IndexedDBBackend Class

The keys and the values are opaque byte arrays. The keys are encoded so that their byte order (MemoryExtensions.SequenceCompareTo, i.e. memcmp) is the order of the IndexedDB keys (https://w3c.github.io/IndexedDB/#compare-two-keys): a backend sorts and compares the keys as byte strings (e.g. the BLOB columns of SQLite), and never decodes them. The values are the serialized JavaScript values, including the bytes of their blobs and files.

The data of an origin is changed in transactions (IndexedDBBackend.BeginTransaction) that the library commits or aborts. The library guarantees that:

• the calls for a database (of an origin) are never concurrent (but the calls for different databases can be);
• at most one IdbTransactionMode.ReadWrite or IdbTransactionMode.VersionChange transaction of a database is open at a time;
• the IdbTransactionMode.ReadOnly transactions that are open at the same time as a read-write transaction do not read its object stores;
• no transaction of a database is open while it is deleted.

So a backend can run a read-write transaction as a transaction of its storage (e.g. BEGIN, COMMIT and ROLLBACK on a SQLite connection), and the read-only transactions without isolation. The methods are called on the threads of the event loops of the windows and the workers that use the databases: an implementation must be thread-safe, and its exceptions make the requests fail with an UnknownError (or the transaction abort).

The database names, the object store names and the index names are arbitrary strings (possibly empty, with lone surrogates). The object stores and the indexes are identified by ids assigned by the library, which are unique in a database and never reused while the database exists.