* Somewhat complete the implementation of Kademlia records.
This commit relates to [libp2p-146] and [libp2p-1089].
* All records expire (by default, configurable).
* Provider records are also stored in the RecordStore, and the RecordStore
API extended.
* Background jobs for periodic (re-)replication and (re-)publication
of records. Regular (value-)records are subject to re-replication and
re-publication as per standard Kademlia. Provider records are only
subject to re-publication.
* For standard Kademlia value lookups (quorum = 1), the record is cached
at the closest peer to the key that did not return the value, as per
standard Kademlia.
* Expiration times of regular (value-)records is computed exponentially
inversely proportional to the number of nodes between the local node
and the closest node known to the key (beyond the k closest), as per
standard Kademlia.
The protobuf messages are extended with two fields: `ttl` and `publisher`
in order to implement the different semantics of re-replication (by any
of the k closest peers to the key, not affecting expiry) and re-publication
(by the original publisher, resetting the expiry). This is not done yet in
other libp2p Kademlia implementations, see e.g. [libp2p-go-323]. The new protobuf fields
have been given somewhat unique identifiers to prevent future collision.
Similarly, periodic re-publication of provider records does not seem to
be done yet in other implementations, see e.g. [libp2p-js-98].
[libp2p-146]: https://github.com/libp2p/rust-libp2p/issues/146
[libp2p-1089]: https://github.com/libp2p/rust-libp2p/issues/1089
[libp2p-go-323]: https://github.com/libp2p/go-libp2p-kad-dht/issues/323
[libp2p-js-98]: https://github.com/libp2p/js-libp2p-kad-dht/issues/98
* Tweak kad-ipfs example.
* Add missing files.
* Ensure new delays are polled immediately.
To ensure task notification, since `NotReady` is returned right after.
* Fix ipfs-kad example and use wasm_timer.
* Small cleanup.
* Incorporate some feedback.
* Adjustments after rebase.
* Distinguish events further.
In order for a user to easily distinguish the result of e.g.
a `put_record` operation from the result of a later republication,
different event constructors are used. Furthermore, for now,
re-replication and "caching" of records (at the closest peer to
the key that did not return a value during a successful lookup)
do not yield events for now as they are less interesting.
* Speed up tests for CI.
* Small refinements and more documentation.
* Guard a node against overriding records for which it considers
itself to be the publisher.
* Document the jobs module more extensively.
* More inline docs around removal of "unreachable" addresses.
* Remove wildcard re-exports.
* Use NonZeroUsize for the constants.
* Re-add method lost on merge.
* Add missing 'pub'.
* Further increase the timeout in the ipfs-kad example.
* Readd log dependency to libp2p-kad.
* Simplify RecordStore API slightly.
* Some more commentary.
* Change Addresses::remove to return Result<(),()>.
Change the semantics of `Addresses::remove` so that the error case
is unambiguous, instead of the success case. Use the `Result` for
clearer semantics to that effect.
* Add some documentation to .
* Address some TODOs, refactor queries and public API.
The following left-over issues are addressed:
* The key for FIND_NODE requests is generalised to any Multihash,
instead of just peer IDs.
* All queries get a (configurable) timeout.
* Finishing queries as soon as enough results have been received is simplified
to avoid code duplication.
* No more panics in provider-API-related code paths. The provider API is
however still untested and (I think) still incomplete (e.g. expiration
of provider records).
* Numerous smaller TODOs encountered in the code.
The following public API changes / additions are made:
* Introduce a `KademliaConfig` with new configuration options for
the replication factor and query timeouts.
* Rename `find_node` to `get_closest_peers`.
* Rename `get_value` to `get_record` and `put_value` to `put_record`,
introducing a `Quorum` parameter for both functions, replacing the
existing `num_results` parameter with clearer semantics.
* Rename `add_providing` to `start_providing` and `remove_providing`
to `stop_providing`.
* Add a `bootstrap` function that implements a (almost) standard
Kademlia bootstrapping procedure.
* Rename `KademliaOut` to `KademliaEvent` with an updated list of
constructors (some renaming). All events that report query results
now report a `Result` to uniformly permit reporting of errors.
The following refactorings are made:
* Introduce some constants.
* Consolidate `query.rs` and `write.rs` behind a common query interface
to reduce duplication and facilitate better code reuse, introducing
the notion of a query peer iterator. `query/peers/closest.rs`
contains the code that was formerly in `query.rs`. `query/peers/fixed.rs` contains
a modified variant of `write.rs` (which is removed). The new `query.rs`
provides an interface for working with a collection of queries, taking
over some code from `behaviour.rs`.
* Reduce code duplication in tests and use the current_thread runtime for
polling swarms to avoid spurious errors in the test output due to aborted
connections when a test finishes prematurely (e.g. because a quorum of
results has been collected).
* Some additions / improvements to the existing tests.
* Fix test.
* Fix rebase.
* Tweak kad-ipfs example.
* Incorporate some feedback.
* Provide easy access and conversion to keys in error results.
* Kademlia: Optimise iteration over closest entries.
The current implementation for finding the entries whose keys are closest
to some target key in the Kademlia routing table involves copying the
keys of all buckets into a new `Vec` which is then sorted based on the
distances to the target and turned into an iterator from which only a
small number of elements (by default 20) are drawn.
This commit introduces an iterator over buckets for finding the closest
keys to a target that visits the buckets in the optimal order, based on
the information contained in the distance bit-string representing the
distance between the local key and the target.
Correctness is tested against full-table scans.
Also included:
* Updated documentation.
* The `Entry` API was moved to the `kbucket::entry` sub-module for
ease of maintenance.
* The pending node handling has been slightly refactored in order to
bring code and documentation in agreement and clarify the semantics
a little.
* Rewrite pending node handling and add tests.
