[jira] Updated: (JEXL-97) JEXL parses long expressions with lots of parenthesis slowly

["Jeff Ichnowski (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/JEXL-97?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jeff Ichnowski updated JEXL-97:
-------------------------------

    Attachment: proposed.patch

Attaching a proposal for a patch to fix this issue.  The change will make the parser slightly more permissive in what it allows for the left-hand side of an assignment expression.  If this is not acceptable, we could also add a check during or after the parse, to make sure assignment expressions are correct.

> JEXL parses long expressions with lots of parenthesis slowly
> ------------------------------------------------------------
>
>                 Key: JEXL-97
>                 URL: https://issues.apache.org/jira/browse/JEXL-97
>             Project: Commons JEXL
>          Issue Type: Bug
>    Affects Versions: 2.0, 1.1, 1.0
>         Environment: Java
>            Reporter: Jeff Ichnowski
>            Priority: Minor
>         Attachments: proposed.patch
>
>
> JEXL's parser uses an unbounded JavaCC LOOKAHEAD to distinguish assignment expressions from other expressions.  The result is certain expressions take exponential time to parse.  The example snippet below demonstrates the problem.  On my machine parsing the expression below takes ~120 seconds.  Changing the parser to remove the LOOKAHEAD can get this to parse in milliseconds.  The lookahead appears to be in all versions of the parser source.
> import org.apache.commons.jexl.Expression;
> import org.apache.commons.jexl.ExpressionFactory;
> public class SlowParse {
>     public static void main(String[] args) throws Exception {
>         String input = 
>             "(((((((((((((((((((((((((z+y)/x)*w)-v)*u)/t)-s)*r)/q)+p)-o)*n)-m)+l)*k)+j)/i)+h)*g)+f)/e)+d)-c)/b)+a)";
>         // Make sure everything is loaded...
>         Expression expr = ExpressionFactory.createExpression(input);
>         long start = System.nanoTime();
>         expr = ExpressionFactory.createExpression(input);
>         long end = System.nanoTime();
>         System.out.printf("Parse took %.1f seconds\n", (end-start)/1e+9);
>     }
> }

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