Boolean Expressions of Fielded Buffers

Oracle Tuxedo has the Fboolev32 function for evaluating Boolean expressions in which the “variables” are the values of fields. The expressions are a subset of the C programming language with a nice addition of regular expression match operators:

• expression %% expression yields a 1 if the first expression is fully matched by the second expression (the regular expression).
• expression !% expression yields a 1 if the first expression is not matched by the second expression.

Since expressions do not have a subscript operator for strings, regular expressions are used to match the prefix, postfix, or the nth character:

import tuxedo as t
t.Fboolev32({"TA_STATUS": "OK123"}, "TA_STATUS %% 'OK.*'")

These operators are something new to most developers and sometimes you get expressions like this one:

import tuxedo as t
t.Fboolev32({"TA_STATUS": "OK123"}, "TA_STATUS %! 'OK.*'")

What will be the result? A crash of your process!

Instead of the !% operator, the developer typed in %! which is parsed as two operators:

• % for the modulo operation
• ! for negation

What happens next is:

• 'OK.*' is a non-empty string and evaluates to 1
• ! negates 1 and evaluates to 0
• TA_STATUS is converted to a number, most likely a 0. But it does not matter
• 0 % 0 is division by 0 and we get a SIGFPE signal deliver to the process

Most of the software out there does not have a SIGFPE signal handler installed and crash:

>>> import tuxedo as t
>>> t.Fboolev32({"TA_STATUS": "OK123"}, "TA_STATUS %! 'OK.*'")
Floating-point exception

Now image if those Boolean expressions were written by the user… If you use Boolean expressions in your Oracle Tuxedo application, remember to install the SIGFPE handler.