[capnproto] Passing and calling capabilities with pycapnp

[c***@gmail.com]

I have a use-case which is similar to streaming RPC to a server written in
C++ - here is a simplified example:

# Setup a client and connect it to our task server
client = capnp.TwoPartyClient('localhost:8000')
task_mgr = client.bootstrap().cast_as(schema.Task)

class Notifier(schema.Notifier.Server):
def notify(self, params, **kwargs):
print "notifying"

task = task_mgr.create(type=0)
n = Notifier()
task.add_notifier(n).wait()

task.run().wait()

capnp.wait_forever()

The C++ server will kick off the task which will call the notifier's notify
asynchronously. The C++ client works as expected (I get notify callbacks
when the task wants to notify). The python client seems to be unable to
pump the message loop. I see an example with a threaded client which
involves repeatedly chaining promises to make something like this work, but
is there an easier way?

I was hoping that the capnp.wait_forever() would take care of pumping the
loop and executing any callbacks, similar to
my kj::NEVER_DONE.wait(client.getWaitScope()); in the C++ client...

['Kenton Varda' via Cap'n Proto]

It looks like capnp.wait_forever() is actually implemented as
kj::NEVER_DONE.wait() under the hood.

Can you provide more complete example code that we would be able to build
and run?

-Kenton

Post by c***@gmail.com
I have a use-case which is similar to streaming RPC to a server written in
# Setup a client and connect it to our task server
client = capnp.TwoPartyClient('localhost:8000')
task_mgr = client.bootstrap().cast_as(schema.Task)
print "notifying"
task = task_mgr.create(type=0)
n = Notifier()
task.add_notifier(n).wait()
task.run().wait()
capnp.wait_forever()
The C++ server will kick off the task which will call the notifier's
notify asynchronously. The C++ client works as expected (I get notify
callbacks when the task wants to notify). The python client seems to be
unable to pump the message loop. I see an example with a threaded client
which involves repeatedly chaining promises to make something like this
work, but is there an easier way?
I was hoping that the capnp.wait_forever() would take care of pumping the
loop and executing any callbacks, similar to my kj::NEVER_DONE.wait(client.getWaitScope());
in the C++ client...
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[c***@gmail.com]

Hi Kenton,

Sorry for the delay, but I believe this was an issue with how I was using
pycapnp. It turns out that pycapnp's binding is very sensitive to the
naming of arguments. In the example above,

class Notifier(schema.Notifier.Server):
def notify(self, params, **kwargs):
print "notifying"

notify's "params" argument was named "data" in the capnp schema file.
After changing the name, everything works fine! Not sure what can be done
about this in a language like Python unfortunately...

-Cody

Post by 'Kenton Varda' via Cap'n Proto
It looks like capnp.wait_forever() is actually implemented as
kj::NEVER_DONE.wait() under the hood.
Can you provide more complete example code that we would be able to build
and run?
-Kenton

Post by c***@gmail.com
I have a use-case which is similar to streaming RPC to a server written
# Setup a client and connect it to our task server
client = capnp.TwoPartyClient('localhost:8000')
task_mgr = client.bootstrap().cast_as(schema.Task)
print "notifying"
task = task_mgr.create(type=0)
n = Notifier()
task.add_notifier(n).wait()
task.run().wait()
capnp.wait_forever()
The C++ server will kick off the task which will call the notifier's
notify asynchronously. The C++ client works as expected (I get notify
callbacks when the task wants to notify). The python client seems to be
unable to pump the message loop. I see an example with a threaded client
which involves repeatedly chaining promises to make something like this
work, but is there an easier way?
I was hoping that the capnp.wait_forever() would take care of pumping the
loop and executing any callbacks, similar to
my kj::NEVER_DONE.wait(client.getWaitScope()); in the C++ client...
--
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"Cap'n Proto" group.
To unsubscribe from this group and stop receiving emails from it, send an
Visit this group at https://groups.google.com/group/capnproto.