// Each S3 object has an associated ETag that can be
// used to e.g. quickly compare objects or check whether
// the content of an object has changed.
//
// In general, an S3 ETag is an MD5 checksum of the object
// content. However, there are many exceptions to this rule.
//
// # Single-part Upload
//
// In case of a basic single-part PUT operation - without server
// side encryption or object compression - the ETag of an object

 *       cancelled, cancellation never propagates to a task that has started to run -- neither to
 *       the callable itself nor to any {@code Future} returned by an {@code AsyncCallable}.
 *       (However, cancellation can prevent an <i>unstarted</i> task from running.) Therefore, the
 *       next task will wait for any running callable (or pending {@code Future} returned by an

   * key set contains a key if and only if this multimap maps that key to at least one value.
   *
   * <p>Changes to the returned set will update the underlying multimap, and vice versa. However,
   * <i>adding</i> to the returned set is not possible.
   */
  Set<K> keySet();

  /**
   * Returns a view collection containing the key from each key-value pair in this multimap,

   * <p>This is guaranteed to return zero if the dataset contains only exactly one finite value. It
   * is not guaranteed to return zero when the dataset consists of the same value multiple times,
   * due to numerical errors. However, it is guaranteed never to return a negative result.
   *
   * <h3>Non-finite values</h3>
   *
   * <p>If the dataset contains any non-finite values ({@link Double#POSITIVE_INFINITY}, {@link

   * key set contains a key if and only if this multimap maps that key to at least one value.
   *
   * <p>Changes to the returned set will update the underlying multimap, and vice versa. However,
   * <i>adding</i> to the returned set is not possible.
   */
  Set<K> keySet();

  /**
   * Returns a view collection containing the key from each key-value pair in this multimap,

ciphertext  := sealed_chunk_0   ||       sealed_chunk_1   ||       sealed_chunk_2   ||       ...
```

In case of a S3 multi-part operation each part is en/decrypted with the scheme shown in Figure 1. However, for each part a unique secret key is derived from the OEK and the part number using a PRF. So in case of multi-part not the OEK but the output of `PRF(OEK, part_id)` is used as secret key.

#### Cryptographic Primitives

 *       OptionalLong} and {@code OptionalDouble}, the use of which is recommended; Guava does not
 *       have these.
 * </ul>
 *
 * <p><b>There are no plans to deprecate this class in the foreseeable future.</b> However, we do
 * gently recommend that you prefer the new, standard Java class whenever possible.
 *
 * <p>See the Guava User Guide article on <a

improvements made in alternate versions of the program, if they
receive widespread use, become available for other developers to
incorporate.  Many developers of free software are heartened and
encouraged by the resulting cooperation.  However, in the case of
software used on network servers, this result may fail to come about.
The GNU General Public License permits making a modified version and
letting the public access it on a server without ever releasing its

 * {@code asMap} has a few subtleties. As long as the set of keys remains unchanged, adding or
 * removing mappings does not affect the key iteration order. However, if you remove all values
 * associated with a key and then add the key back to the multimap, that key will come last in the
 * key iteration order.
 *

 * {@code asMap} has a few subtleties. As long as the set of keys remains unchanged, adding or
 * removing mappings does not affect the key iteration order. However, if you remove all values
 * associated with a key and then add the key back to the multimap, that key will come last in the
 * key iteration order.
 *