feat(packages): add commons package

This is an import of 166ca8da12
with some changes to make it fit into the mono repo.
- TypedEventEmitter has been replaced with EventEmitter2 because EventEmitter2 is faster and TypedEventEmitter had some troubles with the new way of compiling.
- tsc-esm has been replaced with microbundle. The problems that lib0 doesn't export its types correctly has been solved using yarn patch.

Signed-off-by: Tilman Vatteroth <git@tilmanvatteroth.de>

commons/src/connection-keep-alive-handler.ts

@@ -0,0 +1,77 @@
+/*
+ * SPDX-FileCopyrightText: 2022 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+import { MessageType } from './messages/message-type.enum.js'
+import type { YDocMessageTransporter } from './y-doc-message-transporter.js'
+import { createEncoder, toUint8Array, writeVarUint } from 'lib0/encoding'
+
+/**
+ * Provides a keep alive ping for a given {@link WebSocket websocket} connection by sending a periodic message.
+ */
+export class ConnectionKeepAliveHandler {
+  private pongReceived = false
+  private static readonly pingTimeout = 30 * 1000
+  private intervalId: NodeJS.Timer | undefined
+
+  /**
+   * Constructs the instance and starts the interval.
+   *
+   * @param messageTransporter The websocket to keep alive
+   */
+  constructor(private messageTransporter: YDocMessageTransporter) {
+    this.messageTransporter.on('disconnected', () => this.stopTimer())
+    this.messageTransporter.on('ready', () => this.startTimer())
+    this.messageTransporter.on(String(MessageType.PING), () => {
+      this.sendPongMessage()
+    })
+    this.messageTransporter.on(
+      String(MessageType.PONG),
+      () => (this.pongReceived = true)
+    )
+  }
+
+  /**
+   * Starts the ping timer.
+   */
+  public startTimer(): void {
+    this.pongReceived = false
+    this.intervalId = setInterval(
+      () => this.check(),
+      ConnectionKeepAliveHandler.pingTimeout
+    )
+    this.sendPingMessage()
+  }
+
+  public stopTimer(): void {
+    clearInterval(this.intervalId)
+  }
+
+  /**
+   * Checks if a pong has been received since the last run. If not, the connection is probably dead and will be terminated.
+   */
+  private check(): void {
+    if (this.pongReceived) {
+      this.pongReceived = false
+      this.sendPingMessage()
+    } else {
+      this.messageTransporter.disconnect()
+      console.error(
+        `No pong received in the last ${ConnectionKeepAliveHandler.pingTimeout} seconds. Connection seems to be dead.`
+      )
+    }
+  }
+
+  private sendPingMessage(): void {
+    const encoder = createEncoder()
+    writeVarUint(encoder, MessageType.PING)
+    this.messageTransporter.send(toUint8Array(encoder))
+  }
+
+  private sendPongMessage(): void {
+    const encoder = createEncoder()
+    writeVarUint(encoder, MessageType.PONG)
+    this.messageTransporter.send(toUint8Array(encoder))
+  }
+}