[jira] [Created] (JEXL-330) JexlException.Parsing.getMessage() throws StringIndexOutOfBoundsException when parse error is in long expression

["David Costanzo (Jira)" <ji...@apache.org>]

David Costanzo created JEXL-330:
-----------------------------------

             Summary: JexlException.Parsing.getMessage() throws StringIndexOutOfBoundsException when parse error is in long expression
                 Key: JEXL-330
                 URL: https://issues.apache.org/jira/browse/JEXL-330
             Project: Commons JEXL
          Issue Type: Bug
    Affects Versions: 3.1
            Reporter: David Costanzo


JEXL makes some nice diagnostic messages available from {{Exception.getMessage()}}. However, in the case where a {{JexlException.Parsing}} is thrown in the middle of a long expression,  {{getMessage()}} throws a {{StringIndexOutOfBoundsException}} instead of returning a nice diagnostic message.

I encountered this in JEXL 3.1, but have confirmed that it is reproducible using a recent clone of the GitHub repository.

*Impact:*
In the case where the JEXL programmer includes the badly-formed expression, my program, which uses JEXL, throws an unhanded exception, instead of printing out a clear message to the JEXL programmer.


*Steps to Reproduce:* 
{code:java}
@Test
public void testLongParseError() throws IOException {
    JexlEngine jexl = new JexlBuilder().create();

    // Extended form of: 'literal' + VARIABLE   'literal'
    // missing + operator here ---------------^
    String longExpression = "" + //
        "'THIS IS A VERY VERY VERY VERY VERY VERY VERY " + //
        "VERY VERY LONG STRING CONCATENATION ' + VARIABLE ' <--- " + //
        "error: missing + between VARIABLE and literal'";

    try {
        jexl.createExpression(longExpression);
        Assert.fail("parsing malformed expression did not throw exception");
    } catch (JexlException.Parsing exception) {
        Assert.assertEquals("???", exception.getMessage());
    }
}
{code}
 

*What Happens:*

{{createExpression()}} throws a {{JexlException.Parsing}}, as expected.
Calling {{getMessage()}} on the resulting {{JexlException.Parsing}}, in turn, throws {{StringIndexOutOfBoundsException}}.

 

*Expected Result:*
{{getMessage()}} returns a brief description of the syntax error.

 

*Technical Details:*
The problem might be in {{JexlException.parseError}}. In the case where the expression is long (in this case, the part after the VARIABLE), it tries to extract a snippet of the error.
{code:java}
protected String parserError(String prefix, String expr) {
    int length = expr.length();
    if (length < MAX_EXCHARLOC) {
        return prefix + " error in '" + expr + "'";
    } else {
        int begin = info.getColumn(); // <---- column in original expression, not within expr
                                      //        In this case, begin > length
        int end = begin + (MAX_EXCHARLOC / 2);
        begin -= (MAX_EXCHARLOC / 2);
        if (begin < 0) {
            end -= begin;
            begin = 0;
        }
        return prefix + " error near '... "
                + expr.substring(begin, end > length ? length : end) + " ...'";
    }
}
{code}
However, the expression that it's given is already an extract, not the entire line:
{code:java}
' <--- error: missing + between VARIABLE and literal'{code}
{{info.getColumn()}} returns an index in the _original_ expression, which is already already past the end of the {{expr}}.  So when {{JexlException.parseError}} invokes {{expr.substring()}}, it throws {{StringIndexOutOfBoundsException}}.



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