Catch node causing Infinite error loop

[Michael Steenkamp]

If any part of an error handling chain attached to a catch node throws an error, then node-red gets into an infinite error loop.

Is this the intended behaviour of the catch node?

Example flow below:

[{"id":"5eeb1212.a114ec","type":"function","name":"throw error","func":"throw new Error(\"error!\");","outputs":"0","valid":true,"x":609.8889465332031,"y":350.8888854980469,"z":"762eff0a.89d1","wires":[]},{"id":"8e498c01.71b67","type":"inject","name":"","topic":"","payload":"","payloadType":"date","repeat":"","crontab":"","once":false,"x":325.8888854980469,"y":349.8888854980469,"z":"762eff0a.89d1","wires":[["5eeb1212.a114ec"]]},{"id":"8bd3c819.742c38","type":"catch","name":"","x":314.8888854980469,"y":416.8888854980469,"z":"762eff0a.89d1","wires":[["d6967162.29699","5eeb1212.a114ec"]]},{"id":"d6967162.29699","type":"debug","name":"","active":true,"console":"false","complete":"false","x":606.8889465332031,"y":416.8888854980469,"z":"762eff0a.89d1","wires":[]}]

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[Dave C-J]

See Item 3 here - http://www.telegraph.co.uk/culture/comedy/10363116/Tommy-Cooper-25-great-jokes.html

:-)

[Nicholas O'Leary]

Hi Michael,

yes it is possible to get yourself into an infinite loop with the catch node. There are a couple of strategies for avoiding that. The main one is to put your error handling flow into a subflow with its own catch node inside. If the error recovery throws an error, the catch node in the subflow will get triggered and you can take an alternative route.

I think we can do more to avoid loops - its a new feature and sometimes they need trying out in the real world to figure this stuff out.

My current thought is to add the id of the catch node that handles the message to the error property of the message - we can then detect if a message is looping back to the same catch node and either ignore it, or log a warning or do something else.

If you have any thoughts as to how you'd like/expect it to work, I'm open to ideas.

Nick

On 23 April 2015 at 10:24, Dave C-J <dce...@gmail.com> wrote:

See Item 3 here - http://www.telegraph.co.uk/culture/comedy/10363116/Tommy-Cooper-25-great-jokes.html

:-)

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[Nicholas O'Leary]

In the imminent 0.10.8 release, if a message is passed to a catch node from the same source node 10 times, then it is dropped and a warning logged. The theory here is that there are valid scenarios where you may want the message to loop through the catch node whilst retrying some action until it succeeds, so we don't want to rule out loops all together. Allowing 10 loops feels the right level for basic retry flows to work without any special measures needed. If a flow wants to retry more times, it simply has to delete the msg.error property (as that is what is used to track how many times it has passed through).

Nick