fix(NODE-5296): construct error messages for AggregateErrors in Node16+

global.d.ts

@@ -12,6 +12,7 @@ declare global {
       serverless?: 'forbid' | 'allow' | 'require';
       auth?: 'enabled' | 'disabled';
       idmsMockServer?: true;
+      nodejs?: string;
     };
 
     sessions?: {

src/error.ts

@@ -108,6 +108,10 @@ export interface ErrorDescription extends Document {
   errInfo?: Document;
 }
 
+function isAggregateError(e: Error): e is Error & { errors: Error[] } {
+  return 'errors' in e && Array.isArray(e.errors);
+}
+
 /**
  * @public
  * @category Error
@@ -131,15 +135,28 @@ export class MongoError extends Error {
   cause?: Error; // depending on the node version, this may or may not exist on the base
 
   constructor(message: string | Error) {
+    super(MongoError.buildErrorMessage(message));
     if (message instanceof Error) {
-      super(message.message);
       this.cause = message;
-    } else {
-      super(message);
     }
+
     this[kErrorLabels] = new Set();
   }
 
+  /** @internal */
+  private static buildErrorMessage(e: Error | string): string {
+    if (typeof e === 'string') {
+      return e;
+    }
+    if (isAggregateError(e) && e.message.length === 0) {
+      return e.errors.length === 0
+        ? 'AggregateError has an empty errors array. Please check the `cause` property for more information.'
+        : e.errors.map(({ message }) => message).join(', ');
+    }
+
+    return e.message;
+  }
+
   override get name(): string {
     return 'MongoError';
   }

test/integration/node-specific/errors.ts

@@ -0,0 +1,54 @@
+import { expect } from 'chai';
+
+import { MongoClient, MongoError, MongoServerSelectionError } from '../../mongodb';
+
+describe('Error (Integration)', function () {
+  describe('AggregateErrors', function () {
+    for (const { errors, message } of [
+      {
+        errors: [],
+        message:
+          'AggregateError has an empty errors array. Please check the `cause` property for more information.'
+      },
+      { errors: [new Error('message 1')], message: 'message 1' },
+      {
+        errors: [new Error('message 1'), new Error('message 2')],
+        message: 'message 1, message 2'
+      }
+    ]) {
+      it(
+        `constructs the message properly with an array of ${errors.length} errors`,
+        { requires: { nodejs: '>=16' } },
+        () => {
+          const error = new AggregateError(errors);
+          const mongoError = new MongoError(error);
+
+          expect(mongoError.message).to.equal(message);
+        }
+      );
+    }
+
+    context('when the message on the AggregateError is non-empty', () => {
+      it(`uses the AggregateError's message`, { requires: { nodejs: '>=16' } }, () => {
+        const error = new AggregateError([new Error('non-empty')]);
+        error.message = 'custom error message';
+        const mongoError = new MongoError(error);
+        expect(mongoError.message).to.equal('custom error message');
+      });
+    });
+
+    it('sets the AggregateError to the cause property', { requires: { nodejs: '>=16' } }, () => {
+      const error = new AggregateError([new Error('error 1')]);
+      const mongoError = new MongoError(error);
+      expect(mongoError.cause).to.equal(error);
+    });
+  });
+
+  it('NODE-5296: handles aggregate errors from dns lookup', async function () {
+    const error = await MongoClient.connect('mongodb://localhost:27222', {
+      serverSelectionTimeoutMS: 1000
+    }).catch(e => e);
+    expect(error).to.be.instanceOf(MongoServerSelectionError);
+    expect(error.message).not.to.be.empty;
+  });
+});

test/tools/runner/filters/node_version_filter.js

@@ -0,0 +1,26 @@
+'use strict';
+
+const { satisfies } = require('semver');
+
+/**
+ * Filter for specific nodejs versions
+ *
+ * example:
+ * metadata: {
+ *    requires: {
+ *      nodejs: '>=14'
+ *    }
+ * }
+ */
+class NodeVersionFilter {
+  filter(test) {
+    const nodeVersionRange = test?.metadata?.requires?.nodejs;
+    if (!nodeVersionRange) {
+      return true;
+    }
+
+    return satisfies(process.version, nodeVersionRange);
+  }
+}
+
+module.exports = NodeVersionFilter;