Escaping EL Issue

Question

We are having escaping issues in some expressions. Just an example (using Nifi 1.21.0):

Expression	Value
{"$${key}": "value"}	{"${key}": "value"}
{"$${key}": "${literal('value')}"}	{"$${key}": "value"}

As one can see, the second expression is not escaping the dollar sign as it should (from the docs, see "Escaping Expression Language"), and just stays as "$$".

Any comments/hints would be much appreciated.

MattWho · Accepted Answer

@jisaitua

Definitely some weird unexpected behavior there. I was able to reproduce your issue, as well as some other unexpected behavior around same area.

As a workaround to your specific issue, the following NiFi Expression Language (NEL) will get you what you are looking for:

{${literal('')}"$${key}":"${literal('value')}"}

I also filed an Apache NiFi jira for this issue:
https://issues.apache.org/jira/browse/NIFI-11738

I reproduced on an Apache NiFi 1.18 cluster I have running, so it is not an issue that just recently appeared.

If you found that the provided solution(s) assisted you with your query, please take a moment to login and click Accept as Solution below each response that helped.

Thank you,

Matt

jisaitua · Answer

Thank you @MattWho, the trick worked! Sadly, it worked for this simple case, but for more complex cases we couldn't find a pattern to apply it. However, we found another workaround by using literals like this:

Expression	Value
`{ "${literal('$${key1}')}": "${literal('$${value1}')}", "key2": "${literal('$${value2}')}", "${literal('$${key3}')}": "value3", "key4": "${literal('value4')}" }`	`{ "${key1}": "${value1}", "key2": "${value2}", "${key3}": "value3", "key4": "value4" }`

It's a nasty hack, but it gets the job done! Thanks again for your help and for filling a bug report.

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