Resumable and composable access handlers in the stream subsystem

[Yichun Zhang (agentzh)]

Hi guys!

This is just a feature request. I hope that the stream subsystem of
NGINX can support access handlers that are both resumable and
composable, just like the access phase handlers in the http subsystem.

The former means that the access handler can yield (like returning
NGX_DONE) and resume later upon new events. This is important when we
want to do nonblocking I/O in this context.

The latter means that different modules can register their own access
handlers without overriding each other, so the user can, for example,
combine the access_by_lua* directives of ngx_stream_lua_module and the
standard ngx_stream_access_module in the same stream server.

What do you think?

Best regards,
-agentzh