fix(ws): close existing connections

[bettercalljason]

Close all existing websocket connections to ensure a graceful shutdown.

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?

Issue Number: closes #13534

Existing connections are not closed automatically, according to https://github.com/websockets/ws/blob/master/doc/ws.md#serverclosecallback.

Application shutdown hangs when shutdown hooks are enabled and there are existing websocket connections. This is because the server.close callback that is awaited only resolves after all connections are closed. This is the call chain:

1. process.cleanup
2. NestApplication.dispose
3. SocketModule.close
4. WsAdapter.close
5. server.close

What is the new behavior?

All existing websocket connections are closed to ensure a graceful shutdown.

Does this PR introduce a breaking change?

• Yes
• No

Other information

[coveralls]

Pull Request Test Coverage Report for Build 7a20893c-f508-44d3-8a50-e1b7ed027b27

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 92.124%

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Totals
Change from base Build e56f6d99-d9bc-426a-b9ef-ed11406d7e1c:	0.0%
Covered Lines:	6737
Relevant Lines:	7313

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💛 - Coveralls

[benjGam]

Hi, where will this piece of code will be invoked buddy ?

[bettercalljason]

Hi @benjGam

This will be invoked in here: https://github.com/nestjs/nest/blob/master/packages/websockets/socket-module.ts#L108.

Since WsAdapter extends AbstractWsAdapter the AbstractWsAdapter.close method was called before this proposed change.

[benjGam]

Okay, didn't see that, thanks for your reply