Socket: close on exec

[gizahNL]

Perhaps I've just been blind, and missed something in the documentation, but for the live of me I can't seem to find a way to set close on exec on Sockets.

It would be nice to be able to set sockets to close on exec, to prevent child processes and other forks of inheriting sockets.

[clue]

It's a good idea.

Unfortunately however, PHP doesn't support setting FD_CLOEXEC, O_CLOEXEC or SOCK_CLOEXEC by default, unless you install specific extensions. As of PHP 8.4+ (https://www.php.net/manual/en/migration84.constants.php), you may specify the SOCK_CLOEXEC flag for socket_create() (https://www.php.net/manual/en/function.socket-create.php) which is both undocumented at the moment and requires a very new PHP version with an extension which we both can't really rely on at the time of writing this. Should this become more wide-spread in PHP, I think we're happy to accept PRs and contributions in ReactPHP to eventually expose this as a flag and/or make it the default.

In the meantime, you may technically build a custom ServerInterface or ConnectorInterface implementation with the above information if your installation does provide the required flags. If this turns out to be viable, I suppose we're happy to accept PRs.

That said, even if this flag was exposed, there's a high chance you may not be able to rely on all your dependencies and extensions to always set this flag reliably.

As an alternative, you can also prevent inheriting FDs by closing any excessive file descriptors just before spawning/exec'ing a child process (see also reactphp/child-process#51). This is something I've implemented in a number of ReactPHP-based projects such as clue/reactphp-sqlite#7 and others. There's some discussion to make this the default in the next ChildProcess version we're currently working on as discussed in reactphp/child-process#72.

As you can see, many options and I hope this helps! 👍 If so, consider supporting this project, for example by becoming a sponsor ❤️