document the limitations of protocol(), sockdomain(), socktype()

Determining these for a new_from_fd() socket has the following problems:

protocol() depends on SO_PROTOCOL, and socktype() on SO_TYPE, not
implemented on all systems.

sockdomain() depends on sockname(), which is documented as
unimplemented for AF_UNIX sockets on HP-UX.

I'm not sure that detail is useful in the documentation.

diff --git a/dist/IO/lib/IO/Socket.pm b/dist/IO/lib/IO/Socket.pm
index 9e6f769..b5fc448 100644 (file)
--- a/dist/IO/lib/IO/Socket.pm
+++ b/dist/IO/lib/IO/Socket.pm
@@ -540,6 +540,12 @@ value returned.
 
 =back
 
+=head1 LIMITATIONS
+
+On some systems, for an IO::Socket object created with new_from_fd(),
+or created with accept() from such an object, the protocol(),
+sockdomain() and socktype() methods may return undef.
+
 =head1 SEE ALSO
 
 L<Socket>, L<IO::Handle>, L<IO::Socket::INET>, L<IO::Socket::UNIX>