[jira] [Created] (NIFI-7147) ReplaceText processor strips backslashes with regex replace

["Denes Arvay (Jira)" <ji...@apache.org>]

Denes Arvay created NIFI-7147:
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             Summary: ReplaceText processor strips backslashes with regex replace
                 Key: NIFI-7147
                 URL: https://issues.apache.org/jira/browse/NIFI-7147
             Project: Apache NiFi
          Issue Type: Bug
          Components: Extensions
    Affects Versions: 1.11.1
            Reporter: Denes Arvay


ReplaceText processor strips backslashes if the Replacement Strategy is Regex Replace and the Replacement Value contains expression and backreference.

I was able to reduce the problem to the following example:
- Search Value: {{(.)}}
- Replacement Value: {{${'$1'}}}
- Input: {{\a}}
- Expected output: {{\a}}
- Actual output: {{a}} -> the backslash has been removed

I did some investigation and the cause seems to be the usage of {{Matcher.matcher.appendReplacement}} at [1], which according to the documentation [2] treats backslashes (and dollar signs) in a special manner: _"Note that backslashes (\) and dollar signs ($) in the replacement string may cause the results to be different than if it were being treated as a literal replacement string."_

See the following example, it's very similar to what happens at [1] when running with the example above.
{code:java}
Matcher matcher = Pattern.compile("(.)").matcher("A");
matcher.find();
matcher.appendReplacement(sb, "\\a");
{code}
The result is {{a}} in the StringBuilder, not {{\a}} as I would expect at first. If the backslash in {{\a}} is escaped (i.e. {{\\a}}) the result is {{\a}}.

This issue relates to NIFI-5813 and it seems the {{normalizeReplacementString}} method [3] works incorrectly: in NIFI-5813 it escapes things it shouldn't while it doesn't escape what it should.


[1] https://github.com/apache/nifi/blob/rel/nifi-1.11.1/nifi-nar-bundles/nifi-standard-bundle/nifi-standard-processors/src/main/java/org/apache/nifi/processors/standard/ReplaceText.java#L555
[2] https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/util/regex/Matcher.html#appendReplacement(java.lang.StringBuffer,java.lang.String)
[3] https://github.com/apache/nifi/blob/rel/nifi-1.11.1/nifi-nar-bundles/nifi-standard-bundle/nifi-standard-processors/src/main/java/org/apache/nifi/processors/standard/ReplaceText.java#L681



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