[clue]

This changeset improves error reporting when custom error handler is used (set_error_handler()), as discussed in reactphp/socket#290. Joining a multicast group could report a PHP warning before throwing, so a custom error handler would see this warning and one converting warnings to exceptions would throw an ErrorException instead of the documented RuntimeException. This has been the case since #6 switched to the stream based API in v0.2.0 (2015).

The RuntimeException now also includes the underlying error reason and code, such as Unable to join multicast group: Invalid argument with code 22 (EINVAL). Otherwise, the behavior is unchanged.

Builds on top of #6 and reactphp/socket#290

[Copilot]

🟢 Approval recommended

The focused implementation and regression test address the reported behavior with no identified blocking issues.

No open issues 🎉

What changed in this PR

Improves multicast receiver error reporting so custom PHP error handlers do not intercept join-group warnings, while preserving the documented RuntimeException.

Changes:

• Suppresses warnings during multicast group joining and restores the previous error handler afterward.
• Includes the socket error reason and code in exceptions, with regression coverage.

File	Description
tests/​FunctionalTest.php	Verifies exception details and that the custom error handler is not called.
src/​Factory.php	Suppresses join-group warnings and adds underlying socket error details to exceptions.

_{Review effort: Balanced}