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* 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
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#include <cstdint>
#include <sstream>
#include <hidl/HidlInternal.h>
#include <utils/Errors.h>
#include <utils/StrongPointer.h>
namespace android {
namespace hardware {
// HIDL formally separates transport error codes from interface error codes. When developing a HIDL
// interface, errors relevant to a service should be placed in the interface design for that HAL.
// For instance:
// interface I* {
// enum FooStatus { NO_FOO, NO_BAR }; // service-specific errors
// doFoo(...) generates (FooStatus foo);
// };
// When calling into this interface, a Return<*> (in this case Return<FooStatus> object will be
// returned). For most clients, it's expected that they'll just get the result from this function
// and use it directly. If there is a transport error, the process will just abort. In general,
// transport errors are expected only in extremely rare circumstances (bug in the
// code/cosmic radiation/etc..). Aborting allows process to restart using their normal happy path
// code.
// For certain processes though which are critical to the functionality of the phone (e.g.
// hwservicemanager/init), these errors must be handled. Return<*>::isOk and
// Return<*>::isDeadObject are provided for these cases. Whenever this is done, special attention
// should be paid to testing the unhappy paths to make sure that error handling is handled
// properly.
// Transport implementation detail. HIDL implementors, see Return below. HAL implementations should
// return HIDL-defined errors rather than use this.
class Status final {
// Note: forked from
// - frameworks/base/core/java/android/os/android/os/
// - frameworks/native/libs/binder/include/binder/Status.h
enum Exception {
EX_NONE = 0,
// This is special and Java specific; see
// This is special, and indicates to C++ binder proxies that the
// transaction has failed at a low level.
// 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;
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 {
Status mStatus {};
mutable bool mCheckedStatus = false;
// called when an unchecked status is discarded
// makes sure this status is checked according to the preference
// set by setProcessHidlReturnRestriction
void onIgnored() const;
template <typename T, typename U>
friend Return<U> StatusOf(const Return<T> &other);
void onValueRetrieval() const;
void assertOk() const;
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;
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
enum class HidlReturnRestriction {
// Okay to ignore checking transport errors. This would instead rely on init to reset state
// after an error in the underlying transport. This is the default and expected for most
// usecases.
// Log when there is an unchecked error.
// Fatal when there is an unchecked error.
* This should be called during process initialization (e.g. before binder threadpool is created).
* Note: default of HidlReturnRestriction::NONE should be good for most usecases. See above.
* The restriction will be applied when Return objects are deconstructed.
void setProcessHidlReturnRestriction(HidlReturnRestriction restriction);
template<typename T> class Return : public details::return_status {
T mVal {};
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 {
onValueRetrieval(); // assert okay
return mVal;
T withDefault(T t) const { return isOk() ? mVal : t; }
template<typename T> class Return<sp<T>> : public details::return_status {
sp<T> mVal {};
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 {
onValueRetrieval(); // assert okay
return mVal;
sp<T> withDefault(sp<T> t) const { return isOk() ? mVal : t; }
template<> class Return<void> : public details::return_status {
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