Datastore
=========

As stated in the :doc:`../threat_model`, Datastore is an **untrusted** server
that provides persistent storage. Since Datastore can be malicious, you must
protect the confidentiality and integrity of any sensitive data you store on it.

Datastore is structured as a `key-value store
<https://en.wikipedia.org/wiki/Key-value_database>`_. In this context, key
refers to an unique identifier that is used to index the value in the database,
and does not refer to a crypographic key.

All key-value entries in Datastore exist in a single, global namespace and
Datastore does not perform any access control. Therefore, any *value* entry can
be overwritten or deleted by any user who knows the corresponding storage *key*.

An implementation of Datastore is provided for you (see source code in userlib_)
and is already imported into proj2.go_.

The client application can interact with Datastore using the API documented
below.

.. function:: userlib.DatastoreSet(key UUID, value []byte)

    Stores the given *value* at the given storage *key*.

    Unlike the :doc:`keystore`, key-value entries in the Datastore are mutable;
    if *key* already maps to a *value*, then *value* can be overwritten with a
    call to *DatastoreSet()* using the same *key*.

    :param key: Unique identifier used to index *value* in the database.
    :type key: UUID
    :param value: Value
    :type value: []byte

    **Example:**

    .. code-block:: go

        UUID := uuid.New()
        data := []byte("This is some data")
        userlib.DatastoreSet(UUID, data)

.. function:: userlib.DatastoreGet(key UUID) (value []byte, ok bool)

    If the given *key* does exist in Datastore, return the *value* stored at
    *key* and *ok* is set to true.

    If the given *key* does not exist in Datastore, then *ok* is set to false.

    :param key: Key
    :type key: UUID

    :rtype: []byte

    **Example:**

    .. code-block:: go

        UUID := uuid.New()
        data := []byte("This is some data")
        userlib.DatastoreSet(UUID, data)
        download_data, _ := userlib.DatastoreGet(UUID)
        if data != download_data {
            panic("The data should match.")
        }

.. function:: userlib.DatastoreDelete(key UUID)

    Delete the given key-value entry from the Datastore, if it exists.

    :param key: Key
    :type key: UUID

    **Example:**

    .. code-block:: go

        UUID := uuid.New()
        data := []byte("This is some data")
        userlib.DatastoreSet(UUID, data)
        userlib.DatastoreDelete(UUID)
        _, ok := userlib.DatastoreGet(UUID)
        if ok {
            panic("The data is still there.")
        }

.. _userlib: https://github.com/cs161-staff/project2-userlib/blob/master/userlib.go
.. _proj2.go: https://github.com/cs161-staff/project2-starter-code/blob/main/proj2.go