[PATCH] epollexclusive: handle future rb_io_t deprecation

[Eric Wong <BOFH@YHBT.net>]

From: Eric Wong <bofh@yhbt.net>

It looks like Ruby 3.3+ will hide rb_io_t internals and
get rid of the venerable `GetOpenFile' macro in favor of
`rb_io_descriptor'.  `rb_io_descriptor' has been public
API since Ruby 3.1 and should be safe to use, and
is necessary for `raindrops' (a dependency of ours):

  https://yhbt.net/raindrops-public/20230609104805.39022-1-samuel.williams@oriontransfer.co.nz/
  https://bugs.ruby-lang.org/issues/19057#note-17

We'll also avoid an unnecessary call to `rb_io_get_io' in
`get_readers' since `epio' (aka `self') can only be of
the Unicorn::Waiter IO subclass.  However, we must still use
`rb_io_get_io' when handling non-self args in `prep_readers'.
---
 Note: I've only tested this patch on 2.7 atm, ENOSPC.

 ext/unicorn_http/epollexclusive.h | 27 ++++++++++++++++++---------
 ext/unicorn_http/extconf.rb       |  4 +++-
 2 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/ext/unicorn_http/epollexclusive.h b/ext/unicorn_http/epollexclusive.h
index 8f4ea9a0..c74a7799 100644
--- a/ext/unicorn_http/epollexclusive.h
+++ b/ext/unicorn_http/epollexclusive.h
@@ -22,6 +22,18 @@
 #endif
 
 #if USE_EPOLL
+#if defined(HAVE_RB_IO_DESCRIPTOR) /* Ruby 3.1+ */
+#	define my_fileno(io) rb_io_descriptor(io)
+#else /* Ruby <3.1 */
+static int my_fileno(VALUE io)
+{
+	rb_io_t *fptr;
+	GetOpenFile(io, fptr);
+	rb_io_check_closed(fptr);
+	return fptr->fd;
+}
+#endif /* Ruby <3.1 */
+
 /*
  * :nodoc:
  * returns IO object if EPOLLEXCLUSIVE works and arms readers
@@ -38,9 +50,8 @@ static VALUE prep_readers(VALUE cls, VALUE readers)
 
 	Check_Type(readers, T_ARRAY);
 	for (i = 0; i < RARRAY_LEN(readers); i++) {
-		int rc;
+		int rc, fd;
 		struct epoll_event e;
-		rb_io_t *fptr;
 		VALUE io = rb_ary_entry(readers, i);
 
 		e.data.u64 = i; /* the reason readers shouldn't change */
@@ -53,9 +64,8 @@ static VALUE prep_readers(VALUE cls, VALUE readers)
 		 * cycles on maintaining level-triggering.
 		 */
 		e.events = EPOLLEXCLUSIVE | EPOLLIN;
-		io = rb_io_get_io(io);
-		GetOpenFile(io, fptr);
-		rc = epoll_ctl(epfd, EPOLL_CTL_ADD, fptr->fd, &e);
+		fd = my_fileno(rb_io_get_io(io));
+		rc = epoll_ctl(epfd, EPOLL_CTL_ADD, fd, &e);
 		if (rc < 0) rb_sys_fail("epoll_ctl");
 	}
 	return epio;
@@ -65,7 +75,7 @@ static VALUE prep_readers(VALUE cls, VALUE readers)
 #if USE_EPOLL
 struct ep_wait {
 	struct epoll_event event;
-	rb_io_t *fptr;
+	int epfd;
 	int timeout_msec;
 };
 
@@ -78,7 +88,7 @@ static void *do_wait(void *ptr) /* runs w/o GVL */
 	 * at-a-time (c.f. fs/eventpoll.c in linux.git, it's quite
 	 * easy-to-understand for anybody familiar with Ruby C).
 	 */
-	return (void *)(long)epoll_wait(epw->fptr->fd, &epw->event, 1,
+	return (void *)(long)epoll_wait(epw->epfd, &epw->event, 1,
 					epw->timeout_msec);
 }
 
@@ -92,9 +102,8 @@ get_readers(VALUE epio, VALUE ready, VALUE readers, VALUE timeout_msec)
 
 	Check_Type(ready, T_ARRAY);
 	Check_Type(readers, T_ARRAY);
-	epio = rb_io_get_io(epio);
-	GetOpenFile(epio, epw.fptr);
 
+	epw.epfd = my_fileno(epio);
 	epw.timeout_msec = NUM2INT(timeout_msec);
 	n = (long)rb_thread_call_without_gvl(do_wait, &epw, RUBY_UBF_IO, NULL);
 	if (n < 0) {
diff --git a/ext/unicorn_http/extconf.rb b/ext/unicorn_http/extconf.rb
index 80d00e56..11099cd0 100644
--- a/ext/unicorn_http/extconf.rb
+++ b/ext/unicorn_http/extconf.rb
@@ -33,5 +33,7 @@
   message("no, needs Ruby 2.6+\n")
 end
 
-have_func('epoll_create1', %w(sys/epoll.h))
+if have_func('epoll_create1', %w(sys/epoll.h))
+  have_func('rb_io_descriptor') # Ruby 3.1+
+end
 create_makefile("unicorn_http")