Add CapnProto message size limit

[antonio2368]

Changelog category (leave one):

• Improvement

Changelog entry (a user-readable short description of the changes that goes into CHANGELOG.md):

Add CapnProto message size limit. It can be changed with format_capn_proto_max_message_size.

Close #90298

Documentation entry for user-facing changes

• Documentation is written (mandatory for new features)

[clickhouse-gh]

Workflow [PR], commit [28f472b]

Summary: ❌

job_name	test_name	status	info	comment
Integration tests (amd_binary, 4/5)		failure
	test_merge_tree_s3/test.py::test_merge_canceled_by_s3_errors[node-broken_s3]	FAIL	cidb, issue
AST fuzzer (amd_tsan)		failure
	Logical error: Function A with argument with type Nothing and default implementation for Nothing is expected to return result with type Nothing, got B	FAIL	cidb
BuzzHouse (amd_debug)		failure
	Logical error: 'Inconsistent AST formatting in Function_arrayElement: the query:	FAIL	cidb, issue
BuzzHouse (amd_ubsan)		failure
	UndefinedBehaviorSanitizer: undefined behavior (STID: 4443-51fd)	FAIL	cidb

[Copilot]

Pull request overview

This PR adds a configurable size limit for CapnProto messages to prevent excessive memory allocation from malformed or corrupted data. The default limit is set to 1 GiB.

Key Changes:

• Introduces a new setting format_capn_proto_max_message_size with a default value of 1 GiB
• Implements message size validation in the CapnProto input format reader
• Adds a test case to verify the size limit enforcement

Reviewed changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/Core/FormatFactorySettings.h	Declares the new format_capn_proto_max_message_size setting
src/Formats/FormatSettings.h	Adds the max_message_size field to CapnProto format settings with 1 GiB default
src/Formats/FormatFactory.cpp	Wires the new setting into the format settings initialization
src/Processors/Formats/Impl/CapnProtoRowInputFormat.h	Adds max_message_size member variable to store the limit
src/Processors/Formats/Impl/CapnProtoRowInputFormat.cpp	Implements the message size check and throws an error when exceeded
src/Core/SettingsChangesHistory.cpp	Records the new setting in version 25.12 settings history
tests/queries/0_stateless/03756_capn_proto_message_size_limit.sql	Adds test case for the size limit enforcement