[zeromq-dev] zproject api design and binding question

[Arnaud Loonstra]

I've been testing the cffi binding but it's missing some features. I've 
already added one for handling double pointers.
For the record I've been fixing variadics here:

https://github.com/sphaero/zproject/tree/fix_cffi

Still needs testing and fixing destroying

Test file here:
https://gist.github.com/sphaero/f5b2c89a52a1cd3c55bccd61b0ae7ff8

erroring on:

Traceback (most recent call last):
   File "test.py", line 66, in <module>
     input.recv(input, b"m", copy._p)
AttributeError: cdata 'struct _zmsg_t *' points to an opaque type: 
cannot read fields
python3: src/zmsg.c:64: zmsg_destroy: Assertion `zmsg_is (self)' failed.

Rg,

Arnaud

On 5/7/19 4:51 PM, Arnaud Loonstra wrote:
> This indeed seems to a problem with at least Python's ctypes binding. 
> Perhaps we could mention this somewhere?
> 
> I'm now trying the cffi binding. However you'd need to be some wizard to 
> get this working without prior knowledge.
> 
> I got the binding to build and install. Now trying a simple test to get 
> started:
> 
> ```
> from czmq_cffi import *
> 
> Zactor.test(True)
> 
> output = Zsock(0) # 0 == PAIR
> output.connect(b"@inproc://zmsg.test")
> assert(output)
> 
> input = Zsock(0) # 0 == PAIR
> input.bind(b">inproc://zmsg.test")
> assert (input);
> 
> msg = Zmsg()
> assert (msg);
> frame = Zframe(b"Hello", 5)
> assert (frame);
> msg.prepend(frame)
> assert (msg.size() == 1)
> assert (msg.content_size () == 5);
> rc = msg.send(output)
> assert (rc == 0)
> 
> msg = input.recv(input);
> assert (msg)
> assert (msg.size() == 1)
> assert (msg.content_size() == 5)
> ```
> 
> However it fails:
> ```
> Traceback (most recent call last):
>    File "test.py", line 20, in <module>
>      msg.prepend(frame);
>    File 
> "/home/arnaud/src/libsphactor/bindings/py3test/lib/python3.7/site-packages/czmq_cffi-4.2.1-py3.7-linux-x86_64.egg/czmq_cffi/Zmsg.py", 
> line 80, in prepend
>      return utils.lib.zmsg_prepend(self._p, frame_p._p)
> TypeError: initializer for ctype 'struct _zframe_t * *' must be a 
> pointer to same type, not cdata 'struct _zframe_t *'
> ```
> So how to do that? How to get the pointer from Zrame object?
> 
> @Kevin, you here? You wrote the cffi binding generator, not?
> I think it would be helpful for others if we create a unittest.
> 
> Rg,
> 
> Arnaud
> 
> 
> 
> 
> On 5/2/19 4:20 PM, Arnaud Loonstra wrote:
>> Hey all,
>>
>> I'm using zproject to design and build a library to extend zactor a 
>> bit. However I'm now running into a design issue when using callbacks.
>>
>> For example I have in my api:
>> https://github.com/sphaero/libsphactor/blob/master/api/sphactor.api
>>
>>      <callback_type name = "handler_fn">
>>          Callback function for socket activity
>>          <argument name = "msg" type = "zmsg" />
>>          <argument name = "arg" type = "anything" />
>>          <return type = "zmsg" />
>>      </callback_type>
>>
>> So a callback which accepts a zmsg and returns a zmsg.
>>
>> Works perfectly in C. However when I bind to Python it doesn't work. 
>> It seems Python(ctypes) only handles returning simple types from 
>> callbacks:
>>
>> https://bugs.python.org/issue5710
>>
>> I can see this doesn't apply to any api's I've found so for in czmq or 
>> zyre.
>>
>> My question is whether it is bad api design from my side? Or are there 
>> any workarounds or better approaches for this?
>>
>> Rg,
>>
>> Arnaud
>> _______________________________________________
>> zeromq-dev mailing list
>> zeromq-dev at lists.zeromq.org
>> https://lists.zeromq.org/mailman/listinfo/zeromq-dev
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