06 - atomic update

examples/simulations/interrupted-installation/simulation.hpp

@@ -0,0 +1,60 @@
+#pragma once
+
+#include <string>
+
+namespace ota::installation {
+
+    enum class Progress { Idle,
+                          Writing,
+                          Prepared,
+                          TrialRequested };
+    enum class BootRecord { ASelected,
+                            BTrial,
+                            Invalid };
+    enum class WriteResult { OldRecord,
+                             NewRecord,
+                             InvalidRecord };
+    enum class RecoveryAction { RestartPreparation,
+                                ReadyToActivate,
+                                PreserveTrial,
+                                SeparateRecovery };
+
+    // This object stands for persistent storage. Each assignment is a completed
+    // durable operation in the model, not a real storage implementation.
+    struct Storage {
+        std::string a_contents = "release-1";
+        std::string b_contents;
+        std::string release;
+        Progress progress = Progress::Idle;
+        BootRecord boot = BootRecord::ASelected;
+        int attempts_left = 0;
+    };
+
+    const std::string &expected_contents();
+    const char *name(RecoveryAction action);
+    const char *boot_choice(BootRecord record);
+
+    class Installer {
+    public:
+        explicit Installer(Storage &storage) : storage_(storage) {}
+        void begin();
+        void write_partial();
+        void finish_write();
+        void verify();
+        void save_prepared();
+        void request_trial(WriteResult result = WriteResult::NewRecord);
+        void save_requested();
+        RecoveryAction recover();
+
+    private:
+        void require_writable() const;
+        Storage &storage_;
+        // Lost when the installer is reconstructed after a simulated reset.
+        bool verified_ = false;
+    };
+
+    // Ordered operations; cut points are before step 0 and after each step.
+    constexpr int installation_steps = 7;
+    void perform_step(Installer &installer, int step);
+
+}// namespace ota::installation