[kamilmysliwiec]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

WsAdapter and several microservices transports load their packages with createRequire(import.meta.url)('pkg') in their constructors. webpack 5 follows that, but esbuild and rolldown don't (evanw/esbuild#1828): the package is left out of the bundle without a warning, and a bundled app that runs without node_modules exits with The "ws" package is missing. ClientMqtt, ClientNats, ClientRMQ and ServerGrpc fail the same way, even when the package is in the bundle through another import. Under --format=cjs, import.meta.url is empty, so these loads fail even when the package is installed. This came with the ESM migration in v12; v11 used () => require('pkg'), which esbuild could see.

Issue Number: Closes #18284

Thanks to @sumanthratna for the report and the esbuild reproduction.

What is the new behavior?

• @nestjs/platform-ws imports WebSocketServer from ws statically. ws is a regular dependency of the package, so it's always bundled.
• ClientMqtt, ClientRMQ and ClientNats load their packages on connect(), and ServerGrpc and ServerRMQ when they listen, with a literal import(), as ServerKafka and ServerRedis already do. A close() during the first load cancels the connection attempt instead of leaving a client open. createClient() of ClientMqtt and ClientRMQ still loads the package if it's called before connect().
• KafkaReplyPartitionAssigner reuses the kafkajs that ClientKafka has already loaded.
• The loadPackageSync docstring now says which bundlers follow createRequire loaders.

Checked with esbuild 0.28.2 (ESM output, each bundle run from a folder without node_modules): before, new WsAdapter(server) exited with "ws package is missing" and ServerGrpc bundled 0 grpc-js modules; after, ws is in the bundle, ServerGrpc bundles grpc-js and binds, and ClientMqtt and ClientNats connect to local brokers.

Does this PR introduce a breaking change?

• Yes
• No

A missing transport package is now reported (same message, same exit) when the client connects or the server starts listening, instead of when it is constructed.

Other information

• ClientGrpcProxy still loads @grpc/grpc-js synchronously, because getService() is synchronous. Like the protoLoader option (whose package name is only known at runtime), it can't be bundled by esbuild or rolldown: mark these packages as external (e.g. --packages=external) and keep them in node_modules.
• With esbuild, @nestjs/microservices now also needs @grpc/grpc-js to be installed or marked external, as already applies to kafkajs, ioredis, mqtt, @nats-io/transport-node and amqp-connection-manager.
• ws is CommonJS, so bundling it into ESM output with esbuild needs a require banner, e.g. --banner:js="import { createRequire } from 'node:module'; const require = createRequire(import.meta.url);".
• Tests: unit tests for platform-ws, microservices and common pass; the ws, gRPC, MQTT and NATS integration suites pass locally. RabbitMQ and Kafka integration suites weren't run locally (no broker).