namespace apext::tsync

The namespace apext::tsync provides interfaces and data containers for the Freshness Value Management of Adaptive time synchronization. Via the interface FVM, freshness values are encapsulated in FVContainer instances to protect time messages against replay attacks. If an unrecoverable error occurs during initialization or if a value is temporarily unavailable, this is mapped via the error codes of TsyncFvmErrorDomain [SWS_TS_14202]. Standardized error objects are instantiated in an exception-safe and thread-safe manner via MakeErrorCode [SWS_TS_14213].

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Context

The namespace apext::tsync represents a platform-specific extension of the AUTOSAR Adaptive time synchronization (ara::tsync). Its central task is Freshness Value Management (FVM), which provides mechanisms to ensure the freshness of time information in order to prevent replay attacks and outdated states in time-synchronized networks. Core components include the interface FVM, the data container FVContainer, the error domain TsyncFvmErrorDomain, and the exception class TsyncFvmException.

The class FVContainer encapsulates a freshness value by managing its length in bits as well as the value itself in the form of a byte vector. The interface FVM acts as a functional bridge for ara::tsync. FVM is likely to act as an abstraction interface through which time-synchronizing instances of ara::tsync obtain or verify current freshness values. Question Q-f92f53d92ec347e5 (open) The error domain TsyncFvmErrorDomain and associated utility functions ensure standardized error reporting [SWS_TS_14212].

Context diagram: Components of namespace apext::tsync and their interaction with ara::tsync. Sources: [SWS_TS_14202], [SWS_TS_14212].

Lifecycle

The lifecycle of components in namespace apext::tsync is divided into initialization, operational, and termination phases. For the initialization phase, the enumeration TsyncFvmErrc defines the error value kFVInitializeFailed (= 2), which is specified as an unrecoverable error and indicates that the Freshness Value Manager could not be used [SWS_TS_14202]. The error kFVInitializeFailed presumably indicates that an initialization phase of the FVM must be completed before retrieving freshness values, the failure of which precludes further use. Question Q-d9c097d736bae053 (open)

During ongoing operation, FVContainer instances have a temporary lifetime: they are instantiated on demand, populated with the vector and bit length, and passed to the synchronizing protocol instances. In contrast, the error domain object TsyncFvmErrorDomain has a static lifetime across the entire process duration. The function GetTsyncFvmErrorDomain() returns a reference to the global instance object [SWS_TS_14212]. Both GetTsyncFvmErrorDomain() and the factory function MakeErrorCode() are declared as constexpr and noexcept and specified as exception-safe and thread-safe [SWS_TS_14212], [SWS_TS_14213]. This allows concurrent error generation and querying without synchronization locks.

Usage Path

The typical usage path in interaction with time synchronization encompasses the provision and evaluation of freshness values:

1. A component from ara::tsync requests a current freshness value via the interface FVM to secure a time message.
2. Upon successful value determination, FVM creates or populates an instance of FVContainer with the bit length and byte vector of the value and returns it to the caller.
3. If the freshness value temporarily cannot be provided at runtime, FVM reports the recoverable error kFVNotAvailable [SWS_TS_14202]. For this purpose, a suitable ara::core::ErrorCode object with vendor-specific supplementary data is generated via MakeErrorCode() [SWS_TS_14213].
4. The calling component evaluates the result and decides on retries or fallback measures.

Sequence diagram: Retrieval of a freshness value and handling of potential error states. Sources: [SWS_TS_14202], [SWS_TS_14213].

Error Scenarios

Error handling in apext::tsync is based on the architecture of ara::core::ErrorDomain and ara::core::ErrorCode. The error codes of TsyncFvmErrorDomain are listed in the enumeration TsyncFvmErrc, whose base type is ara::core::ErrorDomain::CodeType [SWS_TS_14202]:

• kFVNotAvailable (= 1): Recoverable error indicating that the freshness value is currently not available [SWS_TS_14202]. Callers can repeat the request or skip the current processing cycle.
• kFVInitializeFailed (= 2): Unrecoverable error indicating that the Freshness Value Manager could not be initialized or used [SWS_TS_14202]. This leads to the termination of the dependent time synchronization services.

Concrete error objects are created via the utility function MakeErrorCode(TsyncFvmErrc code, ara::core::ErrorDomain::SupportDataType data), which accepts the enumerator and vendor-specific supplementary data [SWS_TS_14213]. The declarations are located in header apext/tsync/fvm_error_domain.h, while forward declarations can be obtained via apext/tsync/tsync_fwd.h [SWS_TS_14202]. For exception-based error paths, the namespace provides the class TsyncFvmException. TsyncFvmException is likely to be thrown when errors of TsyncFvmErrorDomain are reported in exception contexts instead of via ara::core::ErrorCode. Question Q-a779e133b471f03d (open)