MongoDB indexes store a KeyString in the key of a wiredtiger entry with an empty associated value. The format of these keystrings vary with the type of index and version. The KeyString contains a bson encoded object of the field being indexed, as well as other specific bytes for efficient encoding and other metadata.

See mongo/src/mongo/db/storage/key_string/README.md for more information on index key format.

We should extend the decode tool to decode index entries so we can inspect their contents in the event of a corrupt index.