fix: rename event emitter class (#2173)

We add types to a `EventEmitter` class which extends the plain js `EventTarget`.

The name is chosen to give familiarity to node developers but it's not generally a good idea.

This refactor:

1. Exports a new `TypedEventTarget` interface which adds types to `EventTarget`
2. Renames `EventEmitter` to `TypedEventEmitter` to draw a distinction between them
3. Re-exports `TypedEventEmitter` as `EventEmitter` to preserve backwards compatibility

In the future all consuming code should rely on the `TypedEventTarget` interface while implementing code uses `TypedEventEmitter` as an implementation of a `TypedEventEmitter`.

By depending on the interface and not the implementation consuming code is isolated from problems that arise when two versions of `@libp2p/interface` is in the dependency tree and the event subsystems would otherwise be compatible due to type overlap.

This manifests as an error message about incompatible implementations of the private `#listeners` field in EventEmitter.

Backwards compatibility is achieved by exporting the `TypedEventEmitter` class as the older `EventEmitter` name.  This should be removed in a future PR to the v1.0 branch once external modules (e.g. Gossipsub) have been updated to use the new `TypedEventEmitter` symbol.

## Change checklist

- [x] I have performed a self-review of my own code
- [ ] I have made corresponding changes to the documentation if necessary (this includes comments as well)
- [ ] I have added tests that prove my fix is effective or that my feature works

packages/interface-compliance-tests/src/mocks/connection-manager.ts

@@ -6,7 +6,7 @@ import { isMultiaddr, type Multiaddr } from '@multiformats/multiaddr'
 import { connectionPair } from './connection.js'
 import type { Libp2pEvents, PendingDial } from '@libp2p/interface'
 import type { Connection } from '@libp2p/interface/connection'
-import type { EventEmitter } from '@libp2p/interface/events'
+import type { TypedEventTarget } from '@libp2p/interface/events'
 import type { PubSub } from '@libp2p/interface/pubsub'
 import type { Startable } from '@libp2p/interface/startable'
 import type { ConnectionManager } from '@libp2p/interface-internal/connection-manager'
@@ -16,7 +16,7 @@ export interface MockNetworkComponents {
   peerId: PeerId
   registrar: Registrar
   connectionManager: ConnectionManager
-  events: EventEmitter<Libp2pEvents>
+  events: TypedEventTarget<Libp2pEvents>
   pubsub?: PubSub
 }
 
@@ -51,7 +51,7 @@ export const mockNetwork = new MockNetwork()
 export interface MockConnectionManagerComponents {
   peerId: PeerId
   registrar: Registrar
-  events: EventEmitter<Libp2pEvents>
+  events: TypedEventTarget<Libp2pEvents>
 }
 
 class MockConnectionManager implements ConnectionManager, Startable {

packages/interface-compliance-tests/src/mocks/peer-discovery.ts

@@ -1,4 +1,4 @@
-import { EventEmitter } from '@libp2p/interface/events'
+import { TypedEventEmitter } from '@libp2p/interface/events'
 import { peerDiscovery } from '@libp2p/interface/peer-discovery'
 import * as PeerIdFactory from '@libp2p/peer-id-factory'
 import { multiaddr } from '@multiformats/multiaddr'
@@ -12,7 +12,7 @@ interface MockDiscoveryInit {
 /**
  * Emits 'peer' events on discovery.
  */
-export class MockDiscovery extends EventEmitter<PeerDiscoveryEvents> implements PeerDiscovery {
+export class MockDiscovery extends TypedEventEmitter<PeerDiscoveryEvents> implements PeerDiscovery {
   public readonly options: MockDiscoveryInit
   private _isRunning: boolean
   private _timer: any

packages/interface-compliance-tests/src/mocks/upgrader.ts

@@ -1,18 +1,18 @@
 import { mockConnection } from './connection.js'
 import type { Libp2pEvents } from '@libp2p/interface'
 import type { Connection, MultiaddrConnection } from '@libp2p/interface/connection'
-import type { EventEmitter } from '@libp2p/interface/events'
+import type { TypedEventTarget } from '@libp2p/interface/events'
 import type { Upgrader, UpgraderOptions } from '@libp2p/interface/transport'
 import type { Registrar } from '@libp2p/interface-internal/registrar'
 
 export interface MockUpgraderInit {
   registrar?: Registrar
-  events?: EventEmitter<Libp2pEvents>
+  events?: TypedEventTarget<Libp2pEvents>
 }
 
 class MockUpgrader implements Upgrader {
   private readonly registrar?: Registrar
-  private readonly events?: EventEmitter<Libp2pEvents>
+  private readonly events?: TypedEventTarget<Libp2pEvents>
 
   constructor (init: MockUpgraderInit) {
     this.registrar = init.registrar

packages/interface-compliance-tests/src/pubsub/utils.ts

@@ -1,4 +1,4 @@
-import { EventEmitter } from '@libp2p/interface/events'
+import { TypedEventEmitter } from '@libp2p/interface/events'
 import { createEd25519PeerId } from '@libp2p/peer-id-factory'
 import { pEvent } from 'p-event'
 import pWaitFor from 'p-wait-for'
@@ -19,7 +19,7 @@ export async function createComponents (): Promise<MockNetworkComponents> {
   const components: any = {
     peerId: await createEd25519PeerId(),
     registrar: mockRegistrar(),
-    events: new EventEmitter()
+    events: new TypedEventEmitter()
   }
   components.connectionManager = mockConnectionManager(components)
 

packages/interface-compliance-tests/src/transport/dial-test.ts

@@ -1,5 +1,5 @@
 import { AbortError } from '@libp2p/interface/errors'
-import { EventEmitter } from '@libp2p/interface/events'
+import { TypedEventEmitter } from '@libp2p/interface/events'
 import { expect } from 'aegir/chai'
 import all from 'it-all'
 import drain from 'it-drain'
@@ -27,7 +27,7 @@ export default (common: TestSetup<TransportTestFixtures>): void => {
       registrar = mockRegistrar()
       upgrader = mockUpgrader({
         registrar,
-        events: new EventEmitter()
+        events: new TypedEventEmitter()
       });
 
       ({ addrs, transport, connector } = await common.setup())

packages/interface-compliance-tests/src/transport/listen-test.ts

@@ -1,5 +1,5 @@
 /* eslint max-nested-callbacks: ["error", 8] */
-import { CustomEvent, EventEmitter } from '@libp2p/interface/events'
+import { CustomEvent, TypedEventEmitter } from '@libp2p/interface/events'
 import { expect } from 'aegir/chai'
 import drain from 'it-drain'
 import { pipe } from 'it-pipe'
@@ -27,7 +27,7 @@ export default (common: TestSetup<TransportTestFixtures>): void => {
       registrar = mockRegistrar()
       upgrader = mockUpgrader({
         registrar,
-        events: new EventEmitter()
+        events: new TypedEventEmitter()
       });
 
       ({ transport, addrs } = await common.setup())

packages/interface/src/events.ts

@@ -15,7 +15,23 @@ interface Listener {
  * https://github.com/microsoft/TypeScript/issues/299
  * etc
  */
-export class EventEmitter<EventMap extends Record<string, any>> extends EventTarget {
+export interface TypedEventTarget <EventMap extends Record<string, any>> extends EventTarget {
+  addEventListener<K extends keyof EventMap>(type: K, listener: EventHandler<EventMap[K]> | null, options?: boolean | AddEventListenerOptions): void
+
+  listenerCount (type: string): number
+
+  removeEventListener<K extends keyof EventMap>(type: K, listener?: EventHandler<EventMap[K]> | null, options?: boolean | EventListenerOptions): void
+
+  removeEventListener (type: string, listener?: EventHandler<Event>, options?: boolean | EventListenerOptions): void
+
+  safeDispatchEvent<Detail>(type: keyof EventMap, detail: CustomEventInit<Detail>): boolean
+}
+
+/**
+ * An implementation of a typed event target
+ * etc
+ */
+export class TypedEventEmitter<EventMap extends Record<string, any>> extends EventTarget implements TypedEventTarget<EventMap> {
   #listeners = new Map<any, Listener[]>()
 
   listenerCount (type: string): number {
@@ -98,3 +114,6 @@ class CustomEventPolyfill<T = any> extends Event {
 }
 
 export const CustomEvent = globalThis.CustomEvent ?? CustomEventPolyfill
+
+// TODO: remove this in v1
+export { TypedEventEmitter as EventEmitter }

packages/interface/src/index.ts

@@ -16,7 +16,7 @@
 
 import type { Connection, NewStreamOptions, Stream } from './connection/index.js'
 import type { ContentRouting } from './content-routing/index.js'
-import type { EventEmitter } from './events.js'
+import type { TypedEventTarget } from './events.js'
 import type { KeyChain } from './keychain/index.js'
 import type { Metrics } from './metrics/index.js'
 import type { PeerId } from './peer-id/index.js'
@@ -303,7 +303,7 @@ export interface PendingDial {
 /**
  * Libp2p nodes implement this interface.
  */
-export interface Libp2p<T extends ServiceMap = ServiceMap> extends Startable, EventEmitter<Libp2pEvents<T>> {
+export interface Libp2p<T extends ServiceMap = ServiceMap> extends Startable, TypedEventTarget<Libp2pEvents<T>> {
   /**
    * The PeerId is a unique identifier for a node on the network.
    *

packages/interface/src/peer-discovery/index.ts

@@ -1,4 +1,4 @@
-import type { EventEmitter } from '../events.js'
+import type { TypedEventTarget } from '../events.js'
 import type { PeerInfo } from '../peer-info/index.js'
 
 /**
@@ -26,4 +26,4 @@ export interface PeerDiscoveryEvents {
   'peer': CustomEvent<PeerInfo>
 }
 
-export interface PeerDiscovery extends EventEmitter<PeerDiscoveryEvents> {}
+export interface PeerDiscovery extends TypedEventTarget<PeerDiscoveryEvents> {}

packages/interface/src/pubsub/index.ts

@@ -1,5 +1,5 @@
 import type { Stream } from '../connection/index.js'
-import type { EventEmitter } from '../events.js'
+import type { TypedEventTarget } from '../events.js'
 import type { PeerId } from '../peer-id/index.js'
 import type { Pushable } from 'it-pushable'
 import type { Uint8ArrayList } from 'uint8arraylist'
@@ -65,7 +65,7 @@ export interface PubSubRPC {
   messages: PubSubRPCMessage[]
 }
 
-export interface PeerStreams extends EventEmitter<PeerStreamEvents> {
+export interface PeerStreams extends TypedEventTarget<PeerStreamEvents> {
   id: PeerId
   protocol: string
   outboundStream?: Pushable<Uint8ArrayList>
@@ -152,7 +152,7 @@ export interface TopicValidatorFn {
   (peer: PeerId, message: Message): TopicValidatorResult | Promise<TopicValidatorResult>
 }
 
-export interface PubSub<Events extends Record<string, any> = PubSubEvents> extends EventEmitter<Events> {
+export interface PubSub<Events extends Record<string, any> = PubSubEvents> extends TypedEventTarget<Events> {
   /**
    * The global signature policy controls whether or not we sill send and receive
    * signed or unsigned messages.

packages/interface/src/transport/index.ts

@@ -1,5 +1,5 @@
 import type { Connection, MultiaddrConnection } from '../connection/index.js'
-import type { EventEmitter } from '../events.js'
+import type { TypedEventTarget } from '../events.js'
 import type { AbortOptions } from '../index.js'
 import type { StreamMuxerFactory } from '../stream-muxer/index.js'
 import type { Multiaddr } from '@multiformats/multiaddr'
@@ -11,7 +11,7 @@ export interface ListenerEvents {
   'close': CustomEvent
 }
 
-export interface Listener extends EventEmitter<ListenerEvents> {
+export interface Listener extends TypedEventTarget<ListenerEvents> {
   /**
    * Start a listener
    */

packages/kad-dht/src/dual-kad-dht.ts

@@ -1,6 +1,6 @@
 import { type ContentRouting, contentRouting } from '@libp2p/interface/content-routing'
 import { CodeError } from '@libp2p/interface/errors'
-import { EventEmitter, CustomEvent } from '@libp2p/interface/events'
+import { TypedEventEmitter, CustomEvent } from '@libp2p/interface/events'
 import { type PeerDiscovery, peerDiscovery, type PeerDiscoveryEvents } from '@libp2p/interface/peer-discovery'
 import { type PeerRouting, peerRouting } from '@libp2p/interface/peer-routing'
 import { logger } from '@libp2p/logger'
@@ -121,7 +121,7 @@ function multiaddrIsPublic (multiaddr: Multiaddr): boolean {
  * A DHT implementation modelled after Kademlia with S/Kademlia modifications.
  * Original implementation in go: https://github.com/libp2p/go-libp2p-kad-dht.
  */
-export class DefaultDualKadDHT extends EventEmitter<PeerDiscoveryEvents> implements DualKadDHT, PeerDiscovery {
+export class DefaultDualKadDHT extends TypedEventEmitter<PeerDiscoveryEvents> implements DualKadDHT, PeerDiscovery {
   public readonly wan: DefaultKadDHT
   public readonly lan: DefaultKadDHT
   public readonly components: KadDHTComponents

packages/kad-dht/src/index.ts

@@ -1,7 +1,7 @@
 import { DefaultDualKadDHT } from './dual-kad-dht.js'
 import type { ProvidersInit } from './providers.js'
 import type { Libp2pEvents, AbortOptions } from '@libp2p/interface'
-import type { EventEmitter } from '@libp2p/interface/events'
+import type { TypedEventTarget } from '@libp2p/interface/events'
 import type { Metrics } from '@libp2p/interface/metrics'
 import type { PeerId } from '@libp2p/interface/peer-id'
 import type { PeerInfo } from '@libp2p/interface/peer-info'
@@ -314,7 +314,7 @@ export interface KadDHTComponents {
   metrics?: Metrics
   connectionManager: ConnectionManager
   datastore: Datastore
-  events: EventEmitter<Libp2pEvents>
+  events: TypedEventTarget<Libp2pEvents>
 }
 
 export function kadDHT (init?: KadDHTInit): (components: KadDHTComponents) => DualKadDHT {

packages/kad-dht/src/kad-dht.ts

@@ -1,4 +1,4 @@
-import { CustomEvent, EventEmitter } from '@libp2p/interface/events'
+import { CustomEvent, TypedEventEmitter } from '@libp2p/interface/events'
 import { type Logger, logger } from '@libp2p/logger'
 import pDefer from 'p-defer'
 import { PROTOCOL_DHT, PROTOCOL_PREFIX, LAN_PREFIX } from './constants.js'
@@ -39,7 +39,7 @@ export interface SingleKadDHTInit extends KadDHTInit {
  * A DHT implementation modelled after Kademlia with S/Kademlia modifications.
  * Original implementation in go: https://github.com/libp2p/go-libp2p-kad-dht.
  */
-export class DefaultKadDHT extends EventEmitter<PeerDiscoveryEvents> implements KadDHT {
+export class DefaultKadDHT extends TypedEventEmitter<PeerDiscoveryEvents> implements KadDHT {
   public protocol: string
   public routingTable: RoutingTable
   public providers: Providers

packages/kad-dht/src/network.ts

@@ -1,5 +1,5 @@
 import { CodeError } from '@libp2p/interface/errors'
-import { EventEmitter, CustomEvent } from '@libp2p/interface/events'
+import { TypedEventEmitter, CustomEvent } from '@libp2p/interface/events'
 import { logger } from '@libp2p/logger'
 import { abortableDuplex } from 'abortable-iterator'
 import drain from 'it-drain'
@@ -35,7 +35,7 @@ interface NetworkEvents {
 /**
  * Handle network operations for the dht
  */
-export class Network extends EventEmitter<NetworkEvents> implements Startable {
+export class Network extends TypedEventEmitter<NetworkEvents> implements Startable {
   private readonly log: Logger
   private readonly protocol: string
   private running: boolean

packages/kad-dht/src/query/manager.ts

@@ -1,6 +1,6 @@
 import { setMaxListeners } from 'events'
 import { AbortError } from '@libp2p/interface/errors'
-import { EventEmitter, CustomEvent } from '@libp2p/interface/events'
+import { TypedEventEmitter, CustomEvent } from '@libp2p/interface/events'
 import { logger } from '@libp2p/logger'
 import { PeerSet } from '@libp2p/peer-collections'
 import { anySignal } from 'any-signal'
@@ -143,7 +143,7 @@ export class QueryManager implements Startable {
 
     // query a subset of peers up to `kBucketSize / 2` in length
     const startTime = Date.now()
-    const cleanUp = new EventEmitter<CleanUpEvents>()
+    const cleanUp = new TypedEventEmitter<CleanUpEvents>()
 
     try {
       if (options.isSelfQuery !== true && this.initialQuerySelfHasRun != null) {

packages/kad-dht/src/query/query-path.ts

@@ -9,7 +9,7 @@ import { queryErrorEvent } from './events.js'
 import type { CleanUpEvents } from './manager.js'
 import type { QueryEvent, QueryOptions } from '../index.js'
 import type { QueryFunc } from '../query/types.js'
-import type { EventEmitter } from '@libp2p/interface/events'
+import type { TypedEventTarget } from '@libp2p/interface/events'
 import type { PeerId } from '@libp2p/interface/peer-id'
 import type { Logger } from '@libp2p/logger'
 import type { PeerSet } from '@libp2p/peer-collections'
@@ -60,7 +60,7 @@ export interface QueryPathOptions extends QueryOptions {
   /**
    * will emit a 'cleanup' event if the caller exits the for..await of early
    */
-  cleanUp: EventEmitter<CleanUpEvents>
+  cleanUp: TypedEventTarget<CleanUpEvents>
 
   /**
    * A timeout for queryFunc in ms
@@ -185,7 +185,7 @@ export async function * queryPath (options: QueryPathOptions): AsyncGenerator<Qu
   yield * toGenerator(queue, signal, cleanUp, log)
 }
 
-async function * toGenerator (queue: Queue, signal: AbortSignal, cleanUp: EventEmitter<CleanUpEvents>, log: Logger): AsyncGenerator<QueryEvent, void, undefined> {
+async function * toGenerator (queue: Queue, signal: AbortSignal, cleanUp: TypedEventTarget<CleanUpEvents>, log: Logger): AsyncGenerator<QueryEvent, void, undefined> {
   let deferred = defer()
   let running = true
   const results: QueryEvent[] = []

packages/kad-dht/src/routing-table/index.ts

@@ -1,4 +1,4 @@
-import { EventEmitter } from '@libp2p/interface/events'
+import { TypedEventEmitter } from '@libp2p/interface/events'
 import { logger } from '@libp2p/logger'
 import { PeerSet } from '@libp2p/peer-collections'
 import Queue from 'p-queue'
@@ -43,7 +43,7 @@ export interface RoutingTableEvents {
  * A wrapper around `k-bucket`, to provide easy store and
  * retrieval for peers.
  */
-export class RoutingTable extends EventEmitter<RoutingTableEvents> implements Startable {
+export class RoutingTable extends TypedEventEmitter<RoutingTableEvents> implements Startable {
   public kBucketSize: number
   public kb?: KBucket
   public pingQueue: Queue

packages/kad-dht/src/routing-table/k-bucket.ts

@@ -27,7 +27,7 @@ FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 OTHER DEALINGS IN THE SOFTWARE.
 */
 
-import { EventEmitter } from '@libp2p/interface/events'
+import { TypedEventEmitter } from '@libp2p/interface/events'
 import type { PeerId } from '@libp2p/interface/peer-id'
 
 function arrayEquals (array1: Uint8Array, array2: Uint8Array): boolean {
@@ -122,10 +122,8 @@ export interface Bucket {
 /**
  * Implementation of a Kademlia DHT k-bucket used for storing
  * contact (peer node) information.
- *
- * @extends EventEmitter
  */
-export class KBucket extends EventEmitter<KBucketEvents> {
+export class KBucket extends TypedEventEmitter<KBucketEvents> {
   public localNodeId: Uint8Array
   public root: Bucket
   private readonly numberOfNodesPerKBucket: number

packages/kad-dht/src/topology-listener.ts

@@ -1,4 +1,4 @@
-import { CustomEvent, EventEmitter } from '@libp2p/interface/events'
+import { CustomEvent, TypedEventEmitter } from '@libp2p/interface/events'
 import { logger } from '@libp2p/logger'
 import type { KadDHTComponents } from '.'
 import type { PeerId } from '@libp2p/interface/peer-id'
@@ -17,7 +17,7 @@ export interface TopologyListenerEvents {
 /**
  * Receives notifications of new peers joining the network that support the DHT protocol
  */
-export class TopologyListener extends EventEmitter<TopologyListenerEvents> implements Startable {
+export class TopologyListener extends TypedEventEmitter<TopologyListenerEvents> implements Startable {
   private readonly log: Logger
   private readonly components: KadDHTComponents
   private readonly protocol: string

packages/kad-dht/test/routing-table.spec.ts

@@ -1,6 +1,6 @@
 /* eslint-env mocha */
 
-import { EventEmitter, CustomEvent } from '@libp2p/interface/events'
+import { TypedEventEmitter, CustomEvent } from '@libp2p/interface/events'
 import { mockConnectionManager } from '@libp2p/interface-compliance-tests/mocks'
 import { PeerSet } from '@libp2p/peer-collections'
 import { peerIdFromString } from '@libp2p/peer-id'
@@ -33,7 +33,7 @@ describe('Routing Table', () => {
   beforeEach(async function () {
     this.timeout(20 * 1000)
 
-    const events = new EventEmitter<Libp2pEvents>()
+    const events = new TypedEventEmitter<Libp2pEvents>()
 
     components = {
       peerId: await createPeerId(),