Add basic SQLite storage backend

src/storage/backend/sqlite/SQLite.h

@@ -0,0 +1,61 @@
+// See the file "COPYING" in the main distribution directory for copyright.
+
+#pragma once
+
+#include "zeek/storage/Backend.h"
+
+// Forward declare these to avoid including sqlite3.h here
+struct sqlite3;
+struct sqlite3_stmt;
+
+namespace zeek::storage::backend::sqlite {
+
+class SQLite : public Backend {
+public:
+    SQLite(std::string_view tag) : Backend(false, tag) {}
+    ~SQLite() override = default;
+
+    static BackendPtr Instantiate(std::string_view tag);
+
+    /**
+     * Called by the manager system to open the backend.
+     */
+    ErrorResult DoOpen(RecordValPtr options) override;
+
+    /**
+     * Finalizes the backend when it's being closed.
+     */
+    void Close() override;
+
+    /**
+     * Returns whether the backend is opened.
+     */
+    bool IsOpen() override { return db != nullptr; }
+
+    /**
+     * The workhorse method for Put().
+     */
+    ErrorResult DoPut(ValPtr key, ValPtr value, bool overwrite = true, double expiration_time = 0,
+                      ErrorResultCallback* cb = nullptr) override;
+
+    /**
+     * The workhorse method for Get().
+     */
+    ValResult DoGet(ValPtr key, ValResultCallback* cb = nullptr) override;
+
+    /**
+     * The workhorse method for Erase().
+     */
+    ErrorResult DoErase(ValPtr key, ErrorResultCallback* cb = nullptr) override;
+
+    // TODO: add support for checking for expired data
+
+private:
+    ErrorResult checkError(int code);
+
+    sqlite3* db = nullptr;
+    std::string full_path;
+    std::string table_name;
+};
+
+} // namespace zeek::storage::backend::sqlite