Add MQTT v5 protocol version support

[Copilot]

Overview

This PR adds support for MQTT v5 (protocol version 5) while maintaining full backward compatibility with the existing MQTT v3.1.1 (protocol version 4) implementation.

Closes #[issue number]

Problem

The adapter was hard-coded to use MQTT v3.1.1 (protocol version 4), preventing users from taking advantage of MQTT v5 features such as:

• Enhanced authentication mechanisms
• Request/response patterns
• User properties
• Message expiry intervals
• Topic aliases
• Reason codes and better error handling

Reference:

ioBroker.mqtt/lib/securityChecker.js

Line 24 in 6d9dc1f

protocolVersion: 4,

Solution

Added a configurable protocolVersion option that allows users to select between MQTT v3.1.1 and MQTT v5:

Admin UI Configuration

• Added new "Protocol settings" section in the admin interface
• Dropdown selector with two options:
  • MQTT v3.1.1 (default) - Protocol version 4
  • MQTT v5 - Protocol version 5
• Translations provided for all 11 supported languages

Client Mode

The adapter's MQTT client now respects the configured protocol version when connecting to external brokers:

const opts = {
    clientId: clientId,
    protocolId: 'MQTT',
    protocolVersion: config.protocolVersion || 4, /* default to v3.1.1 */
    // ... other options
};

Server Mode

The adapter's MQTT broker automatically supports both protocol versions simultaneously. The mqtt-connection library handles protocol negotiation automatically based on each client's connection request, so no configuration is needed - the server accepts both MQTT v3.1.1 and v5 clients out of the box.

Security Checker

The public IP accessibility checker now uses the configured protocol version to ensure security checks work correctly with both protocol versions.

Technical Details

• Libraries: Both mqtt (v5.14.1) and mqtt-connection (v4.1.0) fully support MQTT v5
• Default Behavior: Protocol version 4 (MQTT v3.1.1) when not configured
• Backward Compatible: Existing installations continue working without any configuration changes

Testing

• Added 2 new tests in test/testProtocolVersion.js to verify protocol version configuration
• All 39 tests pass (37 existing + 2 new)
• Verified backward compatibility with default settings
• Confirmed both client and server modes work correctly

Files Changed

• admin/jsonConfig.json - Added protocol version selector
• admin/i18n/*.json - Added translations (11 languages)
• lib/client.js - Use configurable protocol version
• lib/server.js - Added documentation comment
• lib/securityChecker.js - Accept protocol version parameter
• main.js - Pass protocol version to security checker
• test/testProtocolVersion.js - New tests for protocol version functionality

Migration

No migration needed - the adapter defaults to MQTT v3.1.1 (protocol version 4) for backward compatibility. Users who want to use MQTT v5 can simply select it in the adapter configuration.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>MQTT v5 support</issue_title>
<issue_description>I see the current implementation hard codes to v3.1.1 (aka, confusingly, v4):

ioBroker.mqtt/lib/securityChecker.js

Line 24 in 6d9dc1f

protocolVersion: 4,

Any plans to support MQTT v5?</issue_description>

<agent_instructions>Please check what would be needed to support v3.1.1 of mqtt and also v5 and propose changes and - if relevant - selection options for the users</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@Apollon77 Would be an enhancement and check what effects such an upgrade would mean ...

Fixes #487

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