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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#include <string>
#include "mongo/util/assert_util.h"
#include "mongo/util/mongoutils/str.h"
namespace mongo {
/**
* A status object for use with C APIs that call into C++ code. When using StatusForAPI for error
* reporting, call any C++ within an enterCXX() block, which can translate exceptions into
* StatusForApi objects by way of handleException().
*
* The ErrorEnum type parameter is a C enum with error codes that will be exposed to the clients of
* the C interface. This enum _must_ include a value that maps to 0, which will be the default value
* for a clean Status object (usually indicating success).
*/
template <typename ErrorEnum>
struct StatusForAPI {
StatusForAPI() noexcept = default;
StatusForAPI(const ErrorEnum e, const int ec, std::string w)
: error(e), exception_code(ec), what(std::move(w)) {}
void clean() noexcept {
error = {};
exception_code = {};
what.clear();
}
ErrorEnum error = {};
int exception_code = {};
std::string what;
};
/**
* Used to set a fallback error message when it is not safe to allocate memory.
*/
inline void setErrorMessageNoAlloc(std::string& errorString) {
errorString.clear();
// Expected to be small enough to fit in the capacity that string always has.
const char severeErrorMessage[] = "Severe Error";
if (errorString.capacity() > sizeof(severeErrorMessage)) {
errorString = severeErrorMessage;
}
}
template <typename ErrorEnum>
class ExceptionForAPI : public std::exception {
public:
explicit ExceptionForAPI(const ErrorEnum code, std::string m)
: _mesg(std::move(m)), _code(code) {}
virtual ~ExceptionForAPI() {}
ErrorEnum statusCode() const noexcept {
return this->_code;
}
const char* what() const noexcept {
return this->_mesg.c_str();
}
private:
std::string _mesg;
ErrorEnum _code;
};
template <typename ErrorEnum>
std::nullptr_t handleException(StatusForAPI<ErrorEnum>& status) noexcept {
try {
status = translateException(stdx::type_identity<StatusForAPI<ErrorEnum>>());
} catch (...) {
try {
translateExceptionFallback(status);
} catch (...) /* Ignore any errors at this point. */
{
}
}
return nullptr;
}
class ReentrancyGuard {
private:
// This templated "holder" struct stores a thread-local static variable that doesn't need a
// corresponding definition in a .cpp file, allowing us to use this same header from multiple
// libraries that do not link common objects.
// TODO: When we switch to C++17, we can use simply use the "inline" keyword instead of relying
// on templates.
template <typename T = void>
struct GuardHolder {
thread_local static bool inLibrary;
};
bool& inLibrary() {
return GuardHolder<>::inLibrary;
}
public:
ReentrancyGuard() {
uassert(ErrorCodes::ReentrancyNotAllowed,
mongoutils::str::stream() << "Reentry into library is not allowed",
!inLibrary());
inLibrary() = true;
}
~ReentrancyGuard() {
inLibrary() = false;
}
ReentrancyGuard(ReentrancyGuard const&) = delete;
ReentrancyGuard& operator=(ReentrancyGuard const&) = delete;
};
template <typename T>
thread_local bool ReentrancyGuard::GuardHolder<T>::inLibrary = false;
template <typename Status,
typename Function,
typename ReturnType = typename std::result_of<Function()>::type>
struct enterCXXImpl;
template <typename Status, typename Function>
struct enterCXXImpl<Status, Function, void> {
template <typename Callable>
static int call(Callable&& function, Status& status, const ReentrancyGuard&& = {}) noexcept {
try {
function();
} catch (...) {
handleException(status);
}
return status.error;
}
};
template <typename Status, typename Function, typename Pointer>
struct enterCXXImpl<Status, Function, Pointer*> {
template <typename Callable>
static Pointer* call(Callable&& function,
Status& status,
const ReentrancyGuard&& = {}) noexcept try {
return function();
} catch (...) {
return handleException(status);
}
};
template <typename Status>
struct StatusGuard {
private:
Status fallback;
Status* status;
public:
explicit StatusGuard(Status* const statusPtr) noexcept
: status(statusPtr ? statusPtr : &fallback) {
if (status == statusPtr) {
status->clean();
}
}
StatusGuard(StatusGuard const&) = delete;
StatusGuard& operator=(StatusGuard const&) = delete;
operator Status&() noexcept {
return *status;
}
};
template <typename Status, typename Callable>
auto enterCXX(Status* const statusPtr, Callable&& c) noexcept
-> decltype(mongo::enterCXXImpl<Status, Callable>::call(std::forward<Callable>(c),
*statusPtr)) {
return mongo::enterCXXImpl<Status, Callable>::call(std::forward<Callable>(c),
StatusGuard<Status>(statusPtr));
}
} // namespace mongo
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