feat(NODE-5613): add awaited field to SDAM heartbeat events (#3895)

Author: durran

src/sdam/events.ts

@@ -132,10 +132,13 @@ export class TopologyClosedEvent {
 export class ServerHeartbeatStartedEvent {
   /** The connection id for the command */
   connectionId: string;
+  /** Is true when using the streaming protocol. */
+  awaited: boolean;
 
   /** @internal */
-  constructor(connectionId: string) {
+  constructor(connectionId: string, awaited: boolean) {
     this.connectionId = connectionId;
+    this.awaited = awaited;
   }
 }
 
@@ -151,12 +154,15 @@ export class ServerHeartbeatSucceededEvent {
   duration: number;
   /** The command reply */
   reply: Document;
+  /** Is true when using the streaming protocol. */
+  awaited: boolean;
 
   /** @internal */
-  constructor(connectionId: string, duration: number, reply: Document | null) {
+  constructor(connectionId: string, duration: number, reply: Document | null, awaited: boolean) {
     this.connectionId = connectionId;
     this.duration = duration;
     this.reply = reply ?? {};
+    this.awaited = awaited;
   }
 }
 
@@ -172,11 +178,14 @@ export class ServerHeartbeatFailedEvent {
   duration: number;
   /** The command failure */
   failure: Error;
+  /** Is true when using the streaming protocol. */
+  awaited: boolean;
 
   /** @internal */
-  constructor(connectionId: string, duration: number, failure: Error) {
+  constructor(connectionId: string, duration: number, failure: Error, awaited: boolean) {
     this.connectionId = connectionId;
     this.duration = duration;
     this.failure = failure;
+    this.awaited = awaited;
   }
 }

src/sdam/monitor.ts

@@ -209,15 +209,25 @@ function resetMonitorState(monitor: Monitor) {
 
 function checkServer(monitor: Monitor, callback: Callback<Document | null>) {
   let start = now();
-  monitor.emit(Server.SERVER_HEARTBEAT_STARTED, new ServerHeartbeatStartedEvent(monitor.address));
+  const topologyVersion = monitor[kServer].description.topologyVersion;
+  const isAwaitable = topologyVersion != null;
+  monitor.emit(
+    Server.SERVER_HEARTBEAT_STARTED,
+    new ServerHeartbeatStartedEvent(monitor.address, isAwaitable)
+  );
 
   function failureHandler(err: Error) {
     monitor[kConnection]?.destroy({ force: true });
     monitor[kConnection] = undefined;
 
     monitor.emit(
       Server.SERVER_HEARTBEAT_FAILED,
-      new ServerHeartbeatFailedEvent(monitor.address, calculateDurationInMs(start), err)
+      new ServerHeartbeatFailedEvent(
+        monitor.address,
+        calculateDurationInMs(start),
+        err,
+        isAwaitable
+      )
     );
 
     const error = !(err instanceof MongoError)
@@ -237,8 +247,6 @@ function checkServer(monitor: Monitor, callback: Callback<Document | null>) {
     const { serverApi, helloOk } = connection;
     const connectTimeoutMS = monitor.options.connectTimeoutMS;
     const maxAwaitTimeMS = monitor.options.heartbeatFrequencyMS;
-    const topologyVersion = monitor[kServer].description.topologyVersion;
-    const isAwaitable = topologyVersion != null;
 
     const cmd = {
       [serverApi?.version || helloOk ? 'hello' : LEGACY_HELLO_COMMAND]: 1,
@@ -278,17 +286,18 @@ function checkServer(monitor: Monitor, callback: Callback<Document | null>) {
       const duration =
         isAwaitable && rttPinger ? rttPinger.roundTripTime : calculateDurationInMs(start);
 
+      const awaited = isAwaitable && hello.topologyVersion != null;
       monitor.emit(
         Server.SERVER_HEARTBEAT_SUCCEEDED,
-        new ServerHeartbeatSucceededEvent(monitor.address, duration, hello)
+        new ServerHeartbeatSucceededEvent(monitor.address, duration, hello, awaited)
       );
 
       // if we are using the streaming protocol then we immediately issue another `started`
       // event, otherwise the "check" is complete and return to the main monitor loop
-      if (isAwaitable && hello.topologyVersion) {
+      if (awaited) {
         monitor.emit(
           Server.SERVER_HEARTBEAT_STARTED,
-          new ServerHeartbeatStartedEvent(monitor.address)
+          new ServerHeartbeatStartedEvent(monitor.address, true)
         );
         start = now();
       } else {
@@ -324,7 +333,12 @@ function checkServer(monitor: Monitor, callback: Callback<Document | null>) {
       monitor[kConnection] = conn;
       monitor.emit(
         Server.SERVER_HEARTBEAT_SUCCEEDED,
-        new ServerHeartbeatSucceededEvent(monitor.address, calculateDurationInMs(start), conn.hello)
+        new ServerHeartbeatSucceededEvent(
+          monitor.address,
+          calculateDurationInMs(start),
+          conn.hello,
+          false
+        )
       );
 
       callback(undefined, conn.hello);