = std::enable_if_t<std::is_enum_v<E>>> |
| 123 | operator E() const { |
| 124 | return E(val_); |
| 125 | } |
| 126 | }; |
| 127 | |
| 128 | template <typename E = Errno, bool include_message = true> |
| 129 | struct ResultError { |
| 130 | template <typename T, typename P, typename = std::enable_if_t<std::is_convertible_v<P, E>>> |
| 131 | ResultError(T&& message, P&& code) |
| 132 | : message_(std::forward<T>(message)), code_(E(std::forward<P>(code))) {} |
| 133 | |
| 134 | template <typename T> |
| 135 | // NOLINTNEXTLINE(google-explicit-constructor) |
| 136 | operator android::base::expected<T, ResultError<E>>() const { |
| 137 | return android::base::unexpected(ResultError<E>(message_, code_)); |
| 138 | } |
| 139 | |
| 140 | std::string message() const { return message_; } |
| 141 | const E& code() const { return code_; } |
| 142 | |
| 143 | private: |
| 144 | std::string message_; |
| 145 | E code_; |
| 146 | }; |
| 147 | |
| 148 | template <typename E> |
| 149 | struct ResultError<E, /* include_message */ false> { |
| 150 | template <typename P, typename = std::enable_if_t<std::is_convertible_v<P, E>>> |
| 151 | ResultError(P&& code) : code_(E(std::forward<P>(code))) {} |
| 152 | |
| 153 | template <typename T> |
| 154 | operator android::base::expected<T, ResultError<E, false>>() const { |
| 155 | return android::base::unexpected(ResultError<E, false>(code_)); |
| 156 | } |
| 157 | |
| 158 | const E& code() const { return code_; } |
| 159 | |
| 160 | private: |
| 161 | E code_; |
| 162 | }; |
| 163 | |
| 164 | template <typename E> |
| 165 | inline bool operator==(const ResultError<E>& lhs, const ResultError<E>& rhs) { |
| 166 | return lhs.message() == rhs.message() && lhs.code() == rhs.code(); |
| 167 | } |
| 168 | |
| 169 | template <typename E> |
| 170 | inline bool operator!=(const ResultError<E>& lhs, const ResultError<E>& rhs) { |
| 171 | return !(lhs == rhs); |
| 172 | } |
| 173 | |
| 174 | template <typename E> |
| 175 | inline std::ostream& operator<<(std::ostream& os, const ResultError<E>& t) { |
| 176 | os << t.message(); |
| 177 | return os; |
| 178 | } |
| 179 | |
| 180 | namespace internal { |
| 181 | // Stream class that does nothing and is has zero (actually 1) size. It is used instead of |
| 182 | // std::stringstream when include_message is false so that we use less on stack. |
| 183 | // sizeof(std::stringstream) is 280 on arm64. |
| 184 | struct DoNothingStream { |
| 185 | template <typename T> |
| 186 | DoNothingStream& operator<<(T&&) { |
| 187 | return *this; |
| 188 | } |
| 189 | |
| 190 | std::string str() const { return ""; } |
| 191 | }; |
| 192 | } // namespace internal |
| 193 | |
| 194 | template <typename E = Errno, bool include_message = true, |
| 195 | typename = std::enable_if_t<!std::is_same_v<E, int>>> |
| 196 | class Error { |
| 197 | public: |
| 198 | Error() : code_(0), has_code_(false) {} |
| 199 | template <typename P, typename = std::enable_if_t<std::is_convertible_v<P, E>>> |
| 200 | // NOLINTNEXTLINE(google-explicit-constructor) |
| 201 | Error(P&& code) : code_(std::forward<P>(code)), has_code_(true) {} |
| 202 | |
| 203 | template <typename T, typename P, typename = std::enable_if_t<std::is_convertible_v<E, P>>> |
| 204 | // NOLINTNEXTLINE(google-explicit-constructor) |
| 205 | operator android::base::expected<T, ResultError<P>>() const { |
| 206 | return android::base::unexpected(ResultError<P>(str(), static_cast<P>(code_))); |
| 207 | } |
| 208 | |
| 209 | template <typename T, typename P, typename = std::enable_if_t<std::is_convertible_v<E, P>>> |
| 210 | // NOLINTNEXTLINE(google-explicit-constructor) |
| 211 | operator android::base::expected<T, ResultError<P, false>>() const { |
| 212 | return android::base::unexpected(ResultError<P, false>(static_cast<P>(code_))); |
| 213 | } |
| 214 | |
| 215 | template <typename T> |
| 216 | Error& operator<<(T&& t) { |
| 217 | static_assert(include_message, "<< not supported when include_message = false"); |
| 218 | // NOLINTNEXTLINE(bugprone-suspicious-semicolon) |
| 219 | if constexpr (std::is_same_v<std::remove_cv_t<std::remove_reference_t<T>>, ResultError<E>>) { |
| 220 | if (!has_code_) { |
| 221 | code_ = t.code(); |
| 222 | } |
| 223 | return (*this) << t.message(); |
| 224 | } |
| 225 | int saved = errno; |
| 226 | ss_ << t; |
| 227 | errno = saved; |
| 228 | return *this; |
| 229 | } |
| 230 | |
| 231 | const std::string str() const { |
| 232 | static_assert(include_message, "str() not supported when include_message = false"); |
| 233 | std::string str = ss_.str(); |
| 234 | if (has_code_) { |
| 235 | if (str.empty()) { |
| 236 | return code_.print(); |
| 237 | } |
| 238 | return std::move(str) + ": " + code_.print(); |
| 239 | } |
| 240 | return str; |
| 241 | } |
| 242 | |
| 243 | Error(const Error&) = delete; |
| 244 | Error(Error&&) = delete; |
| 245 | Error& operator=(const Error&) = delete; |
| 246 | Error& operator=(Error&&) = delete; |
| 247 | |
| 248 | template <typename T, typename... Args> |
| 249 | friend Error ErrorfImpl(const T&& fmt, const Args&... args); |
| 250 | |
| 251 | template <typename T, typename... Args> |
| 252 | friend Error ErrnoErrorfImpl(const T&& fmt, const Args&... args); |
| 253 | |
| 254 | private: |
| 255 | Error(bool has_code, E code, const std::string& message) : code_(code), has_code_(has_code) { |
| 256 | (*this) << message; |
| 257 | } |
| 258 | |
| 259 | std::conditional_t<include_message, std::stringstream, internal::DoNothingStream> ss_; |
| 260 | E code_; |
| 261 | const bool has_code_; |
| 262 | }; |
| 263 | |
| 264 | inline Error<Errno> ErrnoError() { |
| 265 | return Error<Errno>(Errno{errno}); |
| 266 | } |
| 267 | |
| 268 | template <typename E> |
| 269 | inline E ErrorCode(E code) { |
| 270 | return code; |
| 271 | } |
| 272 | |
| 273 | // Return the error code of the last ResultError object, if any. |
| 274 | // Otherwise, return `code` as it is. |
| 275 | template <typename T, typename E, typename... Args> |
| 276 | inline E ErrorCode(E code, T&& t, const Args&... args) { |
| 277 | if constexpr (std::is_same_v<std::remove_cv_t<std::remove_reference_t<T>>, ResultError<E>>) { |
| 278 | return ErrorCode(t.code(), args...); |
| 279 | } |
| 280 | return ErrorCode(code, args...); |
| 281 | } |
| 282 | |
| 283 | template <typename T, typename... Args> |
| 284 | inline Error<Errno> ErrorfImpl(const T&& fmt, const Args&... args) { |
| 285 | return Error(false, ErrorCode(Errno{}, args...), fmt::format(fmt, args...)); |
| 286 | } |
| 287 | |
| 288 | template <typename T, typename... Args> |
| 289 | inline Error<Errno> ErrnoErrorfImpl(const T&& fmt, const Args&... args) { |
| 290 | return Error<Errno>(true, Errno{errno}, fmt::format(fmt, args...)); |
| 291 | } |
| 292 | |
| 293 | #define Errorf(fmt, ...) android::base::ErrorfImpl(FMT_STRING(fmt), ##__VA_ARGS__) |
| 294 | #define ErrnoErrorf(fmt, ...) android::base::ErrnoErrorfImpl(FMT_STRING(fmt), ##__VA_ARGS__) |
| 295 | |
| 296 | template <typename T, typename E = Errno, bool include_message = true> |
| 297 | using Result = android::base::expected<T, ResultError<E, include_message>>; |
| 298 | |
| 299 | // Specialization of android::base::OkOrFail<V> for V = Result<T, E>. See android-base/errors.h |
| 300 | // for the contract. |
| 301 | |
| 302 | namespace impl { |
| 303 | template <typename U> |
| 304 | using Code = std::decay_t<decltype(std::declval<U>().error().code())>; |
| 305 | |
| 306 | template <typename U> |
| 307 | using ErrorType = std::decay_t<decltype(std::declval<U>().error())>; |
| 308 | |
| 309 | template <typename U> |
| 310 | constexpr bool IsNumeric = std::is_integral_v<U> || std::is_floating_point_v<U> || |
| 311 | (std::is_enum_v<U> && std::is_convertible_v<U, size_t>); |
| 312 | |
| 313 | // This base class exists to take advantage of shadowing |
| 314 | // We include the conversion in this base class so that if the conversion in NumericConversions |
| 315 | // overlaps, we (arbitrarily) choose the implementation in NumericConversions due to shadowing. |
| 316 | template <typename T> |
| 317 | struct ConversionBase { |
| 318 | ErrorType<T> error_; |
| 319 | // T is a expected<U, ErrorType<T>>. |
| 320 | operator const T() const && { |
| 321 | return unexpected(std::move(error_)); |
| 322 | } |
| 323 | |
| 324 | operator const Code<T>() const && { |
| 325 | return error_.code(); |
| 326 | } |
| 327 | |
| 328 | }; |
| 329 | |
| 330 | // User defined conversions can be followed by numeric conversions |
| 331 | // Although we template specialize for the exact code type, we need |
| 332 | // specializations for conversions to all numeric types to avoid an |
| 333 | // ambiguous conversion sequence. |
| 334 | template <typename T, typename = void> |
| 335 | struct NumericConversions : public ConversionBase<T> {}; |
| 336 | template <typename T> |
| 337 | struct NumericConversions<T, |
| 338 | std::enable_if_t<impl::IsNumeric<impl::Code<T>>> |
| 339 | > : public ConversionBase<T> |
| 340 | { |
| 341 | #pragma push_macro("SPECIALIZED_CONVERSION") |
| 342 | #define SPECIALIZED_CONVERSION(type)\ |
| 343 | operator const expected<type, ErrorType<T>>() const &&\ |
| 344 | { return unexpected(std::move(this->error_));} |
| 345 | |
| 346 | SPECIALIZED_CONVERSION(int) |
| 347 | SPECIALIZED_CONVERSION(short int) |
| 348 | SPECIALIZED_CONVERSION(unsigned short int) |
| 349 | SPECIALIZED_CONVERSION(unsigned int) |
| 350 | SPECIALIZED_CONVERSION(long int) |
| 351 | SPECIALIZED_CONVERSION(unsigned long int) |
| 352 | SPECIALIZED_CONVERSION(long long int) |
| 353 | SPECIALIZED_CONVERSION(unsigned long long int) |
| 354 | SPECIALIZED_CONVERSION(bool) |
| 355 | SPECIALIZED_CONVERSION(char) |
| 356 | SPECIALIZED_CONVERSION(unsigned char) |
| 357 | SPECIALIZED_CONVERSION(signed char) |
| 358 | SPECIALIZED_CONVERSION(wchar_t) |
| 359 | SPECIALIZED_CONVERSION(char16_t) |
| 360 | SPECIALIZED_CONVERSION(char32_t) |
| 361 | SPECIALIZED_CONVERSION(float) |
| 362 | SPECIALIZED_CONVERSION(double) |
| 363 | SPECIALIZED_CONVERSION(long double) |
| 364 | |
| 365 | #undef SPECIALIZED_CONVERSION |
| 366 | #pragma pop_macro("SPECIALIZED_CONVERSION") |
| 367 | // For debugging purposes |
| 368 | using IsNumericT = std::true_type; |
| 369 | }; |
| 370 | |
| 371 | #ifdef __cpp_concepts |
| 372 | template <class U> |
| 373 | // Define a concept which **any** type matches to |
| 374 | concept Universal = std::is_same_v<U, U>; |
| 375 | #endif |
| 376 | } // namespace impl |
| 377 | |
| 378 | template <typename T, typename E, bool include_message> |
| 379 | struct OkOrFail<Result<T, E, include_message>> |
| 380 | : public impl::NumericConversions<Result<T, E, include_message>> { |
| 381 | using V = Result<T, E, include_message>; |
| 382 | using Err = impl::ErrorType<V>; |
| 383 | using C = impl::Code<V>; |
| 384 | private: |
| 385 | OkOrFail(Err&& v): impl::NumericConversions<V>{std::move(v)} {} |
| 386 | OkOrFail(const OkOrFail& other) = delete; |
| 387 | OkOrFail(const OkOrFail&& other) = delete; |
| 388 | public: |
| 389 | // Checks if V is ok or fail |
| 390 | static bool IsOk(const V& val) { return val.ok(); } |
| 391 | |
| 392 | // Turns V into a success value |
| 393 | static T Unwrap(V&& val) { |
| 394 | if constexpr (std::is_same_v<T, void>) { |
| 395 | assert(IsOk(val)); |
| 396 | return; |
| 397 | } else { |
| 398 | return std::move(val.value()); |
| 399 | } |
| 400 | } |
| 401 | |
| 402 | // Consumes V when it's a fail value |
| 403 | static const OkOrFail<V> Fail(V&& v) { |
| 404 | assert(!IsOk(v)); |
| 405 | return OkOrFail<V>{std::move(v.error())}; |
| 406 | } |
| 407 | |
| 408 | // We specialize as much as possible to avoid ambiguous conversion with |
| 409 | // templated expected ctor |
| 410 | operator const Result<C, E, include_message>() const && { |
| 411 | return unexpected(std::move(this->error_)); |
| 412 | } |
| 413 | #ifdef __cpp_concepts |
| 414 | // The idea here is to match this template method to any type (not simply trivial types). |
| 415 | // The reason for including a constraint is to take advantage of the fact that a constrained |
| 416 | // method always has strictly lower precedence than a non-constrained method in template |
| 417 | // specialization rules (thus avoiding ambiguity). So we use a universally matching constraint to |
| 418 | // mark this function as less preferable (but still accepting of all types). |
| 419 | template <impl::Universal U> |
| 420 | #else |
| 421 | template <typename U> |
| 422 | #endif |
| 423 | operator const Result<U, E, include_message>() const&& { |
| 424 | return unexpected(std::move(this->error_)); |
| 425 | } |
| 426 | |
| 427 | static std::string ErrorMessage(const V& val) { return val.error().message(); } |
| 428 | }; |
| 429 | |
| 430 | // Macros for testing the results of functions that return android::base::Result. |
| 431 | // These also work with base::android::expected. |
| 432 | // For advanced matchers and customized error messages, see result-gtest.h. |
| 433 | |
| 434 | #define ASSERT_RESULT_OK(stmt) \ |
| 435 | if (const auto& tmp = (stmt); !tmp.ok()) \ |
| 436 | FAIL() << "Value of: " << #stmt << "\n" \ |
| 437 | << " Actual: " << tmp.error().message() << "\n" \ |
| 438 | << "Expected: is ok\n" |
| 439 | |
| 440 | #define EXPECT_RESULT_OK(stmt) \ |
| 441 | if (const auto& tmp = (stmt); !tmp.ok()) \ |
| 442 | ADD_FAILURE() << "Value of: " << #stmt << "\n" \ |
| 443 | << " Actual: " << tmp.error().message() << "\n" \ |
| 444 | << "Expected: is ok\n" |
| 445 | |
| 446 | } // namespace base |
| 447 | } // namespace android |