Counter client example hangs after execution

[relu91]

It seems that there is a resource leak in the counter example. My first impression is that CoAp client does not get properly cleaned up after the interaction with the remote thing. Maybe integrating coapjs/node-coap#317 would help to solve the problem.

How to reproduce

Run node packages/cli/dist/cli.js examples/scripts/counter.js and in another shell node packages/cli/dist/cli.js -c examples/scripts/counter-client.js. The client application hangs without properly exiting.

[danielpeintner]

@JKRhb do you know more?

[JKRhb]

Hmm, when I try to execute counter-client.js I get the following error:

Invalid URL: /counter
Fetch error: Error: WoTImpl fetched invalid JSON from 'coap://localhost:5683/counter': Unexpected token I in JSON at position 0

Because of that I am not sure if the error arises from the CoAP library or from the Helper class. Does it terminate when fetching the TD with HTTP instead?

In any case, I think the close method will probably help with resolving issues like these :) I added it now to #634. I am still waiting for the merge of one types related PR over at node-coap, once that one is merged the close method will hopefully land soon.

[relu91]

Thank you for testing @JKRhb, are you in sync with master? we've just merged a PR that should have solved the issue that you're mentioning.

[JKRhb]

Thank you for testing @JKRhb, are you in sync with master? we've just merged a PR that should have solved the issue that you're mentioning.

Oh, yeah, you are right, I rebuilt the project and now I can reproduce the issue :) The issue seems to already occur when the TD is fetched – I commented out everything within the try block and the example still did not terminate. I guess #634 will probably fix this but it is a bit strange that the Agent does not close automatically as it should when there are no more messages in flight. When using HTTP instead for fetching, the problem does not occur I guess?

[danielpeintner]

When using HTTP instead for fetching, the problem does not occur I guess?

Correct.
To be sure I tried it locally and with pure HTTP the client closes fine.

[JKRhb]

Edit: I initially thought I found a solution but it turned out to not actually solve the problem :/ I'll have another look into this...

Edit2: It is really odd that the problem only occurs when using CoAP for fetching a TD via the CLI. Using the fetch helper function in other contexts works perfectly fine. Maybe we could replace the fetching protocol in the example with HTTP for now and open another issue for this specific problem?

At least on my system, there seems to be another, IPv6 related issue ("Destination Unreachable" according to Wireshark) causing the client to hang during these lines:

https://github.com/eclipse/thingweb.node-wot/blob/3a9c4ca6fe6eccefbf5ba0930df23fecd8daffbd/examples/scripts/counter-client.js#L37-L39

Does the execution of the client example hang there for you as well?

[danielpeintner]

Edit2: It is really odd that the problem only occurs when using CoAP for fetching a TD via the CLI.

In my case the client also hangs if I replace

WoTHelpers.fetch("coap://localhost:5683/counter")

with

WoTHelpers.fetch("http://localhost:8080/counter")

Did you mean that?

Does the execution of the client example hang there for you as well?

In my case the client does not hand. Having said that, I do not have any IPv6 addresses so I cannot tell what would happen if I would...

[relu91]

I've opened the PR above which fixes the problem 😸 , let's wait for review -> merge -> and release

[JKRhb]

@relu91 Can you check if the problem is still present after the merge of coapjs/node-coap#329 and the new node-coap version? :) (Thanks again for the fix btw!)

[relu91]

Yeah, I was testing it this morning. Good news first: it solves the "hang after fetch" problem. But the example still hangs 😢 . The problem is that node-wot does not usually stop clients after the execution of an affordance. Therefore, the coap client is never closed if you use it for an affordance. Now the problem is when we should close it?

1. We can't close just before returning from the affordance because the application needs to read the value from the socket (e.g using the value function)
2. We could in principle close it when the client has fully consumed the stream. I've tried it but it causes some problems with the HTTP client (probably because it is not clear to me if the same client riuse it)
3. Ideally it would be good to have a destroy method in the ConsumedThing interface that clean up all the resources (closing open clients)

Ideas? opinions?

[danielpeintner]

3. Ideally it would be good to have a destroy method in the ConsumedThing interface that clean up all the resources (closing open clients)

This would a discussion point for the Scripting API, right?

[relu91]

This would a discussion point for the Scripting API, right?

yeah, I think we can discuss it there.

[danielpeintner]

Another question that does come into my mind. "Why" did CoAP not hang in v0.7.x and does hang in v0.8.x. Does it relate again with the "stream" changes ?

[relu91]

Another option is to consider to have some setting in the coap agent to automatically close the socket when a request/respose cycle is finished. @JKRhb what do you think?

[relu91]

"Why" did CoAP not hang in v0.7.x and does hang in v0.8.x. Does it relate again with the "stream" changes ?

That's a good question, TBH not sure why, one possible answer:

• we used to close the client in consumed-thing class since we didn't have to defer it because of streaming modes

[JKRhb]

Just tried out the counter example once more and #744 finally fixed it :) Sorry for the all the trouble :/

[relu91]

Well done @JKRhb !!