base/include/hidl/Status.h

/*
 * Copyright (C) 2015 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef ANDROID_HARDWARE_BINDER_STATUS_H
#define ANDROID_HARDWARE_BINDER_STATUS_H

#include <cstdint>
#include <sstream>

#include <hidl/HidlInternal.h>
#include <utils/Errors.h>
#include <utils/StrongPointer.h>

namespace android {
namespace hardware {

// An object similar in function to a status_t except that it understands
// how exceptions are encoded in the prefix of a Parcel. Used like:
//
//     Parcel data;
//     Parcel reply;
//     status_t status;
//     binder::Status remote_exception;
//     if ((status = data.writeInterfaceToken(interface_descriptor)) != OK ||
//         (status = data.writeInt32(function_input)) != OK) {
//         // We failed to write into the memory of our local parcel?
//     }
//     if ((status = remote()->transact(transaction, data, &reply)) != OK) {
//        // Something has gone wrong in the binder driver or libbinder.
//     }
//     if ((status = remote_exception.readFromParcel(reply)) != OK) {
//         // The remote didn't correctly write the exception header to the
//         // reply.
//     }
//     if (!remote_exception.isOk()) {
//         // The transaction went through correctly, but the remote reported an
//         // exception during handling.
//     }
//
class Status final {
public:
    // Keep the exception codes in sync with android/os/Parcel.java.
    enum Exception {
        EX_NONE = 0,
        EX_SECURITY = -1,
        EX_BAD_PARCELABLE = -2,
        EX_ILLEGAL_ARGUMENT = -3,
        EX_NULL_POINTER = -4,
        EX_ILLEGAL_STATE = -5,
        EX_NETWORK_MAIN_THREAD = -6,
        EX_UNSUPPORTED_OPERATION = -7,

        // This is special and Java specific; see Parcel.java.
        EX_HAS_REPLY_HEADER = -128,
        // This is special, and indicates to C++ binder proxies that the
        // transaction has failed at a low level.
        EX_TRANSACTION_FAILED = -129,
    };

    // A more readable alias for the default constructor.
    static Status ok();
    // Authors should explicitly pick whether their integer is:
    //  - an exception code (EX_* above)
    //  - status_t
    //
    // Prefer a generic exception code when possible or a status_t
    // for low level transport errors. Service specific errors
    // should be at a higher level in HIDL.
    static Status fromExceptionCode(int32_t exceptionCode);
    static Status fromExceptionCode(int32_t exceptionCode,
                                    const char *message);
    static Status fromStatusT(status_t status);

    Status() = default;
    ~Status() = default;

    // Status objects are copyable and contain just simple data.
    Status(const Status& status) = default;
    Status(Status&& status) = default;
    Status& operator=(const Status& status) = default;

    // Set one of the pre-defined exception types defined above.
    void setException(int32_t ex, const char *message);
    // Setting a |status| != OK causes generated code to return |status|
    // from Binder transactions, rather than writing an exception into the
    // reply Parcel.  This is the least preferable way of reporting errors.
    void setFromStatusT(status_t status);

    // Get information about an exception.
    int32_t exceptionCode() const  { return mException; }
    const char *exceptionMessage() const { return mMessage.c_str(); }
    status_t transactionError() const {
        return mException == EX_TRANSACTION_FAILED ? mErrorCode : OK;
    }

    bool isOk() const { return mException == EX_NONE; }

    // For debugging purposes only
    std::string description() const;

private:
    Status(int32_t exceptionCode, int32_t errorCode);
    Status(int32_t exceptionCode, int32_t errorCode, const char *message);

    // If |mException| == EX_TRANSACTION_FAILED, generated code will return
    // |mErrorCode| as the result of the transaction rather than write an
    // exception to the reply parcel.
    //
    // Otherwise, we always write |mException| to the parcel.
    // If |mException| !=  EX_NONE, we write |mMessage| as well.
    int32_t mException = EX_NONE;
    int32_t mErrorCode = 0;
    std::string mMessage;
};  // class Status

// For gtest output logging
std::ostream& operator<< (std::ostream& stream, const Status& s);

template<typename T> class Return;

namespace details {
    class return_status {
    private:
        Status mStatus {};
        mutable bool mCheckedStatus = false;

        template <typename T, typename U>
        friend Return<U> StatusOf(const Return<T> &other);
    protected:
        void assertOk() const;
    public:
        return_status() {}
        return_status(const Status& s) : mStatus(s) {}

        return_status(const return_status &) = delete;
        return_status &operator=(const return_status &) = delete;

        return_status(return_status&& other) noexcept { *this = std::move(other); }
        return_status& operator=(return_status&& other) noexcept;

        ~return_status();

        bool isOkUnchecked() const {
            // someone else will have to check
            return mStatus.isOk();
        }

        bool isOk() const {
            mCheckedStatus = true;
            return mStatus.isOk();
        }

        // Check if underlying error is DEAD_OBJECT.
        // Check mCheckedStatus only if this method returns true.
        bool isDeadObject() const {
            bool dead = mStatus.transactionError() == DEAD_OBJECT;

            // This way, if you only check isDeadObject your process will
            // only be killed for more serious unchecked errors
            if (dead) {
                mCheckedStatus = true;
            }

            return dead;
        }

        // For debugging purposes only
        std::string description() const {
            // Doesn't consider checked.
            return mStatus.description();
        }
    };
}  // namespace details

template<typename T> class Return : public details::return_status {
private:
    T mVal {};
public:
    Return(T v) : details::return_status(), mVal{v} {}
    Return(Status s) : details::return_status(s) {}

    // move-able.
    // precondition: "this" has checked status
    // postcondition: other is safe to destroy after moving to *this.
    Return(Return&& other) noexcept = default;
    Return& operator=(Return&&) noexcept = default;

    ~Return() = default;

    operator T() const {
        assertOk();
        return mVal;
    }

    T withDefault(T t) {
        return isOk() ? mVal : t;
    }
};

template<typename T> class Return<sp<T>> : public details::return_status {
private:
    sp<T> mVal {};
public:
    Return(sp<T> v) : details::return_status(), mVal{v} {}
    Return(T* v) : details::return_status(), mVal{v} {}
    // Constructors matching a different type (that is related by inheritance)
    template<typename U> Return(sp<U> v) : details::return_status(), mVal{v} {}
    template<typename U> Return(U* v) : details::return_status(), mVal{v} {}
    Return(Status s) : details::return_status(s) {}

    // move-able.
    // precondition: "this" has checked status
    // postcondition: other is safe to destroy after moving to *this.
    Return(Return&& other) noexcept = default;
    Return& operator=(Return&&) noexcept = default;

    ~Return() = default;

    operator sp<T>() const {
        assertOk();
        return mVal;
    }

    sp<T> withDefault(sp<T> t) {
        return isOk() ? mVal : t;
    }
};


template<> class Return<void> : public details::return_status {
public:
    Return() : details::return_status() {}
    Return(const Status& s) : details::return_status(s) {}

    // move-able.
    // precondition: "this" has checked status
    // postcondition: other is safe to destroy after moving to *this.
    Return(Return &&) = default;
    Return &operator=(Return &&) = default;

    ~Return() = default;
};

static inline Return<void> Void() {
    return Return<void>();
}

namespace details {
// Create a Return<U> from the Status of Return<T>. The provided
// Return<T> must have an error status and have it checked.
template <typename T, typename U>
Return<U> StatusOf(const Return<T> &other) {
    if (other.mStatus.isOk() || !other.mCheckedStatus) {
        details::logAlwaysFatal("cannot call statusOf on an OK Status or an unchecked status");
    }
    return Return<U>{other.mStatus};
}
}  // namespace details

}  // namespace hardware
}  // namespace android

#endif // ANDROID_HARDWARE_BINDER_STATUS_H