ara::per - Key-Value & File Storage

#include <ara/per/key_value_storage.h>

// Open KVS declared as portPrototype in Application Design
auto kvsResult = ara::per::OpenKeyValueStorage(
    ara::core::InstanceSpecifier{"CalibApp/CalibKVS"});
auto& kvs = kvsResult.Value();

// Read with default fallback
auto offset = kvs.GetValue<float>("sensorOffset")
                 .ValueOr(0.0f);

// Write and sync to persistent storage
kvs.SetValue("sensorOffset", 0.25f);
kvs.SyncToStorage(); // Must be called explicitly to flush

// Remove a key
kvs.RemoveKey("legacyConfig");
kvs.SyncToStorage();

#include <ara/per/file_storage.h>

auto fsResult = ara::per::OpenFileStorage(
    ara::core::InstanceSpecifier{"CertApp/CertStorage"});
auto& fs = fsResult.Value();

// Open a logical file (path is relative to storage root)
auto fileResult = fs.OpenFileReadWrite("tls_cert.pem");
auto& file = fileResult.Value();

// Read content
ara::core::Vector<ara::core::Byte> buffer(4096);
auto bytesRead = file.Read(buffer);

// Write
ara::core::String certData = LoadCert();
file.Write(ara::core::Span<const ara::core::Byte>{
    reinterpret_cast<const ara::core::Byte*>(certData.data()),
    certData.size()});

🔬 Deep Dive — Core Concepts Expanded

This section builds on the foundational concepts covered above with additional technical depth, edge cases, and configuration nuances that separate competent engineers from experts. When working on production ECU projects, the details covered here are the ones most commonly responsible for integration delays and late-phase defects.

Key principles to reinforce:

• Configuration over coding: In AUTOSAR and automotive middleware environments, correctness is largely determined by ARXML configuration, not application code. A correctly implemented algorithm can produce wrong results due to a single misconfigured parameter.
• Traceability as a first-class concern: Every configuration decision should be traceable to a requirement, safety goal, or architecture decision. Undocumented configuration choices are a common source of regression defects when ECUs are updated.
• Cross-module dependencies: In tightly integrated automotive software stacks, changing one module's configuration often requires corresponding updates in dependent modules. Always perform a dependency impact analysis before submitting configuration changes.