libp2p-swarm 0.41.1

The libp2p swarm
Documentation
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# 0.41.1

- Update to `libp2p-swarm-derive` `v0.31.0`.

# 0.41.0

- Update to `libp2p-core` `v0.38.0`.

- Add new `on_connection_event` method to `ConnectionHandler` that accepts a `ConnectionEvent` enum and update
  `inject_*` methods to call `on_connection_event` with the respective `ConnectionEvent` variant and deprecate
  `inject_*`.
  To migrate, users should replace the `ConnectionHandler::inject_*` calls with a single
  implementation of `ConnectionHandler::on_connection_event` treating each `ConnectionEvent` variant in
  the same way its corresponding `inject_*` call was treated.
  See [PR 3085].

- Add new `on_behaviour_event` method with the same signature as `inject_event`, make the
  default implementation of `inject_event` call `on_behaviour_event` and deprecate it.
  To migrate, users should replace the `ConnectionHandler::inject_event` call
  with `ConnectionHandler::on_behaviour_event`.
  See [PR 3085].

- Add new `on_swarm_event` method to `NetworkBehaviour` that accepts a `FromSwarm` enum and update
  `inject_*` methods to call `on_swarm_event` with the respective `FromSwarm` variant and deprecate
  `inject_*`.
  To migrate, users should replace the `NetworkBehaviour::inject_*` calls with a single
  implementation of `NetworkBehaviour::on_swarm_event` treating each `FromSwarm` variant in
  the same way its corresponding `inject_*` call was treated.
  See [PR 3011].

- Add new `on_connection_handler_event` method with the same signature as `inject_event`, make the
  default implementation of `inject_event` call `on_connection_handler_event` and deprecate it.
  To migrate, users should replace the `NetworkBehaviour::inject_event` call
  with `NetworkBehaviour::on_connection_handler_event`.
  See [PR 3011].

- Export `NetworkBehaviour` derive as `libp2p_swarm::NetworkBehaviour`.
  This follows the convention of other popular libraries. `serde` for example exports the `Serialize` trait and macro as
  `serde::Serialize`. See [PR 3055].

- Feature-gate `NetworkBehaviour` macro behind `macros` feature flag. See [PR 3055].

- Make executor in Swarm constructor explicit. See [PR 3097].

  Supported executors:
  - Tokio

    Previously
    ```rust
    let swarm = SwarmBuilder::new(transport, behaviour, peer_id)
        .executor(Box::new(|fut| {
                tokio::spawn(fut);
        }))
        .build();
    ```
    Now
    ```rust
    let swarm = Swarm::with_tokio_executor(transport, behaviour, peer_id);
    ```
  - Async Std

    Previously
    ```rust
    let swarm = SwarmBuilder::new(transport, behaviour, peer_id)
        .executor(Box::new(|fut| {
                async_std::task::spawn(fut);
        }))
        .build();
    ```
    Now
    ```rust
    let swarm = Swarm::with_async_std_executor(transport, behaviour, peer_id);
    ```
  - ThreadPool (see [Issue 3107])

    In most cases ThreadPool can be replaced by executors or spawning on the local task.

    Previously
    ```rust
    let swarm = Swarm::new(transport, behaviour, peer_id);
    ```

    Now
    ```rust
    let swarm = Swarm::with_threadpool_executor(transport, behaviour, peer_id);
    ```
  - Without

    Spawns the tasks on the current task, this may result in bad performance so try to use an executor where possible. Previously this was just a fallback when no executor was specified and constructing a `ThreadPool` failed.

    New
    ```rust
    let swarm = Swarm::without_executor(transport, behaviour, peer_id);
    ```

  Deprecated APIs:
  - `Swarm::new`
  - `SwarmBuilder::new`
  - `SwarmBuilder::executor`

- Update `rust-version` to reflect the actual MSRV: 1.62.0. See [PR 3090].

[PR 3085]: https://github.com/libp2p/rust-libp2p/pull/3085
[PR 3011]: https://github.com/libp2p/rust-libp2p/pull/3011
[PR 3055]: https://github.com/libp2p/rust-libp2p/pull/3055
[PR 3097]: https://github.com/libp2p/rust-libp2p/pull/3097
[Issue 3107]: https://github.com/libp2p/rust-libp2p/issues/3107
[PR 3090]: https://github.com/libp2p/rust-libp2p/pull/3090

# 0.40.1

- Bump rand to 0.8 and quickcheck to 1. See [PR 2857].

- Update to `libp2p-core` `v0.37.0`.

- Introduce `libp2p_swarm::keep_alive::ConnectionHandler` in favor of removing `keep_alive` from
  `libp2p_swarm::dummy::ConnectionHandler`. `dummy::ConnectionHandler` now literally does not do anything. In the same
  spirit, introduce `libp2p_swarm::keep_alive::Behaviour` and `libp2p_swarm::dummy::Behaviour`. See [PR 2859].

[PR 2857]: https://github.com/libp2p/rust-libp2p/pull/2857
[PR 2859]: https://github.com/libp2p/rust-libp2p/pull/2859/

- Pass actual `PeerId` of dial to `NetworkBehaviour::inject_dial_failure` on `DialError::ConnectionLimit`. See [PR 2928].

[PR 2928]: https://github.com/libp2p/rust-libp2p/pull/2928


# 0.39.0

- Remove deprecated `NetworkBehaviourEventProcess`. See [libp2p-swarm v0.38.0 changelog entry] for
  migration path.

- Update to `libp2p-core` `v0.36.0`.

- Enforce backpressure on incoming streams via `StreamMuxer` interface. In case we hit the configured limit of maximum
  number of inbound streams, we will stop polling the `StreamMuxer` for new inbound streams. Depending on the muxer
  implementation in use, this may lead to instant dropping of inbound streams. See [PR 2861].

[libp2p-swarm v0.38.0 changelog entry]: https://github.com/libp2p/rust-libp2p/blob/master/swarm/CHANGELOG.md#0380
[PR 2861]: https://github.com/libp2p/rust-libp2p/pull/2861/

# 0.38.0

- Deprecate `NetworkBehaviourEventProcess`. When deriving `NetworkBehaviour` on a custom `struct` users
  should either bring their own `OutEvent` via `#[behaviour(out_event = "MyBehaviourEvent")]` or,
  when not specified, have the derive macro generate one for the user.

  See [`NetworkBehaviour`
  documentation](https://docs.rs/libp2p/latest/libp2p/swarm/trait.NetworkBehaviour.html) and [PR
  2784] for details.

  Previously

  ``` rust
  #[derive(NetworkBehaviour)]
  #[behaviour(event_process = true)]
  struct MyBehaviour {
      gossipsub: Gossipsub,
      mdns: Mdns,
  }

  impl NetworkBehaviourEventProcess<Gossipsub> for MyBehaviour {
      fn inject_event(&mut self, message: GossipsubEvent) {
        todo!("Handle event")
      }
  }

  impl NetworkBehaviourEventProcess<MdnsEvent> for MyBehaviour {
      fn inject_event(&mut self, message: MdnsEvent) {
        todo!("Handle event")
      }
  }
  ```

  Now

  ``` rust
  #[derive(NetworkBehaviour)]
  #[behaviour(out_event = "MyBehaviourEvent")]
  struct MyBehaviour {
      gossipsub: Gossipsub,
      mdns: Mdns,
  }

  enum MyBehaviourEvent {
      Gossipsub(GossipsubEvent),
      Mdns(MdnsEvent),
  }

  impl From<GossipsubEvent> for MyBehaviourEvent {
      fn from(event: GossipsubEvent) -> Self {
          MyBehaviourEvent::Gossipsub(event)
      }
  }

  impl From<MdnsEvent> for MyBehaviourEvent {
      fn from(event: MdnsEvent) -> Self {
          MyBehaviourEvent::Mdns(event)
      }
  }

  match swarm.next().await.unwrap() {
    SwarmEvent::Behaviour(MyBehaviourEvent::Gossipsub(event)) => {
      todo!("Handle event")
    }
    SwarmEvent::Behaviour(MyBehaviourEvent::Mdns(event)) => {
      todo!("Handle event")
    }
  }
  ```

- When deriving `NetworkBehaviour` on a custom `struct` where the user does not specify their own
  `OutEvent` via `#[behaviour(out_event = "MyBehaviourEvent")]` and where the user does not enable
  `#[behaviour(event_process = true)]`, then the derive macro generates an `OutEvent` definition for
  the user.

  See [`NetworkBehaviour`
  documentation](https://docs.rs/libp2p/latest/libp2p/swarm/trait.NetworkBehaviour.html) and [PR
  2792] for details.

- Update dial address concurrency factor to `8`, thus dialing up to 8 addresses concurrently for a single connection attempt. See `Swarm::dial_concurrency_factor` and [PR 2741].

- Update to `libp2p-core` `v0.35.0`.

[PR 2741]: https://github.com/libp2p/rust-libp2p/pull/2741/
[PR 2784]: https://github.com/libp2p/rust-libp2p/pull/2784
[PR 2792]: https://github.com/libp2p/rust-libp2p/pull/2792

# 0.37.0

- Update to `libp2p-core` `v0.34.0`.

- Extend log message when exceeding inbound negotiating streams with peer ID and limit. See [PR 2716].

- Remove `connection::ListenersStream` and poll the `Transport` directly. See [PR 2652].

[PR 2716]: https://github.com/libp2p/rust-libp2p/pull/2716/
[PR 2652]: https://github.com/libp2p/rust-libp2p/pull/2652

# 0.36.1

- Limit negotiating inbound substreams per connection. See [PR 2697].

[PR 2697]: https://github.com/libp2p/rust-libp2p/pull/2697

# 0.36.0

- Don't require `Transport` to be `Clone`. See [PR 2529].

- Update to `libp2p-core` `v0.33.0`.

- Make `behaviour::either` module private. See [PR 2610]

- Rename `IncomingInfo::to_connected_point` to `IncomingInfo::create_connected_point`. See [PR 2620].

- Rename `TProtoHandler` to `TConnectionHandler`, `ToggleProtoHandler` to `ToggleConnectionHandler`, `ToggleIntoProtoHandler` to `ToggleIntoConnectionHandler`. See [PR 2640].

[PR 2529]: https://github.com/libp2p/rust-libp2p/pull/2529
[PR 2610]: https://github.com/libp2p/rust-libp2p/pull/2610
[PR 2620]: https://github.com/libp2p/rust-libp2p/pull/2620
[PR 2640]: https://github.com/libp2p/rust-libp2p/pull/2640

# 0.35.0

- Add impl `IntoIterator` for `MultiHandler`. See [PR 2572].
- Remove `Send` bound from `NetworkBehaviour`. See [PR 2535].

[PR 2572]: https://github.com/libp2p/rust-libp2p/pull/2572/
[PR 2535]: https://github.com/libp2p/rust-libp2p/pull/2535/

# 0.34.0 [2022-02-22]

- Rename `ProtocolsHandler` to `ConnectionHandler`. Upgrade should be as simple as renaming all
  occurences of `ProtocolsHandler` to `ConnectionHandler` with your favorite text manipulation tool
  across your codebase. See [PR 2527].

- Fold `libp2p-core`'s `Network` into `Swarm`. See [PR 2492].

- Update to `libp2p-core` `v0.32.0`.

- Disconnect pending connections with `Swarm::disconnect`. See [PR 2517].

- Report aborted connections via `SwarmEvent::OutgoingConnectionError`. See [PR 2517].

[PR 2492]: https://github.com/libp2p/rust-libp2p/pull/2492
[PR 2517]: https://github.com/libp2p/rust-libp2p/pull/2517
[PR 2527]: https://github.com/libp2p/rust-libp2p/pull/2527

# 0.33.0 [2022-01-27]

- Patch reporting on banned peers and their non-banned and banned connections (see [PR 2350]).

- Update dependencies.

- Migrate to Rust edition 2021 (see [PR 2339]).

- Update `Connection::address` on `inject_address_change` (see [PR 2362]).

- Move `swarm::Toggle` to `swarm::behaviour::Toggle` (see [PR 2375]).

- Add `Swarm::connected_peers` (see [PR 2378]).

- Implement `swarm::NetworkBehaviour` on `either::Either` (see [PR 2370]).

- Allow overriding _dial concurrency factor_ per dial via
  `DialOpts::override_dial_concurrency_factor`. See [PR 2404].

- Report negotiated and expected `PeerId` as well as remote address in
  `DialError::WrongPeerId` (see [PR 2428]).

- Allow overriding role when dialing through `override_role` option on
  `DialOpts`. This option is needed for NAT and firewall hole punching. See [PR
  2363].

- Merge NetworkBehaviour's inject_\* paired methods (see PR 2445).

[PR 2339]: https://github.com/libp2p/rust-libp2p/pull/2339
[PR 2350]: https://github.com/libp2p/rust-libp2p/pull/2350
[PR 2362]: https://github.com/libp2p/rust-libp2p/pull/2362
[PR 2370]: https://github.com/libp2p/rust-libp2p/pull/2370
[PR 2375]: https://github.com/libp2p/rust-libp2p/pull/2375
[PR 2378]: https://github.com/libp2p/rust-libp2p/pull/2378
[PR 2404]: https://github.com/libp2p/rust-libp2p/pull/2404
[PR 2428]: https://github.com/libp2p/rust-libp2p/pull/2428
[PR 2363]: https://github.com/libp2p/rust-libp2p/pull/2363
[PR 2445]: https://github.com/libp2p/rust-libp2p/pull/2445

# 0.32.0 [2021-11-16]

- Use `instant` and `futures-timer` instead of `wasm-timer` (see [PR 2245]).

- Enable advanced dialing requests both on `Swarm::dial` and via
  `NetworkBehaviourAction::Dial`. Users can now trigger a dial with a specific
  set of addresses, optionally extended via
  `NetworkBehaviour::addresses_of_peer`.

   Changes required to maintain status quo:

  - Previously `swarm.dial(peer_id)`
     now `swarm.dial(DialOpts::peer_id(peer_id).build())`
     or `swarm.dial(peer_id)` given that `DialOpts` implements `From<PeerId>`.

  - Previously `swarm.dial_addr(addr)`
     now `swarm.dial(DialOpts::unknown_peer_id().address(addr).build())`
     or `swarm.dial(addr)` given that `DialOpts` implements `From<Multiaddr>`.

  - Previously `NetworkBehaviourAction::DialPeer { peer_id, condition, handler }`
     now

     ```rust
     NetworkBehaviourAction::Dial {
       opts: DialOpts::peer_id(peer_id)
         .condition(condition)
         .build(),
       handler,
     }
     ```

  - Previously `NetworkBehaviourAction::DialAddress { address, handler }`
     now

     ```rust
     NetworkBehaviourAction::Dial {
       opts: DialOpts::unknown_peer_id()
         .address(address)
         .build(),
       handler,
     }
     ```

   See [PR 2317].

[PR 2245]: https://github.com/libp2p/rust-libp2p/pull/2245
[PR 2317]: https://github.com/libp2p/rust-libp2p/pull/2317

# 0.31.0 [2021-11-01]

- Make default features of `libp2p-core` optional.
  [PR 2181]https://github.com/libp2p/rust-libp2p/pull/2181

- Update dependencies.

- Provide default implementations for all functions of `NetworkBehaviour`,
  except for `new_handler`, `inject_event` and `poll`.
  This should make it easier to create new implementations. See [PR 2150].

- Remove `Swarm` type alias and rename `ExpandedSwarm` to `Swarm`. Reduce direct
  trait parameters on `Swarm` (previously `ExpandedSwarm`), deriving parameters
  through associated types on `TBehaviour`. See [PR 2182].

- Require `ProtocolsHandler::{InEvent,OutEvent,Error}` to implement `Debug` (see
  [PR 2183]).

- Implement `ProtocolsHandler` on `either::Either`representing either of two
  `ProtocolsHandler` implementations (see [PR 2192]).

- Require implementation to provide handler in
  `NetworkBehaviourAction::DialPeer` and `NetworkBehaviourAction::DialAddress`.
  Note that the handler is returned to the `NetworkBehaviour` on connection
  failure and connection closing. Thus it can be used to carry state, which
  otherwise would have to be tracked in the `NetworkBehaviour` itself. E.g. a
  message destined to an unconnected peer can be included in the handler, and
  thus directly send on connection success or extracted by the
  `NetworkBehaviour` on connection failure (see [PR 2191]).

- Include handler in `NetworkBehaviour::inject_dial_failure`,
  `NetworkBehaviour::inject_connection_closed`,
  `NetworkBehaviour::inject_listen_failure` (see [PR 2191]).

- Include error in `NetworkBehaviour::inject_dial_failure` and call
  `NetworkBehaviour::inject_dial_failure` on `DialPeerCondition` evaluating to
  false. To emulate the previous behaviour, return early within
  `inject_dial_failure` on `DialError::DialPeerConditionFalse`. See [PR 2191].

- Make `NetworkBehaviourAction` generic over `NetworkBehaviour::OutEvent` and
  `NetworkBehaviour::ProtocolsHandler`. In most cases, change your generic type
  parameters to `NetworkBehaviourAction<Self::OutEvent,
  Self::ProtocolsHandler>`. See [PR 2191].

- Return `bool` instead of `Result<(), ()>` for `Swarm::remove_listener`(see
  [PR 2261]).

- Concurrently dial address candidates within a single dial attempt (see [PR 2248]) configured via
  `Swarm::dial_concurrency_factor`.

  - On success of a single address, report errors of the thus far failed dials via
    `SwarmEvent::ConnectionEstablished::outgoing`.

  - On failure of all addresses, report errors via the new `SwarmEvent::OutgoingConnectionError`.

  - Remove `SwarmEvent::UnreachableAddr` and `SwarmEvent::UnknownPeerUnreachableAddr` event.

  - In `NetworkBehaviour::inject_connection_established` provide errors of all thus far failed addresses.

  - On unknown peer dial failures, call `NetworkBehaviour::inject_dial_failure` with a peer ID of `None`.

  - Remove `NetworkBehaviour::inject_addr_reach_failure`. Information is now provided via
    `NetworkBehaviour::inject_connection_established` and `NetworkBehaviour::inject_dial_failure`.

[PR 2150]: https://github.com/libp2p/rust-libp2p/pull/2150
[PR 2182]: https://github.com/libp2p/rust-libp2p/pull/2182
[PR 2183]: https://github.com/libp2p/rust-libp2p/pull/2183
[PR 2192]: https://github.com/libp2p/rust-libp2p/pull/2192
[PR 2191]: https://github.com/libp2p/rust-libp2p/pull/2191
[PR 2248]: https://github.com/libp2p/rust-libp2p/pull/2248
[PR 2261]: https://github.com/libp2p/rust-libp2p/pull/2261

# 0.30.0 [2021-07-12]

- Update dependencies.

- Drive `ExpandedSwarm` via `Stream` trait only.

  - Change `Stream` implementation of `ExpandedSwarm` to return all
    `SwarmEvents` instead of only the `NetworkBehaviour`'s events.

  - Remove `ExpandedSwarm::next_event`. Users can use `<ExpandedSwarm as
    StreamExt>::next` instead.

  - Remove `ExpandedSwarm::next`. Users can use `<ExpandedSwarm as
    StreamExt>::filter_map` instead.

  See [PR 2100] for details.

- Add `ExpandedSwarm::disconnect_peer_id` and
  `NetworkBehaviourAction::CloseConnection` to close connections to a specific
  peer via an `ExpandedSwarm` or `NetworkBehaviour`. See [PR 2110] for details.

- Expose the `ListenerId` in `SwarmEvent`s that are associated with a listener.

  See [PR 2123] for details.

[PR 2100]: https://github.com/libp2p/rust-libp2p/pull/2100
[PR 2110]: https://github.com/libp2p/rust-libp2p/pull/2110/
[PR 2123]: https://github.com/libp2p/rust-libp2p/pull/2123

# 0.29.0 [2021-04-13]

- Remove `Deref` and `DerefMut` implementations previously dereferencing to the
  `NetworkBehaviour` on `Swarm`. Instead one can access the `NetworkBehaviour`
  via `Swarm::behaviour` and `Swarm::behaviour_mut`. Methods on `Swarm` can now
  be accessed directly, e.g. via `my_swarm.local_peer_id()`. You may use the
  command below to transform fully qualified method calls on `Swarm` to simple
  method calls [PR 1995]https://github.com/libp2p/rust-libp2p/pull/1995.

  ``` bash
  # Go from e.g. `Swarm::local_peer_id(&my_swarm)` to `my_swarm.local_peer_id()`.
  grep -RiIl --include \*.rs --exclude-dir target . --exclude-dir .git | xargs sed -i "s/\(libp2p::\)*Swarm::\([a-z_]*\)(&mut \([a-z_0-9]*\), /\3.\2(/g"
  ```

- Extend `NetworkBehaviour` callbacks, more concretely introducing new `fn
  inject_new_listener` and `fn inject_expired_external_addr` and have `fn
  inject_{new,expired}_listen_addr` provide a `ListenerId` [PR
  2011](https://github.com/libp2p/rust-libp2p/pull/2011).

# 0.28.0 [2021-03-17]

- New error variant `DialError::InvalidAddress`

- `Swarm::dial_addr()` now returns a `DialError` on error.

- Remove the option for a substream-specific multistream select protocol override.
  The override at this granularity is no longer deemed useful, in particular because
  it can usually not be configured for existing protocols like `libp2p-kad` and others.
  There is a `Swarm`-scoped configuration for this version available since
  [1858]https://github.com/libp2p/rust-libp2p/pull/1858.

# 0.27.2 [2021-02-04]

- Have `ToggleProtoHandler` ignore listen upgrade errors when disabled.
  [PR 1945]https://github.com/libp2p/rust-libp2p/pull/1945/files.

# 0.27.1 [2021-01-27]

- Make `OneShotHandler`s `max_dial_negotiate` limit configurable.
  [PR 1936]https://github.com/libp2p/rust-libp2p/pull/1936.

- Fix handling of DialPeerCondition::Always.
  [PR 1937]https://github.com/libp2p/rust-libp2p/pull/1937.

# 0.27.0 [2021-01-12]

- Update dependencies.

# 0.26.0 [2020-12-17]

- Update `libp2p-core`.

- Remove `NotifyHandler::All` thus removing the requirement for events send from
  a `NetworkBehaviour` to a `ProtocolsHandler` to be `Clone`.
  [PR 1880]https://github.com/libp2p/rust-libp2p/pull/1880.

# 0.25.1 [2020-11-26]

- Add `ExpandedSwarm::is_connected`.
  [PR 1862]https://github.com/libp2p/rust-libp2p/pull/1862.

# 0.25.0 [2020-11-25]

- Permit a configuration override for the substream upgrade protocol
  to use for all (outbound) substreams.
  [PR 1858]https://github.com/libp2p/rust-libp2p/pull/1858.

- Changed parameters for connection limits from `usize` to `u32`.
  Connection limits are now configured via `SwarmBuilder::connection_limits()`.

- Update `libp2p-core`.

- Expose configurable scores for external addresses, as well as
  the ability to remove them and to add addresses that are
  retained "forever" (or until explicitly removed).
  [PR 1842]https://github.com/libp2p/rust-libp2p/pull/1842.

# 0.24.0 [2020-11-09]

- Update dependencies.

# 0.23.0 [2020-10-16]

- Require a `Boxed` transport to be given to the `Swarm`
  or `SwarmBuilder` to avoid unnecessary double-boxing of
  transports and simplify API bounds.
  [PR 1794]https://github.com/libp2p/rust-libp2p/pull/1794

- Respect inbound timeouts and upgrade versions in the `MultiHandler`.
  [PR 1786]https://github.com/libp2p/rust-libp2p/pull/1786.

- Instead of iterating each inbound and outbound substream upgrade looking for
  one to make progress, use a `FuturesUnordered` for both pending inbound and
  pending outbound upgrades. As a result only those upgrades are polled that are
  ready to progress.

  Implementors of `InboundUpgrade` and `OutboundUpgrade` need to ensure to wake
  up the underlying task once they are ready to make progress as they won't be
  polled otherwise.

  [PR 1775]https://github.com/libp2p/rust-libp2p/pull/1775

# 0.22.0 [2020-09-09]

- Bump `libp2p-core` dependency.

- Adds `ProtocolsHandler::InboundOpenInfo` type which mirrors the existing
  `OutboundOpenInfo` type. A value of this type is passed as an extra argument
  to `ProtocolsHandler::inject_fully_negotiated_inbound` and
  `ProtocolsHandler::inject_listen_upgrade_error`.

- `SubstreamProtocol` now has a second type parameter corresponding to
  inbound or outbound information, a value of which is part of `SubstreamProtocol`
  now. Consequently `ProtocolsHandlerEvent::OutboundSubstreamRequest` no longer
  has a separate `info` field.

# 0.21.0 [2020-08-18]

- Add missing delegation calls in some `ProtocolsHandler` wrappers.
See [PR 1710]https://github.com/libp2p/rust-libp2p/pull/1710.

- Add as_ref and as_mut functions to Toggle
[PR 1684]https://github.com/libp2p/rust-libp2p/pull/1684.

- The `cause` of `SwarmEvent::ConnectionClosed` is now an `Option`,
and `None` indicates an active connection close not caused by an
error.

- `DialError::Banned` has been added and is returned from `Swarm::dial`
if the peer is banned, thereby also invoking the `NetworkBehaviour::inject_dial_failure`
callback.

- Update the `libp2p-core` dependency to `0.21`, fixing [1584]https://github.com/libp2p/rust-libp2p/issues/1584.

- Fix connections being kept alive by `OneShotHandler` when not handling any
  requests [PR 1698]https://github.com/libp2p/rust-libp2p/pull/1698.

# 0.20.1 [2020-07-08]

- Documentation updates.

- Ignore addresses returned by `NetworkBehaviour::addresses_of_peer`
that the `Swarm` considers to be listening addresses of the local node. This
avoids futile dialing attempts of a node to itself, which can otherwise
even happen in genuine situations, e.g. after the local node changed
its network identity and a behaviour makes a dialing attempt to a
former identity using the same addresses.

# 0.20.0 [2020-07-01]

- Updated the `libp2p-core` dependency.

- Add `ProtocolsHandler::inject_listen_upgrade_error`, the inbound
analogue of `ProtocolsHandler::inject_dial_upgrade_error`, with an
empty default implementation. No implementation is required to
retain existing behaviour.

- Add `ProtocolsHandler::inject_address_change` and
`NetworkBehaviour::inject_address_change` to notify of a change in
the address of an existing connection.

# 0.19.1 [2020-06-18]

- Bugfix: Fix MultiHandler panicking when empty
  ([PR 1598]https://github.com/libp2p/rust-libp2p/pull/1598).