Background
Currently, "twistd" assumes one-run-one-plugin. It would be nice to load up
multiple plug-ins in Twisted, for many reasons. These include: serving the
same in-memory content via separate protocols, adding manhole to other
plug-ins (so the end-deployer can add it to other things, as opposed to the
original implementor, and a catch-all category of "auxiliary services".
Auxiliary services are those which are not useful in and of themselves, but
add value to a service which does something else of use.
Examples of auxiliary services -- a logging service (that connects to some
logging protocol on start-up), a metrics service (that sends statistics to
a collector like statsd or riemann) or an error-sending service (to
something like Sentry).
Proposal
tl;dr: four new tickets (codenamed SUBCOMMANDS, SERVICES, MANHOLE and
PROVIDERS) and one old ticket (3538)
SUBCOMMANDS: Add '+' as a special character in t.p.usage.Options. This
behavior will be off by default, and controlled by an attribute on the
Options instance "allowMultipleSubcommands".
The attribute will only be checked when the first sub-command starts, to
allow setting it based on global flags. When the option is on, '-+' will be
passed as '+' to the Options instance, to allow sending plain '+' to
sub-commands.
Glyph thinks there's a ticket for it. I couldn't find it in "search for
tickets in 'core' whose description mentionds 'command'". Unless anyone can
find it, I'll open a new ticket.
SERVICES (depends on SUBCOMMANDS): In twistd, set the flag aMS if
'--allow-multiple-services' is given. Add to the application all services.
3538 (depends on SERVICES): If '--allow-multiple-services' is given, and
'--python <.tac file>' is given, process subcommands as usual.
PROVIDERS: Add a function,
"providersInHierarchy(IService, IInterface) -> List[IInterface]"
that returns all services in the hierarchy which provide the interface.
This ticket does not depend on any other tickets.
MANHOLE (depends on PROVIDERS, SERVICES): Add a built-in twistd plugin
named "manhole". The plugin will expose manhole as PB/telnet with a
namespace that includes
{'services': providersInHierarchy(manholeService, IService)}
This ticket technically could only depend on PROVIDERS, but to be useful,
it also depends on SERVICES
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