Missing Response on Shell Channel about almond

[alexarchambault]

It should send something on the shell channel, it's done here.

Are you sure the problem couldn't come from the ZMQ setup? Like socket being a ZMQ.REQ. shell channels should be router / dealer ones I think (so says your link). They're setup this way in jupyter-scala.

[const-ae]

Thanks for your quick response.
After some hours of debugging I finally found the problem, you are right that your application was preparing to send the execution confirmation, but it was actually never send. The problem there is that the ZMQ Router silently drops messages if it has no identifier information where to send it. Here is the relevant part of the documentation, I could easily solve this problem by setting an identifier explicitly in my code:

val socket = context.socket(ZMQ.REQ)
  socket.setIdentity("manager_id".getBytes(ZMQ.CHARSET))
  socket.connect("tcp://127.0.0.1:53886")

So this issue is actually my fault (as you expected)

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But one problem I encountered while debugging this issue is that in your message receiving method, you require the user to use a non-empty key. Otherwise the code will try to use the identifier, which is the first part of the message, as the header, because the check for the delimiter is ignored. Although the workaround is of course easy, if you know the problem is, I think this could be fixed without much effort.