Nadav Har'El b4a9fe9928 test/alternator: another test for expression with a lot of ORs ...

We already have a test, test_limits.py::test_deeply_nested_expression_2,
which checks that in the long condition expression

        a<b or (a<b or (a<b or (a<b or (....))))

with more than MAX_DEPTH (=400) repeats is rejected by Alternator,
as part of commit 04e5082d52 which
restricted the depth of the recursive parser to prevent crashing Scylla.

However, I got curious what will happen without the parentheses:

        a<b or a<b or a<b or a<b or ...

It turns out that our parser actually parses this syntax without
recursion - it's just a loop (a "*" in the Antlr alternator/expressions.g
allows reading more and more ORs in a loop). So Alternator doesn't limit
the length of this expression more than the length limit of 4096 bytes
which we also have. We can fit 584 repeats in the above expression in
4096 bytes, and it will not be rejected even though 584 > 400.
This test confirms that this is indeed the case.

The test is Scylla-only because on DynamoDB, this expression is rejected
because it has more than 300 "OR" operators. Scylla doesn't have this
specific limit - we believe the other limitations (on total expression
length, and on depth) are better for protecting Scylla. Remember that
in an expression like "(((((((((((((" there is a very high recursion
depth of the parser but zero operators, so counting the operators does
nothing to protect Scylla.

Signed-off-by: Nadav Har'El <nyh@scylladb.com>

Closes scylladb/scylladb#23973

2025-05-07 13:57:18 +03:00

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