Previously the blocking functions all closed over the state store from
their first query, with would not have worked properly when a restore
occurred. This makes sure they get a frest state store pointer each time,
and that pointer is synchronized with the abandon watch.
Consolidate code duplication and tests into a single lib package. Most of these functions were from various **/util.go functions that couldn't be imported due to cyclic imports. The consul/lib package is intended to be a terminal node in an import DAG and a place to stash various consul-only helper functions. Pulled in hashicorp/go-uuid instead of consolidating UUID access.
The design of the session TTLs is based on the Google Chubby approach
(http://research.google.com/archive/chubby-osdi06.pdf). The Session
struct has an additional TTL field now. This attaches an implicit
heartbeat based failure detector. Tracking of heartbeats is done by
the current leader and not persisted via the Raft log. The implication
of this is during a leader failover, we do not retain the last
heartbeat times.
Similar to Chubby, the TTL represents a lower-bound. Consul promises
not to terminate a session before the TTL has expired, but is allowed
to extend the expiration past it. This enables us to reset the TTL on
a leader failover. The TTL is also extended when the client does a
heartbeat. Like Chubby, this means a TTL is extended on creation,
heartbeat or failover.
Additionally, because we must account for time requests are in transit
and the relative rates of clocks on the clients and servers, Consul
will take the conservative approach of internally multiplying the TTL
by 2x. This helps to compensate for network latency and clock skew
without violating the contract.
Reference: https://docs.google.com/document/d/1Y5-pahLkUaA7Kz4SBU_mehKiyt9yaaUGcBTMZR7lToY/edit?usp=sharing
Added a "delete" behavior for session invalidation, in addition to
the default "release" behavior. On session invalidation, the sessions
Behavior field is checked and if it is set to "delete", all nodes owned
by the session are deleted. If it is "release", then just the locks
are released as default.
