chore(cli-repl): warn about missing connectivity MONGOSH-1067 (#1171)

Warn the user when the driver appears to connect successfully
but a “ping” command still fails to run.

Author: addaleax

packages/cli-repl/src/mongosh-repl.ts

@@ -187,6 +187,7 @@ class MongoshNodeRepl implements EvaluationListener {
     }
     await this.greet(mongodVersion);
     await this.printStartupLog(instanceState);
+    await this.printBasicConnectivityWarning(instanceState);
 
     this.inspectCompact = await this.getConfig('inspectCompact');
     this.inspectDepth = await this.getConfig('inspectDepth');
@@ -459,6 +460,27 @@ class MongoshNodeRepl implements EvaluationListener {
     this.output.write(text);
   }
 
+  /**
+   * Print a warning if the server is not able to respond to commands.
+   * This can happen in load balanced mode, for example.
+   */
+  async printBasicConnectivityWarning(instanceState: ShellInstanceState): Promise<void> {
+    if (this.shellCliOptions.nodb || this.shellCliOptions.quiet) {
+      return;
+    }
+
+    let err: Error;
+    try {
+      await instanceState.currentDb.adminCommand({ ping: 1 });
+      return;
+    } catch (error: any) {
+      err = error;
+    }
+
+    const text = this.clr('The server failed to respond to a ping and may be unavailable:', ['bold', 'yellow']);
+    this.output.write(text + '\n' + this.formatError(err) + '\n');
+  }
+
   /**
    * Evaluate a piece of input code. This is called by the AsyncRepl eval function
    * and calls the {@link ShellEvaluator} eval function, passing along all of its

packages/cli-repl/test/e2e.spec.ts

@@ -1141,6 +1141,15 @@ describe('e2e', function() {
     });
   });
 
+  describe('with incomplete loadBalanced connectivity', () => {
+    it('prints a warning at startup', async() => {
+      const shell = TestShell.start({ args: [ 'mongodb://localhost:1/?loadBalanced=true' ] });
+      await shell.waitForPrompt();
+      shell.assertContainsOutput('The server failed to respond to a ping and may be unavailable');
+      shell.assertContainsOutput('MongoNetworkError');
+    });
+  });
+
   describe('run Node.js scripts as-is', () => {
     it('runs Node.js scripts as they are when using MONGOSH_RUN_NODE_SCRIPT', async() => {
       const filename = path.resolve(__dirname, 'fixtures', 'simple-console-log.js');