Feat/microservices configurable max buffer size

[jobnow]

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: #16256

Currently, MAX_BUFFER_SIZE is hard-coded in JsonSocket and cannot be configured. This causes issues when applications need to send larger messages between microservices over TCP, as the limit breaks the application when sending messages larger than 128MB (in characters).

The MAX_BUFFER_SIZE was introduced in PR #14134 (v11) but was not made configurable, causing a regression for users who need to send larger messages.

What is the new behavior?

The maxBufferSize option is now configurable through the TCP microservice options:

Server-side:

const app = await NestFactory.createMicroservice(AppModule, {
  transport: Transport.TCP,
  options: {
    host: 'localhost',
    port: 3000,
    maxBufferSize: (1024 * 1024 * 1024) / 4, // 1GB in characters
  },
});

Client-side:

const client = ClientsModule.register([
  {
    name: 'MY_SERVICE',
    transport: Transport.TCP,
    options: {
      host: 'localhost',
      port: 3000,
      maxBufferSize: (1024 * 1024 * 1024) / 4, // 1GB in characters
    },
  },
]);

If maxBufferSize is not provided, the default value of 128MB (in characters) is used, maintaining backward compatibility.

Does this PR introduce a breaking change?

• Yes
• No

This change is fully backward compatible. The maxBufferSize option is optional, and when not provided, the existing default behavior is maintained.

Other information

Changes Made

Core Changes:

1. packages/microservices/helpers/json-socket.ts - Made maxBufferSize configurable via constructor
2. packages/microservices/interfaces/microservice-configuration.interface.ts - Added maxBufferSize option to TcpOptions
3. packages/microservices/interfaces/client-metadata.interface.ts - Added maxBufferSize option to TcpClientOptions
4. packages/microservices/client/client-tcp.ts - Pass maxBufferSize to JsonSocket
5. packages/microservices/server/server-tcp.ts - Pass maxBufferSize to JsonSocket

Tests Added:

• New test file: packages/microservices/test/json-socket/max-buffer-size.spec.ts (14 tests)
• Updated: packages/microservices/test/client/client-tcp.spec.ts (3 tests)
• Updated: packages/microservices/test/server/server-tcp.spec.ts (3 tests)

All tests pass successfully and backward compatibility is verified.

This PR addresses the issue reported in #16256 where users upgrading from NestJS v10 to v11 encountered a hard limit on TCP message sizes that broke their applications.

[coveralls]

Pull Request Test Coverage Report for Build 64764b2d-8c9a-41c2-a348-ab88513c9f5c

Details

• 10 of 10 (100.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.07%) to 89.825%

---

Totals
Change from base Build d3739886-8f7f-46b1-9469-82eecbaff18b:	0.07%
Covered Lines:	7460
Relevant Lines:	8305

---

💛 - Coveralls

[kamilmysliwiec]

lgtm