refactor(NODE-5778): change kConnection to connection, split polling and streaming functions, define exhaustCommand (#3942)

Author: nbbeeken

src/cmap/commands.ts

@@ -317,6 +317,9 @@ export class OpQueryResponse {
   bsonRegExp?: boolean;
   index?: number;
 
+  /** moreToCome is an OP_MSG only concept */
+  moreToCome = false;
+
   constructor(
     message: Buffer,
     msgHeader: MessageHeader,
@@ -598,6 +601,7 @@ export class OpMsgResponse {
   fromCompressed?: boolean;
   responseFlags: number;
   checksumPresent: boolean;
+  /** Indicates the server will be sending more responses on this connection */
   moreToCome: boolean;
   exhaustAllowed: boolean;
   useBigInt64: boolean;

src/cmap/connection.ts

@@ -562,6 +562,15 @@ export class Connection extends TypedEventEmitter<ConnectionEvents> {
       callback(err);
     }
   }
+
+  exhaustCommand(
+    ns: MongoDBNamespace,
+    command: Document,
+    options: CommandOptions | undefined,
+    replyListener: Callback
+  ) {
+    return this.command(ns, command, options, replyListener);
+  }
 }
 
 /** @internal */
@@ -1156,6 +1165,15 @@ export class ModernConnection extends TypedEventEmitter<ConnectionEvents> {
 
     return document;
   }
+
+  exhaustCommand(
+    _ns: MongoDBNamespace,
+    _command: Document,
+    _options: CommandOptions,
+    _replyListener: Callback
+  ) {
+    throw new Error('NODE-5742: not implemented.');
+  }
 }
 
 const kDefaultMaxBsonMessageSize = 1024 * 1024 * 16 * 4;
@@ -1253,7 +1271,7 @@ export async function* readMany(
     const response = await decompressResponse(message);
     yield response;
 
-    if (!('moreToCome' in response) || !response.moreToCome) {
+    if (!response.moreToCome) {
       return;
     }
   }

src/sdam/monitor.ts

@@ -23,8 +23,6 @@ const kServer = Symbol('server');
 /** @internal */
 const kMonitorId = Symbol('monitorId');
 /** @internal */
-const kConnection = Symbol('connection');
-/** @internal */
 const kCancellationToken = Symbol('cancellationToken');
 /** @internal */
 const kRoundTripTime = Symbol('roundTripTime');
@@ -94,21 +92,17 @@ export class Monitor extends TypedEventEmitter<MonitorEvents> {
   connectOptions: ConnectionOptions;
   isRunningInFaasEnv: boolean;
   [kServer]: Server;
-  [kConnection]?: Connection;
+  connection: Connection | null;
   [kCancellationToken]: CancellationToken;
   /** @internal */
   [kMonitorId]?: MonitorInterval;
   rttPinger?: RTTPinger;
 
-  get connection(): Connection | undefined {
-    return this[kConnection];
-  }
-
   constructor(server: Server, options: MonitorOptions) {
     super();
 
     this[kServer] = server;
-    this[kConnection] = undefined;
+    this.connection = null;
     this[kCancellationToken] = new CancellationToken();
     this[kCancellationToken].setMaxListeners(Infinity);
     this[kMonitorId] = undefined;
@@ -219,8 +213,8 @@ function resetMonitorState(monitor: Monitor) {
 
   monitor[kCancellationToken].emit('cancel');
 
-  monitor[kConnection]?.destroy({ force: true });
-  monitor[kConnection] = undefined;
+  monitor.connection?.destroy({ force: true });
+  monitor.connection = null;
 }
 
 function useStreamingProtocol(monitor: Monitor, topologyVersion: TopologyVersion | null): boolean {
@@ -241,16 +235,17 @@ function useStreamingProtocol(monitor: Monitor, topologyVersion: TopologyVersion
 
 function checkServer(monitor: Monitor, callback: Callback<Document | null>) {
   let start = now();
+  let awaited: boolean;
   const topologyVersion = monitor[kServer].description.topologyVersion;
   const isAwaitable = useStreamingProtocol(monitor, topologyVersion);
   monitor.emit(
     Server.SERVER_HEARTBEAT_STARTED,
     new ServerHeartbeatStartedEvent(monitor.address, isAwaitable)
   );
 
-  function failureHandler(err: Error, awaited: boolean) {
-    monitor[kConnection]?.destroy({ force: true });
-    monitor[kConnection] = undefined;
+  function onHeartbeatFailed(err: Error) {
+    monitor.connection?.destroy({ force: true });
+    monitor.connection = null;
 
     monitor.emit(
       Server.SERVER_HEARTBEAT_FAILED,
@@ -269,7 +264,39 @@ function checkServer(monitor: Monitor, callback: Callback<Document | null>) {
     callback(err);
   }
 
-  const connection = monitor[kConnection];
+  function onHeartbeatSucceeded(hello: Document) {
+    if (!('isWritablePrimary' in hello)) {
+      // Provide hello-style response document.
+      hello.isWritablePrimary = hello[LEGACY_HELLO_COMMAND];
+    }
+
+    const duration =
+      isAwaitable && monitor.rttPinger
+        ? monitor.rttPinger.roundTripTime
+        : calculateDurationInMs(start);
+
+    monitor.emit(
+      Server.SERVER_HEARTBEAT_SUCCEEDED,
+      new ServerHeartbeatSucceededEvent(monitor.address, duration, hello, isAwaitable)
+    );
+
+    // 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) {
+      monitor.emit(
+        Server.SERVER_HEARTBEAT_STARTED,
+        new ServerHeartbeatStartedEvent(monitor.address, true)
+      );
+      start = now();
+    } else {
+      monitor.rttPinger?.close();
+      monitor.rttPinger = undefined;
+
+      callback(undefined, hello);
+    }
+  }
+
+  const { connection } = monitor;
   if (connection && !connection.closed) {
     const { serverApi, helloOk } = connection;
     const connectTimeoutMS = monitor.options.connectTimeoutMS;
@@ -299,51 +326,29 @@ function checkServer(monitor: Monitor, callback: Callback<Document | null>) {
       );
     }
 
-    connection.command(ns('admin.$cmd'), cmd, options, (err, hello) => {
-      if (err) {
-        return failureHandler(err, isAwaitable);
-      }
-
-      if (!('isWritablePrimary' in hello)) {
-        // Provide hello-style response document.
-        hello.isWritablePrimary = hello[LEGACY_HELLO_COMMAND];
-      }
-
-      const duration =
-        isAwaitable && monitor.rttPinger
-          ? monitor.rttPinger.roundTripTime
-          : calculateDurationInMs(start);
-
-      monitor.emit(
-        Server.SERVER_HEARTBEAT_SUCCEEDED,
-        new ServerHeartbeatSucceededEvent(monitor.address, duration, hello, isAwaitable)
-      );
+    if (isAwaitable) {
+      awaited = true;
+      return connection.exhaustCommand(ns('admin.$cmd'), cmd, options, (error, hello) => {
+        if (error) return onHeartbeatFailed(error);
+        return onHeartbeatSucceeded(hello);
+      });
+    }
 
-      // 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) {
-        monitor.emit(
-          Server.SERVER_HEARTBEAT_STARTED,
-          new ServerHeartbeatStartedEvent(monitor.address, true)
-        );
-        start = now();
-      } else {
-        monitor.rttPinger?.close();
-        monitor.rttPinger = undefined;
-
-        callback(undefined, hello);
-      }
-    });
+    awaited = false;
+    connection
+      .commandAsync(ns('admin.$cmd'), cmd, options)
+      .then(onHeartbeatSucceeded, onHeartbeatFailed);
 
     return;
   }
 
   // connecting does an implicit `hello`
   connect(monitor.connectOptions, (err, conn) => {
     if (err) {
-      monitor[kConnection] = undefined;
+      monitor.connection = null;
 
-      failureHandler(err, false);
+      awaited = false;
+      onHeartbeatFailed(err);
       return;
     }
 
@@ -357,7 +362,7 @@ function checkServer(monitor: Monitor, callback: Callback<Document | null>) {
         return;
       }
 
-      monitor[kConnection] = conn;
+      monitor.connection = conn;
       monitor.emit(
         Server.SERVER_HEARTBEAT_SUCCEEDED,
         new ServerHeartbeatSucceededEvent(