145 lines
5.9 KiB
C++
145 lines
5.9 KiB
C++
/*
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* Copyright (C) 2016 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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// Portable error handling functions. This is only necessary for host-side
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// code that needs to be cross-platform; code that is only run on Unix should
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// just use errno and strerror() for simplicity.
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//
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// There is some complexity since Windows has (at least) three different error
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// numbers, not all of which share the same type:
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// * errno: for C runtime errors.
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// * GetLastError(): Windows non-socket errors.
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// * WSAGetLastError(): Windows socket errors.
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// errno can be passed to strerror() on all platforms, but the other two require
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// special handling to get the error string. Refer to Microsoft documentation
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// to determine which error code to check for each function.
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#pragma once
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#include <assert.h>
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#include <string>
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namespace android {
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namespace base {
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// Returns a string describing the given system error code. |error_code| must
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// be errno on Unix or GetLastError()/WSAGetLastError() on Windows. Passing
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// errno on Windows has undefined behavior.
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std::string SystemErrorCodeToString(int error_code);
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} // namespace base
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} // namespace android
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// Convenient macros for evaluating a statement, checking if the result is error, and returning it
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// to the caller.
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//
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// Usage with Result<T>:
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//
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// Result<Foo> getFoo() {...}
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//
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// Result<Bar> getBar() {
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// Foo foo = OR_RETURN(getFoo());
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// return Bar{foo};
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// }
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//
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// Usage with status_t:
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//
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// status_t getFoo(Foo*) {...}
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//
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// status_t getBar(Bar* bar) {
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// Foo foo;
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// OR_RETURN(getFoo(&foo));
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// *bar = Bar{foo};
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// return OK;
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// }
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//
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// Actually this can be used for any type as long as the OkOrFail<T> contract is satisfied. See
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// below.
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// If implicit conversion compilation errors occur involving a value type with a templated
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// forwarding ref ctor, compilation with cpp20 or explicitly converting to the desired
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// return type is required.
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#define OR_RETURN(expr) \
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({ \
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decltype(expr)&& tmp = (expr); \
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typedef android::base::OkOrFail<std::remove_reference_t<decltype(tmp)>> ok_or_fail; \
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if (!ok_or_fail::IsOk(tmp)) { \
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return ok_or_fail::Fail(std::move(tmp)); \
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} \
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ok_or_fail::Unwrap(std::move(tmp)); \
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})
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// Same as OR_RETURN, but aborts if expr is a failure.
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#if defined(__BIONIC__)
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#define OR_FATAL(expr) \
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({ \
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decltype(expr)&& tmp = (expr); \
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typedef android::base::OkOrFail<std::remove_reference_t<decltype(tmp)>> ok_or_fail; \
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if (!ok_or_fail::IsOk(tmp)) { \
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__assert(__FILE__, __LINE__, ok_or_fail::ErrorMessage(tmp).c_str()); \
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} \
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ok_or_fail::Unwrap(std::move(tmp)); \
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})
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#else
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#define OR_FATAL(expr) \
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({ \
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decltype(expr)&& tmp = (expr); \
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typedef android::base::OkOrFail<std::remove_reference_t<decltype(tmp)>> ok_or_fail; \
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if (!ok_or_fail::IsOk(tmp)) { \
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fprintf(stderr, "%s:%d: assertion \"%s\" failed", __FILE__, __LINE__, \
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ok_or_fail::ErrorMessage(tmp).c_str()); \
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abort(); \
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} \
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ok_or_fail::Unwrap(std::move(tmp)); \
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})
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#endif
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namespace android {
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namespace base {
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// The OkOrFail contract for a type T. This must be implemented for a type T if you want to use
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// OR_RETURN(stmt) where stmt evalues to a value of type T.
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template <typename T, typename = void>
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struct OkOrFail {
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// Checks if T is ok or fail.
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static bool IsOk(const T&);
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// Turns T into the success value.
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template <typename U>
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static U Unwrap(T&&);
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// Moves T into OkOrFail<T>, so that we can convert it to other types
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OkOrFail(T&& v);
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OkOrFail() = delete;
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OkOrFail(const T&) = delete;
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// And there need to be one or more conversion operators that turns the error value of T into a
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// target type. For example, for T = Result<V, E>, there can be ...
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//
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// // for the case where OR_RETURN is called in a function expecting E
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// operator E()&& { return val_.error().code(); }
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//
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// // for the case where OR_RETURN is called in a function expecting Result<U, E>
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// template <typename U>
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// operator Result<U, E>()&& { return val_.error(); }
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// Returns the string representation of the fail value.
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static std::string ErrorMessage(const T& v);
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};
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} // namespace base
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} // namespace android
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