socket: expand docs+tests for recv_io/send_io

* ext/socket/unixsocket.c (unix_send_io): document args
  (unix_recv_io): ditto
* test/socket/test_unix.rb (test_fd_passing_class_mode): added

I was working on these when I encountered the problem in
with BasicSocket.for_fd not handling mode args:
https://bugs.ruby-lang.org/issues/11778

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@52922 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 7 insertions, 0 deletions

diff --git a/ext/socket/unixsocket.c b/ext/socket/unixsocket.c
index f768fbc126..2442bc1d12 100644
--- a/ext/socket/unixsocket.c
+++ b/ext/socket/unixsocket.c
@@ -201,6 +201,8 @@ sendmsg_blocking(void *data)
  *   p stdout.fileno #=> 6
  *
  *   stdout.puts "hello" # outputs "hello\n" to standard output.
+ *
+ * _io_ may be any kind of IO object or integer file descriptor.
  */
 static VALUE
 unix_send_io(VALUE sock, VALUE val)
@@ -297,6 +299,11 @@ recvmsg_blocking(void *data)
  *     }
  *   }
  *
+ * _klass_ will determine the class of _io_ returned (using the
+ * IO.for_fd singleton method or similar).
+ * If _klass_ is +nil+, an integer file descriptor is returned.
+ *
+ * _mode_ is the same as the argument passed to IO.for_fd
  */
 static VALUE
 unix_recv_io(int argc, VALUE *argv, VALUE sock)