before this change, we rely on the default-generated fmt::formatter
created from operator<<, but fmt v10 dropped the default-generated
formatter.
in this change, we define formatters for `alternator::calculate_value_caller`,
and drop its operator<<.
Refs #13245
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#17259
DynamoDB limits of all expressions (ConditionExpression, UpdateExpression,
ProjectionExpression, FilterExpression, KeyConditionExpression) to just
4096 bytes. Until now, Alternator did not enforce this limit, and we had
an xfailing test showing this.
But it turns out that not enforcing this limit can be dangerous: The user
can pass arbitrarily-long and arbitrarily nested expressions, such as:
a<b and (a<b and (a<b and (a<b and (a<b and (a<b and (...))))))
or
(((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((((
and those can cause recursive algorithms in Alternator's parser and
later when applying expressions to recurse very deeply, overflow the
stack, and crash.
This patch includes new tests that demonstrate how Scylla crashes during
parsing before enforcing the 4096-byte length limit on expressions.
The patch then enforces this length limit, and these tests stop crashing.
We also verify that deeply-nested expressions shorter than the 4096-byte
limit are apparently short enough for our recursion ability, and work
as expected.
Unforuntately, running these tests many times showed that the 4096-byte
limit is not low enough to avoid all crashes so this patch needs to do
more:
The parsers created by ANTLR are recursive, and there is no way to limit
the depth of their recursion (i.e., nothing like YACC's YYMAXDEPTH).
Very deep recursion can overflow the stack and crash Scylla. After we
limited the length of expression strings to 4096 bytes this was *almost*
enough to prevent stack overflows. But unfortunetely the tests revealed
that even limited to 4096 bytes, the expression can sometimes recurse
too deeply: Consider the expression "((((((....((((" with 4000 parentheses.
To realize this is a syntax error, the parser needs to do a recursive
call 4000 times. Or worse - because of other Antlr limitations (see rants
in comments in expressions.g) it's actually 12000 recursive calls, and
each of these calls have a pretty large frame. In some cases, this
overflows the stack.
The solution used in this patch is not pretty, but works. We add to rules
in alternator/expressions.g that recurse (there are two of those - "value"
and "boolean_expression") an integer "depth" parameter, which we increase
when the rule recurses. Moreover, we add a so-called predicate
"{depth<MAX_DEPTH}?" that stops the parsing when this limit is reached.
When the parsing is stopped, the user will see a special kind of parse
error, saying "expression nested too deeply".
With this last modification to expressions.g, the tests for deeply-nested but
still-below-4096-bytes expressions
(test_limits.py::test_deeply_nested_expression_*) would not fail sporadically
as they did without it.
While adding the "expression nested too deeply" case, I also made the
general syntax-error reporting in Alternator nicer: It no longer prints
the internal "expression_syntax_error" type name (an exception type will
only be printed if some sort of unexpected exception happens), and it
prints the character position where the syntax error (or too deep
nested expression) was recognized.
Fixes#14473
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Closes#14477
Following the advice in the FIXME note, helper functions for parsing
expressions are now based on string views to avoid a few unnecessary
conversions to std::string.
Tests: unit(dev)
Closes#10013
Instead of lengthy blurbs, switch to single-line, machine-readable
standardized (https://spdx.dev) license identifiers. The Linux kernel
switched long ago, so there is strong precedent.
Three cases are handled: AGPL-only, Apache-only, and dual licensed.
For the latter case, I chose (AGPL-3.0-or-later and Apache-2.0),
reasoning that our changes are extensive enough to apply our license.
The changes we applied mechanically with a script, except to
licenses/README.md.
Closes#9937
We had a bug when a Query/Scan had both projection (ProjectionExpression
or AttributesToGet) and filtering (FilterExpression or Query/ScanFilter).
The problem was that projection left only the requested attributes, and
the filter might have needed - and not got - additional attributes.
The solution in this patch is to add the generated JSON item also
the extra attributes needed by filtering (if any), run the filter on
that, and only at the end remove the extra filtering attributes from
the item to be returned.
The two tests
test_query_filter.py::test_query_filter_and_attributes_to_get
test_filter_expression.py::test_filter_expression_and_projection_expression
Which failed before this patch now pass so we drop their "xfail" tag.
Fixes#6951.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
The source file alternator/executor.cc has grown too much, reaching almost
4,000 lines. In this patch I move about 400 lines out of executor.cc:
1. Some functions related to serialization of sets and lists were moved to
serialization.cc,
2. Functions related to evaluating parsed expressions were moved to
expressions.cc.
The header file expressions_eval.hh was also removed - the calculate_value()
functions now live in expressions.cc, so we can just define them in
expressions.hh, no need for a separate header files.
This patch just moves code around. It doesn't make any functional changes.
Refs #5783.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
This patch provides a complete implementation for the FilterExpression
parameter - the newer syntax for filtering the results of the Query or
Scan operations.
The implementation is pretty straightforward - we already added earlier
a result-filtering framework to Alternator, and used it for the older
filtering syntax - QuryFilter and ScanFilter. All we had to do now was
to run the FilterExpression (which has the same syntax as a
ConditionExpression) on each individual items. The previous cleanup
patches were important to reduce the friction of running these expressions
on the items.
After the previous patches fixing small esoteric bugs in a few expression
functions, with this patch *all* the tests in test_filter_expression.py
now pass, and so do the two FilterExpression tests in test_query.py and
test_scan.py. As far as I know (and of course minus any bugs we'll discover
later), this marks the FilterExpression feature complete.
Fixes#5038.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
In the DynamoDB API, expressions (e.g., ConditionExpression and many more)
may contain references to column names ("#name") or to values (":val")
given in a separate part of the request - ExpressionAttributeNames and
ExpressionAttributeValues respectively.
Before this patch, we resolved these references as part of the expression's
evaluation. This approach had two downsides:
1. It often misdiagnosed (both false negatives and false positives) cases
of unused names and values in expressions. We already had two xfailing
tests with examples - which pass after this patch. This patch also
adds two additional tests, which failed before this patch and pass
with it.
2. In one of the following patches we will add support for FilterExpression,
where the same expression is used repeatedly on many items. It is a waste
(as well as makes the code uglier) to resolve the same references again
and again each time the expression is evaluated. We should be able
to do it just once.
So this patch introduces an intermediate step between parsing and evaluating
an expression - "resolving" the expression. The new resolve_*() functions
modify the already parsed expression, replacing references to attribute
names and constant values by the actual names and values taken from the
request. The resolve_*() functions also keep track which references were
used, making it very easy to check (as DynamoDB does) if there are any
unused names or values, before starting the evaluation.
The interface of evaluate() functions become much simpler - they no longer
need to know the original request (which was previously needed for
ExpressionAttributeNames/Values), the table's schema (which was previously
needed only for some error checking), keep track of which references were
used. This simplification is helpful for using the expressions in contexts
where these things (request and schema) are no longer conveniently available,
namely in FilterExpression.
A small side-benefit of this patch is that it moves a bit of code, which
handled resolving of references in expressions, from executor.cc to
expressions.cc. This is just the first step in a bigger effort to
reduce the size of executor.cc by moving code to smaller source files.
There is no attempt in this patch to move as much code as we can.
We will move more code in a separate patch in this series.
Fixes#6572.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
This patch adds support for the ConditionExpression parameter of the
item-writing operations in Alternator: PutItem, UpdateItem and DeleteItem.
We already supported conditional updates/put/delete using the "Expected"
parameter. The ConditionExpression parameter implemented here provides a
very similar feature, using a different - and also newer and more powerful -
syntax.
The implementation here reuses much of our existing expression-parsing
infrastructure. Unsurprisingly, ConditionExpression's syntax has much in
common with UpdateExpression which we already support) and also many of the
comparison functions already implemented for "Expected". However, it's still
quite a bit of new code, because of the many different comparisons, functions,
and syntax variations we need to support.
This patch also expands alternator-test/test_condition_expression.py with
a few additional corner cases discovered during the development of this
patch.
Almost all of the tests for this feature (35 out of 39) now pass.
Two tests still fail because we don't yet support nested attributes (this
is a missing feature across Alternator), and two tests fail because of minor
ideosyncracies in DynamoDB's error path that we chose not to duplicate
yet (but still remember the difference in the form of an xfailing test).
Fixes#5035
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
DynamoDB has two similar parameters - AttributesToGet and
ProjectionExpression - which are supported by the GetItem, Scan and
Query operations. Until now we supported only the older AttributesToGet,
and this patch adds support to the newer ProjectionExpression.
Besides having a different syntax, the main difference between
AttributesToGet and ProjectionExpression is that the latter also
allows fetching only a specific nested attribute, e.g., a.b[3].c.
We do not support this feature yet, although it would not be
hard to add it: With our current data representation, it means
fetching the top-level attribute 'a', whose value is a JSON, and then
post-filtering it to take out only the '.b[3].c'. We'll do that
later.
This patch also adds more test cases to test_projection_expression.py.
All tests except three which check the nested attributes now pass,
and those three xfail (they succeed on DynamoDB, and fail as expected
on Alternator), reminding us what still needs to be done.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
The DynamoDB protocol is based on JSON, and most DynamoDB requests describe
the operation and its parameters via JSON objects such as maps and lists.
However, in some types of requests an "expression" is passed as a single
string, and we need to parse this string. These cases include:
1. Attribute paths, such as "a[3].b.c", are used in projection
expressions as well as inside other expressions described below.
2. Condition expressions, such as "(NOT (a=b OR c=d)) AND e=f",
used in conditional updates, filters, and other places.
3. Update expressions, such as "SET #a.b = :x, c = :y DELETE d"
This patch introduces the framework to parse these expressions, and
an implementation of parsing update expressions. These update expressions
will be used in the UpdateItem operation in the next patch.
All these expression syntaxes are very simple: Most of them could be
parsed as regular expressions, or at most a simple hand-written lexical
analyzer and recursive-descent parser. Nevertheless, we decided to specify
these parsers in the same ANTLR3 language already used in the Scylla
project for parsing CQL, hopefully making these parsers easier to reason
about, and easier to change if needed - and reducing the amount of boiler-
plate code.
The parsing of update expressions is most complete except that in SET
actions, only the "path = value" form is supported and not yet forms
forms such as "path1 = path2" (which does read-before-write) or
"path1 = path1 + value" or "path = function(...)".
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
