fix: add pending connection limit

doc/LIMITS.md

@@ -20,6 +20,8 @@ In order to prevent excessive resource consumption by a libp2p node it's importa
 
 It's possible to limit the amount of incoming and outgoing connections a node is able to make.  When this limit is reached and an attempt to open a new connection is made, existing connections may be closed to make room for the new connection.
 
+We can also limit the number of connections in a "pending" state. These connections have been opened by a remote peer but peer IDs have yet to be exchanged and/or connection encryption and multiplexing negotiated. Once this limit is hit further connections will be closed unless the remote peer has an address in the [allow list](#allowdeny-lists).
+
 ```js
 const node = await createLibp2pNode({
   connectionManager: {
@@ -32,7 +34,12 @@ const node = await createLibp2pNode({
      * If the number of open connections goes below this number, the node
      * will try to connect to nearby peers from the peer store
      */
-    minConnections: 20
+    minConnections: 20,
+
+    /**
+     * How many connections can be open but not yet upgraded
+     */
+    maxIncomingPendingConnections: 10
   }
 })
 ```

examples/package.json

@@ -10,7 +10,7 @@
   "license": "MIT",
   "dependencies": {
     "@libp2p/pubsub-peer-discovery": "^6.0.2",
-    "@libp2p/floodsub": "^4.0.0",
+    "@libp2p/floodsub": "^4.0.1",
     "@nodeutils/defaults-deep": "^1.1.0",
     "execa": "^6.1.0",
     "fs-extra": "^10.1.0",

package.json

@@ -113,7 +113,7 @@
     "@libp2p/interface-peer-info": "^1.0.3",
     "@libp2p/interface-peer-routing": "^1.0.1",
     "@libp2p/interface-peer-store": "^1.2.2",
-    "@libp2p/interface-pubsub": "^2.1.0",
+    "@libp2p/interface-pubsub": "^3.0.0",
     "@libp2p/interface-registrar": "^2.0.3",
     "@libp2p/interface-stream-muxer": "^3.0.0",
     "@libp2p/interface-transport": "^2.0.0",
@@ -174,7 +174,7 @@
     "@libp2p/bootstrap": "^4.0.0",
     "@libp2p/daemon-client": "^3.0.1",
     "@libp2p/daemon-server": "^3.0.1",
-    "@libp2p/floodsub": "^4.0.0",
+    "@libp2p/floodsub": "^4.0.1",
     "@libp2p/interface-compliance-tests": "^3.0.2",
     "@libp2p/interface-connection-encrypter-compliance-tests": "^2.0.2",
     "@libp2p/interface-mocks": "^6.0.1",
@@ -211,4 +211,4 @@
   "browser": {
     "nat-api": false
   }
-}
+}

src/connection-manager/index.ts

@@ -33,7 +33,8 @@ const defaultOptions: Partial<ConnectionManagerInit> = {
   pollInterval: 2000,
   autoDialInterval: 10000,
   movingAverageInterval: 60000,
-  inboundConnectionThreshold: 5
+  inboundConnectionThreshold: 5,
+  maxIncomingPendingConnections: 10
 }
 
 const METRICS_SYSTEM = 'libp2p'
@@ -152,6 +153,12 @@ export interface ConnectionManagerInit {
    * host, reject subsequent connections
    */
   inboundConnectionThreshold?: number
+
+  /**
+   * The maximum number of parallel incoming connections allowed that have yet to
+   * complete the connection upgrade - e.g. choosing connection encryption, muxer, etc
+   */
+  maxIncomingPendingConnections?: number
 }
 
 export interface ConnectionManagerEvents {
@@ -175,6 +182,7 @@ export class DefaultConnectionManager extends EventEmitter<ConnectionManagerEven
   private readonly allow: Multiaddr[]
   private readonly deny: Multiaddr[]
   private readonly inboundConnectionRateLimiter: RateLimiterMemory
+  private incomingPendingConnections: number
 
   constructor (init: ConnectionManagerInit) {
     super()
@@ -218,6 +226,8 @@ export class DefaultConnectionManager extends EventEmitter<ConnectionManagerEven
       points: this.opts.inboundConnectionThreshold,
       duration: 1
     })
+
+    this.incomingPendingConnections = 0
   }
 
   init (components: Components): void {
@@ -719,9 +729,17 @@ export class DefaultConnectionManager extends EventEmitter<ConnectionManagerEven
     })
 
     if (allowConnection) {
+      this.incomingPendingConnections++
+
       return true
     }
 
+    // check pending connections
+    if (this.incomingPendingConnections === this.opts.maxIncomingPendingConnections) {
+      log('connection from %s refused - incomingPendingConnections exceeded by peer %s', maConn.remoteAddr)
+      return false
+    }
+
     if (maConn.remoteAddr.isThinWaistAddress()) {
       const host = maConn.remoteAddr.nodeAddress().address
 
@@ -734,6 +752,8 @@ export class DefaultConnectionManager extends EventEmitter<ConnectionManagerEven
     }
 
     if (this.getConnections().length < this.opts.maxConnections) {
+      this.incomingPendingConnections++
+
       return true
     }
 
@@ -742,6 +762,6 @@ export class DefaultConnectionManager extends EventEmitter<ConnectionManagerEven
   }
 
   afterUpgradeInbound () {
-
+    this.incomingPendingConnections--
   }
 }

src/pubsub/dummy-pubsub.ts

@@ -1,10 +1,12 @@
 import { EventEmitter } from '@libp2p/interfaces/events'
 import type { PeerId } from '@libp2p/interface-peer-id'
-import type { PublishResult, PubSub, PubSubEvents, StrictNoSign, StrictSign } from '@libp2p/interface-pubsub'
+import type { PublishResult, PubSub, PubSubEvents, StrictNoSign, StrictSign, TopicValidatorFn } from '@libp2p/interface-pubsub'
 import errCode from 'err-code'
 import { messages, codes } from '../errors.js'
 
 export class DummyPubSub extends EventEmitter<PubSubEvents> implements PubSub {
+  public topicValidators = new Map<string, TopicValidatorFn>()
+
   isStarted (): boolean {
     return false
   }

src/upgrader.ts

@@ -126,7 +126,6 @@ export class DefaultUpgrader extends EventEmitter<UpgraderEvents> implements Upg
     const accept = await this.components.getConnectionManager().acceptIncomingConnection(maConn)
 
     if (!accept) {
-      await maConn.close()
       throw errCode(new Error('connection denied'), codes.ERR_CONNECTION_DENIED)
     }
 
@@ -201,7 +200,6 @@ export class DefaultUpgrader extends EventEmitter<UpgraderEvents> implements Upg
         }
       } catch (err: any) {
         log.error('Failed to upgrade inbound connection', err)
-        await maConn.close(err)
         throw err
       }
 
@@ -228,6 +226,7 @@ export class DefaultUpgrader extends EventEmitter<UpgraderEvents> implements Upg
         remotePeer
       })
     } finally {
+      this.components.getConnectionManager().afterUpgradeInbound()
       timeoutController.clear()
     }
   }

test/connection-manager/index.spec.ts

@@ -304,4 +304,47 @@ describe('Connection Manager', () => {
     await expect(connectionManager.acceptIncomingConnection(maConn))
       .to.eventually.be.true()
   })
+
+  it('should limit the number of inbound pending connections', async () => {
+    const connectionManager = new DefaultConnectionManager({
+      ...defaultOptions,
+      maxIncomingPendingConnections: 1
+    })
+
+    const dialer = stubInterface<Dialer>()
+    dialer.dial.resolves(stubInterface<Connection>())
+
+    const components = new Components({
+      dialer
+    })
+
+    // set mocks
+    connectionManager.init(components)
+
+    // start the upgrade
+    const maConn1 = mockMultiaddrConnection({
+      source: [],
+      sink: async () => {}
+    }, await createEd25519PeerId())
+
+    await expect(connectionManager.acceptIncomingConnection(maConn1))
+      .to.eventually.be.true()
+
+    // start the upgrade
+    const maConn2 = mockMultiaddrConnection({
+      source: [],
+      sink: async () => {}
+    }, await createEd25519PeerId())
+
+    // should be false because we have not completed the upgrade of maConn1
+    await expect(connectionManager.acceptIncomingConnection(maConn2))
+      .to.eventually.be.false()
+
+    // finish the maConn1 pending upgrade
+    connectionManager.afterUpgradeInbound()
+
+    // should be true because we have now completed the upgrade of maConn1
+    await expect(connectionManager.acceptIncomingConnection(maConn2))
+      .to.eventually.be.true()
+  })
 })