ipfs / ipfs-cluster / 3577

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master: 65%

Pull #655

travis-ci-com

State: Use go-datastore to implement the state interface

Since the beginning, we have used a Go map to store the shared state (pinset)
in memory. The mapstate knew how to serialize itself so that libp2p-raft would
know how to write to disk when it:

* Saved snapshots of the state on shutdown
* Sent the state to a newcomer peer

hashicorp.Raft assumes an in-memory state which is snapshotted from time to
time and read from disk on boot.

This commit adds a `dsstate` implementation of the state interface using
`go-datastore`. This allows to effortlessly switch to a disk-backed state in
the future (as we will need), and also have at our disposal the different
implementations and utilities of Datastore for fine-tuning (caching, batching
etc.).

`mapstate` has been reworked to use dsstate. Ideally, we would not even need
`mapstate`, as it would suffice to initialize `dsstate` with a
`MapDatastore`. BUT, we still need it separate to be able to auto-migrate to
the new format.

This will be the last migration with the current system. Once this has been
released and users have been able to upgrade we will just remove `mapstate` as
it is now.

License: MIT
Signed-off-by: Hector Sanjuan <code@hector.link>

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