Motivation

Before this PR, the gethostbyname() PHP function always returns either an internal IP address on success, or an unchanged hostname on failure. That's because Emscripten's default DNS implementation doesn't perform real lookups.

This PR enables actual DNS resolution for PHP-WASM running in Node.js via Node's dns
module. When PHP code calls gethostbyname('wordpress.org'), it now resolves and returns
the real IP address.

Implementation details

The implementation works similarly to FileLockManager:

phpwasm-emscripten-library-dns-lookup-for-node.js defines a new build-time JavaScript library linked with PHP.wasm. It overrides the __emscripten_lookup_name shipped by Emscripten with a custom callback that calls PHPLoader.syscalls.gethostbyname() to resolve the IP.

PHPLoader.syscalls is an object passed to loadNodeRuntime() via options.emscriptenOptions. It's an object that, for now, defines a single method: gethostbyname().

Even though you may pass an actual object instance, we create the instance in the parent worker and call gethostbyname() using a Comlink proxy. This is because require('dns').lookup() is asynchronous in Node. JSPI builds can easily await the returned value, but Asyncify builds can't. Not without spending a dozen hours tweaking the ASYNCIFY_ONLY list in the PHP compile Dockerfile. Therefore, we use a synchronous Comlink proxy to turn an asynchronous gethostbyname() call into a synchronous one in Asyncify builds.

Test plan

CI. See the tests shipped with this PR, confirm they pass and make sense.

cc @bcotrim @fredrikekelund